Unit Exam 3
Epithalamus (pineal gland)
- AS the name implies the Epithalamus lies superior (above) the thalamus and the subthalmus lies inferior. Major part of the epithalamus, is that is located at the posterosuperior portion of the diencephalon, is an endocrine organ called the pineal gland. It secretes the hormone melatonin, which helps regulate the sleep/wake.
Peripheral Nervous System (PNS)
- consists of cranial nerves, spinal nerves and its branches -Numerous organs of nervous system called nerves carries signals to and from central nervous system -Bundle of long neurons_Axons are packaged together with b mood vessels surrounding connective tissue sheath -PNS Neuroglia Types: Schwann Cell~ Myelinate certain axons PNS. Plays a role in repair of damaged axons. Satelite Cell~Surround and support cell bodies. Helps regulates extracellular environment around the neuronal cell similar to astrocytes
Gustation
-A large part of our experience eating food does depend on the sense of gustation (taste). Similar to olfaction, gustation involves chemoreceptors that respond to chemicals. Taste begins with stimulation of speciliazed receptors called taste buds which are small cluster of receptor cells and supporting cells scattered across the tongue and parts of the oral cavity. Each taste bud its contacted by sensory neurons that transmit stimuli to the CNS. Notice that your tongue is covered with rounded projections called papillae. Papillae are classified into four groups based on shape : -Vallate (or circumvallate) papillae are the largest and are dome-shaped; each contains hundreds of taste buds -Fungiform papillae are mushroom-shaped, and each contains only a few taste buds. -Folate papillae are ridges on the sides of the tongue and contain taste buds only in childhood. -Filiform papillae are long, thin cylinders scattered across the tongue. They do not contain any taste buds but have sensory nerve endings that detect the texture and temperature of food. Taste buds are typically......
Reflex
-A reflex is a programmed, autonomic motor response to a specific sensory input. The series of events that culminates in a reflex response is reflex arc. -Monosynaptic the simplest reflex arcs involves only a single synapse within the spinal cord between sensory and motor neurons -Polysynaptic a more complicated type of reflex arc, involving multiple synapses
Dura Mater in the Spinal cord
-As with the brain, the spinal cord has the meningeal layers: dura, arachnoid, pia mater. The spinal meninges are similar in structure to those of the brain except for the dura mater, which lacks a periosteal layer and consists only a meningeal layer. Also, the spinal Pia plays a role that the cranial Pia does not, it helps tp anchor the spinal cord in the vertebral cavity.
White and Gray Matter CNS
-Both in the brain and spinal cord consist of white matter contains myelinated axons, and gray matter which is made up of neuron cell bodies, dendrites, and unmyelinated axons. Majority of the brain is covered in gray matter, deeper layer is the white matter. -Each lobe of cerebrum contains bun does of white matter called tracts which receives input from and send output to the different clusters of cell bodies and dendrites in the cerebral gray matter called nuclei -This communication connects the different parts of the brain and spinal cord. -Spinal cord consists of internally gray matter containing nuclei that process stumli and is surrounded by white matter tracts
Four Major parts of an Adult Brain
-Cerebrum performs higher mental functions; interprets sensory stimuli; plans and imitates movement -Diencephalon processes, integrates, and relay information; maintains homeostasis; regulates biological rhythms -Cerebellum monitors and coordinates movement -Brainstem maintains homeostasis; controls certain reflexes, monitors movement; integrates and relays information
Central Nervous System (CNS)
-Consists of brain and spinal cord ,100billion cells called neurons or nerve cells -CNS Neuroglia Types: Astrocytes (largest)~ it anchors neurons and blood vessels, regulates extracellular environment. Faciliate formation of blood brain barrier and repairs damaged tissue Oligodendrocytes (smaller)~ myelinated certain axons in the CNS Microglia (least smallest and branching)~Acts as phagocytes. Cleanup crew, cleans up after damaged brain matter is in the environment Ependymal cells~Lines cavities, cilia, circulates fluid around brain and spinal cord
Nucleus v.s Ganglion
-First order neurons are pseudo unipolar neurons that has three main components: a cell body and two axons. -The cell body is located un a posterior root ganglion, found lateral to the spinal cord. The cell bodies of cranial nerves are situated in cranial nerve ganglia present in the head and back. -The peripheral process of the neuron is a long axon. At one end , it splits into nerve endings; associated with each nerve ending is a sensory receptor. At on the other end, the peripheral process terminates near the neuron's cell body. -The central process exists the cell body and travels through the posterior root of the spinal cord to enter the posterior horn ( or into the brainstem for cranial nerves)
LOBES
-Frontal lobe the anterimost lobe, the posterior boundary is the central sulcus and anterior is the central sulcus is the precentral gyrus -Parietal lobe posterior to the frontal lobes are paired parietal lobes. The major gyrus of each of these lobes is the postcentral gyrus, which sits just posterior to the central sulcus -Temporal lobe the paired temporal lobes are on the lateral surfaces of the hemisphere, separated from the frontal and parietal lobes by the lateral fissure -Occipital lobe the posterior lobe of the cerebral hemisphere, it is separated from the parietal lobe by the parieto-occipital sulcus -Insula the paired insulas, are visible one. you pry the frontal, parietal, and temporal lobes apart at the lateral fissure
Shallow and deep groves
-Gyrus elevated ridge -Sulcus shallow groove -Fissure deep groves
Receptors
-Sensory transduction, the conversion of a stimulus into an elec- trical signal, takes place at a sensory receptor. During sensory transduction, a receptor potential is generated, which may trigger an action potential. -Interceptors detect stimuli originating within the body. -Exteroceptors detect stimuli originating outside the body. -Mechanoreceptors detect stimuli that mechanically deform the tissue; thermoreceptors detect thermal stimuli; chemoreceptors detect the presence or concentration of chemicals; photoreceptors detect light; and nociceptors detect painful stimuli. • Sensory, or afferent, neurons detect and transmit sensory stimuli. Somatic sensory neurons are first-order pseudounipolar neurons. -Large-diameter and heavily myelinated sensory neurons transmit impulses the fastest. -The receptive field of a neuron is the area served by that neuron. -The size of a receptive field may be measured by assessing the two-point discrimination threshold. -The skin can be divided into dermatomes that are innervated by a single cranial or spinal nerve. Visceral pain is often perceived as cutaneous pain along the dermatome for the nerve that supplies organ. This is known as referred pain
Hypothalamus
-Hypothalamus is a collection of nuclei that sits anterior and inferior to the thalamus. It makes up 1% of themes of the brain. -Hypothalamic nuclei performs several functions that are vital to our vital. Including the sleep wake cycle, regulating the AUTONOMIC NERVOUS SYSTEM, thirst and hunger, and body temperature. -The hypothalamus has. a close anatomical and functional connection to the endocrine organ called the pituitary gland. The pituitary gland attaches to the inferior hypothalamus by an extension referred to as the infundibulum , and hypothalamic tissue makes up the posterior portion of the this gland. -The hypothalamus secretes a variety of hormones that affect the pituitary gland, hypothalamic releasing or inhibiting hormones increase or decrease the secretion of other hormones from the pituitary gland>(it also secretes hormones that influence secretion from the endocrine glands throughout the body. The hypothalamus also produces two additional hormones that do not act on the pituitary gland: Anitidiueretic hormones (ADH) which influences water balance in the body, and oxytocin which is in women stimulation contractions of the uterus during childbirth and in both sexes may promote emotional bonding. -The hypothalamus receives input from a lot of sources, including the cerebral cortex and basal nuclei. It also connects with the limbic system via two small projections called the mammillary bodies . The structures receive input from the hippocampus, with which they play a role in regulating memory and behavior. Input also arrives at the hypothalamic nuclei from sources outside the nervous system, including the endocrine system, receptors that detect changes in the body temperature, and receptors that detect the blood's concentration.
Major ion channels
-Leak channel always open for stimuli -Ligand Gated Channel open in response to a certain chemical, called a ligand, binding to a channel or to a receptor associated with the channel. -Voltage Gated Channel open or close in response to change in the cell's membrane potential -Mechanically Gated Channel open or close in response to mechanical stimulation such as stretch, pressure, and vibration
Mechanoreceptors
-Merkel cell fiber discriminative touch with fine spatial resolution -Tactile Corpuscle discriminative touch with less spatial resolution -Ruffini ending( bulbous corpuscle) stretch and movement -Lamellated corpuscle vibration and deep pressure
3 divisions of the brainstem
-Midbrain if you been startled by a loud noise your midbrain is to blame. It is found just inferior to the diencephalon. It is the shortest component of the brainstem and is also known as the mesencephalon due to its reflecting embryonic origin. It has many diverse functions including roles in movement, sensation, and certain reflexes like the startle of reflex. -Pons inferior to the midbrain is pons, whose anterior surface is Rouen did and prominent. The anterior pons contains the descending motor tracts from the crus cerebri, some of which pass through the pons on their way to the spinal cord. Posterior to these tracts is an area that contains reticular formation nuclei and cranial nerve nuclei. Surrounding the pontine tegmentum are the middle cerebellar peduncicles. The pontine nuclei have diverse roles. Nuclei help regulate movements, including those required for breathing. Others particularly the cranial nerve nuclei, participate in reflexes, and some are involved in complex function such as sleep and arousal Medulla Oblongata the inferiormost portion of the brainstem is the medulla, which blends with the spinal cord after it passes through the foramen magnum.
Blood Brain Barrier (BBB)
-Most chemicals and disease-causing organisms such as bacteria and virus are denied access to the cells of the brain by blood brain. barrier, which keeps the CSF and brain extracellular fluid separate from the blood. The blood brain barrier consists mainly of simple squamous epithelial cells (endothelial cells) of the blood capillaries in the brain and their basal laminae, as well as astrocytes. Endothelial Cells are very unique: []The cells of most capillaries are joined by tight junctions. However, brain capillaries have an exceptionally large number of tight junctions. This is due mostly to the effect of astrocytes on the developing brain. []They limit endocytosis and exocytosis. Substances cannot pass between endothelial cells due to the tight junctions, so instead they must go through the phospholipid bilayers of the cells plasma membranes. Though larger, polar molecules such as proteins generally don't cross the plasma membrane freely and so rely on endocytosis and exocytosis to get into and out of the cell. Many substances in the extracellular fluid of the brain cannot enter the blood. -Certain substances can cross the blood brain barrier rather easily, including those to which the plasma membrane is in general freely permeable, such as water, oxygen, carbon diox- ide, and nonpolar, lipid-based compounds. Other substances that cross easily include those for which protein channels or carriers exist, such as glucose, amino acids, and ions. How. ever, most large, polar molecules are effectively prevented from crossing the blood brain barrier in any significant amounts. This can be both beneficial and harmful--although the blood brain barrier prevents many toxins and organisms from entering the brain, it also prevents the entry of many therapeutic drugs. For example, only a handful of antibiotics penetrate the blood brain barrier in significant enough con- centrations to treat bacterial infections in the brain, making such infections difficult to treat
refactory period
-Neurons are limited in how often they can fire an action potentials, for a brief time after a neuron has produced an action potential, the membrane cannot be stimulated to fire another one also known as the refractory period and con lists of two phases: -Absolute refractory period no additional stimulus no matter how strong is able to produce an additional action potential. This period coincides with and inactivated states: sodium ion channels may not be activated until they return to their resting states with their activation gates closed and their inactivation gates open -Relative refractory period immediately following the absolute refractory period is the relative refractory period, during which only a strong stimulus period is marked by a return of voltage-gated sodium ion channels to their resting state while some potassium ion channels remain activated. Its difficult to depolarize the membrane to activated and the membrane is repolarizing or even hyperpolarzing
Olfaction
-Olfaction begins in the olfactory epithelium a small patch of specialized epithelium located in the superior region of each nasal cavity. ( the olfactory epithelium is yellowish brown and the size of the thumbnail. -Olfactory neurons are modified bipolar neurons that detect odorants. Olfactory neurons are known as chemoreceptors, since they respond to the presence of certain chemicals in the air rather than to neurotransmitters. Humans can have up to 100 million olfactory neurons -The axons of the olfactory neurons are bundled into groups 10-100 and travel through tiny holes in the cribriform plate of the the ethmoid bone to each the CNS. Collectively these axons forms the olfactory nerve (CN I). These axons terminate by snoozing on other neurons called mitral cells in the olfactory bulb , a structure located in the brain just superior to the ethmoid bone and inferior to the frontal lobe of the brain. Axons leave the olfactory bulb into the olfactory tract and transmit olfactory stimuli to other parts of the brain. -When odorant reach the olfactory epithelium, most of them bind to odorant-binding proteins, which shuttle them to receptors on the cilia. When the odorants reach their receptors: 1. Binding of an odorant to its receptor activates a G-protein 2.The activated G-protein triggers adenylate cyclase to convert ATP into cyclic AMP (cAMP) 3. cAMP opens ion channels that allow sodium and calcium ions to enter the cell Olfactory pathway 1. the axons of olfactory neurons (making up the olfactory nerve) carry olfactory stimuli to the olfactory bulb in the CNS. The axons of the olfactory neurons terminate in the olfactory bulb just inferior to the frontal lobe. The axon terminals synapse with the dendrites of mitral cells will have an action potential 2. An olfactory stimulus travels from the olfactory bulb to the primary olfactory cortex in the temporal bone. If an action potential is in stated, it will travel along the axons of the mitral cells, forming the bulk of the olfactory tract. The stimuli are delivered to the primary olfactory cortex, located in the inferomedial temporal lobe near the optic chiasma. This is the only sensory pathway that has no synapse in the the thalamus. The primary olfactory cortex is responsible for awareness and indication of an odor. It is also a common location for seizures, which are often preceded by the sensation of an unpleasant smell.
Somatic motor vs Autonomic motor Division
-Somatic Motor Division consists of neurons that transmit signals to skeletal muscles. Skeletal muscle tissue is under conscious control so this division is sometimes called the voluntary motor division -Autonomic (visceral) consists of neuron s that carry signals primarily to thoracic and abdominal viscera. The ANS regulated secretion from certain glands, the contraction of smooth muscle, and the contraction of cardiac muscle in the heart
Somatic v.s. Visceral SENSORY
-Somatic sensory Division soma=body, consists of neurons that carry signals from skeletal muscles, bones, joints, and skin. This division also includes sensory neurons that transmit signals from the organs of vision, hearing, taste, smell, and balance (special senses) -Visceral Sensory Division consists of neurons that transmit signals from viscera (organs) such as heart, lungs, stomach, intestines, kidneys, and urinary bladder. Sensory inout from both divisions is carried from sensory receptors to the spinal cord and/or the brain by cranial and spinal nerves of the PNS.
Stretch Reflex & Function of the muscle spindle and Golgi Tendon
-Stretch Reflex is a monosynaptic reflex that returns a muscle to its optimal length after being stretched -Muscle Spindle and Golgi Tendon: muscle spindles and golgi tendon organs detect sensory component of reflexes that monitor and control movement. -Muscle spindles contains intramural muscle fibers, which detect stretch -Golgi tendon organs detect the tension generated by a muscle contraction
Thalamus
-Thalamus consists of two large egg shaped masses of gray matter together make up 80% of the diencephalon. Between the two masses lies a cavity known as the third ventricle -Thalamic nuclei receive input from many sources, including cerebral Cortex, the cerebellum, the basal nuclei, structures of the limbic system and the sensory (except for smell) and their main output travels to the cerebral cortex. The thalamus is the "main entrance" into the cerebral cortex nearly all stimuli destined must first pass through the thalamus. Allowing the thalamus to control which information reaches the cerebral cortex and where the in formation is sent relating to cortical activity. For the reason the the thalamus plays a role in almost all processes occurring in the brain including imitation and regulation of movement, integration of sensory stimuli, emotions, memory, arousal, consciousness, and the level of responsiveness and excitability of the cerebral cortex.
Layers of meninges
-The 3 Brain meninges are made of protective dense irregular collagenous connective tissue. -Dura Mater the outermost layer of the meninges very tough abundant with collagen. Between the dura and the cranial bones is a potential space called the epidural space, is potential Because normally the dura is bound tightly to the bone and nothing is found between them except blood vessels. Deep to the dura is another very narrow space, called the subdural space, that houses a thin layer of serous fluid and certain veins that drain the brain. It has two layers: [] Periosteal dura the outermost periosteal dura is attached to the inner surface of the bones of the cranial cavity, it's function as the periosteum of those bones and has extensive blood supply that resides in the epidural space. []Meningeal dura the meningeal dura is the inner, avascular layer that lies superficial to the arachnoid mater. In certain areas the the two layers separate and form cavities called dura sinuses. The dural sinuses are venous channels that drain CSF and deoxygenated blood from the brain's many veins. -Arachnoid Mater the middle meningeal layer a little bit thinner (dense irregular collagenous connective tissue) but more so elastic, superficial to the Pia mater. It has inward extensions called arachnoid trabeculae. These trabeculae made up of bundles of collagen fibers and fibroblasts, anchor the arachnoid mater to the deeper Pia mater. Also small bundles of the arachnoid project up through the meningeal dura into the dural sinuses. The arachnoid granulation plays an important role in returning CSF to the bloodstream. -Pia Mater Deepest innermost layer, separated between the arachnoid and Pia mater is the subarachnoid space containing CSF and the major blood vessels of the brain. Pia Mater is the only meningeal layer that touches the brain directly, and it closely follows each contour of the brain and dives into its scull and fissures . The Pia Mater is permeable to substances to move between two fluids and helps to balance the concentration of different solutes in them.
Motor Neurons
-The CNS imitates movement when upper motor neurons in the the motor cortices make the "decision" to move -Lower motor neurons contact the muscle fiber and imitate a muscle contraction. -Lower motor neurons are multipolar neurons whose cell bodies are located in the anterior horn of the spinal cord or in the brainstem. Groups of lower motor neurons that innervates the same muscle are located together in the spinal cord in motor neuron pools
Cerebellum
-The cerebellum makes up the posterior and inferior portion of the brain. It functions with the cerebral cortex, basal nuclei, brainstem, and spinal cord to coordinate ongoing movement and reduce motor error. -It is composed of two cerebellar hemispheres connected bye a structure called the vermis. The cerebellar surface contains ridges known as folia, which are separated by shallow sulk, this arrangement increases the cerebellar surface of the cerebral cortex. The cerebellum is divided into three different lobes: anterior lobe, posterior lobe, and the small flocculonodular lobe. -The cerebellar cortex is so extensively folded that the white matter resembles tree branches and so is named the arbor vitae -The role of the cerebellum in movement as well as interaction with the cerebral cortex, basal nuclei, brainstem and spinal cord.
Describe a typical nerve
-The main organs of the PNS are peripheral nerves or (just nerves), which consists the axons of many neurons bound together by a common connective tissue sheath. -The many nerves of the PNS contact or innervate, the majority of structures in the body. -Most nerves are mixed nerves meaning they contain both sensory and motor neurons , since why a damage nerve affects both sensory and motor functions. Sensory nerves carry only sensory information and motor nerves carries motor information. Motor though does contain a small amount of sensory information to respond to muscle tension and stretch. -Epineurium is when the nerve is wrapped by a connective sheath called the epineurium. -Fasciles are within the nerve, and are a bundle of axons into smaller groups -Perineruium are fascicles bounded by another connective sheath -Nested to the fascicles are blood vessels that supply axons with oxygen and nutrients -Endoneurium each axon within a fascicle is surrounded by its own connective sheath
Propagation and connection continued
-The rate at which propagation is called conducted speed and it determines how rapidly signaling can occur within the nervous system. Conduction speed is influenced by two main factors: the diameter of the axon and the presence or absence of a myelin sheath. The diameter of the axon affects the conduction of current through the axon because larger axons have lower resistance to conduction and therefore current flows through them more easily. -Two types of conduction can take place in an axon: saltatory conduction and continuous conduction. Remember myelin is an excellent insulator of electrical charge. So the flow of current is far more efficient in a myelinated axon, which causes saltatory conduction to be significantly faster than continuous conduction.
Limbic System
-This system includes a region of the medial cerebrum sometimes referred to as the limbic lob e, the hippocampus, a collection of gray matter called the amygdala, and the pathways that connect these regions of gray matter with one another and with other parts of the brain. Structures: -fornix is the primary white matter output tract of the limbic system -limbic lobe containing the cingulate gyrus and parahippocampai gyrus. Gray matter cortex involved in memory formation and retrieval, emotion, and learning -Hippocampus nucelus involved in learning and memory -Amygdala nucleus involved in behavioral expression of emotion, mainly fear
Upper and Lower Neurons
-Upper Motor neurons reside mostly in the motor areas of the cerebral cortex. They stimulate the local interneurons in the brainstem or spinal cord. The interneurons pass the message to lower motor neurons of the PNS, which innervate muscle fibers -Every motion requires the selection of a motor program by the upper motor neurons of the primary motor cortex in the cerebral cortex which plan and execute voluntary motion. -Each part of the body is represented by a specific region of the primary motor cortex
Voltage Gated Channels involving Action
-Voltage gated potassium ion channel has two states: resting the channel is closed and activated the channel is open and allows potassium ions to cross the axolemma. -Voltage gated sodium has three states: Resting state inactivation gate opened, activation gate closed, no sodium ions cross the membrane when the channel is in. the resting state. Activated state both activation and inactivation gates opened. When an action potential is initiated, the voltage change opens the activation gates and the channel is in it activation state Inactivated state inactivation gated closed activation gate opened, when the inactivation gate closes, the channel is in its inactivated state. -Neuronal action potentials have three general phrases: depolarization, the membrane potential rises toward zero and then becomes briefly positive. The membrane potential returns to a negative value during the repolarization phase and then becomes temporarily more negative than resting during the hyperpolarization. Each phase occurs because of the selective opening and closing of specific voltage-gated ion channel
Reflex responses components of a reflex arch
-You also jerk your hand away when touching a hot pot. These are all programmed, automatic responses to stimuli called reflexes. Most reflexes are protective, preventing tissue damage. -Each reflexes begins with a sensory stimulus and finishes with a rapid motor response. Between the sensory stimulus and the motor response, neural integration takes place within the CNS, mainly in the brainstem and spinal cord. The overall sequence of a reflex is: 1. The sensory (afferent) division: PNS detects and delivers stimulus to CNS 2. CNS integrates stimulus 3. Motor (efferent) division: PNS delivers motor response from CNS to effectors
Synapses
-how signals are transmitted between neurons at locations called synapses, where a neuron meets its target cell. Neuronal synapses happen occur between an axon and another part of a neuron; they may occur between an axon and all dendrite, an axon and a cell body and an axon and another axon. -We use certain types name when describing the neurons sending and receiving the messages: -Presynaptic neuron the presynaptic neurons is the n neuron that is sending the message from it'd axon terminal -Postsynaptic neuron the postsynaptic neuron is the neuron that is receiving the message from its dendrite, cell boy, or axon -The transfer of chemical or electrical signals between neurons at a synapse called synaptic transmission, and is the fundamental process for most functions of the nervous system. Synaptic transmission allows voluntary movement, cognition, sensation, and emotion. Two types: -Electrical Synapse_ occurs between cells that are electrically coupled via gap junctions. In these synapses the axolemmas of the two neurons are nearly touching and the gap junctions contain precisely aligned channels that form pores through which ions and other small substances may travel. They are either bidirectional -Chemical Synapse_ majority of synapses ar
Action Potential
-is a uniform, rapid depolarization and repolarization of the membrane potential of a cell. For a muscle fiber, the change imitates events that lead to muscle fiber contraction. Within the nervous system, signals are sent through an axon to another neuron, a muscle fiber or gland. -Only axons generate action potentials; dendrites and cell bodies generate local potential only. Action potential are generated in the initial segment of the axon; called the trigger zone
The Ventricular System
-the brain has cavities called ventricles. The ventricles are continuous with one another and with the cavity in the spinal cord, called the central canal . Both the v ventricles and the central canal are lined with ependymal cells and filled with cushioning cerebrospinal fluid -Right/left Ventricles cavities within the right and left cerebral hemispheres are the right and left lateral ventricles -Third Ventricles the narrow third ventricle is housed between the two lobes of the diencephalon. It is continuous with the lateral ventricles via an opening that connects all three called the intereventricular foramen -Fourth Ventricle the third ventricle drains into the fourth ventricle via the cerebral aqueduct, a small canal that passes through the midbrain of the brainstem. The fourth ventricle is situated between the pons and the cerebellum and is continuous inferiorly with the central canal of the spinal cord -Cerebrospinal fluid (CSF) is a clear, colorless liquid similar in composition to plasma. CSF protects the brain by cushioning it maintaining a constant increasing the buoyancy of the brain. Without it the brain would crush itself with its own weight. -The general pathway for the formation, circulation, and reabsorption of CSF 1. Fluid and electrolytes leak out of the capillaries of the chroiod plexuses 2.Ependymal cells secrete CSF into the ventricles. The fluid and electrolytes that have escaped the capillaries enter the ependymal cells. Some CSF then flows into the subarachnoid space 3. CSF circulates through and around the brain and spinal cord in the subarachnoid space. 4. Some of the CSF is resorbed into the blood in the dural sinuses via the arachnoid granulations. As the CSF flows through the subarachnoid space, some of it is reabsorbed through the arachnoid granulations. The reabsorbed CSF ends up in the dural sinuses, where it mixes with venous blood.
Spinal Cord: Epidural space, Subdural Space, and Subarachnoid Space
1. Epidural Space the spinal cord lacks a periosteal dura so, an epidural space exists between the meningeal dura and the walls of the vertebral foramina. This space is filled with veins and adipose tissue, which helps to cushion and protect the spinal cord. 2. Subdural Space Like epidural space around the brain, subdural space in the spinal cord is only a potential space; normally, the dura and arachnoid adhere to each other. 3. Subarachnoid Space Like the subarachnoid space lies between the brain, the spinal subarachnoid space lies between the arachnoid and Pia and is filled with a very thin layer if CSF. The area inferior to the base of the spinal cord contains a larger volume of the CSF.
Components of Neurons
1. Soma- cell body containing a nucleus 2. Dendrites- branches that receive signals from other cells and transmit information to the soma 3.Axon- sends outgoing signals to other cells, they are considered processes that can generate and conduct action potentials 4.Axon hillock- each axon arises from an area of the cell body called the axon. hillock, and tapers to form the slender axon which is often wrapped in the insulating myelin sheath. **Action potential begins in the axon hillock and terminates into the axon terminals**
Neuron Classification
multipolar, bipolar, pseudounipolar
Polarization
A ligand binds a ligand-gated cation channel, and cations (such as sodium ions) follow their electrochemical gradient and enter the cell. -Depolarization the influx of positive charges makes the membrane potential less negative -Repolarization when a cell returns back to resting membrane potential, a ligand binds to a cation (POTASSIUM ION CHANNEL) channel for which the electrochemical gradient is reversed allowing cations to flow out of the cell into the ECF -Hyperpolarization loss of positive charges (or gain negative charges) makes the inside of the cell more negative, causing hyperpolarization
propagation (conduction)
A single action potential in one spot of the membrane can't perform its main function, which is to act as a method of long distance signaling. To do this, it has to be conducted or propagated down the length of the axon. The propagation of the action potential along the axon creates a flow of charged particles or a current. Action potentials are self propagating, meaning that each action potentials till triggers another one in a neighboring section of the axon. **EXAMPLE: Imagine this process like a string of dominoes, when the first one is tipped over, the next one falls which triggers the next to fall and the process continues until the end of the line is reached. Only the first domino needs the push and once they start to fall, the process sustains itself until the end.** -The transmission of action potentials occurs at a constant speed and largely in one direction from the trigger zone to the axon terminals. Propagation takes in a single direction because the membrane in the previous section (behind the action potential is still in the refractory period). Events during of Propagation: 1. The axolemma depolarize the threshold due to local potentials 2. As sodium ion channels activate an action potential is triggered and spreads positive charges down the axon 3. The next section of the axolemma depolarizes to threshold and fire an action potential as the previous section of the axolemma repolarizes 4. The current continues to move down the axon and the process repeats
Spinal Nerves (roots and rami)
Anterior root-carries somatic and visceral motor signals from the CNS to skeletal muscles and gland cells Posterior root-carries sensory signals from the PNS to the spinal cord -Rami or ramus- are small branches containing visceral motor (autonomic neurons) of the sympathetic nervous system Anterior ramus- travels on the anterior side of the body and the upper/ lower limbs. Each ramus branches multiple times along its course through the body and supplies different skeletal muscles and regions of the skin. Both anterior and posterior rami are mixed nerves, containing both sensory and somatic motor axons
CSF
Cerebrospinal fluid (CSF) is clear, colorless liquid similar in composition to plasma. CSF protects the brain by cushioning it and maintaining a constant temperature within the cranial cavity, removing wastes, and increasing the buoyancy of the brain can crush itself under its own weight. It is formed in the ventricles by a luster of capillaries and ependymal cells called the choroid plexus, and is reabsorbed into the blood through the arachnoid granulation.
How does cranial bones and vertebral column protect the CNS?
Creates a physical strong border to keep everything inside including CSF.
Cranial nerves
I. (S) Olfactory Is the nerve for smell, originates from the neurons of the olfactory epithelium in the roof of the nasal cavity. II. (S) Optic is the nerve for vision. It comes from neurons in the posterior eye III. (M) Oculomotor innervates 4out of 6 of the eye muscles including: superior rectus, inferior rectus, medial rectus, inferior oblique and the elevator palpebral superiors muscle, constricts the pupil, and changes the shape if the lends for better near vision IV. (M) Trochlear innervates superior oblique muscle of the eye V. (B) Trigeminal supplies much of the skin of the face and muscles of mastication VI. (M) Abducens innervates one of the six extrinsic eye muscles (lateral rectus) VII. (B) Facial innervates the muscles of facial expression; trigger secretion from the lacrimal, salivary, and nasal mucous glands, provide taste sensation; and provide some somatic sensation VIII. (S) Vestibulocochlear detects the position of the body and detects sound waves IX. (B) Glossopharyngeal supplies taste sensation; provides some somatic sensation; detects changes in blood pressure; supplies muscles involved in swallowing and triggers secretion from certain salivary glands X. (B) Vagus provides some somatic and visceral sensation; provides taste sensation to the pharynx; detects the carbon dioxide concentration in the blood; and supplies muscles of swallowing. It supplies parasympathetic innervation to most of the thoracic and abdominal viscera. XI. (M) Accessory Innervates certain muscles of the larynx and the trapezius and sternocleidomastoid muscles XII. (M) Hypoglossal innervates the intrinsic and extrinsic muscles of the tongue
ATPas Pump
Ions moving against their electrochemical gradients via ATP consuming pumps. One of the most important pumps is the sodium potassium ion pump, which brings two potassium ions into the cytosol and three sodium ions into the ECF -Ina neuron as well as a muscle fiber the concentration of sodium ions is higher in the ECF than in the cytosol and the opposite is true for the potassium ions their concentration is higher in the ECF. -When gated channels for a specific ion are triggered to open, those ions will follow their electrochemical gradient into or out of the cell
Pyramids of the Medulla Oblongata
On the anterior surface of the medulla are elevated edges known as pyramids, which contains upper motor neuron fibers of a tract of white originating from the primary motor cortex called the corticospinal tract. Within the pyramids most fibers of the right and left corticospinal tract cross over and switch sides (decussate) were they then descend into the spinal cord. On the posterior surface of the medulla are two other reacts of white matter , the posterior column, along with the nuclei that receive signals from them: the nucleus gracilis and nucleus cuneatus. -It contains a protuberance lateral to each pyramid called the olive. This structure contains a nucleus called the inferior olivary nucleus that receives sensory fibers from the spinal cord and passes them to the cerebellum.
Chemical snyapse (continuing)
The events at a chemical synapse start with an action potential reach- ing the axon terminal of the presynaptic neuron, which triggers exocytosis of neurotransmitters stored in synaptic vesicles. The neu- rotransmitters bind to receptors on the membrane of the postsynaptic neuron and cause a local postsynaptic potential. • One of two things may happen during a postsynaptic potential: • The postsynaptic neuron may be depolarized by an excitatory postsynaptic potential (EPSP). • The postsynaptic neuron may be hyperpolarized by an inhibitory postsynaptic potential (IPSP). • Neural integration is the process of putting together all the excitatory and inhibitory stimuli that determine whether a neuron will or won't fire an action potential. o Summation is the phenomenon that combines local postsynaptic potentials. • In temporal summation, a single presynaptic neuron fires at a rapid pace. In spatial summation, multiple presynaptic neu- rons fire simultaneously. • The effects of synaptic transmission are terminated by removal of the neurotransmitters from the synaptic cleft.
Gustation pathway
To activate taste receptors is to help to reach the taste buds in the crevices between the papillae. This happens with the help salvia, which dissolves substance. When the taste stimulus reaches a gustatory cell it must transducer into electrical signal. This happens beginning with the depolarization of the gustatory cell: 1. Changes in ion movements depolarize the gustatory cell's plasma membrane 2. Depolarization of the membrane opens voltage-gated Ca2+ channels and Ca2+ enter the cell 3. The Ca2+ trigger the release of neurotransmitter (seratonin,glumate, acetylene, and GABA) which produce an action potential in the axon of the sensory neuron
First, Second, and Third Order Neurons
Two major ascending tracts in the spinal cord carry somatic sensory stimuli to the brain: posterior columns/ medial leminscal system and anterolateral system. The basic pathway consists of an initial pseudounipolar first order neuron, the sen sorry neuron that detects the initial stimulus in the PNS. The central process of the first-order pseudounipolar neuron then synapses on a second order neuronal interneuron located in the posterior horn of the spinal cord or the brainstem. The axons of second order neurons generally synapse of third order neurons, which are interneurons in the thalamus. Then the axons of third order neurons deliver impulses to the cerebral cortex
Tract v.s Nerve
bundles of many axon within the CNS = tract a bundle of many axons outside the CNS =nerve
Efferent vs Afferent
efferent = motor (carrying ME away) afferent = sensory (carrying toward)
Sensory Receptors
in general sensation, stimuli are detected at the receptive endings of sensory neurons. These receptors have relatively simple structures and are located throughout the body in both the skin and the internal organs. In contrast, the receptors of most special senses are not neurons but instead are specialized cells that detect special sensory stimuli. The sense organs convert these stimuli into electrical signals that are passed on to neurons via neurotransmitters. Olfaction is the only special sense in which the receptor cells are neurons.
neuroglial cells
neuroglia cells-were named for the early scientific idea that these cells "glued together" glia=glue CNS: -Astrocytes anchor neurons and blood vessels, regulate the extracellular environment, facilitate the formation of the blood brain barrier (formation of tight junctions by preventing g certain things in the blood brain barrier), and repair tissue damage. -Oligodendrocyte myelinated certain axons in the CNS -Microglial Cell act as phagocytes, they are activated by injury within the brain and become wandering phagocytes cells that clean up the environment in the brain, ingest dealing-causing organisms, dead neurons, and other cellular debris -Ependymal Cell line cavities, cilia circulate fluid around brain and spinal cord, some secrete this fluid, function in circulating CSF PNS: -Schwann Cell Myelinate certain axons in the PNS, sausage shaped, helps damaged axons -Satellite Cell are flat cells that surround the cell bodies of the neurons in the PNS, they appear to enclose and support the cell bodies, and have intertwined processes that link them with other parts of the neuron, other satellite cells and neighboring Schwann cells
Diencephalon
thalamus, hypothalamus, epithalamus, subthalamus
Myelination
the process of myelin sheath formation, During this process in the PNS a Schwann cell wraps itself outward away from the axon in successively tighter bands, making it 100 layers thick. -In the CNS the arms go an oligocendorcyte wrap inward toward the axon in the opposite direction of the Schwann cell. -In both the CNS AND PNS: axons are a lot longer than a single oligendrocyte or Schwann cell, so more than one cell is required to myelinated the entire axon. The segments of an axon that are covered by neuroglia are called internodes ranging from 0.15 to 1.5 mm, between each internode is a gap called a node of Ranvier where no myelin is found. -white matter is composed of myelinated axons while as gray matter is composed of cell bodies and dendrites
Local Potential
when a neuron is stimulated just once a full action potential rarely results. Instead a small local change in the membrane potential of the neuron has two effects: -it causes a depolarization in which positive charges enter the cytosol and make the membrane potential less negative (change from -70 to -60 mV) -May cause hyperpolarization in which either positive charges exit or negative charges enter the cytosol to make the membrane potential more negative (change from -70 to -80 mV) -Local Potentials are sometimes called graded potentials because they vary greatly in size some produce a larger change in membrane potential than others.
Anatomy of the Spinal Cord
• The spinal cord has two main roles: It acts as a relay station to connect the brain with the rest of the body, and it carries out some processing and integration. • The spinal cord is protected by its spinal meninges. There is a fat-filled epidural space between the dura and the vertebral periosteum. • The spinal cord begins at the foramen magnum and terminates as the conus medullaris between the first and second lumbar vertebrae. • Spinal nerves project off each side of the spinal cord. The termi- nal bundle of spinal nerves is the cauda equina. • Spinal gray matter is surrounded by an outer sheath of spinal white matter. The spinal gray matter is divided into three regions known as horns: [] The anterior horn houses the cell bodies of lower motor neurons. [] The posterior horn contains the cell bodies of neurons that process and transmit sensory stimuli. [] The lateral horn contains cell bodies of the ANS. • There are three regions of white matter called funiculi: the posterior funiculus, the lateral funiculus, and the anterior funiculus. Each funiculus contains ascending and/or descending tracts.
Neurotransmitters terminator
• There are two types of neurotransmitter receptors: (1) ionotropic receptors and (2) metabotropic receptors. • The effects of a neurotransmitter are described as excitatory if they generally induce ESPs and inhibitory if they generally induce IPSPs. Many neurotransmitters are capable of generating both EPSPs and IPSPs. • The major neurotransmitters include the following: • Acetylcholine is mostly excitatory, and is degraded by acetylcholinesterase. • The biogenic amines include the catecholamines (norepinephrine, dopamine, and epinephrine), serotonin, and histamine. o The amino acid neurotransmitters include glutamate, glycine, and y-aminobutyric acid (GABA). Glutamate is the major excitatory neurotransmitter in the brain. Both GABA and glycine are major inhibitory neurotransmitters in the CNS.
Types of Reflexes
•A simple stretch reflex is a monosynaptic reflex that returns a muscle to its optimal length after being stretched. •The Golgi tendon reflex causes the muscle to lengthen in response to increased muscle tension. •The flexion, or withdrawal, reflex stimulates contraction of flexor muscles to withdraw the affected limb from a painful stim- ulus. The crossed-extension reflex occurs simultaneously and causes contraction of the extensor muscles of the opposite limb. •The cranial nerves are responsible for the gag reflex and the corneal blink reflex. • Disorders of nerves of the PS are peripheral neuropathies.
Spinal Nerves: Plexuses
•The cervical plexuses consist of the anterior rami of C1-Cx; they innervate the skin of the neck and portions of the head, chest, and shoulders. Their motor branches innervate certain muscles of the neck, and the phrenic nerve innervates the diaphragm muscle. • The brachial plexuses stem from C5-T1, and innervate the skin and muscles of the upper limb. The nerves of the brachial plexus include the axillary nerve, the radial nerve, the musculocutane- ous nerve, the median nerve, and the ulnar nerve. • The anterior rami of the thoracic spinal nerves form the intercostal nerves. • The lumbar plexuses stem from the anterior rami of L1-LA and innervate structures of the pelvis and the lower limb. Their nerves include the obturator nerve and the femoral nerve. • The sacral plexuses stem from the anterior rami of spinal nerves L4-S, and innervate structures of the pelvis, the gluteal region, and much of the lower limb. The largest nerve in the body is the sciatic nerve, which splits into the tibial nerve and the common fibular nerve
