A&p exam 6

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Cauda equina

Cauda equina syndrome is a relatively rare but serious condition that describes extreme pressure and swelling of the nerves at the end of the spinal cord. It gets its name from Latin,"horse's tail," because the nerves at the end of the spine visually resemble a horse's tail as they extend from the spinal cord down the back of each leg. Cauda equina syndrome is a serious medical emergency that requires testing and possibly urgent surgical intervention. If patients with cauda equina syndrome do not get treatment quickly, adverse results can include permanent paralysis, impaired bladder and/or bowel control, difficulty walking, and/or other neurological and physical problems.

depolarization

Cells that can be stimulated electrically are said to be excitable. This means that if an electrical signal is applied or delivered to these cells, they will respond by becoming functional. This process is driven by electrochemical gradients. Electrochemical Gradients Electrochemical gradients are differences in ion concentration on the inside and outside of a cell. Generally speaking, if a cell membrane has more charges on one side of the membrane than the other, then there is an electrical difference along that membrane. In most excitable cells, this gradient is largely based on the concentration of sodium ions and potassium ions. Typically, when a cell is not actively excited, there will be more positively charged ions outside of the membrane, which makes the charge at rest inside the membrane negative. These electrochemical gradients are maintained by sodium-potassium pumps, which use ATP to remove positive charges from the cell. Depolarization When it is time to become active, voltage-gated ion channels (sodium channels) will open once the membrane charge reaches the threshold voltage. This is the minimum charge necessary for a cell to become active. When the threshold voltage is reached (which is typically -55 mV) the ion channels open in order to allow positive charges to rush inside the cell. This is known as depolarization, which is the process of becoming positively charged. After a cell depolarizes, it will eventually reach a maximum positive charge. At this point, the cell will try to return to rest by removing positive charges. This is usually done by potassium ions leaving the inside of the cell to cause the cell to become more negative. Eventually, after the charge gets closer to the original resting membrane level, the sodium potassium pump will re-establish the -70 mV charge.

cerebellar peduncles

Cerebellar peduncle is the part that connects cerebellum to the brain stem. There are 6 cerebellar peduncles in total, 3 on the left and 3 on the right.

cerebrospinal fluid

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spine. It is produced in the choroid plexuses of the ventricles of the brain. It acts as a cushion or buffer for the brain's cortex, providing basic mechanical and immunological protection to the brain inside the skull. The CSF also serves a vital function in cerebral autoregulation of cerebral blood flow. The CSF occupies the subarachnoid space (between the arachnoid mater and the pia mater) and the ventricular system around and inside the brain and spinal cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain, as well as the central canal of the spinal cord. There is also a connection from the subarachnoid space to the bony labyrinth of the inner ear via the perilymphatic duct where the perilymph is continuous with the cerebrospinal fluid.[1]

nerves vs. nerve roots

spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine.[1] There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.

spatial summation

summation of EPSPs is the additive effect produced by many EPSPs that have been generated at many different synapses on the same postsynaptic neuron at the same time.

action potential

the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.

medulla oblongata

the continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centers for the heart and lungs.

spinal cord

the cylindrical bundle of nerve fibers and associated tissue that is enclosed in the spine and connects nearly all parts of the body to the brain, with which it forms the central nervous system.

gray matter

the darker tissue of the brain and spinal cord, consisting mainly of nerve cell bodies and branching dendrites.

negative feedback

the diminution or counteraction of an effect by its own influence on the process giving rise to it, as when a high level of a particular hormone in the blood may inhibit further secretion of that hormone, or where the result of a certain action may inhibit further performance of that action.

hippocampus

the elongated ridges on the floor of each lateral ventricle of the brain, thought to be the center of emotion, memory, and the autonomic nervous system. The hippocampus plays a very important role in storing our memories and connecting them to our emotions, among other roles. This lesson explains all the roles of the hippocampus and its structure in the brain. The Hippocampus and Limbic System The hippocampus is a part of the limbic system. The limbic system is the area in the brain that is associated with memory, emotions, and motivation. The limbic system is located just above the brain stem and below the cortex. The hippocampus itself is highly involved with our memories. The limbic system plays a huge part in our survival roles. It is responsible for our fight or flight responses. This is when a person feels like he is in danger and either needs to fight his way out or run away from the situation. The limbic system also gives us that 'gut feeling.' The limbic system, including the hippocampus, is located in a very protected area of the brain. The hippocampus is a horseshoe-shaped structure. There are actually two pieces that are mirrored in pairs. One of the pairs is located in the right hemisphere. Its mirrored other half of the horseshoe is located in the left hemisphere. The Role of the Hippocampus in Memory The hippocampus plays a very important role in our memories. It attaches memories to the emotions and senses that go with them. For instance, it will take a memory of being happy and calm while in a field and link it with the smell of the flowers. It will associate both the feeling of being happy and the sense of smell to the memory of being in a field. Once the emotions and senses are attached, the hippocampus sends the memory off to be stored. It will actually file the memory in the appropriate part of the cerebral cortex. Here the memory will be put in long term storage, where it can later be retrieved. Brain Damage Most research of the brain has to be done by studying the effects of patients with brain damage. In patients with Alzheimer's disease the hippocampus is one of the first areas that experiences damage. These patients usually have symptoms of memory loss and disorientation. This suggests that the hippocampus is not only responsible for memories, but also plays a role in spatial orientation. Even though the hippocampus and limbic system are placed in the middle of the skull in a protective area, there are still other ways besides Alzheimer's disease for the hippocampus to become damaged. It can become damaged if it is deprived of oxygen or by encephalitis or medial temporal lobe epilepsy. Extensive damage to the hippocampus can result in amnesia, which is the loss of memory. Lesson Summary The hippocampus is part of our limbic system, a vital section of the brain that plays a key role in our survival. The hippocampus itself is responsible for many things, including connecting senses and emotions to our memories. It connects them all together and then sends the memory off to the proper area of the cerebral cortex. The memory is stored and will be able to be retrieved when called upon. Although the hippocampus is in the middle of the brain it can still be damaged, which causes the loss of memories and disorientation.

telencephalon

the most highly developed and anterior part of the forebrain, consisting chiefly of the cerebral hemispheres.

cerebellum

the part of the brain at the back of the skull in vertebrates. Its function is to coordinate and regulate muscular activity.

postsynaptic cell

the postsynaptic membrane is the membrane that receives a signal (binds neurotransmitter) from the presynaptic cell and responds via depolarisation or hyperpolarisation. The postsynaptic membrane is separated from the presynaptic membrane by the synaptic cleft.

presynaptic cell

the presynaptic membrane is the cell membrane of an axon terminal that faces the receiving cell. The postsynaptic membrane is separated from the presynaptic membrane by the synaptic cleft.

TRACTS

tracts bundles of nerve fibers in the CNS 3 types of tracts commissural, association, and projection commissural tracts always connect the right & left parts. corpus callosum is the most important commissural tract association tracts connects areas with one side only projection tracts connects upper & lower areas 2 types of projection tracts ascending projection & descending projection ascending projection carrying impulses to higher parts of the CNS; primarily sensory descending projection carrying impulses down; primarily motor

sodium-potassium exchange pump (= sodium-potassium ATPase)

Na+ /k + -ATPase (sodium-potassium adenosine triphosphatase, also known as the Na+ /K+ pump or sodium-potassium pump) is an enzyme (EC 3.6.3.9) (an electrogenic transmembrane ATPase) found in the plasma membrane of all animal cells. The Na+ /K+ -ATPase enzyme is a solute pump that pumps sodium out of cells while pumping potassium into cells, both against their concentration gradients. This pumping is active (it uses energy from ATP) and is important for cell physiology. An example application is nerve conduction. It has antiporter-like activity but is not actually an antiporter since both molecules are moving against their concentration gradient.

neurotransmitter

Neurotransmitters also known as chemical messengers, are endogenous chemicals that enable neurotransmission. They transmit signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell. Neurotransmitters are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by receptors on the target cells. Many neurotransmitters are synthesized from simple and plentiful precursors such as amino acids, which are readily available from the diet and only require a small number of biosynthetic steps to convert them. Neurotransmitters play a major role in shaping everyday life and functions. Their exact numbers are unknown but more than 100 chemical messengers have been identified.

Proprioception/ tendon organs

Proprioception means "sense of self". In the limbs, the proprioceptors are sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position of the limb in space. The muscle spindle is one type of proprioceptor that provides information about changes in muscle length. The Golgi tendon organ is another type of proprioceptor that provides information about changes in muscle tension.

axosomatic

Relating to or being the synapse between an axon of one nerve cell and the body of another nerve cell.

epidural space

The epidural space is the area between the dura mater (a membrane) and the vertebral wall, containing fat and small blood vessels. The space is located just outside the dural sac which surrounds the nerve roots and is filled with cerebrospinal fluid. Epidural steroid injections are delivered to the epidural space in order to deliver analgesics to the immediate site of pain. The epidural space is vulnerable to developing epidural abscesses, infections that can impair neurological function.

choroid plexus

The ventricles are structures that produce cerebrospinal fluid, and transport it around the cranial cavity. They are lined by ependymal cells, which form a structure called the choroid plexus. It is within the choroid plexus that CSF is produced.

ventricles of the brain

The ventricles of the brain are a communicating network of cavities filled with cerebrospinal fluid (CSF) and located within the brain parenchyma. The ventricular system is composed of 2 lateral ventricles, the third ventricle, the cerebral aqueduct, and the fourth ventricle (see the following images). The choroid plexuses located in the ventricles produce CSF, which fills the ventricles and subarachnoid space, following a cycle of constant production and reabsorption.

frequency

We have emphasized that once the depolarization caused by the stimulus is above threshold, the resulting neuronal action potential is a complete action potential (i.e., it is all-or-nothing). If the stimulus strength is increased, the size of the action potential does not get larger (see figure). If the size (i.e., amplitude) of the action potential is always the same and independent of the size of the stimulus, how then does the nervous system code the intensity of the stimulus? The trick that the nervous system uses is that the strength of the stimulus is coded into the frequency of the action potentials that are generated. Thus, the stronger the stimulus, the higher the frequency at which action potentials are generated (see Figs. 1 and 2 below). Therefore, we say that our nervous system is frequency-modulated and not amplitude-modulated. The frequency of action potentials is directly related to the intensity of the stimulus. Given that the frequency of action potentials is determined by the strength of the stimulus, a plausible question to ask is what is the frequency of action potentials in neurons? Another way of asking this question is how many action potentials can a neuron generate per unit time (e.g., action potentials per second)? Physiologically, action potential frequencies of up to 200-300 per second (Hz) are routinely observed. Higher frequencies are also observed, but the maximum frequency is ultimately limited by the absolute refractory period. Because the absolute refractory period is ~1 ms, there is a limit to the highest frequency at which neurons can respond to strong stimuli. That is to say that the absolute refractory period limits the maximum number of action potentials generated per unit time by the axon. As described previously, the strength of the stimulus must be very high in oder to ensure that the duration of the action potential is as short as the duration of the absolute refractory period. A stronger than normal stimulus is required to overcome the relative refracctory period (see Refractory Periods for a review).

Voltage-dependent calcium channels

Voltage-dependent calcium channels (VDCC) are a group of voltage-gated ion channels found in the membrane of excitable cells (e.g., muscle, glial cells, neurons, etc.) with a permeability to the calcium ion Ca2+.[1][2] These channels are slightly permeable to sodium ions, so they are also called Ca2+-Na+ channels, but their permeability to calcium is about 1000-fold greater than to sodium under normal physiological conditions.[3] At physiologic or resting membrane potential, VDCCs are normally closed. They are activated (i.e., opened) at depolarized membrane potentials and this is the source of the "voltage-dependent" epithet. The concentration of calcium (Ca2+ ions) is normally several thousand times higher outside of the cell than inside. Activation of particular VDCCs allows Ca2+ to rush into the cell, which, depending on the cell type, results in activation of calcium-sensitive potassium channels, muscular contraction,[4] excitation of neurons, up-regulation of gene expression, or release of hormones or neurotransmitters. VDCCs have been immunolocalized in the zona glomerulosa of normal and hyperplastic human adrenal, as well as in aldosterone-producing adenomas (APA), and in the latter T-type VDCCs correlated with plasma aldosterone levels of patients.[5] Excessive activation of VDCCs is a major component of excitotoxicity, as severely elevated levels of intracellular calcium activates enzymes which, at high enough levels, can degrade essential cellular structures.

voltage-gated potassium channel

Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized cell to a resting state.

adrenal cortex

along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, such as aldosterone and cortisol, respectively. It is also a secondary site of androgen synthesis.[2] Recent data suggest that adrenocortical cells under pathological as well as under physiological conditions show neuroendocrine properties; within the normal adrenal, this neuroendocrine differentiation seems to be restricted to cells of the zona glomerulosa and might be important for an autocrine regulation of adrenocortical function.[3]

brain

an organ of soft nervous tissue contained in the skull of vertebrates, functioning as the coordinating center of sensation and intellectual and nervous activity.

mitochondria

an organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur. It has a double membrane, the inner layer being folded inward to form layers (cristae).

arachnoid villi

arachnoid villi microscopic projections of the arachnoid into some of the venous sinuses. Arachnoid granulations, also known as a Pacchionian granulation, are projections of the arachnoid membrane (villi) into the dural sinuses that allow CSF entrance from the subarachnoid space into the venous system.

cerebrospinal fluid

clear watery fluid that fills the space between the arachnoid membrane and the pia mater.

ionotropic effect

ionotropic effect can be applied to the effect of a transmitter substance or hormone on its target. The transmitter or hormone activates or deactivates ionotropic receptors (ligand-gated ion channels). The effect can be either positive or negative, specifically a depolarization or a hyperpolarization respectively. This term is commonly confused with an inotropic effect, which refers to a change in the force of contraction (e.g. in heart muscle ) produced by transmitter substances or hormones.

Temporal summation

is where a high frequency of action potentials in the presynaptic neuron elicits postsynaptic potentials that overlap and summate with each other. The effect is generated by a single neuron as a way of achieving action potential. Temporal summation of EPSPs is the additive effect produced by many EPSPs that have been generated at the same synapse by a series of high-frequency action potentials on the presynaptic neuron.

nerves, roots, and tracts

nerve - a group of fibers (axons) outside the CNS. The spinal nerves contain the fibers of the sensory and motor neurons. A nerve does not contain cell bodies. They are located in the ganglion (sensory) or in the gray matter (motor). tract - a group of fibers inside the CNS. The spinal tracts carry information up or down the spinal cord, to or from the brain. Tracts within the brain carry information from one place to another within the brain. Tracts are always part of white matter. The spinal cord does not run through the lumbar spine (lower back). After the spinal cord stops in the lower thoracic spine, the nerve roots from the lumbar and sacral levels come off the bottom of the cord like a "horse's tail" (cauda equina) and exit the spine (view the spinal nerve roots with Figure 1). Therefore, because the lumbar spine has no spinal cord and comprises a large amount of space for the nerve roots, even serious conditions (such as a large disc herniation) are unlikely to cause paraplegia (loss of motor function in the legs). The white matter of the spinal cord contains tracts which travel up and down the cord. Many of these tracts travel to and from the brain to provide sensory input to the brain, or bring motor stimuli from the brain to control effectors. Ascending tracts, those which travel toward the brain are sensory, descending tracts are motor. Figure 12.30 shows the location of the major tracts in the spinal cord. For most the name will indicate if it is a motor or sensory tract. Most sensory tracts names begin with spino, indicating origin in the spinal cord, and their name will end with the part of the brain where the tract leads. For example the spinothalamic tract travels from the spinal cord to the thalamus. Tracts whose names begin with a part of the brain are motor. For example the corticospinal tract begins with fibers leaving the cerebral cortex and travels down toward motor neurons in the cord.

neuromodulators

neuromodulator is a messenger released from a neuron in the central nervous system, or in the periphery, that affects groups of neurons, or effector cells that have the appropriate receptors. It may not be released at synaptic sites, it often acts through second messengers and can produce long-lasting effects. The release may be local so that only nearby neurons or effectors are influenced, or may be more widespread, which means that the distinction with a neurohormone can become very blurred. A neurohormone is a messenger that is released by neurons into the haemolymph and which may therefore exert its effects on distant peripheral targets. It may differ only in degree from a neuromodulator in the extent of its action.

continuous propagation

propagation flow of charge with the message repeated over and over as it flows down the pathway of an axon continuous propagation occurs on unmyelinated axons, flows one direction, previous section is in a refractory period and cannot be depolarized yet saltatory propagation jumps along myelinated axon onto unmyelinated nodes, impulses move more rapidly and use less energy

spatial summation

sensory summation that involves stimulation of several spatially separated neurons at the same time

neural tube

(in an embryo) a hollow structure from which the brain and spinal cord form. Defects in its development can result in congenital abnormalities such as spina bifida.

depolarization

...excess of positive ions on the outside of the sarcolemma (a stage known as the resting potential). When a nerve impulse stimulates ion channels to open, positive ions flow into the cell and cause depolarization, which leads to muscle cell contraction.

motor nuclei

1. nuclei located in the spinal cord (T1-L2 and S2-S4) and in the brainstem (Edinger-Westphal nucleus, superior and inferior salivatory nuclei, dorsal vagal nucleus, and parts of the ambiguus nucleus) from which general visceral efferent preganglionic fibers arise; may be sympathetic (T1-L2) or parasympathetic (craniosacral); hypothalamic nuclei/areas function in concert with autonomic nuclei.

dorsal root ganglia

A dorsal root ganglion (or spinal ganglion) (also known as a posterior root ganglion), is a cluster of nerve cell bodies (a ganglion) in a posterior root of a spinal nerve. The dorsal root ganglia contain the cell bodies of sensory (afferent) neurons.

metabotropic

A metabotropic receptor is a type of membrane receptor of eukaryotic cells that acts through a secondary messenger. It may be located at the surface of the cell or in vesicles.

metabotropic

A metabotropic receptor is a type of membrane receptor of eukaryotic cells that acts through a secondary messenger. It may be located at the surface of the cell or in vesicles. Based on their structural and functional characteristics, neurotransmitter receptors can be classified into two broad categories: metabotropic and ionotropic receptors. Ionotropic receptors form an ion channel pore. In contrast, metabotropic receptors are indirectly linked with ion channels on the plasma membrane of the cell through signal transduction mechanisms, often G proteins. Hence, G protein-coupled receptors are inherently metabotropic. Other examples of metabotropic receptors include tyrosine kinases and guanylyl cyclase receptors.

synaptic cleft

A microscopic gap called a synaptic cleft exists between the neurons. When a nerve impulse arrives at the axon terminal of one neuron, a chemical substance is released through the presynaptic membrane, traveling in milliseconds across...

spinal nerves

chemical synapses

Chemical synapses are biological junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie perception and thought. They allow the nervous system to connect to and control other systems of the body. At a chemical synapse, one neuron releases neurotransmitter molecules into a small space (the synaptic cleft) that is adjacent to another neuron. The neurotransmitters are kept within small sacs called vesicles, and are released into the synaptic cleft by exocytosis. These molecules then bind to receptors on the postsynaptic cell's side of the synaptic cleft. Finally, the neurotransmitters must be cleared from the synapse through one of several potential mechanisms including enzymatic degradation or re-uptake by specific transporters either on the presynaptic cell or possibly by neuroglia to terminate the action of the transmitter.

CORPUS CALLOSUM

hair follicle receptors

All the way down at the bottom is the root of the hair called the root hair plexus. Now, don't let the word 'plexus' confuse you; it just means a network. In this case, it is a network of sensory nerves that surrounds the base of the hair follicle. It is because of the plexus of nerves that you can feel the movement of even a single hair, like when that pesky mosquito lands on your arm.

electrical synapses

An electrical synapse is a mechanical and electrically conductive link between two neighboring neurons that is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction. At gap junctions, such cells approach within about 3.5 nm of each other,[1] a much shorter distance than the 20- to 40-nanometer distance that separates cells at chemical synapse.[2] In many animals, electrical synapse-based systems co-exist with chemical synapses. Compared to chemical synapses, electrical synapses conduct nerve impulses faster, but, unlike chemical synapses, they lack gain—the signal in the postsynaptic neuron is the same or smaller than that of the originating neuron. Electrical synapses are often found in neural systems that require the fastest possible response, such as defensive reflexes. An important characteristic of electrical synapses is that, most of the time, they are bidirectional (allow impulse transmission in either direction).[3] However, some gap junctions do restrict communication to only one direction.[citation needed]

inhibitory post-synaptic potentials (IPSP)

An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential.[1] The opposite of an inhibitory postsynaptic potential is an excitatory postsynaptic potential (EPSP), which is a synaptic potential that makes a postsynaptic neuron more likely to generate an action potential. They can take place at all chemical synapses, which use the secretion of neurotransmitters to create cell to cell signalling. Inhibitory presynaptic neurons release neurotransmitters that then bind to the postsynaptic receptors; this induces a postsynaptic conductance change as ion channels open or close. An electric current that changes the postsynaptic membrane potential to create a more negative postsynaptic potential is generated. Depolarization can also occur due to an IPSP if the reverse potential is between the resting threshold and the action potential threshold. Another way to look at inhibitory postsynaptic potentials is that they are also a chloride conductance change in the neuronal cell because it decreases the driving force.[2]Microelectrodes can be used to measure postsynaptic potentials at either excitatory or inhibitory synapses. In general, a postsynaptic potential is dependent on the type and combination of receptor channel, reverse potential of the postsynaptic potential, action potential threshold voltage, ionic permeability of the ion channel, as well as the concentrations of the ions in and out of the cell; this determines if it is excitatory or inhibitory. IPSPs always want to keep the membrane potential more negative than the action potential threshold and can be seen as a "transient hyperpolarization".[3] EPSPs and IPSPs compete with each other at numerous synapses of a neuron; this determines whether or not the action potential at the presynaptic terminal will regenerate at the postsynaptic membrane. Some common neurotransmitters involved in IPSPs are GABA and glycine.

ionotropic

An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction. Wikipedia

labeled line

Anatomical or labeled line coding tells the mind/brain where a stimulus is (for example, how you can tell a singing bird is up and to your left, or where is itches on your back) It also tells (usually) which kind it is (a small, red bird, singing two notes, or that it's an itch and not a touch or pain). J. Muller proposed this idea early in the 19th century code, calling it the Law of Specific Nerve Energies. Muller proposed that we see light when visual areas of the brain become active; we hear sound when auditory areas of the brain become active; we feel touch when somatosensory (~ touch) areas of the brain become active, etc. This idea opened the modern study of how the sense work. This idea turned into labeled line (anatomical) coding when it was extended to explain the different qualities you experience within each sense: different colors of light, pitches in sound, touch, vibration, warmth, etc. on the skin, etc. Anatomical coding states that you experience different qualities when different parts of a sensory area become active. For example, if one end of the auditory area of the cerebral cortex becomes active, you experience a high-pitched tone. If the other end of the auditory area of the cortex becomes active, you experience a low- pitched tone. if the middle of the auditory area of the cortex becomes active, you experience intermediate pitched tones.

pineal

a pea-sized conical mass of tissue behind the third ventricle of the brain, secreting a hormonelike substance in some mammals.

neurons

a specialized cell transmitting nerve impulses; a nerve cell. A neuron also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the brain and spinal cord of the central nervous system (CNS), and of the ganglia of the peripheral nervous system (PNS). Specialized types of neurons include: sensory neurons which respond to touch, sound, light and all other stimuli affecting the cells of the sensory organs that then send signals to the spinal cord and brain, motor neurons that receive signals from the brain and spinal cord to cause muscle contractions and affect glandular outputs, and interneurons which connect neurons to other neurons within the same region of the brain, or spinal cord in neural networks. A typical neuron consists of a cell body (soma), dendrites, and an axon. The term neurite is used to describe either a dendrite or an axon, particularly in its undifferentiated stage. Dendrites are thin structures that arise from the cell body, often extending for hundreds of micrometres and branching multiple times, giving rise to a complex "dendritic tree". An axon (also called a nerve fiber when myelinated) is a special cellular extension (process) that arises from the cell body at a site called the axon hillock and travels for a distance, as far as 1 meter in humans or even more in other species. Nerve fibers are often bundled into fascicles, and in the peripheral nervous system, bundles of fascicles make up nerves (like strands of wire make up cables). The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates. At the majority of synapses, signals are sent from the axon of one neuron to a dendrite of another. There are, however, many exceptions to these rules: neurons that lack dendrites, neurons that have no axon, synapses that connect an axon to another axon or a dendrite to another dendrite, etc.

threshold

1. the level that must be reached for an effect to be produced, as the degree of intensity of stimulus that just produces a sensation. 2. that value at which a stimulus just produces a sensation, is just appreciable, or comes just within the limits of perception. 3. renal t. auditory threshold the slightest perceptible sound. threshold of consciousness the lowest limit of sensibility; the point of consciousness at which a stimulus is barely perceived. defibrillation threshold DFT; the minimum amount of energy in joules that will consistently terminate ventricular fibrillation. fibrillation threshold the least intensity of an electrical impulse that will cause cardiac tissue to begin fibrillation. pacing threshold the minimal electrical stimulus required to produce consistent cardiac depolarization. renal threshold that concentration of a substance (threshold substance) in plasma at which it begins to be excreted in the urine. sensing threshold in cardiac pacing terminology, the voltage of the minimum signal that consistently activates pulse generator function.

spinal nerves

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine.[1] There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system. Typical spinal nerve location Each spinal nerve is formed from the combination of nerve fibers from its posterior and anterior roots. The posterior root is the afferent sensory root and carries sensory information to the brain. The anterior root is the efferent motor root and carries motor information from the brain. The spinal nerve emerges from the spinal column through an opening (intervertebral foramen) between adjacent vertebrae. This is true for all spinal nerves except for the first spinal nerve pair (C1), which emerges between the occipital bone and the atlas (the first vertebra). Thus the cervical nerves are numbered by the vertebra below, except spinal nerve C8, which exists below vertebra C7 and above vertebra T1. The thoracic, lumbar, and sacral nerves are then numbered by the vertebra above. In the case of a lumbarized S1 vertebra (aka L6) or a sacralized L5 vertebra, the nerves are typically still counted to L5 and the next nerve is S1.

acetylcholine

Acetylcholine is an organic chemical that functions in the brain and body of many types of animals, including humans, as a neurotransmitter—a chemical released by nerve cells to send signals to other cells

Schwann cells and oligodendrocytes

Both insulate axons by creating myelin. Schwann cells, found in the PNS, are associated with a single axon. One axon may have many Schwann cells wrapped around it leaving small gaps of unmyelinated areas called nodes of Ranvier. Oligodendrocytes are found in the CNS and form myelin around portions of several axons.

cervical and lumbar enlargements (why more cells here?)

Could you identify the source of a section if you had nothing to compare it to? In general, you should be able to differentiate cervical from thoracic from lumbar from sacral. Here is a series of cross sections: The first thing to notice is overall shape. Cervical sections tend to be wide and squashed looking, like an oval. Compare the cervical section to the round lumbar section. The second thing to check for is a ventral horn enlargement. At segments that control a limb, the motor neurons are large and numerous. This causes enlarged ventral horns in two places: the lower cervical sections (C5-C8) and the lumbar/sacral sections. If you see an enlargement, you just need to differentiate cervical from lumbar. This can be done by shape (see above) or by proportion of white matter. The amount of white matter relative to grey matter decreases as you move down the cord. This is logical - in the white matter of the cervical cord you have all of the axons going to or from the entire body, more or less. In sacral cord the white matter contains only those axons going to or from the last couple of dermatomes - all other axons have "gotten off" at higher levels. This is why sacral cord looks like it has so much grey matter - really it has just lost all of the white. So, in summary, here are the level cues so far: wide flat cord, lots of white matter, ventral horn enlargements = cervical. Round cord, ventral horn enlargements = lumbar. Small round cord, almost no white matter = sacral. And the remaining level, thoracic, is the easiest of all. Notice the pointed tips which stick out between the small dorsal and ventral horns. This extra cell column is called the intermediate horn, or the intermediolateral cell column. It is the source of all of the sympathetics in the body, and occurs only in thoracic sections.

decussation

Decussation describes the point where the nerves cross from one side of the brain to the other, and typically the nerves from the left side of the body decussate to the right side of the brain and the nerves from the right side of the body decussate to the left brain, however depending on the function of the nerves the level of decussation is variable.

Epinephrine

Epinephrine, also known as adrenalin or adrenaline, is primarily a medication and hormone.[3][4] As a medication it is used for a number of conditions including: anaphylaxis, cardiac arrest, and superficial bleeding.[1] Inhaled epinephrine may be used to improve the symptoms of croup.[5] It may also be used for asthma when other treatments are not effective. It is given intravenously, by injection into a muscle, by inhalation, or by injection just under the skin.[1] Common side effects include shakiness, anxiety, and sweating. A fast heart rate and high blood pressure may occur. Occasionally it may result in an abnormal heart rhythm. While the safety of its use during pregnancy and breastfeeding is unclear, the benefits to the mother must be taken into account.[1] Epinephrine is normally produced by both the adrenal glands and certain neurons.[3] It plays an important role in the fight-or-flight response by increasing blood flow to muscles, output of the heart, pupil dilation, and blood sugar.[6][7] Epinephrine does this by its effects on alpha and beta receptors.[7] It is found in many animals and some one cell organisms.[8][9]

exocytosis

Exocytosis is a form of active transport in which a cell transports molecules (such as proteins) out of the cell (exo- + cytosis) by expelling them in an energy-using process. Exocytosis and its counterpart, endocytosis, are used by all cells because most chemical substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane by passive means. In exocytosis, secretory vesicles carry their contents across the cell membrane and into the extracellular space. These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane. However, the mechanism of the secretion of intravesicular contents out of the cell is very different from the incorporation in the cell membrane of ion channels, signaling molecules, or receptors. While for membrane recycling and the incorporation in the cell membrane of ion channels, signaling molecules, or receptors complete membrane merger is required, for cell secretion there is transient vesicle fusion with the cell membrane in a process called exocytosis, dumping its contents out of the cell's environment. Examination of cells following secretion using electron microscopy demonstrate increased presence of partially empty vesicles following secretion. This suggested that during the secretory process, only a portion of the vesicular content is able to exit the cell. This could only be possible if the vesicle were to temporarily establish continuity with the cell plasma membrane, expel a portion of its contents, then detach, reseal, and withdraw into the cytosol (endocytose). In this way, the secretory vesicle could be reused for subsequent rounds of exo-endocytosis, until completely empty of its contents.[3]

gyri and sulci

Externally, the cerebrum has a highly convoluted appearance, consisting of sulci (grooves or depressions) and gyri (ridges or elevations). It is divided into two anatomically symmetrical hemispheres by the longitudinal fissure - a major sulcus that runs in the median sagittal plane. The falx cerebri (a fold of dura mater) descends vertically to fill this fissure. The two cerebral hemispheres are connected by a white matter structure, called the corpus callosum. The main sulci are: Central sulcus - groove separating the frontal and parietal lobes. Lateral sulcus - groove separating the frontal and parietal lobes from the temporal lobe. Lunate sulcus - groove located in the occipital cortex. The main gyri are: Precentral gyrus - ridge directly anterior to central sulcus, location of primary motor cortex. Postcentral gyrus - ridge directly posterior to central sulcus, location of primary somatosensory cortex. Superior temporal gyrus - ridge located inferior to lateral sulcus, responsible for the reception and processing of sound.

first, second, and third order neurons in a sensory pathway

First order neuron conducts the nerve impulse from the receptor to the spinal cord or brain stem Second order neuron conducts the impulse from the brainstem- spinal cord to the thalamus (ALWAYS ENDS IN THE THALAMUS) Third order neuron conducts nerve impulses from the thalamus to the primary somatosensory area.

adrenal steroids glucocorticoids (eg. cortisol) corticotropin releasing hormone (CRH) adrenocorticotropic hormone (ACTH) cortisol

Five classes of steroid hormones are produced in the adrenal cortex: glucocorticoids, mineralocorticoids, progestins, androgens, and estrogens. However, the amount of progestin, androgen, and estrogen produced by the adrenal is a minor fraction of the total amount of these steroids produced in the body. By contrast, glucocorticoids and mineralocorticoids are produced almost exclusively in the adrenal cortex. Glucocorticoids have a broad physiologic role that includes both regulation of glucose metabolic pathways and modulation of the immune system. Mineralocorticoids are key regulators of mineral and water balance. Glucocorticoid, any steroid hormone that is produced by the adrenal gland and known particularly for its anti-inflammatory and immunosuppressive actions. The adrenal gland is an organ situated on top of the kidney. It consists of an outer cortex (adrenal cortex) and an inner medulla (adrenal medulla). The hormones secreted from the cortex are steroids, generally classified as glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone, which causes sodium retention and potassium excretion by the kidney). Those substances emanating from the medulla are amines, such as epinephrine and norepinephrine. Glucocorticoids together with mineralocorticoids are used in replacement therapy in acute or chronic adrenal insufficiency (Addison disease). Glucocorticoids, including a range of synthetic analogs (e.g., prednisolone, triamcinolone, and dexamethasone), are also used as anti-inflammatory and immunosuppressant agents. As anti-inflammatory agents, they are used in the treatment of bronchial asthma. Glucocorticoids indirectly inhibit the activity of phospholipase A2, an enzyme that plays an essential role in the synthesis of prostaglandins and leukotrienes; its inhibition by lipocortin-1 underlies part of the anti-inflammatory effects of glucocorticoids. Glucocorticoids also reduce the synthesis of some proteins that directly mediate the inflammatory response. Corticotropin-releasing hormone (CRH) also known as corticotropin-releasing factor (CRF) or corticoliberin is a peptide hormone and neurotransmitter involved in the stress response. It is a releasing hormone that belongs to corticotropin-releasing factor family. In humans, it is encoded by the CRH gene.[1] Its main function is the stimulation of the pituitary synthesis of ACTH, as part of the HPA Axis. Corticotropin-releasing hormone (CRH) is a 41-amino acid peptide derived from a 196-amino acid preprohormone. CRH is secreted by the paraventricular nucleus (PVN) of the hypothalamus in response to stress. Increased CRH production has been observed to be associated with Alzheimer's disease and major depression,[2] and autosomal recessive hypothalamic corticotropin deficiency has multiple and potentially fatal metabolic consequences including hypoglycemia.[1] In addition to being produced in the hypothalamus, CRH is also synthesized in peripheral tissues, such as T lymphocytes, and is highly expressed in the placenta. In the placenta, CRH is a marker that determines the length of gestation and the timing of parturition and delivery. A rapid increase in circulating levels of CRH occurs at the onset of parturition, suggesting that, in addition to its metabolic functions, CRH may act as a trigger for parturition.[1] Adrenocorticotropic hormone (ACTH), also known as corticotropin (INN, BAN) (brand names Acortan, ACTH, Acthar, Acton, Cortigel, Trofocortina),[1][2] is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland.[3] It is an important component of the hypothalamic-pituitary-adrenal axis and is often produced in response to biological stress (along with its precursor corticotropin-releasing hormone from the hypothalamus). Its principal effects are increased production and release of cortisol by the cortex of the adrenal gland. Primary adrenal insufficiency, also called Addison's disease, occurs when adrenal gland production of cortisol is chronically deficient, resulting in chronically elevated ACTH levels; when a pituitary tumor is the cause of elevated ACTH (from the anterior pituitary) this is known as Cushing's disease and the constellation of signs and symptoms of the excess cortisol (hypercortisolism) is known as Cushing's syndrome. Conversely, deficiency of ACTH is a cause of secondary adrenal insufficiency, often as a result of hypopituitarism. ACTH is also related to the circadian rhythm in many organisms.[4] Cortisol is a steroid hormone, in the glucocorticoid class of hormones, and is produced in humans by the zona fasciculata of the adrenal cortex within the adrenal gland.[1] It is released in response to stress and low blood-glucose concentration. It functions to increase blood sugar through gluconeogenesis, to suppress the immune system, and to aid in the metabolism of fat, protein, and carbohydrates.[2] It also decreases bone formation.[3] Hydrocortisone (INN, USAN, BAN) is a name for cortisol when it is used as a medication. Hydrocortisone is used to treat people who lack adequate naturally generated cortisol. It is on the World Health Organization's List of Essential Medicines needed in a basic health system.[4]

tonic vs. phasic (sensory adaptation)

Four functional receptor types are 1. chemoreceptors 2. photoreceptors 3. thermoreceptors 4. mechanoreceptors The thing they have in common is that they change the polarization of the cell and may eventually cause an action potential. Sensory nerve endings act in a similar way as dendrites. Response to a stimulus is local and graded and contributes toward changing a cell toward or away from threshold. While similar to an EPSP they are called receptor or generator potentials Receptor response fall into 2 categories, phasic and tonic receptors Phasic receptors send APs in quick sensation when first stimulated but soon reduce the AP frequency even if the stimulus continues. They adapt to the stimulation. Examples? odor, touch, temperature Tonic receptors produce a constant signal (AP frequency) while a stimulus is applied. Examples? photoreceptors, mechanoreceptors

G protein

G proteins are so-called because they bind the guanine nucleotides GDP and GTP. They are heterotrimers (i.e., made of three different subunits) associated with. the inner surface of the plasma membrane and. transmembrane receptors of hormones, etc. These are called G protein-coupled receptors

sensory receptors and sensory organs

General (somatic) senses Sensory receptors not localized in one place in the body (pain, temp, pressure, touch) Special senses Sensory receptors localized in one particular organ in the body (vision, hearing, taste, smell, equilibrium) Photoreceptors Respond to light Mechanoreceptors Respond to stimuli which produce movement or change in shape of receptor; touch and pressure receptors Chemoreceptors Respond to chemicals which stimulate receptors Thermoreceptors Respond to temperatures above or below body temp; hot and cold receptors in skin and mouth Nociceptors (pain receptors) Respond to stimuli which damage tissue, likely to chemicals released by damaged tissue. Proprioceptors Types of mechanoreceptors located in muscles, tendons, ligaments, and joints; sense of position of body parts Visceral receptors Located in the walls of organs; consceious/subconsceious

Growth hormone

Growth hormone (GH), also known as somatotropin (or as human growth hormone [hGH or HGH] in its human form), is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in human development. It is a type of mitogen which is specific only to certain kinds of cells. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by somatotropic cells within the lateral wings of the anterior pituitary gland. GH is a stress hormone that raises the concentration of glucose and free fatty acids.[1][2] It also stimulates production of IGF-1. A recombinant form of hGH called somatropin (INN) is used as a prescription drug to treat children's growth disorders and adult growth hormone deficiency. In the United States, it is only available legally from pharmacies, by prescription from a doctor. In recent years in the United States, some doctors have started to prescribe growth hormone in GH-deficient older patients (but not on healthy people) to increase vitality. While legal, the efficacy and safety of this use for HGH has not been tested in a clinical trial. At this time, HGH is still considered a very complex hormone, and many of its functions are still unknown.[3]

Growth hormone releasing hormone

Growth hormone-releasing hormone (GHRH), also known as somatoliberin or by several other names in its endogenous forms and as somatorelin (INN) in its pharmaceutical form, is a releasing hormone of growth hormone (GH). It is a 44[1]-amino acid peptide hormone produced in the arcuate nucleus of the hypothalamus. GHRH first appears in the human hypothalamus between 18 and 29 weeks of gestation, which corresponds to the start of production of growth hormone and other somatotropes in fetuses.[1]

sensory pathways

How does information travel between body and brain? In this lesson, we'll explore somatic sensory pathways, including ascending and descending tracts, afferent and efferent nerves, and how they work together in the body. Somatic Senses Patrick has a problem. He had an accident, and he can't feel anything from his right leg or foot. If you tickle his left foot, he laughs, but his right foot doesn't get any reaction from him. Likewise, if his left leg brushes up against something hot, he pulls it away and says, 'Ouch!' But, if his right leg brushes up against something hot, he doesn't feel it and so doesn't pull it away. Somatic senses are the senses that have to do with touch. Tickling and pain, like on Patrick's legs, are somatic senses, but so are other things that you might not think of right away, like temperature and movement. Somatosensory pathways relay information between the brain and nerve cells in the skin and organs. For example, these pathways are how Patrick knows that someone is tickling his left foot. But, why doesn't he feel tickling on his right foot? To find out, let's look closer at somatosensory pathways, including the difference between ascending and descending pathways. Ascending Pathways Patrick can't really feel anything in his right leg or foot. As we've seen, this can be a problem, like when his right leg brushes up against something hot, and Patrick doesn't feel it, so he doesn't pull his right leg away, and risks injury. The problem that Patrick is experiencing is with his ascending somatosensory pathway, which is sometimes called the afferent pathway. This is a series of nerves that send information to the brain from the body. Think about the word ascending, which means going up, and you can remember that the ascending pathway sends information up to the brain. The nerves the connect the body to the spinal cord and the spinal cord to the brain are called afferent nerves, and they send information from the body to the brain. You can remember afferent pathway and afferent nerves by thinking about the letter a: ascending and afferent both start with a, and they are the same somatosensory pathway. Let's look at an example of the ascending pathway. In most people, an afferent pathway might send sensory information from the right leg to the brain so that they understand what their right leg is experiencing. Of course, for Patrick, that particular ascending pathway isn't working correctly, even though the afferent pathway for his left leg is working fine. How does the ascending pathway normally work? Information goes from the body part to the spinal cord. From there, it goes up the spinal cord to the brain. As it enters the brain, it shifts to the opposite side, and then goes all the way up to the top of the brain where it settles in the somatosensory cortex, or the part of the brain dedicated to somatic sensory information. Let's look at that in Patrick's body. His left leg (the one that works normally) might send information to his spinal cord about how scratchy his wool pants are. This information then travels up Patrick's spinal cord. Just as it enters his brain, it crosses over to the right side of his brain and then goes up into the somatosensory cortex, where his brain registers that the sensation he's feeling is scratchiness because of the wool pants. Descending Pathways As we've seen, ascending pathways send information from the body up to the brain, but it wouldn't be a very good system if that's the only direction information could flow. Descending somatosensory pathways, also sometimes called efferent pathways, send information from the brain down to the body. Think of the word descending, and you can remember that the descending pathway is sending information down to the body from the brain. Like afferent nerves in afferent pathways, there are efferent nerves in efferent pathways, which are nerves that send information from the brain to the body. Descending somatosensory pathways work in kind of the opposite way that ascending pathways do. Information goes from the motor cortex in the brain (which is right next to the somatosensory cortex) and shifts to the opposite side in the spinal cord. It travels down the spinal cord and out to the muscles and organs of the body. Let's look at an example. Remember that Patrick's ascending pathway has made him aware of the fact that his wool pants are making his left leg itch. Now, the right side of Patrick's brain sends a message from the motor cortex down to the spinal cord. It moves from the right side to the left side in the spinal cord, and then travels down into his left arm. The arm then moves down to scratch his itchy left leg. Notice that the ascending pathways--from the body to the brain--communicate somatic sensory information, whereas the descending pathways--from the brain to the body--communicate motor movement information. In other words, The afferent pathways are about taking sensory information in, and the efferent pathways are about sending motor movement information out. Lesson Summary The somatic senses are senses that have to do with the experience of touch. Somatosensory pathways relay information between the brain and nerves in the skin and organs. Ascending pathways, also called afferent pathways, send somatosensory information from the body up to the brain through a series of afferent nerves. Meanwhile, descending pathways, also called efferent pathways, send motor movement information from the brain down to the body through a series of efferent nerves.

axon

If we compared the human body to a computer, then the nervous system would be the motherboard. It is the main control unit for the body, and through the nervous system, other functions in the body are regulated. Therefore, the nervous system is one of the most important systems in the human body as its effects can be seen in all other systems. The nervous system communicates through the use of cells, called neurons. These cells participate in cell-to-cell communication for the purposes of regulating bodily processes. This is done through the generation of electrochemical stimulation that relays from neurons to other neurons and effector (target) cell. The delivery of this stimulation is going to be mediated by a portion of the neuron known as the axon. Structures of Axons Axons are extended regions of the neuron cell membrane. It starts from a portion of the cell body, known as the axon hillock. From there, the axon extends towards the target cell to what is known as the terminal. Along the cell membrane of the axon will be ion channels and ATP-driven pumps that will regulate ion concentrations within the axon. These ion concentrations will establish the resting membrane potential, which is the electrochemical charge of the membrane when the neuron is at rest. Structures Found in a Neuron Neuron Some axons will also have additional structures to assist with communication. In areas of the nervous system that require faster communication, the axons will contain insulation, known as myelin sheaths. This insulation speeds up the transmission of cell-to-cell communication and stimulation. Not all axons will have these sheaths, but the ones that do function quicker. Communication via Axons At rest, the membrane potential of an axon is typically -70 millivolts. This charge is established by ATP-driven pumps in the membrane known as sodium/potassium pump. This pump ensures that more positive ions are outside of the membrane compared to inside of the cell. When the neuron depolarizes (becomes positively charged), it will transmit this communication down the axon by way of voltage-gated (electrically controlled) ion channels that open up to allow for the charge to relay along the axon. This takes place until the charge reaches the axon terminal. The axon terminal is the site of neurotransmitter release. Neurotransmitters are chemical messengers that are released from the axon and received by effector cells. This process is critical for delivery of the message to the cells and tissues that are being controlled. The terminal, then, is the final point of stimulation in the axon before the charge is delivered. Axon Terminal: Site of Neurotransmitter Release Axon terminal Conclusion The axon is the portion of the cell responsible for delivering cell-to-cell communication. Through transmission of electrical charges and the release of neurotransmitters, axons are able to control target cells in order to regulate bodily processes. Therefore, axons are the key components of neuronal function for the nervous system and other systems under nervous control.

ventral (anterior) roots

In anatomy and neurology, the ventral root or anterior root is the efferent motor root of a spinal nerve. At its distal end, the ventral root joins with the dorsal root to form a mixed spinal nerve.

insula

In each hemisphere of the mammalian brain the insular cortex (often called insula, insulary cortex or insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal and frontal lobes). The insulae are believed to be involved in consciousness and play a role in diverse functions usually linked to emotion or the regulation of the body's homeostasis. These functions include perception, motor control, self-awareness, cognitive functioning, and interpersonal experience. In relation to these, it is involved in psychopathology. The insular cortex is divided into two parts: the larger anterior insula and the smaller posterior insula in which more than a dozen field areas have been identified. The cortical area overlying the insula toward the lateral surface of the brain is the operculum (meaning lid). The opercula are formed from parts of the enclosing frontal, temporal, and parietal lobes.

chemical signal

In multicellular organisms, growth factors, hormones, neurotransmitters, and extracellular matrix components are some of the many types of chemical signals cells use. These substances can exert their effects locally, or they might travel over long distances.

lateral inhibition (for localization improvement

In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception. It is also referred to as lateral antagonism and occurs primarily in visual processes, but also in tactile, auditory, and even olfactory processing.[1] Cells that utilize lateral inhibition appear primarily in the cerebral cortex and thalamus and make up lateral inhibitory networks (LINs).[2] Artificial lateral inhibition has been incorporated into artificial sensory systems, such as vision chips,[3] hearing systems,[4] and optical mice.[5][6] An often under-appreciated point is that although lateral inhibition is visualised in a spatial sense, it is also thought to exist in what is known as "lateral inhibition across abstract dimensions." This refers to lateral inhibition between neurons that are not adjacent in a spatial sense, but in terms of modality of stimulus. This phenomenon is thought to aid in colour discrimination.

excitatory post-synaptic potentials (EPSP)

In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the flow of positively charged ions into the postsynaptic cell, is a result of opening ligand-gated ion channels. These are the opposite of inhibitory postsynaptic potentials (IPSPs), which usually result from the flow of negative ions into the cell or positive ions out of the cell. EPSPs can also result from a decrease in outgoing positive charges, while IPSPs are sometimes caused by an increase in positive charge outflow. The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC).

repolarization

In neuroscience, repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value.

corpora quadrigemina

In the brain, the corpora quadrigemina (Latin for "quadruplet bodies") are the four colliculi—two inferior, two superior—located on the tectum of the dorsal aspect of the midbrain. They are respectively named the inferior and superior colliculus. The corpora quadrigemina are reflex centers involving vision and hearing.

ganglia vs nuclei

In the central nervous system, a collection of neuron cell bodies is called a nucleus. In the peripheral nervous system, a collection of neuron cell bodies is called a ganglion (plural: ganglia). The one exception to this rule that you may have encountered is the basal ganglia in the brain.

dura mater

In the central nervous system, there are three different layers that cover the spinal cord and brain. These are called the meninges, and their three levels consist of the: pia, arachnoid, and dura mater. Bone is situated above these layers, followed by periosteum (a fibrous membrane that covers bone) and skin. The dura mater is the top layer of the meninges, lying beneath the bone tissue. This material at times opens into sinus cavities (spaces) located around the skull. This is particularly notable with the dural venous sinuses. Here, liquids, like blood and cerebrospinal fluid, drain and collect into the internal jugular vein. Cerebrospinal fluid is a clear liquid that cushions the brain and spinal cord while also transporting nutrients, chemicals, and waste. Dura mater is also the home to meningeal veins. Many types of medical conditions involve the dura mater. The most common come in the form of hematomas. Arterial bleeding can result in an epidural hematoma, which is when blood collects between the dura mater and the skull. If blood collects between the dura and arachnoid mater, a subdural hematoma results. Also, there are some instances where the dura plays a major role in certain types of headaches.

synapses

In the nervous system, a synapse[1] is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron. Some authors generalize this concept to include the communication from a neuron to any other cell type,[2] such as to a motor cell, although such non-neuronal contacts may be referred to as junctions (a historically older term). Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine.[3] Synapses (at least chemical synapses) are stabilized in position by synaptic adhesion molecules (SAMs) projecting from both the pre- and post-synaptic neuron and sticking together where they overlap; SAMs may also assist in the generation and functioning of synapses. The word "synapse" - from the Greek synapsis (συνάπσις), meaning "conjunction", in turn from συνάπτεὶν (συν ("together") and ἅπτειν ("to fasten")) - was introduced in 1897 by English physiologist Michael Foster at the suggestion of English classical scholar Arthur Woollgar Verrall.[4][5] Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so. At a synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target (postsynaptic) cell. Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on an axon, but some postsynaptic sites are located on a dendrite or soma. Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission.[6]

pituitary gland

In this lesson, we'll discuss the functions of the anterior and posterior portions of the pituitary gland, the hormones they release and the relationship with the hypothalamus. Pituitary Gland Located beneath the brain, the pituitary gland is a pea-sized endocrine gland that sits in a bony pocket in the base of the skull called the pituitary fossa. The pituitary fossa is also known as the 'sella turcica,' which translates to 'Turkish saddle' because it resembles a saddle with supports in the front and back used by the Turkish people. Despite its small size, the pituitary gland plays such an important role in controlling the body that it is often called the 'master gland.' There are actually two main parts of the pituitary gland. The front portion, commonly referred to as the anterior pituitary, is also known as the adenohypophysis. The back portion, or posterior pituitary, is called the neurohypophysis. We can keep these two names straight by noting that the words 'anterior' and 'adenohypophysis' both start with the letter 'A.' The pituitary gland is attached to the hypothalamus by the pituitary stalk, which contains nerves and a unique circulatory system, which enables communication between the two. Let's take a closer look at the way the hypothalamus and the pituitary gland work together. Hypothalamus and Pituitary Gland A good way to visualize the relationship between the hypothalamus and the pituitary gland is like the president and his chief of staff. While the hypothalamus, or president, makes the decisions, the pituitary gland, or chief of staff, executes those decisions by sending out commands to the rest of the body. The hypothalamus monitors the body through the circulatory and nervous systems. When it detects that something is out of balance, it sends a message to the pituitary gland that a corrective action is needed. When the pituitary gland gets this message from the hypothalamus, it releases specific hormones into the bloodstream that can stimulate other endocrine glands, organs or tissues depending on what action is needed. It's kind of a like a game of telephone. Instead of the hypothalamus communicating directly with the body, it relies on the pituitary gland to send out the messages. The hypothalamus continues to monitor the state of the body, and when it detects that balance has been restored, it tells the pituitary gland to stop sending out stimulating messages, thereby stopping the corrective action. An example of this process is when we become dehydrated. The hypothalamus is able to detect the increased blood concentration caused by the loss of water. To correct the situation, it uses the posterior pituitary to release anti-diuretic hormone (ADH) into the circulatory system. When ADH reaches the kidneys, it causes more water to be reabsorbed into the bloodstream, diluting the blood. When the hypothalamus detects the return to a normal blood concentration, it stops the release of ADH from the pituitary gland, and the kidneys return to normal functioning. Anterior Pituitary Gland The hypothalamus communicates with the anterior portion of the pituitary gland by way of hormonal messages. These messages come in the form of hypothalamic-releasing and hypothalamic-inhibiting hormones, which tell the anterior pituitary to start or stop an action. Located in the pituitary stalk, a unique arrangement of capillaries and veins, called a portal system, allows the hypothalamic hormones to pass directly to the anterior pituitary without circulating through the body. The anterior pituitary contains glands that produce and store a number of different hormones that control many different functions throughout the body. When a hormone message comes down from the hypothalamus, the anterior pituitary releases its own hormones into the main circulatory system to control the needed action. These pituitary hormones can stimulate other endocrine glands, such as the thyroid, the adrenal cortex and the gonads. The anterior pituitary also sends growth hormone to the bones and muscles and prolactin to the mammary glands to stimulate milk production during pregnancy. Posterior Pituitary Gland The hypothalamus uses the posterior pituitary like a warehouse and distribution center. Anti-diuretic hormone (ADH) and oxytocin are both produced in the hypothalamus and sent through axons to be stored in the posterior pituitary. When the hypothalamus detects that either of these hormones are needed, they are released from the posterior pituitary into the circulatory system to do their jobs. As mentioned earlier, ADH works on the kidneys to increase the reabsorption of water into the bloodstream, but it also causes the constriction of blood vessels to increase blood pressure. Oxytocin is responsible for stimulating uterine contractions during childbirth and the release of milk during nursing. The posterior pituitary differs from the anterior in two distinct ways. First, it interacts with the hypothalamus through direct axon connections, not by hormonal messages. Secondly, it does not produce any of its own hormones but rather stores and releases hormones produced in the hypothalamus. That means that this part of the pituitary gland contains no glands at all. Lesson Summary The pituitary gland is a pea-sized endocrine gland located beneath the hypothalamus in a bony pocket called the pituitary fossa, or sella turcica. The anterior pituitary is called the adenohypophosis, and the posterior pituitary is called the neurohypophosis. The hypothalamus communicates with the anterior pituitary by sending hypothalamic-releasing and hypothalamic-inhibiting hormones through a portal system located in the pituitary stalk. These hypothalamic hormones tell the anterior pituitary to start or stop the release of its own hormones into the bloodstream. Some hormones of the anterior pituitary control other endocrine glands, such as the thyroid, the adrenal cortex and the gonads. It also sends growth hormone to the bones and muscles and prolactin to the mammary glands. The hypothalamus produces anti-diuretic hormone (ADH) and oxytocin and sends them through axons to be stored in the posterior pituitary, where they can be released into the circulatory system when needed. The posterior pituitary does not produce any of its own hormones and does not contain any glands.

lateral, third, [cerebral aqueduct], fourth

Lateral Ventricles The left and right lateral ventricles are located within their respective hemispheres of the cerebrum. They have 'horns' which project into the frontal, occipital and temporal lobes. The volume of the lateral ventricles increases with age. Third Ventricle The lateral ventricles are connected to the third ventricle by the foramen of Monro. The third ventricle is situated in between the right and the left thalamus. The anterior surface of the ventricle contains two protrusions: Supra-optic recess - located above the optic chiasm. Infundibular recess - located above the optic stalk. Fourth Ventricle The fourth ventricle is the last in the system - it receives CSF from the third ventricle via the cerebral aqueduct. It lies within the brainstem, at the junction between the pons and medulla oblongata. From the 4th ventricle, the fluid drains into two places: Central spinal canal - Baths the spinal cord Subarachnoid cisterns - Baths the brain, between arachnoid mater and pia mater. Here the CSF is reabsorbed back into the circulation.

meninges

Meninges, singular meninx, three membranous envelopes—pia mater, arachnoid, and dura mater—that surround the brain and spinal cord. Cerebrospinal fluid fills the ventricles of the brain and the space between the pia mater and the arachnoid. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system. The pia mater is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord. It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels that travel to the brain and spinal cord.

tactile disc/ Merkel disc

Merkel nerve endings are mechanoreceptors that are found in the basal epidermis and hair follicles. They are classified as slowly adapting type I mechanoreceptors. They are large, myelinated nerve endings. They provide information on pressure, position, and deep static touch features such as shapes and edges. Merkel cells in the basal epidermis of the skin store neuropeptides which they release to associated nerve endings in response to pressure. In burns, Merkel endings are most commonly lost. Each ending consists of a Merkel cell in close apposition with an enlarged nerve terminal. This is sometimes referred to as a Merkel cell-neurite complex, or a Merkel disk receptor. A single afferent nerve fibre branches to innervate up to 90 such endings.

Muscle spindles/stretch receptors

Muscle spindles are sensory receptors within the belly of a muscle that primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. This information can be processed by the brain to determine the position of body parts. The responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles, by activating motor neurons via the stretch reflex to resist muscle stretch.

action potential

Ok, so Angela and Jodie want to pass messages, but first, Angela needs to get to the roof of her apartment building. An action potential is a chain reaction down the length of an axon, which causes the neurotransmitter to fire at the neighboring neuron. It's kind of like Angela walking up the stairs in her building, from floor to floor, until she reaches the roof and is able to send Jodie her message. How does an action potential work? To understand, let's think about Angela. Before she can get to the roof, before she can even begin to climb the stairs, she has to start somewhere. If she's in the lobby of her building, she's in the normal starting place. A resting potential is the normal state of an axon. It's like the neuron is at rest, and therefore it's called the resting potential. During resting potential, there are lots of ions that are traveling in and out of the axon, kind of like the lobby of Angela's building. Some of the ions travel easily, and some have it a little harder. During a resting potential, there is a higher concentration of potassium ions inside the axon and a higher concentration of sodium ions outside the axon. This makes the inside of the axon have a more negative charge at rest than the outside of the axon. But what happens when an action potential begins? If a neuron has a message that needs to be sent, sodium channels in the axon open, and sodium rushes into the axon. This makes the inside of the axon more positive relative to the outside. This sets off the chain reaction, as more sodium channels open up a little further down the axon, causing that part of the axon to become more positive, and so on. It's kind of like Angela deciding to go up to the roof and pass her message to Jodie. She can't just magically teleport to the roof. Instead, she has to climb up one flight of stairs at a time. She's getting closer and closer to the point where she can pass the message on to Jodie.

presynaptic facilitation and inhibition

Presynaptic Inhibition: Decreases neurotransmitters release. Ex. endorphins inhibit pain sensation Presynaptic Facilitation: Increases neurotransmitters release. Ex. Glutamate

primary and secondary capillaries

Primary capillary plexus picks up hypothalamic hormones (made by hypothalamus) Secondary capillary plexus

sensory neurons

Sensory neurons are nerve cells within the nervous system responsible for converting external stimuli from the organism's environment into internal electrical impulses. For example, some sensory neurons respond to tactile stimuli and can activate motor neurons in order to achieve muscle contraction.

Somatic motor neurons

Somatic motor neurons, which originate in the central nervous system, project their axons to skeletal muscles (such as the muscles of the limbs, abdominal, and intercostal muscles), which are involved in locomotion .

somatostatin

Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones. Somatostatin inhibits insulin and glucagon secretion. Somatostatin has two active forms produced by alternative cleavage of a single preproprotein: one of 14 amino acids (shown in infobox to right), the other of 28 amino acids[1] which is the short form with another 14 amino acids at one end.[2] Among the vertebrates, there exist six different somatostatin genes that have been named SS1, SS2, SS3, SS4, SS5, and SS6.[3] Zebrafish have all 6.[3] The six different genes along with the five different somatostatin receptors allows somatostatin to possess a large range of functions.[4] Humans have only one somatostatin gene, SST.[5][6][7]

somatostatin

Somatostatin, also known as growth hormone-inhibiting hormone or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation ... Wikipedia

somatotopy (primary somatosensory cortex example)

Somatotopy is the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus). Cortex can be divided into three functionally distinct types of areas: sensory, motor, and associative. The main sensory areas of the brain include the primary auditory cortex, the primary somatosensory cortex, and primary visual cortex. In general, the two hemispheres receive information from the opposite side of the body. For example, the right primary somatosensory cortex receives information from the left limbs, and the right visual cortex receives information from the left eye. Sensory areas are often represented in a manner that makes sense topographically. Sensation from neighboring parts of the body map to neighboring parts in sensory cortex.

Specificity

Specificity (also called the true negative rate) measures the proportion of negatives that are correctly identified as such (e.g., the percentage of healthy people who are correctly identified as not having the condition). Thus sensitivity quantifies the avoiding of false negatives, as specificity does for false positives. For any test, there is usually a trade-off between the measures. For instance, in an airport security setting in which one is testing for potential threats to safety, scanners may be set to trigger on low-risk items like belt buckles and keys (low specificity), in order to reduce the risk of missing objects that do pose a threat to the aircraft and those aboard (high sensitivity). This trade-off can be represented graphically as a receiver operating characteristic curve. A perfect predictor would be described as 100% sensitive (e.g., all sick are identified as sick) and 100% specific (e.g., no healthy are identified as sick); however, theoretically any predictor will possess a minimum error bound known as the Bayes error rate.

The adrenal (or suprarenal) glands

The adrenal (or suprarenal) glands are paired retroperitoneal (lying posterior to the peritoneum) endocrine glands situated over the medial aspects of the upper poles of each kidney. They secrete steroid and catecholamine hormones directly into the blood. This article will provide an overview of the adrenal glands in terms of their anatomical location and relations, structure, function, blood supply, lymphatics and neural innervation and will end with some clinical relevance.

amygdala

The amygdala is a section of the brain that is responsible for detecting fear and preparing for emergency events. This lesson discusses the amygdala, its functions, and its role in our perception of fear and other emotions. The Role of Fear Do you have any fears? For some people, their biggest fear may be death. For others, it may be public speaking. In fact, most humans will have at least one or more things that they fear in life, no matter how dangerous or innocent the object of that fear may be. But there is a reason for that. Fear often helps us with self-preservation. We feel fear, as well as related emotions, in order to protect ourselves from danger and to heighten our awareness. This awareness is thought to be controlled by a section of the brain known as the amygdala. Let's discuss the amygdala and how it functions in the well-being of the human body. Definition and Function of the Amygdala The amygdala is an almond-shaped section of nervous tissue located in the temporal (side) lobe of the brain. There are two amygdalae per person normally, with one amygdala on each side of the brain. They are thought to be a part of the limbic system within the brain, which is responsible for emotions, survival instincts, and memory. However, this inclusion has been debated heavily, with evidence that the amygdalae function independently of the limbic system. The amygdala is responsible for the perception of emotions such as anger, fear, and sadness, as well as the controlling of aggression. The amygdala helps to store memories of events and emotions so that an individual may be able to recognize similar events in the future. For example, if you have ever suffered a dog bite, then the amygdalae may help in processing that event and, therefore, increase your fear or alertness around dogs. The size of the amygdala is positively correlated with increased aggression and physical behavior. The amygdala in humans also plays a role in sexual activity and libido, or sex drive. It can change in size and shape based on the age, hormonal activity, and gender of the individual. For example, males who have low testosterone, or who may have been castrated, (had their testicles removed), tend to have smaller amygdalae, and, in turn, may also have a lower sex drive. Fear and the Amygdala It is important to state that the amygdalae are most functional in immediate fear situations. Whenever our senses detect a change in our surroundings that could be dangerous, the amygdalae are responsible for preparing the body for escape or defense. This is part of what is known as the startle circuit of the brain, which controls our response to being startled. The amygdalae, however, can cause problems if they are over-active. Panic is often a result of increased activity of the amygdalae. Usually, the initial response of the amygdalae is brief, particularly if someone is startled, but the situation is not a real threat. Imagine your friend sneaking up behind you and yelling 'BOO'! You will be startled, but the response will be brief once you realize it is just a prank. But in the case of panic, the physiological changes that prepare for emergency situations do not turn off as quickly, which can lead to prolonged fear, regardless of an actual threat. Effects of Damaged Amygdalae Scientists have also noted that damage to the amygdalae may result in various psychological and behavioral changes. Lesions in the amygdalae have been linked to the loss of emotion, loss of fear, hypersexuality, and depression. Compulsive behaviors, such as binge drinking and alcoholism, may occur. In animals, such as monkeys, damage to the amygdalae may result in a loss of maternal and parenting instincts after birth. Lesson Summary The amygdalae are found in the temporal lobes of the brain, and are responsible for the perception of emotions, with fear being the most noticeable. They help to store memories of events for future recognition and protection. The primary response of the amygdala is to prepare for immediate action, but this response is usually short-lived. Prolonged amygdala activity can lead to panic and increased fear. Damage to this region may lead to many negative psychological and social behaviors, such as loss of emotion, increased sexual activity, and compulsive habits.

anterior median fissure

The anterior median fissure of the spinal cord has an average depth of about 3 mm, but this is increased in the lower part of the medulla spinalis. It contains a double fold of pia mater, and its floor is formed by a transverse band of white substance, the anterior white commissure, which is perforated by blood vessels on their way to or from the central part of the medulla spinalis.

arbor vitae

The arbor vitae (Latin for "Tree of Life") is the cerebellar white matter, so called for its branched, tree-like appearance. In some ways it more resembles a fern and is present in both cerebellar hemispheres.[1] It brings sensory and motor information to and from the cerebellum. The arbor vitae is located deep in the cerebellum. Situated within the arbor vitae are the deep cerebellar nuclei; the dentate, globose, emboliform and the fastigial nuclei. These four different structures lead to the efferent projections of the cerebellum.[2] The arbor vitae is subject to pathologies such as a cerebellar hemorrhage. Cerebellar hemorrhages arise from tumors, trauma and arteriovenous malformations among other things.[3] The cells in the arbor vitae could also be infected by pathogens which might cause lasting damage, this in turn could lead to cerebellar ataxia.[4]

basal ganglia

The basal ganglia (or basal nuclei) comprise multiple subcortical nuclei, of varied origin, in the brains of vertebrates, which are situated at the base of the forebrain. Basal ganglia nuclei are strongly interconnected with the cerebral cortex, thalamus, and brainstem, as well as several other brain areas. The basal ganglia are associated with a variety of functions including: control of voluntary motor movements, procedural learning, routine behaviors or "habits" such as bruxism, eye movements, cognition[1] and emotion.[2] The main components of the basal ganglia - as defined functionally - are the dorsal striatum (caudate nucleus and putamen), ventral striatum (nucleus accumbens and olfactory tubercle), globus pallidus, ventral pallidum, substantia nigra, and subthalamic nucleus.[3] It is important to note, however, that the dorsal striatum and globus pallidus may be considered anatomically distinct from the substantia nigra, nucleus accumbens, and subthalamic nucleus. Each of these components has a complex internal anatomical and neurochemical organization. The largest component, the striatum (dorsal and ventral), receives input from many brain areas beyond the basal ganglia, but only sends output to other components of the basal ganglia. The pallidum receives input from the striatum, and sends inhibitory output to a number of motor-related areas. The substantia nigra is the source of the striatal input of the neurotransmitter dopamine, which plays an important role in basal ganglia function. The subthalamic nucleus receives input mainly from the striatum and cerebral cortex, and projects to the globus pallidus. Currently, popular theories implicate the basal ganglia primarily in action selection; that is, it helps determine the decision of which of several possible behaviors to execute at any given time. In more specific terms, the basal ganglia's primary function is likely to control and regulate activities of the motor and premotor cortical areas so that voluntary movements can be performed smoothly.[1][4] Experimental studies show that the basal ganglia exert an inhibitory influence on a number of motor systems, and that a release of this inhibition permits a motor system to become active. The "behavior switching" that takes place within the basal ganglia is influenced by signals from many parts of the brain, including the prefrontal cortex, which plays a key role in executive functions.[2][5]

cardiovascular centers of medulla oblongata

The cardiovascular centre is a part of the human brain responsible for the regulation of the rate at which the heart beats through the nervous and endocrine systems. It is found in the medulla oblongata. Normally, the heart beats without nervous control, but in some situations (e.g., exercise, body trauma), the cardiovascular centre is responsible for altering the rate at which the heart beats. It also mediates respiratory sinus arrhythmia. When a change of blood pH is detected by chemoreceptors or a change of blood pressure is detected by stretch receptors in aortic and carotid bodies, the cardiovascular centre effects changes to the heart rate by sending nerve impulse to pacemaker (or SA node) via sympathetic fibres (to cause faster and stronger cardiac muscle contraction) and the vagus nerve (to cause slower and less strong cardiac muscle contraction). The cardiovascular centre also increases the stroke volume of the heart (that is, the amount of blood it pumps). These two changes help to regulate the cardiac output, so that a sufficient amount of blood reaches tissue.

cell body

The cell body, also called the soma, is the spherical part of the neuron that contains the nucleus. The cell body connects to the dendrites, which bring information to the neuron, and the axon, which sends information to other neurons.

cerebellum

The cerebellum, which stands for "little brain", is a structure of the central nervous system. It has an important role in motor control, with cerebellar dysfunction often presenting with motor signs. In particular, it is active in the coordination, precision and timing of movements, as well as in motor learning. During embryonic development, the anterior portion of the neural tube forms three parts that give rise to the brain and associated structures: Forebrain (prosencephalon) Midbrain (mesencephalon) Hindbrain (rhombencephalon) The hindbrain subsequently divides into the metencephalon (superior) and the myelencephalon (inferior). The cerebellum develops from the metencephalon division. This article will focus on the anatomy of the cerebellum. It will provide a brief overview of its functions and development, and finally it will highlight the clinical relevance of cerebellar disorders. Anatomical Location The cerebellum is located at the back of the brain, immediately inferior to the occipital and temporal lobes, and within the posterior cranial fossa. It is separated from these lobes by the tentorium cerebelli, a tough layer of dura mater. It lies at the same level of and posterior to the pons, from which it is separated by the fourth ventricle. © 2015-2016 TeachMeAnatomy.com [CC-BY-NC-ND 4.0]Fig 1.0 - Anatomical position of the cerebellum. It is inferior to the cerebrum, and posterior to the pons. Fig 1.0 - Anatomical position of the cerebellum. It is inferior to the cerebrum, and posterior to the pons. Anatomical Structure and Divisions The cerebellum consists of two hemispheres which are connected by the vermis, a narrow midline area. Like other structures in the central nervous system, the cerebellum consists of grey matter and white matter: Grey matter - located on the surface of the cerebellum. It is tightly folded, forming the cerebellar cortex. White matter - located underneath the cerebellar cortex. Embedded in the white matter are the four cerebellar nuclei (the dentate, emboliform, globose, and fastigi nuclei). There are three ways that the cerebellum can be subdivided - anatomical lobes, zones and functional divisions Anatomical Lobes There are three anatomical lobes that can be distinguished in the cerebellum; the anterior lobe, the posterior lobe and the flocculonodular lobe. These lobes are divided by two fissures - the primary fissure and posterolateral fissure. © 2015-2016 TeachMeAnatomy.com [CC-BY-NC-ND 4.0]Fig 1.1 - Anatomical lobes of the cerebellum. Fig 1.1 - Anatomical lobes of the cerebellum. Zones There are three cerebellar zones. In the midline of the cerebellum is the vermis. Either side of the vermis is the intermediate zone. Lateral to the intermediate zone are the lateral hemispheres. There is no difference in gross structure between the lateral hemispheres and intermediate zones By Nrets [CC-BY-SA-3.0], from Wikimedia CommonsFig 1.2 - Superior view of an "unrolled" cerebellum, placing the vermis in one plane. Fig 1.2 - Superior view of an "unrolled" cerebellum, placing the vermis in one plane. Functional Divisions The cerebellum can also be divided by function. There are three functional areas of the cerebellum - the cerebrocerebellum, the spinocerebellum and the vestibulocerebellum. Cerebrocerebellum - the largest division, formed by the lateral hemispheres. It is involved in planning movements and motor learning. It receives inputs from the cerebral cortex and pontine nuclei, and sends outputs to the thalamus and red nucleus. This area also regulates coordination of muscle activation and is important in visually guided movements. Spinocerebellum - comprised of the vermis and intermediate zone of the cerebellar hemispheres. It is involved in regulating body movements by allowing for error correction. It also receives proprioceptive information. Vestibulocerebellum - the functional equivalent to the flocculonodular lobe. It is involved in controlling balance and ocular reflexes, mainly fixation on an target. It receives inputs from the vestibular system, and sends outputs back to the vestibular nuclei.

lobes of cortex and their functions frontal parietal temporal occipital

The cerebral cortex is classified into four lobes, according to the name of the corresponding cranial bone that approximately overlies each part. Each lobe contains various cortical association areas - where information from different modalities are collated for processing. Together, these areas function to give us a meaningful perceptual interpretation and experience of our surrounding environment. Frontal Lobe The frontal lobe is located beneath the frontal bone of the calvaria and is the most anterior region of the cerebrum. It is separated from the parietal lobe posteriorly by the central sulcus and from the temporal lobe inferoposteriorly by the lateral sulcus. The association areas of the frontal lobe are responsible for: higher intellect, personality, mood, social conduct and language (dominant hemisphere side only). Parietal Lobe The parietal lobe is found below the parietal bone of the calvaria, between the frontal lobe anteriorly and the occipital lobe posteriorly, from which it is separated by the central sulcus and parieto-occipital sulcus, respectively. It sits superiorly in relation to the temporal lobe, being separated by the lateral sulcus. Its cortical association areas contribute to the control of: language and calculation on the dominant hemisphere side, and visuospatial functions (e.g. 2-point discrimination) on the non-dominant hemisphere side. Temporal Lobe The temporal lobe sits beneath the temporal bone of the calvaria, inferior to the frontal and parietal lobes, from which it is separated by the lateral sulcus. The cortical association areas of the temporal lobe are accountable for memory and language - this includes hearing as it is the location of the primary auditory cortex. Occipital Lobe The occipital lobe is the most posterior part of the cerebrum situated below the occipital bone of the calvaria. It rests inferiorly upon the tentorium cerebelli which segregates the cerebrum from the cerebellum. The parieto-occipital sulcus separates the occipital lobe from the parietal and temporal lobes anteriorly. The primary visual cortex (V1) is located within the occipital lobe and hence its cortical association area is responsible for vision.

primary cortex vs. association cortex (motor or sensory)

The cerebral cortex is connected to various subcortical structures such as the thalamus and the basal ganglia, sending information to them along efferent connections and receiving information from them via afferent connections. Most sensory information is routed to the cerebral cortex via the thalamus. Olfactory information, however, passes through the olfactory bulb to the olfactory cortex (piriform cortex). The vast majority of connections are from one area of the cortex to another rather than to subcortical areas; Braitenberg and Schüz (1991) put the figure as high as 99%.[15] The cortex is commonly described as comprising three parts: sensory, motor, and association areas. [edit] Sensory areas The sensory areas are the areas that receive and process information from the senses. Parts of the cortex that receive sensory inputs from the thalamus are called primary sensory areas. The senses of vision, audition, and touch are served by the primary visual cortex, primary auditory cortex and primary somatosensory cortex. In general, the two hemispheres receive information from the opposite (contralateral) side of the body. For example the right primary somatosensory cortex receives information from the left limbs, and the right visual cortex receives information from the left visual field. The organization of sensory maps in the cortex reflects that of the corresponding sensing organ, in what is known as a topographic map. Neighboring points in the primary visual cortex, for example, correspond to neighboring points in the retina. This topographic map is called a retinotopic map. In the same way, there exists a tonotopic map in the primary auditory cortex and a somatotopic map in the primary sensory cortex. This last topographic map of the body onto the posterior central gyrus has been illustrated as a deformed human representation, the somatosensory homunculus, where the size of different body parts reflects the relative density of their innervation. Areas with lots of sensory innervation, such as the fingertips and the lips, require more cortical area to process finer sensation. [edit] Motor areas The motor areas are located in both hemispheres of the cortex. They are shaped like a pair of headphones stretching from ear to ear. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa. Two areas of the cortex are commonly referred to as motor: Primary motor cortex, which executes voluntary movements Supplementary motor areas and premotor cortex, which select voluntary movements. In addition, motor functions have been described for: Posterior parietal cortex, which guides voluntary movements in space Dorsolateral prefrontal cortex, which decides which voluntary movements to make according to higher-order instructions, rules, and self-generated thoughts. [edit] Association areas Association areas function to produce a meaningful perceptual experience of the world, enable us to interact effectively, and support abstract thinking and language. The parietal, temporal, and occipital lobes - all located in the posterior part of the cortex - organize sensory information into a coherent perceptual model of our environment centered on our body image. The frontal lobe or prefrontal association complex is involved in planning actions and movement, as well as abstract thought. In the past it was theorized that language abilities are localized in the left hemisphere in areas 44/45, the Broca's area, for language expression and area 22, the Wernicke's area, for language reception. However, language is no longer limited to easily identifiable areas. More recent research suggests that the processes of language expression and reception occur in areas other than just the perisylvian structures, such as the prefrontal lobe, basal ganglia, cerebellum, pons, caudate nucleus, and others.

cerebral cortex

The cerebral cortex is the cerebrum's (brain) outer layer of neural tissue in humans and other mammals. It is divided into two cortices, along the sagittal plane: the left and right cerebral hemispheres divided by the medial longitudinal fissure. The cerebral cortex plays a key role in memory, attention, perception, awareness, thought, language, and consciousness. The human cerebral cortex is 2 to 4 millimetres (0.079 to 0.157 in) thick.[1] In large mammals, the cerebral cortex is folded, giving a much greater surface area in the confined volume of the skull. A fold or ridge in the cortex is termed a gyrus (plural gyri) and a groove or fissure is termed a sulcus (plural sulci). In the human brain more than two-thirds of the cerebral cortex is buried in the sulci. The cerebral cortex is composed of gray matter, consisting mainly of cell bodies (with astrocytes being the most abundant cell type in the cortex as well as the human brain in general) and capillaries. It contrasts with the underlying white matter, consisting mainly of the white myelinated sheaths of neuronal axons. The most recent part of the cerebral cortex to develop in the evolutionary history of mammals is the neocortex (also called isocortex), which differentiated into six horizontal layers; the more ancient part of the cerebral cortex, the hippocampus, has at most three cellular layers. Neurons in various layers connect vertically to form small microcircuits, called cortical columns. Different neocortical regions known as Brodmann areas are distinguished by variations in their cytoarchitectonics (histological structure) and functional roles in sensation, cognition and behavior.

dorsal (posterior) roots

The dorsal root of spinal nerve (or posterior root of spinal nerve) is one of two "roots" which emerge from the spinal cord. It emerges directly from the spinal cord, and travels to the dorsal root ganglion. Nerve fibres with the ventral root then combine to form a spinal nerve. The dorsal root transmits sensory information, forming the afferent sensory root of a spinal nerve.

cervical and lumbar enlargements

The cervical enlargement corresponds with the attachments of the large nerves which supply the upper limbs. It extends from about the third cervical to the second thoracic vertebra, its maximum circumference (about 38 mm.) being on a level with the attachment of the sixth pair of cervical nerves. The reason behind the enlargement of the cervical region is because of the increased neural input and output to the upper limbs. An analogous region in the lower limbs occurs at the lumbar enlargement. lumbar enlargement (or lumbosacral enlargement) is a widened area of the spinal cord that gives attachment to the nerves which supply the lower limbs. It commences about the level of L2 and ends at S3, and reaches its maximum circumference, of about 33 mm. Inferior to the lumbar enlargement is the conus medullaris.[1] An analogous region for the upper limbs exists at the cervical enlargement.

denticulate ligaments

The denticulate ligaments, also known as dentate ligaments, are pia-arachnoid covered thick collagenous bundles that extend from spinal cord to the dura mater.

thalamus (of diencephalon

The diencephalon is a part of the brain that is responsible for many functions in the human body. In this lesson, you will learn about the diencephalon, including its location, parts, and functions. Importance of the Diencephalon What do blood pressure, water balance, childbirth, appetite, and sleep all have in common? Besides the fact that all are bodily functions, each is controlled in part by the diencephalon. The diencephalon helps control many different functions of the body, which is why it is important to understand this organ. What, Where and How Big is the Diencephalon? The diencephalon is a part of the brain that includes the thalamus and the hypothalamus. It is the link between the nervous system and the endocrine system. The diencephalon receives signals from the nerves (the nervous system) and interprets the signals, then the pituitary gland (which largely controls the endocrine system) responds by excreting hormones. The thalamus is the size of a walnut, whereas the hypothalamus is the size of an almond; in total, the size of the diencephalon is about the size of an apricot. The diencephalon is located deep in the brain underneath the cerebrum and above the pituitary gland. Now that we know the general function, size, and location of the diencephalon, let's discuss the specific functions of the thalamus and hypothalamus. Function of the Thalamus and Hypothalamus The thalamus sends and receives signals to and from the brain and body. The brain sends a signal to the thalamus, which relays the signal to the body. Similarly, the body sends a signal to the thalamus, and the thalamus relays the signal to the brain. You can think of the thalamus as a mediator; it receives messages then sends the messages to the intended destination. The hypothalamus is responsible for triggering the pituitary gland to release hormones. In conjunction with the pituitary gland, it regulates bodily functions and has many effects. Let's examine five important functions affected by the hypothalamus. 1. Sleep inhibition: When you feel awake, it is in part due to the hypothalamus. The hypothalamus sends signals to other parts of the brain to keep you alert. 2. Appetite: The hormones ghrelin and leptin are produced in the gastrointestinal tract and indicate hunger and fullness. Ghrelin is excreted , and receptors in the hypothalamus receive the ghrelin, thereby causing the hunger feeling. After we eat, the amount of ghrelin decreases, while leptin increases. Receptors in the hypothalamus receive the leptin, indicating fullness. 3. Oxytocin: The hypothalamus signals the pituitary gland to release oxytocin, resulting in contractions during childbirth. 4. Water balance: The hypothalamus helps to maintain water balance when there is a lack of water in the body. The hypothalamus causes the pituitary gland to secrete an anti-diuretic hormone, prompting more water to be absorbed by the kidneys. Also, the hypothalamus signals the thirst sensation so that we know when we need to drink water. 5. Blood pressure: The hypothalamus helps control blood pressure by controlling the heart beat and the dilation of the blood vessels. Lesson Summary The diencephalon is located deep in the brain underneath the cerebrum, and it is the link between the nervous system and the endocrine system. It includes the thalamus and hypothalamus. The thalamus relays signals to and from the brain and body. The hypothalamus triggers the pituitary gland to secrete hormones, and it also helps to control sleep, appetite, oxytocin, water balance and blood pressure.

insulin-like growth factors (IGF)

The insulin-like growth factors (IGFs) are proteins with high sequence similarity to insulin. IGFs are part of a complex system that cells use to communicate with their physiologic environment. This complex system (often referred to as the IGF "axis") consists of two cell-surface receptors (IGF1R and IGF2R), two ligands (Insulin-like growth factor 1 (IGF-I) and Insulin-like growth factor 2 (IGF-2)), a family of six high-affinity IGF-binding proteins (IGFBP-1 to IGFBP-6), as well as associated IGFBP degrading enzymes, referred to collectively as proteases.

intervertebral foramina

The intervertebral foramen (also called neural foramina, and often abbreviated as IV foramina or IVF), is a foramen between two spinal vertebrae. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina. The foramina, or openings, are present between every pair of vertebrae in these areas. A number of structures pass through the foramen. These are the root of each spinal nerve, dorsal root ganglion, the spinal artery of the segmental artery, communicating veins between the internal and external plexuses, recurrent meningeal (sinu-vertebral) nerves, and transforaminal ligaments. When the spinal vertebrae are articulated with each other the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramen constitutes a canal for the protection of the medulla spinalis (spinal cord). The size of the foramina is variable due to placement, pathology, spinal loading, and posture. Foramina can be occluded by arthritic degenerative changes and space-occupying lesions like tumors, metastases and spinal disc herniations. Specifically the intervertebral foramen is bound by, The Superior Notch of the adjacent vertebra, The Inferior Notch of the vertebra, The body of the vertebral body, Facet joints on the transverse process of the vertebra.

liver

The liver is a vital organ that is responsible for many of the processes that keep us alive. This lesson will discuss the key functions of the liver, its location in the body, and the diseases that can affect it. The Liver: A Vital Organ The human body is a fascinating structure, composed of many different parts working together for the purpose of keeping us alive. Within the human body are multiple organs, which are large structures designed to perform certain functions. Many of the organs in the body are familiar to most people. The heart, for example, is used to pump blood throughout the body. The lungs are used to breathe in oxygen and remove carbon dioxide. However, one of the most important organs in the body is also one of the least understood. It is an organ that is vital for digestion. It is an organ that protects us from harmful substances. It's one of the organs that we cannot live without. That organ is the liver, and in this lesson, we will take a look at this valuable part of our bodies. Characteristics of the Liver The liver is located superolateral, or above and to the side, of the stomach. It is found in the abdominal cavity of the body, which is where many of the internal organs reside, and is inferior to, or below, the lungs. The adult liver weighs between 3 and 4 pounds. It is the largest internal organ in the body, and is second to the skin as the largest organ overall. It has a rubbery texture and is reddish-brown in color. One of the most unique characteristics of the liver is that it has the ability to, in some cases, regenerate, or regrow, different sections of itself in the event of damage. The liver has a triangular shape and is divided into four lobes. The left and right anatomical lobes are visible when viewing the liver from the front, while the quadrate and caudate lobes are visible when viewed from the underside. These lobes are divided further into smaller functional sections, called lobules. These lobules have various functions and contribute to processes we'll discuss next. Functions of the Liver The liver has several major functions in the body. First, the liver is responsible for producing enzymes and solutions necessary for digestion. This includes the production of bile, which helps with the breakdown of fat from our food. The liver is also responsible for the storage of sugars for energy use. Glucose, a simple sugar used by the body for energy, is stored as glycogen in the liver until needed. During emergency situations, our bodies will tap into the stored glucose to provide additional energy for survival. Another major function of the liver is to detoxify and remove harmful substances in the bloodstream. Drinking alcohol, for example, is poisonous to the human body. However, you probably wouldn't be able to tell it based on how much we, as humans, consume it. The liver is responsible for processing alcohol so that it does not cause harm to the rest of our bodies. Additionally, the liver will also break down and process other drugs that enter our system, including medications and recreational drugs. Other functions of the liver include: Production of cholesterol, which is a lipid necessary for hormone production Vitamin storage, such as vitamins A and K Digestion and recycling of red blood cells and components when they become old There are also several other functions of the liver. In fact, the liver has so many functions that we cannot live without it, and scientists have not been able to produce an artificial version of this organ. Diseases of the Liver Many diseases can affect the function of the liver. These diseases can range in severity, depending on how much of the liver is damaged and which functions are affected. These diseases include: Hepatitis, which is inflammation of the liver due to infection or irritation Cirrhosis, which is scarring of the liver and is usually a result of heavy alcohol consumption Liver cancer, which is an overgrowth of cells within the liver It's important to remember that the liver can regenerate in certain conditions. So, for some of these diseases, once the disease has been controlled, the liver may regain function. Lesson Summary The liver is one of the most important organs in the body. It's located in the abdominal cavity, below the lungs and to the side of the stomach. It has many functions, including detoxification of drugs, digestive enzyme production, and fat digestion. Finally, many diseases may affect the liver, including hepatitis, cirrhosis, and liver cancer. In certain cases, the liver can regenerate, or regrow, damaged tissues.

meninges

The meninges refer to the membranous coverings of the brain and spinal cord. There are three layers of meninges, known as the dura mater, arachnoid mater and pia mater. © 2015-2016 TeachMeAnatomy.com [CC-BY-NC-ND 4.0]Fig 1.0 - Overview of the meninges, and their relationship to the skull and brain. Fig 1.0 - Overview of the meninges, and their relationship to the skull and brain. These coverings have two major functions: Provide a supportive framework for the cerebral and cranial vasculature. Acting with cerebrospinal fluid to protect the CNS from mechanical damage. The meninges are often involved cerebral pathology, as a common site of infection (meningitis), and intracranial bleeds. In this article, we shall look at the anatomy of the three layers, and their clinical correlations.

mesencephalon

The mesencephalon or midbrain is a part of the brain stem.[1] It is associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.[2] In the anatomy of developing animals, the brain forms from the neural tube, which turns into three vesicles. The mesencephalon (midbrain) is the middle vesicle, and becomes part of the brain stem. The mesencephalon is ancient in origin, meaning its general architecture is shared with the most ancient of vertebrates. Dopamine produced in the substantia nigra plays a role in motivation and habituation of species from humans to insects.

metencephalon

The metencephalon is the embryonic part of the hindbrain that differentiates into the pons and the cerebellum. It contains a portion of the fourth ventricle and the trigeminal nerve (CN V), abducens nerve (CN VI), facial nerve (CN VII), and a portion of the vestibulocochlear nerve (CN VIII).

mesencephalon

The midbrain or mesencephalon is a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation. Anatomically, the midbrain comprises the tectum (or corpora quadrigemina), tegmentum, ventricular mesocoelia (or "iter"), and the cerebral peduncles, as well as several nuclei and fasciculi. During embryonic development, the midbrain arises from the second vesicle, also known as the mesencephalon, of the neural tube. The mesencephalon is considered part of the brainstem. TERMS[ edit ] mesencephalon A part of the brain located rostral to the pons and caudal to the thalamus and the basal ganglia, composed of the tectum (dorsal portion) and the tegmentum (ventral portion).

dendrites

The nervous system serves as the manager of the body, since it controls the functions of every other system. It communicates with bodily systems in order to coordinate performance and to meet the needs of the body from moment to moment. The nervous system uses specialized cells, called neurons, to generate and relay electrical messages, called action potentials, to control these functions. Neurons have several key structures that are necessary for their function, and one of the most important structures in the cell is the dendrite. Function of Dendrites In order for neurons to become active, they must receive action potentials or other stimuli. Dendrites are the structures on the neuron that receive electrical messages. These messages come in two basic forms: excitatory and inhibitory. Excitatory action potentials increase the stimulation of a neuron, while inhibitory action potentials decrease the activity of the neuron. These signals will accumulate in the cell body, or soma, of the neuron after being received by the dendrites. Once action potentials are received by the dendrites, they will be sent to a portion of the soma known as the axon hillock, neck region of the cell body. Once the cell receives enough excitatory action potentials, it will become activated and generate an action potential of its own.

neural crest

The neural crest is a transient embryonic structure in vertebrates that gives rise to most of the peripheral nervous system (PNS) and to several non-neural cell types, including smooth muscle cells of the cardiovascular system, pigment cells in the skin, and craniofacial bones, cartilage, and connective tissue.

antidiuretic hormone = ADH = vasopressin oxytocin

The neurohypophysial hormones form a family of structurally and functionally related peptide hormones. Their main representatives are oxytocin and vasopressin. They are named for being secreted by the neurohypophysis, i.e. the posterior pituitary gland (hypophysis refers to the pituitary gland), itself a neuronal projection from the hypothalamus. Most of the circulating oxytocin and vasopressin hormones are synthesized in magnocellular neurosecretory cells of the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are then transported in neurosecretory granules along axons within the hypothalamo-neurohypophysial tract by axoplasmic flow to axon terminals forming the pars nervosa of the posterior pituitary. There, they are stored in Herring bodies and can be released into the circulation on the basis of hormonal and synaptic signals with assistance from pituicytes.[1][2][3] Vasopressin and oxytocin are also synthesized in the parvocellular neurosecretory cells of the paraventricular nucleus of the hypothalamus, which project to the median eminence, where they are transported and secreted into the hypophyseal portal system to stimulate the anterior pituitary.[4] Thus they can also be considered as hypophysiotropic hormones.[5] Oxytocin mediates contraction of the smooth muscle of the uterus and mammary gland, while vasopressin has antidiuretic action on the kidney, and mediates vasoconstriction of the peripheral vessels.[6] Due to the similarity of the two hormones, there is cross-reaction: oxytocin has a slight antidiuretic function, and high levels of AVP can cause uterine contractions.[7][8] In common with most active peptides, both hormones are synthesised as larger protein precursors that are enzymatically converted to their mature forms.

labeled line coding of meaning

The only information you get about the world comes through your senses: your eyes, your ears, your balance sense, your nose, etc. The fundamental question is: How do the senses provide you with such accurate information about the world? An early idea -- proposed before anyone knew anything about how nerves worked -- said that tiny replicas (~models) of the things we see or hear travel up the peripheral nerves to the brain. We know now that neurons in the peripheral and central nervous systems use specialized neural signals. How can these neural signals represent the objects and events we perceive in the world about us? This is the problem of coding: taking physical processes like light, sound pressure, chemicals, etc., converting them into signals that the mind (or brain) can use, and interpreting that as accurate representations of the world. Individual neurons have two kinds of codes Dendrites code excitation and inhibition by graded depolarization and hyperpolarization. Axons code excitation you the number of all-or-nothing impulses (action potentials) per second (rate). Anatomical or labeled line coding tells the mind/brain where a stimulus is (for example, how you can tell a singing bird is up and to your left, or where is itches on your back) It also tells (usually) which kind it is (a small, red bird, singing two notes, or that it's an itch and not a touch or pain). J. Muller proposed this idea early in the 19th century code, calling it the Law of Specific Nerve Energies. Muller proposed that we see light when visual areas of the brain become active; we hear sound when auditory areas of the brain become active; we feel touch when somatosensory (~ touch) areas of the brain become active, etc. This idea opened the modern study of how the sense work. This idea turned into labeled line (anatomical) coding when it was extended to explain the different qualities you experience within each sense: different colors of light, pitches in sound, touch, vibration, warmth, etc. on the skin, etc. Anatomical coding states that you experience different qualities when different parts of a sensory area become active. For example, if one end of the auditory area of the cerebral cortex becomes active, you experience a high-pitched tone. If the other end of the auditory area of the cortex becomes active, you experience a low- pitched tone. if the middle of the auditory area of the cortex becomes active, you experience intermediate pitched tones. Another, less common kind of kind, temporal or (time) pattern code signals the mind/brain the kind of stimulus by the pattern of nerve impulses. For example, one model of the code for itch is bursts of impulses on certain kinds of neurons from the skin interrupted by periods of no impulses. Labeled line (anatomical) coding is based on two ideas: Each sense (vision, touch, taste, etc,) has neurons, called receptors, that are especially sensitive to (tuned to) a narrow range of stimuli: their adequate stimulus

pia mater

The pia mater is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord. It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels that travel to the brain and spinal cord.

melatonin

The pineal gland is a small endocrine gland located within the brain. Its main secretion is melatonin, which regulates the circadian rhythm of the body. It is also thought to produce hormones that inhibit the action of other endocrine glands in the body.

pons

The pons is part of the brainstem, and in humans and other bipeds lies between the midbrain (above) and the medulla oblongata (below) and in front of the cerebellum. The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio (1543-75).[1] This region of the brainstem includes neural pathways or tracts that conduct signals from the brain down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.[2] The pons in humans measures about 2.5 centimetres (0.98 in) in length. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons and midbrain.[2] The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.[2] Within the pons is the pneumotaxic center consisting of the subparabrachial and the medial parabrachial nuclei. This center regulates the change from inhalation to exhalation.[2]

posterior grey column

The posterior grey column (posterior cornu, dorsal horn, spinal dorsal horn posterior horn) of the spinal cord is one of the three grey columns of the spinal cord. It receives several types of sensory information from the body, including fine touch, proprioception, and vibration. This information is sent from receptors of the skin, bones, and joints through sensory neurons whose cell bodies lie in the dorsal root ganglion.

receptive field

The receptive field of an individual sensory neuron is the particular region of the sensory space (e.g., the body surface, or the visual field) in which a stimulus will trigger the firing of that neuron. This region can be a hair in the cochlea or a piece of skin, retina, tongue or other part of an animal's body. Additionally, it can be the space surrounding an animal, such as an area of auditory space that is fixed in a reference system based on the ears but that moves with the animal as it moves (the space inside the ears), or in a fixed location in space that is largely independent of the animal's location (place cells). Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system.

hypophyseal portal system

The release of hormones is under the control of the hypothalamus, which communicates with the gland via neurotransmitters secreted into the hypophyseal portal vessels. These vessels ensure that the hypothalamic hormones remain concentrated, rather than being diluted in the systemic circulation.

The respiratory centers (RC) are located in the medulla oblongata

The respiratory centers (RC) are located in the medulla oblongata and pons, which are part of the brain stem. The RCs receive controlling signals of neural, chemical and hormonal nature and control the rate and depth of respiratory movements of the diaphragm and other respiratory muscles. Injury to these centers may lead to center respiratory failure, which necessitates mechanical ventilation; usually the prognosis is death. In healthy individuals the presence of elevated carbon dioxide levels in the blood is the stimulant that the RC responds to in order to signal the respiratory muscles to breathe. Chemoreceptors found in carotid bodies and aortic bodies are responsible for detecting decrease in blood pH by this carbon dioxide.

reticular activating system

The reticular activating system (RAS), or extrathalamic control modulatory system, is a set of connected nuclei in the brains of vertebrates that is responsible for regulating wakefulness and sleep-wake transitions. As its name implies, its most influential component is the reticular formation.

subarachnoid space

The spinal arachnoid mater is a delicate membrane, located between the dura mater and the pia mater. It is separated from the latter by the subarachnoid space, which contains cerebrospinal fluid.

arachnoid

a fine, delicate membrane, the middle one of the three membranes or meninges that surround the brain and spinal cord, situated between the dura

cerebral hemispheres

The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the medial longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter, the cerebral cortex, that is supported by an inner layer of white matter. In eutherian (placental) mammals, the hemispheres are linked by the corpus callosum, a very large bundle of nerve fibers. Smaller commissures, including the anterior commissure, the posterior commissure and the fornix also join the hemispheres and these are also present in other vertebrates. These commissures transfer information between the two hemispheres to coordinate localized functions. The central sulcus is a prominent fissure which separates the parietal lobe from the frontal lobe and the primary motor cortex from the primary somatosensory cortex. Macroscopically the hemispheres are roughly mirror images of each other, with only subtle differences, such as the Yakovlevian torque seen in the human brain, which is a slight warping of the right side, bringing it just forward of the left side. On a microscopic level, the cytoarchitecture of the cerebral cortex, shows the functions of cells, quantities of neurotransmitter levels and receptor subtypes to be markedly asymmetrical between the hemispheres.[1][2] However, while some of these hemispheric distribution differences are consistent across human beings, or even across some species, many observable distribution differences vary from individual to individual within a given species.

posterior pituitary and anterior pituitary

There are actually two main parts of the pituitary gland. The front portion, commonly referred to as the anterior pituitary, is also known as the adenohypophysis. The back portion, or posterior pituitary, is called the neurohypophysis. We can keep these two names straight by noting that the words 'anterior' and 'adenohypophysis' both start with the letter 'A.' The pituitary gland is attached to the hypothalamus by the pituitary stalk, which contains nerves and a unique circulatory system, which enables communication between the two. Let's take a closer look at the way the hypothalamus and the pituitary gland work together.

hypothalamus

This lesson will describe the hypothalamus as it relates to the endocrine system. It will examine the anatomic features of the hypothalamus and how it uses the pituitary gland to communicate with the rest of the body. A short quiz will follow. Introduction Every organization needs some form of structure in order for messages to be delivered and received. Without methods of communication, order can break down into chaos in a short matter of time. Just try to imagine how much work the employees of an office would be able to get done if they lost access to their phones and email! In the case of the endocrine system, the hypothalamus plays a super-sized role by making decisions about what actions need to be taken by various endocrine glands throughout the body. Its primary purpose is to make sure that the body stays in a continual state of balance, known as homeostasis. Features of the Hypothalamus The hypothalamus is only about the size of a pearl, and is located in the middle part of the brain. It monitors the state of the body through the circulatory and nervous systems, and effectively links these two systems to the endocrine system through the pituitary gland. Location of the hypothalamus inside the brain Hypothalamus inside the brain The hypothalamus communicates with the anterior portion of the pituitary gland by way of hormonal messages. Neurosecretory cells in the hypothalamus create hypothalamic-releasing and hypothalamic-inhibiting hormones, which tell the anterior pituitary to start or stop an action. Located in the pituitary stalk, a unique arrangement of capillaries and veins, called a portal system, allows the hypothalamic hormones to pass directly to the anterior pituitary without circulating through the body. The hypothalamus uses the posterior portion of the pituitary gland like a warehouse and distribution center. Neurosecretory cells in the hypothalamus create anti-diuretic hormone (ADH) and oxytocin, which are sent through axons in the pituitary stalk to be stored in the posterior pituitary. When the hypothalamus detects that either of these hormones are needed, they are released from the posterior pituitary into the circulatory system to do their jobs. Role of the Hypothalamus A good way to visualize the relationship between the hypothalamus and the pituitary gland is like the President and his Chief of Staff. While the hypothalamus, or President, makes the decisions, the pituitary gland, or Chief of Staff, executes those decisions by sending out commands to the rest of the body. When the hypothalamus detects that something is out of balance, its sends a message to the pituitary gland that a corrective action is needed. When the pituitary gland gets this message from the hypothalamus, it releases specific hormones into the bloodstream that can stimulate other endocrine glands, organs or tissues depending on what action is needed. It's kind of a like a game of telephone. Instead of the hypothalamus communicating directly with the body, it relies on the pituitary gland to send out the messages. The hypothalamus continues to monitor the state of the body, and when it detects that balance has been restored, it tells the pituitary gland to stop sending out stimulating hormones, thereby stopping the corrective action. An example of this process is when we become dehydrated. The hypothalamus is able to detect the increased blood concentration caused by the loss of water. To correct the situation, it uses the posterior pituitary to release anti-diuretic hormone (ADH) into the circulatory system. When ADH reaches the kidneys, it causes more water to be reabsorbed into the bloodstream, diluting the blood. When the hypothalamus detects the return to a normal blood concentration, it stops the release of ADH from the pituitary gland and the kidneys return to normal functioning. Summary The hypothalamus is responsible for maintaining homeostasis. It monitors the state of the body through the circulatory and nervous systems, and effectively links these two systems to the endocrine system through the pituitary gland. When the hypothalamus detects that something is out of balance, its sends a message to the pituitary gland that a corrective action is needed. Depending on the need, either hormones produced in the anterior pituitary, or hypothalamic hormones stored in the posterior pituitary, are released into the body. When balance has been restored, the hypothalamus tells the pituitary gland to stop sending out stimulating hormones, thereby stopping the corrective action.

TRH and TSH

Thyrotropin-releasing hormone (TRH), also called thyrotropin-releasing factor (TRF) or thyroliberin, is a releasing hormone, produced by the hypothalamus, that stimulates the release of thyrotropin (thyroid-stimulating hormone or TSH) and prolactin from the anterior pituitary. It is a tropic, tripeptidal hormone. TRH has been used clinically for the treatment of spinocerebellar degeneration and disturbance of consciousness in humans.[1] Its pharmaceutical form is called protirelin Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, TSH, or hTSH for human TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body.[1] It is a glycoprotein hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.[2][3]

voltage-gated sodium channel

Transmembrane Domains In this section, we examine the voltage-gated sodium channel as a specific example of a protein embedded in the plasma membrane. This type of protein is found in the nerve and muscle cells and is used in the rapid electrical signalling found in these cells. The principle subunit of the voltage-gated sodium channel is a polypeptide chain of more than 1800 amino acids. When the amino acid sequence of any protein embedded in a membrane is examined, typically one or more segments of the polypeptide chain are found to be comprised largely of amino acids with nonpolar side chains. Each of these segments coils is what is called a transmembrane domain, with a length approximately the width of the membrane. Moreover, within a transmembrane domain the side chains necessarily face outward where they readily interact with the lipids of the membrane. By contrast, the peptide bonds, which are quite polar, face inward, separated from the lipid environment of the membrane. In the case of the voltage-gated sodium channel, there are 24 such transmembrane domains in the polypeptide chain, as shown to the right. For clarity in the figure to the right, the alpha-helices are shown spread out and in a row. Also, they are shown divided into four groups. Each of these is an homologous domain with a similar sequence of amino acids. In an actual membrane, of course, the alpha-helices are not in a line, but clustered. This is shown in top view in the figure to the left. At the center of the four domains is the channel through which the sodium ions move. Opening of Channel by Voltage Sensor The voltage-gated sodium channel has several functional parts. One portion of the channel determines its ion selectivity. This particular channel is quite selective for sodium ions. Even the chemically similar potassium ions cannot pass through the channel. Another portion of the channel serves as a gate that can open and close. For many ion channels, the gate opens in response to regulatory molecules that specifically bind to either the inside or outside of the channel. But in the case of the voltage-gated sodium channel, the gate is controlled by a voltage sensor, which responds to the level of the membrane potential. The membrane potential is designated at the left of the figure by the net excess of positive and negative changes. As shown, cells in general have a small net excess of negative ions clustered under the plasma membrane. In a resting neuron or muscle cell the inside is approximately 70 to 90 millivolts (mV) negative with respect to outside. In this diagram and those that follow, a single transmembrane domain is shown as the voltage sensor that operates the gate. This is for diagrammatic simplicity. Actually, several voltage sensors must respond before the gate opens. Finally, an inactivation gate is shown. This limits the period of time the channel remains open, despite steady stimulation. But many other types of ion channels do not have an inactivation gate. The figure to the left shows the movement of the voltage sensor during changes in the membrane potential. The voltage sensor is represented as a transmembrane domain with fixed positive charges. Each of the homologous domains, in fact, has one transmembrane domain in which a positively charged amino acid is found at every third position, giving a total of four to eight positive charges per transmembrane domain. These transmembrane domains are likely to be the actual voltage sensors. At a typical resting membrane potential (for example, -70 mV) the channel is closed. Then should any factor depolarize the membrane potential sufficiently (for example, to -50 mV), the voltage sensor moves outward and the gate opens. (Figures of channel based on figures by B. Hille and B. Zagotta.)

myelin

a mixture of proteins and phospholipids forming a whitish insulating sheath around many nerve fibers, increasing the speed at which impulses are conducted.

By location of origin...proprioceptors vs. exteroceptors vs. interoceptors

What is a sensory receptor? Specialized nerve cell that is designed to respond to a specific sensory stimulus Give examples of sensory stimulus Touch, pressure, pain, light, sound, position in space, and vibration What are the 3 types of sensory receptors? 1. Exteroceptors 2.Interoceptors 3.Proprioceptors What are exteroceptors? Recieve sensory information from outside of the body. Examples: Visual, auditory, tactile, gustatory, and olfactory What are Interoceptors? Recieve sensory information from inside the body. Detect internal body sensation. Examples:from the viscera (hollow organs), stomach pain, pinched spinal nerves, and deep skin inflammation What are proprioceptors? Unconscious information recieved. Detect body position in space and movement. Located in the muscles, tendons, and joints inside the body and semicircular canals of the inner ear

resting potential

When Kendra wants to move, she moves, and when she wants to stop and rest, she does. This is thanks to the neurons that she has in her nervous system. But, how exactly do they work? Like Kendra, neurons aren't active all the time. When a cell is firing, it is in action, but when it is not firing, it is at rest. The resting potential of a neuron is the condition of the neuron when it is resting. There is still potential for it to fire, but it is not firing at the moment, which is why it is called the resting potential. Think about the resting potential like when Kendra is at the starting line; she's not moving yet, but she's ready to move at a moment's notice. So, what is a neuron like during a resting potential? To understand that, you need to know that both inside and outside of the neuron is a liquid that's filled with many different ions and anions. Especially important when talking about the resting potential are the sodium and potassium ions. Both sodium and potassium ions are positive, but the number of each type of ion inside and outside of the cell determines what the charge of the liquid is. For example, at rest there are more potassium ions inside the cell and more sodium ions outside of the cell. This makes the inside of the cell more negative than the outside of the cell during a resting potential. Kendra gets that during resting potential, a neuron is more negative inside than outside. But what happens when a cell fires? Like Kendra taking off for a race, when a cell fires it becomes active. At that point, sodium ions flood the inside of the cell, and potassium ions flow out of the cell. That makes the charge inside the cell more positive than the outside of the cell. This is the opposite of a resting potential, and it causes the neuron to send a message to the next neuron in line--like when Kendra runs the relay and hands the baton off to her teammate.

white matter tracts of cerebral hemispherse

White matter modulates the distribution of action potentials, acting as a relay and coordinating communication between different brain regions. There are three main kinds of white matter tracts: projection, commissural, and association. The largest white matter structure of the brain is the corpus collosum, a form of commissural tract, that connects the right and left hemispheres.

white matter

White matter, named for its relatively light appearance resulting from the lipid content of myelin, refers to axon tracts and commissures. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color in prepared specimens is due to its usual preservation in formaldehyde. White matter, long thought to be passive tissue, actively affects how the brain learns and functions. While grey matter is primarily associated with processing and cognition, white matter modulates the distribution of action potentials, acting as a relay and coordinating communication between different brain regions.[1]

axon terminal = synaptic knob

Your brain is like a machine with many different parts that all work together. The synaptic cleft may not be the most well known part of the brain, but it is vital for brain function. Read on to find out more about what it does and why it matters. Your Brain Your brain is an amazing machine with lots of work to do. The neurons, or nerve cells, in the brain are responsible for communications that make all processes possible. Communication can happen two ways: electrically or chemically. When communication is chemical, the synaptic cleft comes into play. Function of the Synaptic Cleft The synaptic cleft, by definition, is a tiny opening between neurons. When scientists study the synaptic cleft, they are looking at how information is relayed from one neuron to another, but we will dive deeper into this later on in the lesson. The synaptic cleft is seemingly just an empty space, so you may think that it isn't important, but don't be fooled. Think of neuron communication like traveling to a different country—neurons don't all speak the same language. So you may be wondering, how does the information get translated? That's right...the synaptic cleft helps to decode the message. When the electrical signal reaches the presynaptic ending, it is translated into a chemical message that then diffuses across the synaptic cleft to the postsynaptic cell. The receiving neuron takes this information and translates the chemical message back into electrical signals, which then heads into the next neuron where the process is repeated. Let's take a look at how other parts of the brain come into play and how they work together. The Neuron Neurons are the most basic unit of the brain. Your brain has billions of neurons that use electrical signals to communicate with other neurons about all types of things, such as sending hunger pains or picking up a pencil. Neurons have projections called axons and dendrites. Axons bring information away from the cell, and dendrites carry information to the cell. The spot where neurons come together to communicate is called a synapse. The Synapse The synapse is like a wire that connects two cells together. Neurons pass information to each other through the synapse. The synapse contains four main parts: An ending with neurotransmitters The presynaptic ending The postsynaptic cell The synaptic cleft The neurotransmitters are nerves that carry information, and they are located just before the synaptic tip. The presynaptic ending is located in the synapse and is responsible for sending information out. The postsynaptic cell is a cell which has places for the neurotransmitters to land, or receive information. The synaptic cleft, as we know, is the space located between the presynaptic and postsynaptic endings. Neurons communicate by sending an electrical signal. Let's break down how this works. Neurotransmission in Action Neurons communicate by sending out an electrical signal, and they start a chain reaction when they are stimulated by signals. Every neuron on the path takes up the signal and passes it to the next neuron. The dendrites pick up the impulse and send the message to the axon, which then delivers it to the next neuron. Then, the process begins again with another neuron. Finally, once the message hits its target, like a muscle or gland cell, the neurotransmitter is stimulated and causes action. All of this happens in about seven milliseconds. neurotransmitter Neurons Communicate When one neuron communicates with another, it sends an electrical impulse through the presynaptic ending. This releases neurotransmitters into the synaptic cleft, or the space between presynaptic ending and postsynaptic cell. Now, the neurotransmitters can move across the synaptic cleft and bind together with the postsynaptic cell. Take a look at this transmission: synapse Lesson Summary Every single thing you do as a human depends on your neurons. They send electrical impulses that bring messages to other parts of the brain, as well as your nervous system. When the signal gets to the end of the dendrite, it sends a message to the next neuron waiting to receive it through a messenger called a neurotransmitter. While the axons are waiting to receive the message, it first crosses the synapse, or wire between neurons. The synapse has three parts: The presynaptic ending, which releases the message The postsynaptic cell, which receives the message The synaptic cleft, the microscopic space between the pre- and post-synaptic endings The synaptic cleft acts as a translator, taking the information from the sending neuron and converting it to an understandable piece of information for the receiving neuron. Without the synaptic cleft, neurons wouldn't be able to properly communicate, and messages like, 'I'm thirsty,' wouldn't get sent or received.

limbic system

a complex system of nerves and networks in the brain, involving several areas near the edge of the cortex concerned with instinct and mood. It controls the basic emotions (fear, pleasure, anger) and drives (hunger, sex, dominance, care of offspring).

thyroid gland

he thyroid gland is a butterfly-shaped organ located in the base of your neck. It releases hormones that control metabolism—the way your body uses energy. The thyroid's hormones regulate vital body functions, including: Breathing Heart rate Central and peripheral nervous systems Body weight Muscle strength Menstrual cycles Body temperature Cholesterol levels Much more! The thyroid gland is about 2-inches long and lies in front of your throat below the prominence of thyroid cartilage sometimes called the Adam's apple. The thyroid has two sides called lobes that lie on either side of your windpipe, and is usually connected by a strip of thyroid tissue known as an isthmus. Some people do not have an isthmus, and instead have two separate thyroid lobes. How the Thyroid Gland Works The thyroid is part of the endocrine system, which is made up of glands that produce, store, and release hormones into the bloodstream so the hormones can reach the body's cells. The thyroid gland uses iodine from the foods you eat to make two main hormones: Triiodothyronine (T3) Thyroxine (T4) It is important that T3 and T4 levels are neither too high nor too low. Two glands in the brain—the hypothalamus and the pituitary communicate to maintain T3 and T4 balance. The hypothalamus produces TSH Releasing Hormone (TRH) that signals the pituitary to tell the thyroid gland to produce more or less of T3 and T4 by either increasing or decreasing the release of a hormone called thyroid stimulating hormone (TSH). When T3 and T4 levels are low in the blood, the pituitary gland releases more TSH to tell the thyroid gland to produce more thyroid hormones. If T3 and T4 levels are high, the pituitary gland releases less TSH to the thyroid gland to slow production of these hormones. Why You Need a Thyroid Gland T3 and T4 travel in your bloodstream to reach almost every cell in the body. The hormones regulate the speed with which the cells/metabolism work. For example, T3 and T4 regulate your heart rate and how fast your intestines process food. So if T3 and T4 levels are low, your heart rate may be slower than normal, and you may have constipation/weight gain. If T3 and T4 levels are high, you may have a rapid heart rate and diarrhea/weight loss. Listed below are other symptoms of too much T3 and T4 in your body (hyperthyroidism): Anxiety Irritability or moodiness Nervousness, hyperactivity Sweating or sensitivity to high temperatures Hand trembling (shaking) Hair loss Missed or light menstrual periods The following is other symptoms of too little T3 and T4 in your body (hypothyroidism): Trouble sleeping Tiredness and fatigue Difficulty concentrating Dry skin and hair Depression Sensitivity to cold temperature Frequent, heavy periods Joint and muscle pain

refractory period

refractory period is a period of time during which an organ or cell is incapable of repeating a particular action, or (more precisely) the amount of time it takes for an excitable membrane to be ready for a second stimulus once it returns to its resting state following an excitation. It most commonly refers to electrically excitable muscle cells or neurons. Absolute refractory period corresponds to depolarisation and repolarisation, whereas relative refractory period corresponds to hyperpolarization. After orgasm, both men and women experience a resolution stage. At this time, their bodies "recover" from sexual excitement and return to their normal states. For men, the penis becomes flaccid again and he goes through a refractory period. During the refractory period, a man doesn't think about sex or get aroused. His body does not respond to sexual stimulation and he is unable to reach orgasm again until the period is over. The length of the refractory period is different for every man. It may take a half hour or more for his body to perform sexually again. Younger men may need only a few minutes of recovery time, but older men usually have a longer refractory period, sometimes between 12 to 24 hours. For some men, the refractory period can last a few days. Experts aren't sure why the length of refractory periods varies so much among men. But they do know that the length of time needed is not related to potency or testosterone levels. Some men wonder how they can shorten their refractory period. No drugs have been approved for this purpose, but research has shown that Viagra and Cialis - two drugs used to treat erectile dysfunction - may reduce recovery time. Women do not have refractory periods the way men do. But fatigue after orgasm can make them lose interest in sex temporarily. This can happen after one orgasm or multiple orgasms.

axodendritic

relating to or being a nerve synapse between an axon of one neuron and a dendrite of another

cholinergic

relating to or denoting nerve cells in which acetylcholine acts as a neurotransmitter. releasing or responding to acetylcholine.

adrenergic

relating to or denoting nerve cells in which epinephrine (adrenaline), norepinephrine (noradrenaline), or a similar substance acts as a neurotransmitter.

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