Neural Definitions

This document contains definitions of terms used in the neural functioning tutorial.
Edited by H.C. Shin, Ph.D.


- the most abundant neurotransmitter in the body and the primary neurotransmitter between neurons and muscles. The stomach, spleen, bladder, liver, sweat glands, blood vessels, and heart are just some of the organs that this neurotransmitter controls. The body's synthesis of acetylcholine is vital because of the neurotransmitters role in motor behavior and memory. Low levels of acetylcholine can contribute to lack of concentration and forgetfulness and may cause light sleep. The body synthesizes acetylcholine from the nutrients choline, lecithin, and DMAE, and ancillary nutrient cofactors, such as vitamins C, B1, B5, and B6, along with the minerals zinc and calcium. Acetylcholine helps control muscle tone, learning, and primitive drives and emotions. It also controls the release of pituitary hormone vasopressin, which is involved in learning and in the regulation of urine output.
on Alzheimer's Disease?
Action Potential
- British designation for epinephrine.
Brief & Prolonged Afterpotentials.

Alzheimer's Disease (AD)
New Drug for Treatment
Neuronal degeneration
Controversy on beta-amyloid research
Dr. Khalil's beta-amyloid research
Role of Zinc in AD
A collection of nuclei at the base of the temporal lobe, part of the limbic system. Plays a role in several emotional behaviors such as agression and sexual behavior.
Anterior Cerebral Artery
One of the three primary cerebral arteries. Provides blood supply primarily to the frontal and parietal lobes.
Anterior Commissure
A forebrain commissure that provides communication between structures within the temporal lobes.

  • Apoptosis:
    Apoptosis is characterized by cell surface protuberances (blebs), chromatin condensation and nuclear shrinkage (pyknosis), followed by nuclear fragmentation (karonexis) into multiple nuclear bodies. Cytoplasmic changes include polyribosome dispersal and cell shrinkage resulting from the blebbing process. Limited amounts of endoplasmic reticulum remain and mitochondria appear normal and unswollen. Importantly, plasma membrane integrity is maintained . In apoptosis, the membrane bound bodies are removed directly by macrophages. An additional mechanism in the apoptotic pathway, is the activation of endogenous nucleases and subsequent DNA fragmentation into oligonucleosome-length fragments.

    Studies of apoptosis is an exciting new area of research in brain aging. Recent evidence indicates that apoptosis plays an unexpected and important role in the progression AD (Su et al., 1994). What is the mechanism and what types of interventions will rest the program? How does apoptosis contribute to cognitive decline and what variey of stimuli and natural protective mechanisms may protect the aging brain? For a current review see Cotman and Anderson, 1995.

    Area Postrema
    This CVO is part the brainstem bordering the fourth ventricle and can also be demonstrated by immunocytochemical staining for IgG as seen here. The AP is another 'sensory CVO' involved in body fluid homeostasis. It is also thought to play a role in emetic physiology (vomiting).
    A receptor molecule located in the presynaptic neuron's axon terminal. It is thought to play a role in providing feedback to the presynaptic neuron and play a role in modulating synaptic activity.
    Part of the neuron that carries the neural impulse away from the soma toward the target of the neuron. This part of the neuron carries action potentials. 1. A process of a neuron that conducts impulses away from the cell body. 2. A nerve cell process that resembles an axon in structure, specifically the peripheral process of a dorsal root ganglion cell (sensory neuron) that functionally and embryologically is a dendrite, but structurally is indistinguishable from an axon.
    Axon Hillock
    The portion of the axon where the axon leaves the soma. It is here that spatial and temporal summation occur and the action potential begins.
    Axon Terminal
    The ending of the axon that connects to the neural target. It contains the neural transmitters to be released.


    Basal Ganglia
    History of Basal Ganglia., Diagram of Basal Ganglia
    Brain & Behavior


    Central sulcus at this level
    Circumventricular organs
    Circumventricular Organs

    The circumventricular organs (CVO's) are midline structures bordering the 3rd and 4th ventricles and are unique areas of the brain that are outside the blood-brain barrier (BBB). These barrier-deficient areas are recognized as important sites for communicating with the CSF and between the brain and peripheral organs via blood-borne products. CVO's include the pineal gland, median eminence, subfornical organ, area postrema, subcommissural organ, and organum vasculosum of the lamina terminalis. The intermediate and neural lobes of the pituitary are sometimes included, but these structures are described elsewhere.

    any fiber tract that connects between structures on the two sides of the central nervous system.
    The number of molecules of a substance per unit volume.
    Concentration Gradient
    The difference in level of concentration between two areas. There is a tendency for molecules to flow, by chance movements, from regions of high concentrations to low concentrations.
    Conduction of Impulses
    Impulse conduction through actional fiber
    Corpus Callosum
    The largest commissure. Provides communication across the midline for most forebrain structures. Structure
    The external layer of various organs esp. the gray matter covering the brain.
    Electrical energy flowing, that is, the kinetic energy form of electricity.


    Most common causes of dementia
    Processes of the neuron that receives information from other neurons. That is these structures have places with receptors and are able to form synapses with incoming neurons. A branched protoplasmic process of a neuron that conducts impulses to the cell body. There are usually several to a cell. They form synaptic connections with other neurons.
    Dendritic Stalk
    The thickening of the dendrite where it forms synapses.
    Diffusion is the effect that the random movement of molecules have that causes the movement of molecules from a region of high concentration to low concentration. Diffusion will stop (that is the change in the relative levels of concentration) when the concentration of the substance in solution is equal at all points.
    Diffusion potential
    Diffusion potential of axonal membrane
    An inhibitor dampening activity so we stay rooted. Travels along pathways into the brain. Plays different roles: Dopamine in the basil ganglia (in brains interior) show they are critical for executing smooth and controlled movements. Lack of dopamine is a cause of parkinson disease which a person looses the ability to initiate controlled movements. Dopamine moves into frontal lobe regulating flow of information coming in from other areas of the brain. Compromise in the flow of dopamine may cause disrupted or incoherent thought as in schizophrenia.In milder disorders, too much dopamine in the limbic system and not enough in the cortex may produce an overly suspicious personality giving to bouts of paranoia or may inhibit social interaction. A shortage of Dopamine in the frontal lobes may contribute to poor working memory. Dopamine is also thought to produce feelings of bliss (the pleasure chemical). More dopamine into the frontal lobe lessens pain and increases pleasure.


    Electrical Synaptic Transmission
    Part of the electromagnetic force carried by the movement of charged particles.
    Mediate pain at receptor sites. In an injury receptors in skin make electrical signals that goes up the spinal cord to the brain. The brain then evaluates pain by releasing pain killers called endorphins which bind at opiate receptor sites of neurons to mediate pain. Endorphins effect the dopamine pathway that feeds into the frontal lobe. These pathways inhibit the flow of dopamine. Vast quantities of endorphins are released and nerves are shut off so more dopamine flows through pathway to get to frontal lobe therefore replacing pain with pleasure.
    The capacity to do work. What is meant here is that energy makes things happen or change. Without energy, all things stay in their same state.


    Gap Junction
    Influences of the glia on the intercellular milieu


    A structure in the forebrain, part of the limbic system. Seems to be involved in spatial and memory functions.
    Helicopter cut of Hypothalamus at this level


    Inferior Colliculus
    The lower pair of two pairs of bumbs on the posterior side of the midbrain. These structures relay auditory information from brainstem auditory nuclei to the Medial Geniculate Nucleus.
    Internal Carotid Artery
    One of the primary arteries that supplies blood to the brain.
    An electrically charged particle. Ions can be positive (e.g. Na+) or negative (e.g. Cl-). Like charges repel or push each other away, and opposite charges attract or draw each other.


    Kinetic Energy
    Energy being expended in performing work.


    Lateral Ventricles
    The two largest cavities, in the forebrain, where the cerebral spinal fluid is produced.
    Limbic system
    A group of brain structures, including the hippocampus, amygdala, dentate gyrus, cingulate gyrus, gyrus fornicatus, the archicortex, and their interconnections and connections with the hypothalamus, septal area, and a medial area of the mesencephalic tegmentum. The system is activated by motivated behavior and arousal, and it influences the endocrine and autonomic motor systems.


    Massa Intermedia
    A fiber tract that connects the two thalami.

    Mechanisms of Neuronal Cell Death

    Recent research has defined two mechanisms that cause the death of cells. (1) Apoptosis (also referred to as programmed cell death) is a natural form of cell death that occurs during development or tissue regression. (2) Necrosis is an accidental form of cell death that occurs after trauma. In apoptosis the cell controls the program and essentially autodestructs. In necrosis, external stimuli disrupt the cell.

    Median Eminence
    The median eminence of the hypothalamus arises behind the optic chiasma, is continuous with the pituitary stalk, and communicates with the CSF. The ME can be demonstrated by immunocytochemical staining for IgG, which penetrates the BBB.
    More information on Memory?
    Motor End Plate
    Motor End Plate Potential
    Myasthenia gravis
    A sheath of fatty tissue that covers most axons on the nervous system. It serves to speed conduction my limiting true action potentials to the gaps in the sheath. Under the myelin the neural impulse moves at the speed of light. The layer is formed by Schwann Cells in the periphereral nervous system and Oligodendrocytes in the central nervous system.


    Na-K Pump
    Na-K pump?


  • Necrosis
    In contrast, necrosis is characterized by dilation of the endoplasmic reticulum and mitochondria, and ultimately membrane disintegration with subsequent loss of cytoplasmic contents, leading to inflammation and further damage to surrounding healthy tissues. The cells swell and explode.

    The fundamental cellular unit of the nervous system, consisting of a nucleus with all its processes and extensions. Neurons function in initiation and conduction of impulses. In addition, the brain cells influence cells by secreting neurotransmitters that function to alter the affected cell by actually physically contacting it. Alternatively, a neuron may release neurohormones into the bloodstream. Picture of neuron on an electronic chip, More information?, Nerve cells & Behavior
    - substance that is released when the axon terminal of a presynaptic neuron is excited. The substance then travels across the synapse to act on the target cell to either inhibit or excite it. Disorders in the brain physiology of Limiting the duration of transmitter action
    Node of Ranvier
    The gap in the myelin sheath where the action potential occurs during saltatorty conduction.
    - a hormone produced by the adrenal medulla, similar in chemical and pharmacological properties to epinephrine (also a hormone secreted by the adrenal medulla in response to stimulation of the sympathetic nervous system). Norephinephrine and epinephrine are the two active hormones that cause some of the physiological expressions of fear and anxiety and have been found to be in excess in some anxiety disorders when a disturbance in their metabolism occurs.
    The structure in the soma of the neuron that contains the chromosomes.


    Occipital Horn
    The most posterior porjections of the Lateral Ventricles.
    Optic Chiasm
    Part of the pathways that carry the visual information from the retina in the eyes to the lateral geniculat nucleus. In particular at this location, the axons carrying information from the nasal half of each retina cross, that is decussate, which the axons from the temporal retina do not decussate.
    Optic Nerve
    The portion of the axons that originate in the ganglion cell layer of the retina that travels from the retina to the optic chiasm.
    - Oxytocin is a pituitary hormone that stimulates muscle contraction and sensitizes nerves. Dopamine stimulates the production of oxytocin. Fewer oxytocin receptors create less attachment in relationships.


    Parkinson's Disease
    - chemical which plays a critical role in the limbic system known to give a feeling of bliss. It is a natural ingredient in chocolate.
    Pineal Organ
    The pineal is a diencephalic structure of the epithalamus. It's principal cell type is the pinealocyte. At the ultrastructural level, other cellular components of the gland are more easily visualized. The gland is heavily innervated by tyrosine-hydroxylase-positive fibers from the superior cervical ganglia. The other principal cell type is the glia, which are best illustrated by their expression of vimentin. The hallmark of pineal gland function is its role in mediating circadian rhythms of the animal through the production of the hormone melatonin from the amino acid tryptophan. The metabolism of the gland exhibits high-amplitude circadian rhythms in the synthesis and secretion of melatonin with peak production during the dark period.
    Potential Energy
    Energy that is available to do work.
    Presynaptic Neuron
    The neuron which releases the neurotransmitters into the synapse. The axon terminal is part of the presynaptic neuron.
    Posterior Cerebral Artery
    One of the three primary cerebral arteries. Provides blood supply primarily to the temporal and occipital lobes.
    Posterior Communicating Artery
    Part of the cerebral circulation, more particulary, part of the Circle of Willis that allows blood from any of the supply arteries in the neck to provide blood to all of the cerebral arteries.
    Postsynaptic Inhibition
    Postsynaptic Neuron
    The neuron that which receives the neurotransmitters released by the presynaptic neuron. It is in most synapses a dendrite or soma.
    Presynaptic Inhibition
    - fluoxetine hydrochloride, an anti-depressant that boosts serotonin, a neurotransmitter.
    Pyramidal decussation
    - Section 1 at the level of pyramidal decussation, Slide unlabeled, Slide labeled
    Section 2 at the level of pyramidal decussation, Slide unlabeled, Slide labeled


    A molecule in the postsynpatic neuron's1. membrane to which the neurotransmitters bind, which then directly or indirectly will alter the membrane potential by opening or closing ion channels. 2. the terminal structure of a neuron, specialized to receive stimuli and transmit them to the spinal cord and brain. Receptor & Gating Channel
    Red Nucleus
    helicopter cut of RN, at this level
    Refractory Periods
    Absolute & Relative Refractory Periods
    Resting Potential
    The voltage that is across the membrane of an axon when that portion of the action is not conducting an action potential but is in a state ready to conduction an action potential. Measurement of resting potential


    Saltatory conduction
    Saltatory conduction in myelinated axons
    Sensory Processing
    - a chemical, 5-hydrozytryptamine (5-HT), present in blood platelets, the gastrointestinal tract, and certain regions of the brain. It plays an important role in blood clotting, stimulating a strong heart beat, initiating sleep, fighting depression (prescription drugs that treat depression raise the brain's levels of serotonin) and causing migraine headaches in susceptible individuals (because of its ability to constrict blood vessels or cause them to spasm). Serotonin is synthesized from the amino acid L-tryptophan. Serotonin (and, therefore, L-tyrptophan) also serves as a precursor for the pineal hormone melatonin, which regulates the body's clock.
    The part of the neuron where the nucleus is found. Most of the protein production and energy storage is performed at this point in the cell.
    Spinal Cord
    Facts of Spinal Cord,
    [C1 level 1], unlabeled, labeled
    [C1 level 2], unlabeled, labeled
    Split Brain
    More about SP?
    Subcommissural Organ
    The SCO contacts the third ventricle covering the posterior commissure. It comprises a complex of neurosecretory ependymal cells known to secrete various glycoproteins into the CSF. The functional significance of these glycoproteins has not yet been determined.
    Subfornical Organ
    The SFO demonstrated by immunocytochemical staining for IgG, is positioned under the fornix and is one of the 'sensory CVO's' responsible for maintaining blody fluid balances.
    Substance P
    - An 11-amino acid peptide that is believed to be important as a neurotransmitter in the pain fiber system. This substance may also be important in eliciting local tissue reactions resembling inflammation.
    A groove on the surface of the brain.
    Superior Colliculus
    The top pair of the two pair of bump on the posterior surface of the midbrain. Plays a role in vision, perhaps a part of the role vision plays in orienting us to the world, and eye movements.
    Sylvian Acqueduct
    A connecting path for cerebral spinal fluid between the III and IV ventricles.
    Sylvian Fissure
    The deep groove or sulcus that marks the boundary between the frontal lobe and temporal lobe.
    - The point of junction between two neurons in a neural pathway, where the termination of the axon of one neuron comes into close proximity with the cell body or dendrites of another. At this point, where the relationship of the two neurons is one of contact only, the impulse traveling in the first neuron initiates an impulse in the second neuron. Synapses are polarized, i.e., the impulses pass in one direction only. They are susceptible to fatigue, offer a resistance to the passage of impulses, and are markedly susceptible to the effects of oxygen deficiency, anesthetics, and other agents, including therapeutic drugs and toxic chemicals. Electrical Synapse...Chemical Synapse...Synaptic Summation...Various synapses
    Synaptic Cleft
    The space between the two neurons that form the synapse.
    Synaptic Vesicle
    A membrane structure in the axon terminal that contains the neurotransmitters until they are released.


    - A large ovoid mass of gray matter at the base of the brain, the chief center for transmission of sensory impulses to the cerebral cortex.


    A difference in electrical charge between two locations. One region is more positive than the other. This situation represents the potential energy for electricity.