Neurology

GOLGI TYPE 1 (PROJECTION) NEURONS

A Golgi I or Golgi type I neuron is a neuron which has a long axon that begins in the grey matter of the central nervous system and may extend from there.[1] Golgi II neurons, in contrast, are defined as having short axons or no axon at all. This distinction was introduced by the pioneering neuroanatomist Camillo Golgi, on the basis of the appearance under a microscope of neurons stained with the Golgi stain that he had invented. Santiago Ramón y Cajal postulated that higher developed animals had more Golgi type II cells in comparison to Golgi type I neurons.[2]

GOLGI TYPE 2 (LOCAL INTERNEURON) NEURONS

A Golgi II or Golgi type II neuron is a neuron having either no axon or else a short axon that does not send branches out of the gray matter of the central nervous system.

BIPOLAR NEURON

A bipolar neuron or bipolar cell, is a type of neuron which has two extensions. Bipolar cells are specialized sensory neurons for the transmission of special senses. As such, they are part of the sensory pathways for smell, sight, taste, hearing and vestibular functions. Common examples are the bipolar cell of the retina, the ganglia of the vestibulocochlear nerve,[1] and the extensive use of bipolar cells to transmit efferent (motor) signals to control muscles.

DENDRITIC SPINE

A dendritic spine (or spine) is a small membranous protrusion from a neuron's dendrite that typically receives input from a single axon at the synapse. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body.

KINESIN

A kinesin is a protein belonging to a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule (MT) filaments, and are powered by the hydrolysis of adenosine triphosphate (ATP) (thus kinesins are ATPases). ... In contrast, dyneins are motor proteins that move toward the microtubules' negative end.

MIRROR NEURONS

A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Such neurons have been directly observed in primate species. Birds have been shown to have imitative resonance behaviors and neurological evidence suggests the presence of some form of mirroring system. In humans, brain activity consistent with that of mirror neurons has been found in the premotor cortex, the supplementary motor area, the primary somatosensory cortex and the inferior parietal cortex.

MULTIPOLAR NEURON

A multipolar neuron (or multipolar neurone) is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the nerve cell body. Multipolar neurons constitute the majority of neurons in the central nervous system. They include motor neurons and interneurons and are found mostly in the cortex of the brain, the spinal cord, and also in the autonomic ganglia.

TRIGGER ZONE

Action potentials are normally initiated at a low threshold "trigger zone" that is more excitable than any other part of the soma or dendrites. This trigger zone is located at the axon initial segment, the axon hillock (which contains the highest density of Na+-VGCs).

POSTSYNAPTIC RECEPTOR SITES

After release into the synaptic cleft, neurotransmitters interact with receptor proteins on the membrane of the postsynaptic cell, causing ionic channels on the membrane to either open or close. When these channels open, depolarization occurs, resulting in the initiation of another action potential. There are two types of postsynaptic receptors that recognize neurotransmitters. Ionotropic receptors, also referred to as ligand-gated ion channels, act quickly to depolarize the neuron and pass on the action potential (or hyperpolarize the neuron and inhibit additional action potentials). These receptors are made up of five individual protein subunits embedded in the cell membrane, arranged to form a single pore that spans this membrane. When a neurotransmitter associates with the extracellular recognition site, the membrane-spanning subunits of the receptor quickly open to form a pore through which the necessary ions can pass. Depolarization usually occurs a m illisecond or two after the action potential has been received and lasts only up to ten milliseconds.

AXON

An axon (from Greek ἄξων áxōn, axis), is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neuron's cell body. Axons are also known as nerve fibers. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons (pseudounipolar neurons), such as those for touch and warmth, the electrical impulse travels along an axon from the periphery to the cell body, and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons

cingulate gyrus

An important part of the limbic system, the cingulate gyrus helps regulate emotions and pain. The cingulate gyrus is thought to directly drive the body's conscious response to unpleasant experiences. In addition, it is involved in fear and the prediction (and avoidance) of negative consequences and can help orient the body away from negative stimuli. Learning to avoid negative consequences is an important feature of memory.

INHIBITORY POSTYNAPTIC POTENTIAL

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. IPSPs 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 change in the permeability of the postsynaptic neuronal membrane to particular ions. An electric current that changes the postsynaptic membrane potential to create a more negative postsynaptic potential is generated, i.e. the postsynaptic membrane potential becomes more negative than the resting membrane potential, and this is called hyperpolarisation. In order for an action potential to be generated, depolarisation of the postsynaptic membrane needs to occur, where the membrane potential becomes more positive than resting membrane potential. Therefore, hyperpolarisation of the postsynaptic membrane makes it less likely for depolarisation to sufficiently occur to generate an action potential in the postsynaptic neurone. 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] This is because, if the neurotransmitter released into the synaptic cleft causes an increase in the permeability of the postsynaptic membrane to chloride ions by binding to ligand-gated chloride ion channels and causing them to open, then chloride ions, which are in greater concentration in the synaptic cleft, will diffuse into the postsynaptic neurone. As these are negatively charged ions, hyperpolarisation results, making it less likely for an action potential to be generated in the postsynaptic neurone. 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.

INTERNEURON (ASSOCIATION) NEURON

An interneuron (also called internuncial neuron, relay neuron, association neuron, connector neuron, intermediate neuron or local circuit neuron) is a broad class of neurons found in the human body.[citation needed] Interneurons create neural circuits, enabling communication between sensory or motor neurons and the central nervous system (CNS). They have been found to function in reflexes, neuronal oscillations, and neurogenesis in the adult mammalian brain. Interneurons can be further broken down into two groups: local interneurons and relay interneurons. Local interneurons have short axons and form circuits with nearby neurons to analyze small pieces of information. Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions. The interaction between interneurons allow the brain to perform complex functions such as learning, and decision-making.

sensory relay nucleus

Any of the nuclei (2) in the thalamus to which some or all of the information from sensory receptors apart from olfactory receptors is sent before being transmitted to specialized sensory areas of the cerebral cortex.

ASTROCYTE

Astrocytes (Astro from Greek astron = star and cyte from Greek "kytos" = cavity but also means cell), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined. Depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to 40% of all glia.[1] They perform many functions, including biochemical support of endothelial cells that form the blood-brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a role in the repair and scarring process of the brain and spinal cord following traumatic injuries. Astrocytes are a type of glial cells and they hold various roles, mostly supporting neurons.

AXOPLASMIC TRANSPORT SYSTEMS

Axoplasmic transport, also called axonal transport or axonic flow, is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts (i.e. organelles) to and from a neuron's cell body, through the cytoplasm of its axon (the axoplasm). Axons, which can be 1,000 or 10,000 times the length of the cell body, were originally thought not to contain any ribosomes as the means of producing proteins, and so were thought to rely on axoplasmic transport for all their protein needs.[1][2] However, more recently, mRNA translation has been demonstrated in axons.[3][4] Axonal transport is also responsible for moving molecules destined for degradation from the axon back to the cell body, where they are broken down by lysosomes.[5]

emotion

Cognitive interpretation of subjective feelings.

DENDRITE

Dendrites (from Greek δένδρον déndron, "tree"), also dendrons, are the branched projections of a neuron that act to propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. Electrical stimulation is transmitted onto dendrites by upstream neurons (usually their axons) via synapses which are located at various points throughout the dendritic tree. Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which action potentials are produced by the neuron.[1] Dendritic arborization, also known as dendritic branching, is a multi-step biological process by which neurons form new dendritic trees and branches to create new synapses.[1] The morphology of dendrites such as branch density and grouping patterns are highly correlated to the function of the neuron. Malformation of dendrites is also tightly correlated to impaired nervous system function.[2]

DYNEIN

Dynein is a family of cytoskeletal motor proteins that move along microtubules in cells. They convert the chemical energy stored in ATP to mechanical work. Dynein transports various cellular cargos, provides forces and displacements important in mitosis, and drives the beat of eukaryotic cilia and flagella. All of these functions rely on dynein's ability to move towards the minus-end of the microtubules, known as retrograde transport, thus, they are called "minus-end directed motors". In contrast, kinesin motor proteins move toward the microtubules' plus end.

EPENDYMAL CELL

Ependyma is the thin epithelial lining of the ventricular system of the brain and the central canal of the spinal cord, made up of ependymal cells.[1] Ependyma is one of the four types of neuroglia in the central nervous system (CNS). It is involved in the production of cerebrospinal fluid (CSF), and is shown to serve as a reservoir for neuroregeneration. The ependyma is made up of ependymal cells called ependymocytes, a type of glial cell. These cells line the CSF-filled ventricles in the brain and the central canal of the spinal cord. These are nervous tissue cells with a ciliated simple columnar[2] form much like that of some mucosal epithelial cells. The basal membranes of these cells are characterized by tentacle-like extensions that attach to astrocytes.

MICROTUBULES

Fiberlike substances in the soma and processes of nerve cells; transport substances from the soma to the distal elements of the cell or from the distal parts of the cell to the soma.

temporal lobe

Function: Responsible for processing auditory information from the ears (hearing) The Temporal Lobe mainly revolves around hearing and selective listening. It receives sensory information such as sounds and speech from the ears. It is also key to being able to comprehend, or understand meaningful speech. In fact, we would not be able to understand someone talking to us, if it wasn't for the temporal lobe. This lobe is special because it makes sense of the all the different sounds and pitches (different types of sound) being transmitted from the sensory receptors of the ears.

pineal body (pineal gland)

Gland in the hypothalamus; source of hormones that influence daily and seasonal biorhythms. The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join. The pineal gland produces melatonin, a serotonin derived hormone which modulates sleep patterns in both circadian and seasonal cycles.

gray matter

Grey matter (or gray matter) is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and myelinated as well as unmyelinated axons), glial cells (astroglia and oligodendrocytes), synapses, and capillaries. Grey matter is distinguished from white matter, in that it contains numerous cell bodies and relatively few myelinated axons, while white matter contains relatively few cell bodies and is composed chiefly of long-range myelinated axon tracts.[1] The colour difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually has a very light grey colour with yellowish or pinkish hues, which come from capillary blood vessels and neuronal cell bodies

HM

Henry Gustav Molaison (February 26, 1926 - December 2, 2008), known widely as H.M., was an American memory disorder patient who had a bilateral medial temporal lobectomy to surgically resect the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae in an attempt to cure his epilepsy.[1] He was widely studied from late 1957 until his death in 2008.[2][3] His case played an important role in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a branch of psychology that aims to understand how the structure and function of the brain relates to specific psychological processes. He resided in a care institute in Windsor Locks, Connecticut, where he was the subject of ongoing investigation.[4]

HYPERPOLORIZATION

Hyperpolarization is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold. Hyperpolarization is often caused by efflux of K+ (a cation) through K+ channels, or influx of Cl- (an anion) through Cl- channels. On the other hand, influx of cations, e.g. Na+ through Na+ channels or Ca2+ through Ca2+ channels, inhibits hyperpolarization. If a cell has Na+ or Ca2+ currents at rest, then inhibition of those currents will also result in a hyperpolarization. This voltage-gated ion channel response is how the hyperpolarization state is achieved. In neurons, the cell enters a state of hyperpolarization immediately following the generation of an action potential. While hyperpolarized, the neuron is in a refractory period that lasts roughly 2 milliseconds, during which the neuron is unable to generate subsequent action potentials. Sodium-potassium ATPases redistribute K+ and Na+ ions until the membrane potential is back to its resting potential of around -70 millivolts, at which point the neuron is once again ready to transmit another action potential.[1]

POSTSYNAPTIC CELL AND MEMEMBRANE

In a chemical synapse, the postsynaptic membrane is the membrane that receives a signal (binds neurotransmitter) from the presynaptic cell and responds via depolarisation or hyperpolarisation.

PRESYNAPTIC CELL AND MEMBRANE

In a chemical synapse, 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.

SYNAPTIC VESICLE

In a neuron, synaptic vesicles (or neurotransmitter vesicles) store various neurotransmitters that are released at the synapse. The release is regulated by a voltage-dependent calcium channel. Vesicles are essential for propagating nerve impulses between neurons and are constantly recreated by the cell. The area in the axon that holds groups of vesicles is an axon terminal or "bouton"

extrapyramidal systems

In anatomy, the extrapyramidal system is a biological neural network that is part of the motor system causing involuntary actions. The system is called "extrapyramidal" to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the "pyramids" of the medulla. The pyramidal pathways (corticospinal and some corticobulbar tracts) may directly innervate motor neurons of the spinal cord or brainstem (anterior (ventral) horn cells or certain cranial nerve nuclei), whereas the extrapyramidal system centers on the modulation and regulation (indirect control) of anterior (ventral) horn cells. Extrapyramidal tracts are chiefly found in the reticular formation of the pons and medulla, and target lower motor neurons in the spinal cord that are involved in reflexes, locomotion, complex movements, and postural control. These tracts are in turn modulated by various parts of the central nervous system, including the nigrostriatal pathway, the basal ganglia, the cerebellum, the vestibular nuclei, and different sensory areas of the cerebral cortex. All of these regulatory components can be considered part of the extrapyramidal system, in that they modulate motor activity without directly innervating motor neurons.

MICROTUBULE ASSOCIATED PROTEINS

In cell biology, microtubule-associated proteins (MAPs) are proteins that interact with the microtubules of the cellular cytoskeleton.MAPs bind to the tubulin subunits that make up microtubules to regulate their stability. A large variety of MAPs have been identified in many different cell types, and they have been found to carry out a wide range of functions. These include both stabilizing and destabilizing microtubules, guiding microtubules towards specific cellular locations, cross-linking microtubules and mediating the interactions of microtubules with other proteins in the cell.[1] Within the cell, MAPs bind directly to the tubulin dimers of microtubules. This binding can occur with either polymerized or depolymerized tubulin, and in most cases leads to the stabilization of microtubule structure, further encouraging polymerization. Usually, it is the C-terminal domain of the MAP that interacts with tubulin, while the N-terminal domain can bind with cellular vesicles, intermediate filaments or other microtubules. MAP-microtubule binding is regulated through MAP phosphorylation. This is accomplished through the function of the microtubule-affinity-regulating-kinase (MARK) protein. Phosphorylation of the MAP by the MARK causes the MAP to detach from any bound microtubules.[2] This detachment is usually associated with a destabilization of the microtubule causing it to fall apart. In this way the stabilization of microtubules by MAPs is regulated within the cell through phosphorylation.

cerebellum

In humans, the cerebellum plays an important role in motor control, and it may also be involved in some cognitive functions such as attention and language as well as in regulating fear and pleasure responses,[2] but its movement-related functions are the most solidly established. The human cerebellum does not initiate movement, but contributes to coordination, precision, and accurate timing: it receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity.[3] Cerebellar damage produces disorders in fine movement, equilibrium, posture, and motor learning in humans.

Neucleus

In neuroanatomy, a nucleus (plural form: nuclei) is a cluster of neurons in the central nervous system,[1] located deep within the cerebral hemispheres and brainstem.[2] The neurons in one nucleus usually have roughly similar connections and functions.[3] Nuclei are connected to other nuclei by tracts, the bundles (fascicles) of axons (nerve fibers) extending from the cell bodies. A nucleus is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up as a region of gray matter, often bordered by white matter. The vertebrate brain contains hundreds of distinguishable nuclei, varying widely in shape and size. A nucleus may itself have a complex internal structure, with multiple types of neurons arranged in clumps (subnuclei) or layers. The term "nucleus" is in some cases used rather loosely, to mean simply an identifiably distinct group of neurons, even if they are spread over an extended area. The reticular nucleus of the thalamus, for example, is a thin layer of inhibitory neurons that surrounds the thalamus. Some of the major anatomical components of the brain are organized as clusters of interconnected nuclei. Notable among these are the thalamus and hypothalamus, each of which contains several dozen distinguishable substructures. The medulla and pons also contain numerous small nuclei with a wide variety of sensory, motor, and regulatory functions. In the peripheral nervous system (PNS), a cluster of cell bodies of neurons (homologous to a CNS nucleus) is called a ganglion. The fascicles of nerve fibers in the PNS (homologous to CNS tracts) are called nerves.

EXCITATORY POSTSYNAPTIC POTENTIAL

In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic 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). EPSPs, like IPSPs, are graded (i.e. they have an additive effect). When multiple EPSPs occur on a single patch of postsynaptic membrane, their combined effect is the sum of the individual EPSPs. Larger EPSPs result in greater membrane depolarization and thus increase the likelihood that the postsynaptic cell reaches the threshold for firing an action potential.

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. The repolarization phase usually returns the membrane potential back to the resting membrane potential. The efflux of K+ ions results in the falling phase of an action potential. The ions pass through the selectivity filter of the K+ channel pore. There are several K+ channels that contribute to repolarization, including A-type channels, delayed rectifiers, and Ca2+-activated K+ channels.[1] Repolarization typically results from the movement of positively charged K+ ions out of the cell. The repolarization phase of an action potential initially results in hyperpolarization, attainment of a membrane potential, termed the afterhyperpolarization, that is more negative than the resting potential. Repolarization usually takes several milliseconds.[2]

THRESHOLD POTENTIAL

In neuroscience, the threshold potential is the critical level to which a membrane potential must be depolarized to initiate an action potential. Threshold potentials are necessary to regulate and propagate signaling in both the central nervous system (CNS) and the peripheral nervous system (PNS). Most often, the threshold potential is a membrane potential value between -50 and -55 mV,[1] but can vary based upon several factors. A neuron's resting membrane potential (-70 mV) can be altered to either increase or decrease likelihood of reaching threshold via sodium and potassium ions. An influx of sodium into the cell through open, voltage-gated sodium channels can depolarize the membrane past threshold and thus excite it while an efflux of potassium or influx of chloride can hyperpolarize the cell and thus inhibit threshold from being reached.

ACTION POTENTIAL

In physiology, an action potential occurs when the membrane potential of a specific axon location rapidly rises and falls:[1] this depolarisation then causes adjacent locations to similarly depolarise. In the Hodgkin-Huxley (HH) model of Alan Lloyd Hodgkin and Andrew Fielding Huxley, speed of transmission of an action potential was undefined and it was assumed that adjacent areas became depolarised due to released ion interference with neighbouring channels. Measurements of ion diffusion and radii have since shown this to not be possible. Moreover, contradictory measurements of entropy changes and timing disputed the HH as acting alone. More recent work has shown that the HH action potential is not a single entity but is a coupled synchronised oscillating lipid pulse (action potential pulse) powered by entropy from the HH ion exchanges.[2] Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as in some plant cells. In neurons, action potentials play a central role in cell-to-cell communication by providing for (or assisting in, with regard to saltatory conduction) the propagation of signals along the neuron's axon towards boutons at the axon ends which can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin.[a] Action potentials in neurons are also known as "nerve impulses" or "spikes", and the temporal sequence of action potentials generated by a neuron is called its "spike train". A neuron that emits an action potential is often said to "fire". Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane.[b] These channels are shut when the membrane potential is near the (negative) resting potential of the cell, but they rapidly begin to open if the membrane increases to a precisely defined threshold voltage, depolarising the transmembrane potential.[b] When the channels open they allow an inward flow of sodium ions, which changes the electrochemical gradient, which in turn produces a further rise in the membrane potential. This then causes more channels to open, producing a greater electric current across the cell membrane, and so on. The process proceeds explosively until all of the available ion channels are open, resulting in a large upswing in the membrane potential. The rapid influx of sodium ions causes the polarity of the plasma membrane to reverse, and the ion channels then rapidly inactivate. As the sodium channels close, sodium ions can no longer enter the neuron, and then they are actively transported back out of the plasma membrane. Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state. After an action potential has occurred, there is a transient negative shift, called the afterhyperpolarization. In animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels. Sodium-based action potentials usually last for under one millisecond[citation needed], whereas calcium-based action potentials may last for 100 milliseconds or longer[citation needed]. In some types of neurons, slow calcium spikes provide the driving force for a long burst of rapidly emitted sodium spikes. In cardiac muscle cells, on the other hand, an initial fast sodium spike provides a "primer" to provoke the rapid onset of a calcium spike, which then produces muscle contraction.

SYNAPSE

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.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 a 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 and the postsynaptic part is located on a dendrite or soma. Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission.[6] 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.[7]

MOTOR (EFFERENT) NEURON

In the peripheral nervous system, an efferent nerve fiber is the axon of a motor neuron. The nerve fiber is a long process projecting far from the neuron's body that carries nerve impulses away from the central nervous system toward the peripheral effector organs (mainly muscles and glands). A bundle of these fibers is called a motor nerve or an efferent nerve. The opposite direction of neural activity is afferent conduction, which carries impulses by way of the afferent nerve fibers of sensory neurons.

pituitary gland

In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 grams (0.018 oz) in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypophysis rests upon the hypophysial fossa of the sphenoid bone in the center of the middle cranial fossa and is surrounded by a small bony cavity (sella turcica) covered by a dural fold (diaphragma sellae).[2] The anterior pituitary (or adenohypophysis) is a lobe of the gland that regulates several physiological processes (including stress, growth, reproduction, and lactation). The intermediate lobe synthesizes and secretes melanocyte-stimulating hormone. The posterior pituitary (or neurohypophysis) is a lobe of the gland that is functionally connected to the hypothalamus by the median eminence via a small tube called the pituitary stalk (also called the infundibular stalk or the infundibulum). Hormones secreted from the pituitary gland help control: growth, blood pressure, certain functions of the sex organs, thyroid glands and metabolism as well as some aspects of pregnancy, childbirth, nursing, water/salt concentration at the kidneys, temperature regulation and pain relief.

LOCAL POTENTIAL

Local Potentials. a small change in the resting membrane potential of a neuron caused by a stimulus that opens a ligand-regulated sodium gate in the membrane of a neuron.

MICROGLIA

Microglia are a type of neuroglia (glial cell) located throughout the brain and spinal cord.[1] Microglia account for 10-15% of all cells found within the brain.[2] As the resident macrophage cells, they act as the first and main form of active immune defense in the central nervous system (CNS).[3] Microglia (and other neuroglia including astrocytes) are distributed in large non-overlapping regions throughout the CNS.[4][5] Microglia are key cells in overall brain maintenance—they are constantly scavenging the CNS for plaques, damaged or unnecessary neurons and synapses, and infectious agents.[6] Since these processes must be efficient to prevent potentially fatal damage, microglia are extremely sensitive to even small pathological changes in the CNS.[7] This sensitivity is achieved in part by the presence of unique potassium channels that respond to even small changes in extracellular potassium.

MYELIN

Myelin is a fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system. It is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination or myelinogenesis. In humans, myelination begins early in the 3rd trimester,[1] although little myelin exists in the brain at the time of birth. During infancy, myelination occurs quickly, leading to a child's fast development, including crawling and walking in the first year. Myelination continues through the adolescent stage of life.

NEUROFILAMENTS

Neurofilaments (NF) are the 10 nanometer or intermediate filaments found in neurons. They are a major component of the neuronal cytoskeleton, and are believed to function primarily to provide structural support for the axon and to regulate axon diameter. Neurofilaments are composed of polypeptide chains or subunits which belong to the same protein family as the intermediate filaments of other tissues such as keratin subunits, which make 10 nm filaments expressed specifically in epithelia. The family of proteins making intermediate filaments is divided into 5 major classes, the keratins forming the classes I and II. Class III contains the proteins vimentin, desmin, peripherin and glial fibrillary acidic protein (GFAP). The major neurofilament subunits occupy the class IV family of intermediate filaments, along with two other filament proteins of neurons, alpha-internexin and nestin. The class IV intermediate filament genes all share two unique introns not found in other intermediate filament gene sequences, suggesting a common evolutionary origin from one primitive class IV gene. Finally, class V corresponds to intermediate filaments of the nuclear cytoskeleton, the nuclear lamins. The term neurofibril refers to a bundle of neurofilaments.[1]

function of neuron

Neurons (also known as neurones, nerve cells and nerve fibers) are electrically excitable cells in the nervous system that function to process and transmit information. In vertebrate animals, neurons are the core components of the brain, spinal cord and peripheral nerves. Neurons are typically composed of a soma, or cell body, a dendritic tree and an axon. The majority of vertebrate neurons receive input on the cell body and dendritic tree, and transmit output via the axon, although there is great heterogeneity throughout the nervous system, as well as throughout the animal kingdom, in the size, shape and function of neurons. For invertebrate neurons, the information flow is less well defined. Neurons communicate via chemical and electrical synapses, in a process known as synaptic transmission. The fundamental process underlying synaptic transmission is the action potential, a propagating electrical signal that is generated by exploiting the electrically excitable membrane of the neuron. Neurons are highly specialized for the fast processing and transmission of cellular signals.

TRANSMITTER SUBSTANCE

Neurotransmitter, also called chemical transmitter or chemical messenger, any of a group of chemical agents released by neurons (nerve cells) to stimulate neighbouring neurons or muscle or gland cells, thus allowing impulses to be passed from one cell to the next throughout the nervous system.

NEUROTROPHINS

Neurotrophins are a family of proteins that induce the survival,[1] development, and function[2] of neurons. They belong to a class of growth factors, secreted proteins that are capable of signaling particular cells to survive, differentiate, or grow.[3] Growth factors such as neurotrophins that promote the survival of neurons are known as neurotrophic factors. Neurotrophic factors are secreted by target tissue and act by preventing the associated neuron from initiating programmed cell death - thus allowing the neurons to survive. Neurotrophins also induce differentiation of progenitor cells, to form neurons.

NODE OF RANVIER

Nodes of Ranvier are microscopic gaps found within myelinated axons. Their function is to speed up propagation of Action potentials along the axon via saltatory conduction [1]. The Nodes of Ranvier are the gaps between the myelin insulation of Schwann cells which insulate the axon of neuron.

RESTING POTENTIAL

Normal voltage across a nerve-cell membrane; varies between 60 and 90 mV in the cells of various animals.

Wernicke's aphasia

Receptive aphasia, also known as Wernicke's aphasia, fluent aphasia, or sensory aphasia, is a type of aphasia in which an individual is unable to understand language in its written or spoken form. Even though they can speak using grammar, syntax, rate, and intonation, they typically have difficulty expressing themselves meaningfully through speech. Wernicke's aphasia was named after Carl Wernicke who recognized this condition.[1] People with receptive aphasia are typically unaware of how they are speaking and do not realize their speech may lack meaning.[2] This is due to poor comprehension skills and the inability to understand their own speech because of overall self-monitoring deficits.[3] They typically remain unaware of even their most profound language deficits. When experienced with Broca's aphasia, the patient displays global aphasia.

SALTATORY CONDUCTION

Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials. The uninsulated nodes of Ranvier are the only places along the axon where ions are exchanged across the axon membrane, regenerating the action potential between regions of the axon that are insulated by myelin, unlike electrical conduction in a simple circuit.

SCHWANN CELL

Schwann cell, also called neurilemma cell, any of the cells in the peripheral nervous system that produce the myelin sheath around neuronal axons. Schwann cells are named after German physiologist Theodor Schwann, who discovered them in the 19th century. These cells are equivalent to a type of neuroglia called oligodendrocytes, which occur in the central nervous system. The insulating myelin sheath that covers the axons of many neurons is produced by Schwann cells in the peripheral nervous system and by oligodendrocytes in the central nervous system. The insulating myelin sheath that covers the axons of many neurons is produced by Schwann cells in ... Encyclopædia Britannica, Inc. Schwann cells differentiate from cells of the neural crest during embryonic development, and they are stimulated to proliferate by some constituent of the axonal surface. When motor neurons are severed, causing nerve terminals to degenerate, Schwann cells occupy the original neuronal space. The process of degeneration is followed by regeneration; fibres regenerate in such a way that they return to their original target sites. Schwann cells that remain after nerve degeneration apparently determine the route. Demyelinating neuropathies are those in which the Schwann cells are primarily affected and migrate away from the nerve. This process causes the insulating myelin of axon segments to be lost, and conduction of nerve impulses down the axon is blocked. Schwann cells may suffer immune or toxic attack, as in Guillain-Barré syndrome and diphtheria. This also leads to a blockage of electrical conduction. When an injury is primarily to axons, the Schwann cells are also damaged, producing "secondary demyelination."

MICROFILAMENTS

Small tubelike processes in cells that function to control the shape, movement, or fluidity of the cytoplasm or substances within the cell. microglia.

SPATIAL SUMMATION

Spatial summation occurs when multiple presynaptic neurones together release enough neurotransmitter (e.g. acetylcholine) to exceed the threshold of the postsynaptic neurone. For example, neurone A and neurone B may individually release insufficient neurotransmitter but when these quantities are combined, threshold may be exceeded and an action potential generated. Summation, which includes both spatial and temporal summation, is the process that determines whether or not an action potential will be triggered by the combined effects of excitatory and inhibitory signals, both from multiple simultaneous inputs (spatial summation), and from repeated inputs (temporal summation). Depending on the sum total of many individual inputs, summation may or may not reach the threshold voltage to trigger an action potential.[ Neurotransmitters released from the terminals of a presynaptic neuron fall under one of two categories, depending on the ion channels gated or modulated by the neurotransmitter receptor. Excitatory neurotransmitters produce depolarization of the postsynaptic cell, whereas the hyperpolarization produced by an inhibitory neurotransmitter will mitigate the effects of an excitatory neurotransmitter. The only influences that neurons can have on one another are excitation, inhibition, and—through modulatory transmitters—biasing one another's excitability. From such a small set of basic interactions, a chain of neurons can produce only a limited response. A pathway can be facilitated by excitatory input; removal of such input constitutes disfacillitation. A pathway may also be inhibited; removal of inhibitory input constitutes disinhibition, which, if other sources of excitation are present in the inhibitory input, can augment excitation. When a given target neuron receives inputs from multiple sources, those inputs can be spatially summated if the inputs arrive closely enough in time that the influence of the earliest-arriving inputs has not yet decayed. If a target neuron receives input from a single axon terminal and that input occurs repeatedly at short intervals, the inputs can summate temporally.

Function of glia

Supports cells, they do not transmit info over long distances as neurons do Neuroglia, also called glial cells, or simply glia are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the central and peripheral nervous systems.[1] In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells and microglia, and in the peripheral nervous system glial cells include Schwann cells and satellite cells. The term derives from Greek γλία and γλοία "glue"; pronounced in English as either /ˈɡliːə/ or /ˈɡlaɪə/ As the Greek name implies, glia are commonly known as the glue of the nervous system; however, this is not fully accurate. Neuroscience currently identifies four main functions of glial cells: To surround neurons and hold them in place To supply nutrients and oxygen to neurons To insulate one neuron from another To destroy pathogens and remove dead neurons.

SYNAPTIC POTENTIAL

Synaptic potential refers to the difference in voltage between the inside and outside of a postsynaptic neuron. In other words, it is the "incoming" signal of a neuron. Synaptic potential comes in two forms: excitatory and inhibitory. Excitatory post-synaptic potentials (EPSPs) depolarize the membrane and move it closer to the threshold for an action potential. Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the membrane and move it farther away from the threshold. In order to depolarize a neuron enough to cause an action potential, there must be enough EPSPs to both counterbalance the IPSPs and also depolarize the membrane from its resting membrane potential to its threshold. As an example, consider a neuron with a resting membrane potential of -70 mV (millivolts) and a threshold of -50 mV. It will need to be raised 20 mV in order to pass the threshold and fire an action potential. The neuron will account for all the many incoming excitatory and inhibitory signals via neural integration, and if the result is an increase of 20 mV or more, an action potential will occur. Synaptic potentials are small and many are needed to add up to reach the threshold. The two ways that synaptic potentials can add up to potentially form an action potential are spatial summation and temporal summation. Spatial summation refers to several excitatory stimuli from different synapses converging on the same postsynaptic neuron at the same time to reach the threshold needed to reach an action potential. Temporal summation refers to successive excitatory stimuli on the same location of the postsynaptic neuron. Both types of summation are the result of adding together many excitatory potentials. The difference being whether the multiple stimuli are coming from different locations (spatial) or at different times (temporal). Summation has been referred to as a "neurotransmitter induced tug-of-war" between excitatory and inhibitory stimuli. Whether the effects are combined in space or in time, they are both additive properties that require many stimuli acting together to reach the threshold. Synaptic potentials, unlike action potentials, degrade quickly as they move away from the synapse. This is the case for both excitatory and inhibitory postsynaptic potentials. Synaptic potentials are not static. The concept of synaptic plasticity refers to the changes in synaptic potential. A synaptic potential may get stronger or weaker over time depending on a few factors. The quantity of neurotransmitters released can play a large role in the future strength of that synapse's potential. The receptors on the post-synaptic side also play a role, both in their numbers, composition, and physical orientation.

TEMPORAL SUMMATION

Temporal summation occurs when one presynaptic neurone releases neurotransmitter many times over a period of time. The total amount of neurotransmitter released may exceed the threshold value of the postsynaptic neurone. The higher the frequency of the action potential the more quickly the threshold may be exceeded.

sixth cranial nerve (abducens nerve)

The abducens nerve or abducent nerve (the sixth cranial nerve, also called the sixth nerve or simply CNVI) is a somatic efferent nerve that, in humans, controls the movement of a single muscle, the lateral rectus muscle of the eye.

amygdala

The amygdala is one of two almond-shaped groups of nuclei located deep and medially within the temporal lobes of the brain in complex vertebrates, including humans.[2] Shown in research to perform a primary role in the processing of memory, decision-making, and emotional reactions, the amygdalae are considered part of the limbic system.[3]

AXON HILLOCK

The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon. The axon hillock is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon. For many years, it had been believed that the axon hillock was the usual site of action potential initiation. It is now thought that the earliest site of action potential initiation is found just adjacent, in the initial (unmyelinated) segment of the axon.[1] However, the positive point, at which the action potential starts, varies between cells. It can also be altered by hormonal stimulation of the neuron, or by second messenger effects of neurotransmitters. The axon hillock also functions as a tight junction, since it acts as a barrier for lateral diffusion of transmembrane proteins, GPI anchored proteins such as thy1, and lipids embedded in the plasma membrane.

AXON INITIAL SEGMENT

The axon initial segment (AIS) is a specialized membrane region in the axon of neurons where action potentials are initiated. Crucial to the function of the AIS is the presence of specific voltage-gated channels clustered at high densities, giving the AIS unique electrical properties. Here we review recent data on the physiology of the AIS. These data indicate that the role of the AIS is far richer than originally thought, leading to the idea that it represents a dynamic signal processing unit within neurons, regulating the integration of synaptic inputs, intrinsic excitability, and transmitter release. Furthermore, these observations point to a critical role of the AIS in disease.

basal ganglia

The basal ganglia (or basal nuclei) is a group of subcortical nuclei, of varied origin, in the brains of vertebrates including humans, which are situated at the base of the forebrain. Basal ganglia 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 teeth grinding, eye movements, cognition, and emotion.

Describe at least six important functions of glial cells (ESSAY QUESTION)

The central nervous system consists of neurons and glial cells. Neurons constitute about half the volume of the CNS and glial cells make up the rest. Glial cells provide support and protection for neurons. They are thus known as the "supporting cells" of the nervous system. The four main functions of glial cells are: to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy and remove the carcasses of dead neurons (clean up). The three types of CNS supporting cells are Astrocytes, Oligodendrocytes, and Microglia. The supporting cells of the PNS are known as Schwann Cells. Most neurons are surrounded by glial cells (neuroglia), the other cell type found in the nervous tissue. Glial cells are the supportive cells of the nervous system and are 10 times more numerous than neurons. The most well defined role for neuroglia is to provide structure to the delicate nervous tissue. They fill the space between neurons, serving as mortar or "glue" and thus hold nervous tissue together. Unlike neurons, glial cells retain the ability to divide throughout one's lifetime. When neurons are injured, neuroglia are stimulated to divide and form glial scars. Glial cells have different shapes and sizes and their processes are indistinguishable in contrast to the distinct axon and dendrites found in neurons. There are 6 types of glial cells, 4 types are found in the CNS and 2 types in the PNS. The CNS neuroglia are: astrocytes; oligodendrocytes; microglia, and ependymal cells. The 2 types of glia found only in the peripheral nervous system (PNS) are satellite cells and Schwann cells.

frontal lobe

The frontal lobe is the part of the brain that controls important cognitive skills in humans, such as emotional expression, problem solving, memory, language, judgment, and sexual behavior. It is, in essence, the "control panel" of our personality and our ability to communicate. It is also responsible for primary motor function, or our ability to consciously move our muscles, and the two key areas related to speech, including Broca's area. The frontal lobe is larger and more developed in humans than in any other organism. As its name indicates, the frontal lobe is at the front of the brain. The right hemisphere of the frontal lobe controls the left part of the body, and vice versa. The frontal lobe is also the most common place for brain injury to occur. Damage to the frontal lobe can create changes in personality, limited facial expressions, and difficulty in interpreting one's environment, such as not being able to adequately assess risk and danger.

hippocampus

The hippocampus is a major component of the brains of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. The hippocampus is located under the cerebral cortex (allocortical)[1][2][3] and in primates in the medial temporal lobe. It contains two main interlocking parts: the hippocampus proper (also called Ammon's horn)[4] and the dentate gyrus. In Alzheimer's disease (and other forms of dementia), the hippocampus is one of the first regions of the brain to suffer damage; short-term memory loss and disorientation are included among the early symptoms. Damage to the hippocampus can also result from oxygen starvation (hypoxia), encephalitis, or medial temporal lobe epilepsy. People with extensive, bilateral hippocampal damage may experience anterograde amnesia (the inability to form and retain new memories).

Hypothalamus Controls 4 F's

The human entire human brain is involved in producing feeding, fighting, fleeing, and reproductive behaviors, but the hypothalamus is particularly important because none of these 4 behaviors are possible without it.

hypothalamus

The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus is located below the thalamus and is part of the limbic system.[1] In the terminology of neuroanatomy, it forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond. The hypothalamus is responsible for the regulation of certain metabolic processes and other activities of the autonomic nervous system. It synthesizes and secretes certain neurohormones, called releasing hormones or hypothalamic hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger, important aspects of parenting and attachment behaviours, thirst,[2] fatigue, sleep, and circadian rhythms.

MYELIN SHEATH

The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and that facilitates the transmission of nerve impulses, formed from the cell membrane of the Schwann cell in the peripheral nervous system and from oligodendroglia cells. Also called medullary sheath .

DEPOLARIZATION

The inward flow of sodium ions increases the concentration of positively charged cations in the cell and causes depolarization, where the potential of the cell is higher than the cell's resting potential. The sodium channels close at the peak of the action potential, while potassium continues to leave the cell.

limbic system

The limbic system is a set of brain structures located on both sides of the thalamus, immediately beneath the cerebrum.[1] It has also been referred to as the paleomammalian cortex. It is not a separate system but a collection of structures from the telencephalon, diencephalon, and mesencephalon.[2] It includes the olfactory bulbs, hippocampus, hypothalamus, amygdala, anterior thalamic nuclei, fornix, columns of fornix, mammillary body, septum pellucidum, habenular commissure, cingulate gyrus, parahippocampal gyrus, entorhinal cortex, and limbic midbrain areas.[3] The limbic system supports a variety of functions including emotion, behavior, motivation, long-term memory, and olfaction.[4] Emotional life is largely housed in the limbic system, and it has a great deal to do with the formation of memories.

Mammillary body

The mammillary bodies are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix.[1] They consist of two groups of nuclei, the medial mammillary nuclei and the lateral mammillary nuclei.[2]

medulla

The medulla oblongata (or medulla) is located in the brainstem, anterior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions ranging from vomiting to sneezing. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and therefore deals with the autonomic functions of breathing, heart rate and blood pressure.

occipital lobe

The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex.[1] The primary visual cortex is Brodmann area 17, commonly called V1 (visual one). Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the posterior pole of the occipital lobe. V1 is often also called striate cortex because it can be identified by a large stripe of myelin, the Stria of Gennari. Visually driven regions outside V1 are called extrastriate cortex. There are many extrastriate regions, and these are specialized for different visual tasks, such as visuospatial processing, color differentiation, and motion perception. The name derives from the overlying occipital bone, which is named from the Latin ob, behind, and caput, the head. Bilateral lesions of the occipital lobe can lead to cortical blindness (See Anton's syndrome).

cranial nerves III (Oculomotor)

The oculomotor nerve is the third cranial nerve. It enters the orbit via the superior orbital fissure and innervates muscles that enable most movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the muscles that enable pupillary constriction and accommodation (ability to focus on near objects as in reading). The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement. [1]

parietal lobe

The parietal lobe integrates sensory information among various modalities, including spatial sense and navigation (proprioception), the main sensory receptive area for the sense of touch (mechanoreception) in the somatosensory cortex which is just posterior to the central sulcus in the postcentral gyrus,[1] and the dorsal stream of the visual system. The major sensory inputs from the skin (touch, temperature, and pain receptors), relay through the thalamus to the parietal lobe. Several areas of the parietal lobe are important in language processing. The somatosensory cortex can be illustrated as a distorted figure - the homunculus (Latin: "little man"), in which the body parts are rendered according to how much of the somatosensory cortex is devoted to them.[2] The superior parietal lobule and inferior parietal lobule are the primary areas of body or spacial awareness. A lesion commonly in the right superior or inferior parietal lobule leads to hemineglect. Cortical functions of the parietal lobe are: Two point discrimination through touch alone without other sensory input (i.e., visual) Graphesthesia - recognizing writing on skin by touch alone Touch localization (bilateral simultaneous stimulation) The parietal lobe plays important roles in integrating sensory information from various parts of the body, knowledge of numbers and their relations,[3] and in the manipulation of objects. Its function also includes processing information relating to the sense of touch.[4] Portions of the parietal lobe are involved with visuospatial processing. Although multisensory in nature, the posterior parietal cortex is often referred to by vision scientists as the dorsal stream of vision (as opposed to the ventral stream in the temporal lobe). This dorsal stream has been called both the "where" stream (as in spatial vision)[5] and the "how" stream (as in vision for action).[6] The posterior parietal cortex (PPC) receives somatosensory and/or visual input, which then, through motor signals, controls movement of the arm, hand, as well as eye movements.[7]

septum/septal nuclei

The septal nuclei (medial olfactory area) are a set of structures that lie below the rostrum of the corpus callosum, anterior to the lamina terminalis (the layer of gray matter in the brain connecting the optic chiasma and the anterior commissure where the latter becomes continuous with the rostral lamina). The septal nuclei are composed of medium-size neurons which are classified into medial, lateral, and posterior groups. The septal nuclei receive reciprocal connections from the olfactory bulb, hippocampus, amygdala, hypothalamus, midbrain, habenula, cingulate gyrus, and thalamus. The septal area (medial olfactory area) has no relation to the sense of smell, but it is considered a pleasure zone in animals. The septal nuclei play a role in reward and reinforcement along with the nucleus accumbens.

SYNAPTIC CLEFT

The space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter — called also synaptic gap

thalamus

The thalamus is the large mass of gray matter in the dorsal part of the diencephalon of the brain with several functions such as relaying of sensory signals, including motor signals, to the cerebral cortex, and the regulation of consciousness, sleep, and alertness. It is a midline symmetrical structure of two halves, within the vertebrate brain, situated between the cerebral cortex and the midbrain.

cranial nerve IV (trochlear nerve,)

The trochlear nerve,[help 1] also called the fourth cranial nerve or cranial nerve IV, is a motor nerve (a somatic efferent nerve) that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea. The trochlear nerve is unique among the cranial nerves in several respects: 1. It is the smallest nerve in terms of the number of axons it contains. 2. It has the greatest intracranial length. 3. It is the only cranial nerve that exits from the dorsal (rear) aspect of the brainstem. 4. It innervates a muscle, Superior Oblique muscle, on the opposite side (contralateral) from its origin.

audition and vestibular function

The vestibular system, in most mammals, is the sensory system that provides the leading contribution to the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear in most mammals. As movements consist of rotations and translations, the vestibular system comprises two components: the semicircular canals, which indicate rotational movements; and the otoliths, which indicate linear accelerations. The vestibular system sends signals primarily to the neural structures that control eye movements, and to the muscles that keep an animal upright. The projections to the former provide the anatomical basis of the vestibulo-ocular reflex, which is required for clear vision; and the projections to the muscles that control posture are necessary to keep an animal upright. The brain uses information from the vestibular system in the head and from proprioception throughout the body to understand the body's dynamics and kinematics (including its position and acceleration) from moment to moment.

cranial nerve VIII (also called vestibulocochlear)

The vestibulocochlear nerve (auditory vestibular nerve), known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain. The vestibulocochlear nerve consists mostly of bipolar neurons and splits into two large divisions: the cochlear nerve and the vestibular nerve.

OLIGODENDROCYTE

Their main functions are to provide support and insulation to axons in the central nervous system of some vertebrates, equivalent to the function performed by Schwann cells in the peripheral nervous system. Oligodendrocytes do this by creating the myelin sheath, which is 80% lipid and 20% protein.[3] A single oligodendrocyte can extend its processes to 50 axons,[4] wrapping approximately 1 μm of myelin sheath around each axon; Schwann cells, on the other hand, can wrap around only one axon. Each oligodendrocyte forms one segment of myelin for several adjacent axons.[3]

SYNAPTIC KNOB

This knob is adjacent to a tiny cleft or synapse (s). When a nerve impulse reaches this knob, a drug called a neurotransmitter is released from vesicles into the synapse The neurotransmitter diffuses across the gap and binds to receptors on the membrane of the adjacent neuron or muscle cell.

UNIPOLAR

Unipolar neuron, a neuron with a single neurite, round body and with different segments that serve as superficial receptors or terminals

Broca's aphasia (Expressive aphasia)

is characterized by partial loss of the ability to produce language (spoken or written), although comprehension generally remains intact.[1] A person with expressive aphasia will exhibit effortful speech. Speech generally includes important content words, but leaves out function words that have only grammatical significance and not real-world meaning, such as prepositions and articles.[2] This is known as "telegraphic speech". The person may still be understood, but sentences will not be grammatical. In very severe forms of Expressive Aphasia, a person may only speak using single word utterances.[3][4] Comprehension is typically only mildly to moderately impaired in expressive aphasia due to difficulty understanding complex grammar.[3][4]

AFFERENT (SENSORY) NEURON

n the peripheral nervous system (PNS), an afferent nerve fiber is the axon of a sensory neuron. It is a long process extending far from the nerve cell body that carries an action potential from the sensory neuron toward the central nervous system (CNS). Bundles of these axons form a nerve known as an afferent nerve, or sensory nerve. The opposite direction of neural activity is efferent conduction.[1][2][3] The efferent nerve fiber is the axon of a motor neuron. Bundles of these axons form a motor nerve, or efferent nerve. In the nervous system there is a "closed loop" system of sensation, decision, and reactions. This process is carried out through the activity of sensory neurons, interneurons, and motor neurons. A touch or painful stimulus, for example, creates a sensation in the brain only after information about the stimulus travels there via afferent nerve pathways. Afferent neurons are pseudounipolar neurons that have a single long axon with a short central and a long peripheral branch. These cells do not have dendrites.[4] They have a smooth and rounded cell body. Just outside the spinal cord, thousands of afferent neuronal cell bodies are aggregated in a swelling in the dorsal root known as the dorsal root ganglion.[5][4]