NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001.

  • By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.
Cover of Neuroscience

Neuroscience. 2nd edition.

Show details

Glossary

acetylcholine

Neurotransmitter at motor neuron synapses, in autonomic ganglia and a variety of central synapses; binds to two types of receptors—ligand-gated ion channels (nicotinic receptors) and G-protein-coupled receptors (muscarinic receptors).

achromatopsia, cerebral

Loss of color vision as a result of damage to extrastriate visual cortex.

action potential

The electrical signal conducted along axons (or muscle fibers) by which information is conveyed from one place to another in the nervous system.

activation

The time-dependent opening of ion channels in response to a stimulus, typically membrane depolarization.

adaptation

The phenomenon of sensory receptor adjustment to different levels of stimulation; critical for allowing sensory systems to operate over a wide dynamic range.

adenylyl cyclase

Membrane-bound enzyme that can be activated by G-proteins to catalyze the synthesis of cyclic AMP from ATP.

adhesion molecules

see cell adhesion molecules.

adrenaline

see epinephrine.

adrenal medulla

The central part of the adrenal gland that, under visceral motor stimulation, secretes epinephrine and norepinephrine into the bloodstream.

adrenergic

Refers to synaptic transmission mediated by the release of norepinephrine or epinephrine.

adult

The mature form of an animal, usually defined by the ability to reproduce.

afferent

An axon that conducts action potentials from the periphery toward the central nervous system.

agnosia

The inability to name objects.

alpha (α) motor neurons

Neurons in the ventral horn of the spinal cord that innervate skeletal muscle.

amacrine cells

Retinal neurons that mediate lateral interactions between bipolar cell terminals and the dendrites of ganglion cells.

amblyopia

Diminished visual acuity as a result of the failure to establish appropriate visual cortical connections in early life.

amnesia

The pathological inability to remember or establish memories; retrograde amnesia is the inability to recall existing memories, whereas anterograde amnesia is the inability to lay down new memories.

amphetamine

A synthetically produced central nervous system stimulant with cocaine-like effects; drug abuse may lead to dependence.

ampullae

The juglike swellings at the base of the semicircular canals that contain the hair cells and cupulae (see also cupulae).

amygdala

A nuclear complex in the temporal lobe that forms part of the limbic system; its major functions concern autonomic, emotional, and sexual behavior.

androgen insensitivity syndrome

A condition in which, due to a defect in the gene that codes for the androgen receptor, testosterone cannot act on its target tissues.

anencephaly

A congenital defect of neural tube closure, in which much of the brain fails to develop.

anosmia

Loss of the sense of smell.

anterior

Toward the front; sometimes used as a synonym for rostral, and sometimes as a synonym for ventral.

anterior commissure

A small midline fiber tract that lies at the anterior end of the corpus callosum; like the callosum, it serves to connect the two hemispheres.

anterior hypothalamus

Region of the hypothalamus containing nuclei that mediate sexual behaviors; not to be confused with region in rodent called the medial preoptic area, which lies anterior to hypothalamus and also contains nuclei that mediate sexual behavior (most notably the sexually dimorphic nucleus).

anterograde

A movement or influence acting from the neuronal cell body toward the axonal target.

anterolateral pathway (anterolateral system)

Ascending sensory pathway in the spinal cord and brainstem that carries information about pain and temperature to the thalamus.

antiserum

Serum harvested from an animal immunized to an agent of interest.

aphasia

The inability to comprehend and/or produce language as a result of damage to the language areas of the cerebral cortex (or their white matter interconnections).

apoptosis

Cell death resulting from a programmed pattern of gene expression; also known as “programmed cell death.”

aprosodia

The inability to infuse language with its normal emotional content.

arachnoid mater

One of the three coverings of the brain that make up the meninges; lies between the dura mater and the pia mater.

areflexia

Loss of reflexes.

association cortex

Defined by exclusion as those neocortical regions that are not involved in primary sensory or motor processing.

associativity

In the hippocampus, the enhancement of a weakly activated group of synapses when a nearby group is strongly activated.

astrocytes

One of the three major classes of glial cells found in the central nervous system; important in regulating the ionic milieu of nerve cells and, in some cases, transmitter reuptake.

astrotactin

A cell surface molecule that causes neurons to adhere to radial glial fibers during neuronal migration.

athetosis

Slow, writhing movements seen primarily in patients with disorders of the basal ganglia.

ATPase pumps

Membrane pumps that use the hydrolysis of ATP to translocate ions against their electrochemical gradients.

atrophy

The physical wasting away of a tissue, typically muscle, in response to disuse or other causes.

attention

The selection of a particular sensory stimulus or mental process for further analysis.

auditory meatus

Opening of the external ear canal.

auditory space map

Topographic representation of sound source location, as occurs in the inferior colliculus.

autonomic nervous system

The components of the nervous system (peripheral and central) concerned with the regulation of smooth muscle, cardiac muscle, and glands (see also visceral motor system).

axon

The neuronal process that carries the action potential from the nerve cell body to a target.

axoplasmic transport

The process by which materials are carried from nerve cell bodies to their terminals (anterograde transport), or from nerve cell terminals to the neuronal cell body (retrograde transport).

baroreceptors

Sensory receptors in the visceral motor system that respond to changes in blood pressure.

basal ganglia

A group of nuclei lying deep in the subcortical white matter of the frontal lobes that organize motor behavior. The caudate and putamen and the globus pallidus are the major components of the basal ganglia; the subthalamic nucleus and substantia nigra are often included.

basal lamina (basement membrane)

A thin layer of extracellular matrix material (primarily collagen, laminin, and fibronectin) that surrounds muscle cells and Schwann cells. Also underlies all epithelial sheets.

basilar membrane

The membrane that forms the floor of the cochlear duct, on which the cochlear hair cells are located.

basket cells

Inhibitory interneurons in the cerebellar cortex whose cells bodies are located within the Purkinje cell layer and whose axons make basketlike terminal arbors around Purkinje cell bodies.

binocular

Referring to both eyes.

biogenic amines

The bioactive amine neurotransmitters; includes the catecholamines (epinephrine, norepinephrine, dopamine), serotonin, and histamine.

bipolar cells

Retinal neurons that provide a direct link between photoreceptor terminals and ganglion cell dendrites.

bisexuality

Sexual attraction to members of both the opposite and the same phenotypic sex.

blastomere

A cell produced when the egg undergoes cleavage.

blastula

An early embryo during the stage when the cells are typically arranged to form a hollow sphere.

blind spot

The region of visual space that falls on the optic disk; due to the lack of photoreceptors in the optic disk, objects that lie completely within the blind spot are not perceived.

blood-brain barrier

A diffusion barrier between the brain vasculature and the substance of the brain formed by tight junctions between capillary endothelial cells.

bouton (synaptic bouton)

A swelling specialized for the release of neurotransmitter that occurs along or at the end of an axon.

bradykinesia

Pathologically slow movement.

brain-derived neutrophic factor (BDNF)

One member of a family of neutrophic factors, the best-known constituent of which is nerve growth factor.

brainstem

The portion of the brain that lies between the diencephalon and the spinal cord; comprises the midbrain, pons, and medulla.

Broca’s aphasia

Difficulty producing speech as a result of damage to Broca’s area in the left frontal lobe.

Broca’s area

An area in the left frontal lobe specialized for the production of language.

CA1

A region of the hippocampus that shows a robust form of long-term potentiation.

CA3

A region of the hippocampus containing the neurons that form the Schaffer collaterals.

cadherins

A family of calcium-dependent cell adhesion molecules found on the surfaces of growth cones and the cells over which they grow.

calcarine sulcus

The major sulcus on the medial aspect of the occipital lobe; the primary visual cortex lies largely within this sulcus.

cAMP response element binding protein (CREB)

A protein activated by cyclic AMP that binds to specific regions of DNA, thereby increasing the transcription rates of nearby genes.

cAMP response elements (CREs)

Specific DNA sequences that bind transcription factors activated by cAMP (see also cAMP response element binding protein).

carotid bodies

Specialized tissue masses found at the bifurcation of the carotid arteries in humans and other mammals that respond to the chemical composition of the blood (primarily the partial pressure of oxygen and carbon dioxide).

catecholamine

A term referring to molecules containing a catechol ring and an amino group; examples are the neurotransmitters epinephrine, norepinephrine, and dopamine.

cauda equina

The collection of segmental ventral and dorsal roots that extend from the caudal end of the spinal cord to their exit from the spinal canal.

caudal

Posterior, or “tailward.”

caudate nucleus

One of the three major components of the basal ganglia (the other two are the globus pallidus and putamen).

cell adhesion molecules

A family of molecules on cell surfaces that cause them to stick to one another (see also fibronectin and laminin).

central nervous system

The brain and spinal cord of vertebrates (by analogy, the central nerve cord and ganglia of invertebrates).

central pattern generator

Oscillatory spinal cord or brainstem circuits responsible for programmed, rhythmic movements such as locomotion.

central sulcus

A major sulcus on the lateral aspect of the hemispheres that forms the boundary between the frontal and parietal lobes. The anterior bank of the sulcus contains the primary motor cortex; the posterior bank contains the primary sensory cortex.

cerebellar ataxia

A pathological inability to make coordinated movements associated with lesions to the cerebellum.

cerebellar cortex

The superficial gray matter of the cerebellum.

cerebellar peduncles

The three bilateral pairs of axon tracts (inferior, middle, and superior cerebellar peduncles) that carry information to and from the cerebellum.

cerebellum

Prominent hindbrain structure concerned with motor coordination, posture, and balance. Composed of a three-layered cortex and deep nuclei; attached to the brainstem by the cerebellar peduncles.

cerebral aqueduct

The portion of the ventricular system that connects the third and fourth ventricles.

cerebral cortex

The superficial gray matter of the cerebral hemispheres.

cerebral peduncles

The major fiber bundles that connect the brainstem to the cerebral hemispheres.

cerebrocerebellum

The part of the cerebellar cortex that receives input from the cerebral cortex via axons from the pontine relay nuclei.

cerebrospinal fluid

A normally clear and cell-free fluid that fills the ventricular system of the central nervous system; produced by the choroid plexus in the third ventricle.

cerebrum

The largest and most rostral part of the brain in humans and other mammals, consisting of the two cerebral hemispheres.

c-fos

Cellular Feline Osteosarcoma gene product; a transcription factor that binds as a heterodimer, thus activating gene transcription.

chemical synapses

Synapses that transmit information via the secretion of chemical signals (neurotransmitters).

chemoaffinity (chemoaffinity hypothesis)

The idea that nerve cells bear chemical labels that determine their connectivity.

chemotaxis

The movement of a cell up (or down) the gradient of a chemical signal.

chemotropism

The growth of a part of a cell (axon, dendrite, filopodium) up (or down) a chemical gradient.

chimera

An experimentally generated embryo (or organ) comprising cells derived from two or more species (or other genetically distinct sources).

cholinergic

Referring to synaptic transmission mediated by acetylcholine.

chorea

Jerky, involuntary movements of the face or extremities associated with damage to the basal ganglia.

choreoathetosis

The combination of jerky, ballistic, and writhing movements that characterizes the late stages of Huntington’s disease.

choroid plexus

Specialized epithelium in the ventricular system that produces cerebrospinal fluid.

chromosome

Nuclear organelle that bears the genes.

ciliary body

Circular band of muscle surrounding the lens; contraction allows the lens to round up during accommodation.

cingulate cortex

Cortex of the cingulate gyrus that surrounds the corpus callosum; important in emotional and visceral motor behavior.

cingulate gyrus

Prominent gyrus on the medial aspect of the hemisphere, lying just superior to the corpus callosum; forms a part of the limbic system.

cingulate sulcus

Prominent sulcus on the medial aspect of the hemisphere.

circadian rhythms

Variations in physiological functions that occur on a daily basis.

circle of Willis

Arterial anastomosis on the ventral aspect of the midbrain; connects the posterior and anterior cerebral circulation.

cisterns

Large, cerebrospinal-fluid-filled spaces that lie within the subarachnoid space.

class

A taxonomic category subordinate to phylum; comprises animal orders.

climbing fibers

Axons that originate in the inferior olive, ascend through the inferior cerebellar peduncle, and make terminal arborizations that invest the dendritic tree of Purkinje cells.

clone

The progeny of a single cell.

cochlea

The coiled structure within the inner ear where vibrations caused by sound are transduced into neural impulses.

cognition

A general term referring to higher order mental processes; the ability of the central nervous system to attend, identify, and act on complex stimuli.

collapsin

A molecule that causes collapse of growth cones; a member of the semaphorin family of signaling molecules.

colliculi

The two paired hillocks that characterize the dorsal surface of the midbrain; the superior colliculi concern vision, the inferior colliculi audition.

competition

The struggle among nerve cells, or nerve cell processes, for limited resources essential to survival or growth.

concha

A component of the external ear.

conduction aphasia

Difficulty producing speech as a result of damage to the connection between Wernicke’s and Broca’s language areas.

conduction velocity

The speed at which an action potential is propagated along an axon.

conductive hearing loss

Diminished sense of hearing due reduced ability of sounds to be mechanically transmitted to the inner ear. Common causes include occlusion of the ear canal, perforation of the tympanic membrane, and arthritic degeneration of the middle ear ossicles. Contrast with sensorineural hearing loss.

cone opsins

The three distinct photopigments found in cones; the basis for color vision.

cones

Photoreceptors specialized for high visual acuity and the perception of color.

congenital adrenal hyperplasia

Genetic deficiency that leads to overproduction of androgens and a resultant masculinization of external genitalia in genotypic females.

conjugate

The paired movements of the two eyes in the same direction, as occurs in the vestibulo-ocular reflex (see also vergence movements and vestibulo-ocular reflex).

conspecific

Fellow member of a species.

contralateral

On the other side.

contralateral neglect syndrome

Neurological condition in which the patient does not acknowledge or attend to the left visual hemifield or the left half of the body. The syndrome typically results from lesions of the right parietal cortex.

contrast

The difference, usually expressed in terms of a percentage in luminance, between two territories in the visual field (can also apply to color when specified as spectral contrast).

convergence

Innervation of a target cell by axons from more than one neuron.

cornea

The transparent surface of the eyeball in front of the lens; the major refractive element in the optical pathway.

coronal

Referring to a plane through the brain that runs parallel to the coronal suture (the mediolateral plane). Synonymous with frontal plane.

corpus callosum

The large midline fiber bundle that connects the cortices of the two cerebral hemispheres.

corpus striatum

General term applied to the caudate and putamen; name derives from the striated appearance of these basal ganglia nuclei in sections of fresh material.

cortex

The superficial mantle of gray matter covering the cerebral hemispheres and cerebellum, where most of the neurons in the brain are located.

cortico-cortical connections

Connections made between cortical areas in the same hemisphere or betweem the two hemispheres via the cerebral commissures (the corpus callosum and the anterior commissure).

corticospinal tract

Pathway carrying motor information from the primary and secondary motor cortices to the brain stem and spinal cord.

co-transmitters

Two or more types of neurotransmitters within a single synapse; may be packaged into separate populations of synaptic vesicles or co-localized within the same synaptic vesicles.

cranial nerve ganglia

The sensory ganglia associated with the cranial nerves; these correspond to the dorsal root ganglia of the spinal segmental nerves.

cranial nerve nuclei

Nuclei in the brainstem that contain the neurons related to cranial nerves III–XII.

cranial nerves

The 12 pairs of nerves arising from the brainstem that carry sensory information toward (and sometimes motor information away from) the central nervous system.

CREB

see cAMP response element binding protein.

crista

The hair cell-containing sensory epithelium of the semicircular canals.

critical period

A restricted developmental period during which the nervous system is particularly sensitive to the effects of experience.

cuneate nuclei

Sensory relay nuclei that lie in the lower medulla; they contain the second-order sensory neurons that relay mechanosensory information from peripheral receptors in the upper body to the thalamus.

cupulae

Gelatinous structures in the semicircular canals in which the hair cell bundles are embedded.

cytoarchitectonic areas

Distinct regions of the neocortical mantle identified by differences in cell size, packing density, and laminar arrangement.

decerebrate rigidity

Excessive tone in extensor muscles as a result of damage to descending motor pathways at the level of the brainstem.

declarative memory

Memories available to consciousness that can be expressed by language.

decussation

A crossing of fiber tracts in the midline.

deep cerebellar nuclei

The nuclei at the base of the cerebellum that relay information from the cerebellar cortex to the thalamus.

delayed response genes

Genes that are synthesized de novo after a cell is stimulated; usually refers to transcriptional activator proteins that are synthesized after preexisting transcription factors are first activated by an inducing stimulus.

delayed response task

A behavioral paradigm used to test cognition and memory.

delta waves

Slow (<4 Hz) electroencephalographic waves that characterize stage IV (slow-wave) sleep.

dendrite

A neuronal process arising from the cell body that receives synaptic input.

denervation

Removal of the innervation to a target.

dentate gyrus

A region of the hippocampus; so named because it is shaped like a tooth.

depolarization

The displacement of a cell’s membrane potential toward a less negative value.

dermatome

The area of skin supplied by the sensory axons of a single spinal nerve.

determination

Commitment of a developing cell or cell group to a particular fate.

dichromatic

Referring to the majority of mammals (and most color-blind humans), which have only two instead of three cone pigments to mediate color vision.

diencephalon

Portion of the brain that lies just rostral to the midbrain; comprises the thalamus and hypothalamus.

differentiation

The progressive specialization of developing cells.

dihydrotestosterone

A more potent form of testosterone that masculinizes the external genitalia.

disinhibition

Arrangement of inhibitory and excitatory cells in a circuit that generates excitation by the transient inhibition of a tonically active inhibitory neuron.

disjunctive eye movements

Movements of the two eyes in opposite directions (see also vergence movements).

distal

Farther away from a point of reference (the opposite of proximal).

divergence

The branching of an axon to innervate multiple target cells.

dopamine

A catecholamine neurotransmitter.

dorsal

Referring to the back.

dorsal column nuclei

Second-order sensory neurons in the lower medulla that relay mechanosensory information from the spinal cord to the thalamus; comprises the cuneate and gracile nuclei.

dorsal columns

Major ascending tracts in the spinal cord that carry mechanosensory information from the first-order sensory neurons in dorsal root ganglia to the dorsal column nuclei; also called the posterior funiculi.

dorsal horn

The dorsal portion of the spinal cord gray matter; contains neurons that process sensory information.

dorsal root ganglia

The segmental sensory ganglia of the spinal cord; contain the first-order neurons of the dorsal column/medial lemniscus and spinothalamic pathways.

dorsal roots

The bundle of axons that runs from the dorsal root ganglia to the dorsal horn of the spinal cord, carrying sensory information from the periphery.

dura mater

The thick external covering of the brain and spinal cord; one of the three components of the meninges, the other two being the pia mater and arachnoid mater.

dynorphins

A class of endogenous opioid peptides.

dysarthria

Difficulty producing speech as a result of damage to the primary motor centers that govern the muscles of articulation; distinguished from aphasia, which results from cortical damage.

dysmetria

Inaccurate movements due to faulty judgment of distance. Characteristic of cerebellar pathology.

dystonia

Lack of muscle tone.

early inward current

The initial electrical current, measured in voltage clamp experiments, that results from the voltage-dependent entry of a cation such as Na+ or Ca2+; produces the rising phase of the action potential.

ectoderm

The most superficial of the three embryonic germ layers; gives rise to the nervous system and epidermis.

Edinger-Westphal nucleus

Midbrain nucleus containing the autonomic neurons that constitute the efferent limb of the pupillary light reflex.

efferent

An axon that conducts information away from the central nervous system.

electrical synapses

Synapses that transmit information via the direct flow of electrical current at gap junctions.

electrochemical equilibrium

The condition in which no net ionic flux occurs across a membrane because ion concentration gradients and opposing transmembrane potentials are in exact balance.

electrogenic

Capable of generating an electrical current; usually applied to membrane transporters that create electrical currents while translocating ions.

embryo

The developing organism before birth or hatching.

end plate current (EPC)

Postsynaptic current produced by neurotransmitter release and binding at the motor end plate.

end plate potential (EPP)

Depolarization of the membrane potential of skeletal muscle fiber, caused by the action of the transmitter acetylcholine at the neuromuscular synapse.

endocrine

Referring to the release of signaling molecules whose effects are made widespread by distribution in the general circulation.

endocytosis

A budding off of vesicles from the plasma membrane, which allows uptake of materials in the extracellular medium.

endoderm

The innermost of the three embryonic germ layers.

endogenous opioids

Peptides in the central nervous system that have the same pharmacological effects as morphine and other derivatives of opium.

endolymph

The potassium-rich fluid filling both the cochlear duct and the membranous labyrinth; bathes the apical end of the hair cells.

endorphins

One of a group of neuropeptides that are agonists at opioid receptors, virtually all of which contain the sequence Tyr-Gly-Gly-Phe.

end plate

The complex postsynaptic specialization at the site of nerve contact on skeletal muscle fibers.

engram

The term used to indicate the physical basis of a stored memory.

enkephalins

A general term for endogenous opioid peptides.

ependyma

The epithelial lining of the canal of the spinal cord and the ventricles.

ependymal cells

Epithelial cells that line the ventricular system.

epidermis

The outermost layer of the skin; derived from the embryonic ectoderm.

epigenetic

Referring to influences on development that arise from factors other than genetic instructions.

epinephrine (adrenaline)

Catecholamine hormone and neurotransmitter that binds to α- and β-adrenergic G-protein-coupled receptors.

epineurium

The connective tissue surrounding axon fascicles of a peripheral nerve.

epithelium

Any continuous layer of cells that covers a surface or lines a cavity.

equilibrium potential

The membrane potential at which a given ion is in electrochemical equilibrium.

estradiol

One of the biologically important C18 class of steroid hormones capable of inducing estrous in females.

eukaryote

An organism that contains cells with nuclei.

excitatory postsynaptic potential (EPSP)

Neurotransmitter-induced postsynaptic potential change that depolarizes the cell, and hence increases the likelihood of initiating a postsynaptic action potential.

exocytosis

A form of cell secretion resulting from the fusion of the membrane of a storage organelle, such as a synaptic vesicle, with the plasma membrane.

explant

A piece of tissue maintained in culture medium.

external segment

A subdivision of the globus pallidus.

extracellular matrix

A matrix composed of collagen, laminin, and fibronectin that surrounds most cells (see also basal lamina).

extrafusal muscle fibers

Fibers of skeletal muscles; a term that distinguishes ordinary muscle fibers from the specialized intrafusal fibers associated with muscle spindles.

face cells

Neurons in the temporal cortex of rhesus monkeys that respond specifically to faces.

facilitation

The increased transmitter release produced by an action potential that follows closely upon a preceding action potential.

family

A taxonomic category subordinate to order; comprises genera.

fasciculation

The aggregation of neuronal processes to form a nerve bundle; also refers to the spontaneous discharge of motor units after muscle denervation.

α-fetoprotein

A protein that actively sequestors circulating estrogens.

fetus

The developing mammalian embryo at relatively late stages when the parts of the body are recognizable.

fibrillation

Spontaneous contractile activity of denervated muscle fibers.

fibroblast growth factor (FGF)

A peptide growth factor, originally defined by its mitogenic effects on fibroblasts; also acts as an inducer during early brain development.

fibronectin

A large cell adhesion molecule that binds integrins.

filopodium

Slender protoplasmic projection, arising from the growth cone of an axon or a dendrite, that explores the local environment.

fissure

A deep cleft in the brain; distinguished from sulci, which are shallower cortical infoldings.

flexion reflex

Polysynaptic reflex mediating withdrawal from a painful stimulus.

floorplate

Region in the ventral portion of the developing spinal cord; important in the guidance and crossing of growing axons.

folia

The name given to the gyral formations of the cerebellum.

forebrain

The anterior portion of the brain that includes the cerebral hemispheres (includes the telencephalon and diencephalon).

fornix

An axon tract, best seen from the medial surface of the divided brain, that interconnects the hypothalamus and hippocampus.

fourth ventricle

The ventricular space that lies between the pons and the cerebellum.

fovea

Area of the retina specialized for high acuity in the center of the macula; contains a high density of cones and few rods.

foveola

Capillary and rod-free zone in the center of the fovea.

frontal lobe

One of the four lobes of the brain; includes all the cortex that lies anterior to the central sulcus and superior to the lateral fissure.

G-protein-coupled receptors (metabotropic receptors)

A large family of neurotransmitter or hormone receptors, characterized by seven transmembrane domains; the binding of these receptors by agonists leads to the activation of intracellular G-proteins.

G-proteins

Term for two large groups of proteins—the heterotrimeric G-proteins and the small-molecule G-proteins—that can be activated by exchanging bound GDP for GTP.

gamma (γ) motor neurons

Class of spinal motor neurons specifically concerned with the regulation of muscle spindle length; these neurons innervate the intrafusal muscle fibers of the spindle.

ganglion (ganglia)

Collections of hundreds to thousands of neurons found outside the brain and spinal cord along the course of peripheral nerves.

ganglion cell

A neuron located in a ganglion.

gap junction

A specialized intercellular contact formed by channels that directly connect the cytoplasm of two cells.

gastrula

The early embryo during the period when the three embryonic germ layers are formed; follows the blastula stage.

gastrulation

The cell movements (invagination and spreading) that transform the embryonic blastula into the gastrula.

gender identification

Self-perception of one’s alignment with the traits associated with being a phenotypic female or male in a given culture.

gene

A hereditary unit located on the chromosomes; genetic information is carried by linear sequences of nucleotides in DNA that code for corresponding sequences of amino acids.

genome

The complete set of an animal’s genes.

genotype

The genetic makeup of an individual.

genotypic sex

Sexual characterization according to the complement of sex chromosomes; XX is a genotypic female, and XY is a genotypic male.

genus

A taxonomic division that comprises a number of closely related species within a family.

germ cell

The egg or sperm (or the precursors of these cells).

germ layers

The three primary layers of the developing embryo from which all adult tissues arise: ectoderm, mesoderm, and endoderm.

glia (neuroglial cells)

The support cells associated with neurons (astrocytes, oligodendrocytes, and microglia in the central nervous system; Schwann cells in peripheral nerves; and satellite cells in ganglia).

globus pallidus

One of the three major nuclei that make up the basal ganglia in the cerebral hemispheres; relays information from the caudate and putamen to the thalamus.

glomeruli

Characteristic collections of neuropil in the olfactory bulbs; formed by dendrites of mitral cells and terminals of olfactory receptor cells, as well as processes from local interneurons.

glutamate-glutamine cycle

A metabolic cycle of glutamate release and resynthesis involving both neuronal and glial cells.

Golf

A G-protein found uniquely in olfactory receptor neurons.

Golgi tendon organs

Receptors located in muscle tendons that provide mechanosensory information to the central nervous system about muscle tension.

gracile nuclei

Sensory nuclei in the lower medulla; these second-order sensory neurons relay mechanosensory information from the lower body to the thalamus.

gradient

A systematic variation of the concentration of a molecule (or some other agent) that influences cell behavior.

granule cell layer

The layer of the cerebellar cortex where granule cell bodies are found. Also used to refer to cell-rich layers in neocortex and hippocampus.

gray matter

General term that describes regions of the central nervous system rich in neuronal cell bodies and neuropil; includes the cerebral and cerebellar cortices, the nuclei of the brain, and the central portion of the spinal cord.

growth cone

The specialized end of a growing axon (or dendrite) that generates the motive force for elongation.

gyri

The ridges of the infolded cerebral cortex (the valleys between these ridges are called sulci).

hair cells

The sensory cells within the inner ear that transduce mechanical displacement into neural impulses.

helicotrema

The opening at the apex of the cochlea that joins the scala vestibuli and scala tympani.

Hensen’s node

see primitive pit.

heterotrimeric G-proteins

A large group of proteins consisting of three subunits (α, β, and γ) that can be activated by exchanging bound GDP with GTP resulting in the liberation of two signaling molecules—αGTP and the βg-dimer.

higher-order neurons

Neurons that are relatively remote from peripheral targets.

hindbrain

see rhombencephalon.

hippocampus

A cortical structure in the medial portion of the temporal lobe; in humans, concerned with short-term declarative memory, among many other functions.

histamine

A biogenic amine neurotransmitter derived from the amino acid histidine.

homeobox genes

A set of master control genes whose expression establishes the early body plan of developing organisms (see also homeotic mutant).

homeotic mutant

A mutation that transforms one part of the body into another (e.g., insect antennae into legs). Affects homeobox genes.

homologous

Technically, referring to structures in different species that share the same evolutionary history; more generally, referring to structures or organs that have the same general anatomy and perform the same function.

homosexuality

Sexual attraction to an individual of the same phenotypic sex.

horizontal cells

Retinal neurons that mediate lateral interactions between photoreceptor terminals and the dendrites of bipolar cells.

horseradish peroxidase

A plant enzyme widely used to stain nerve cells (after injection into a neuron, it generates a visible precipitate by one of several histochemical reactions).

Huntington’s disease

An autosomal dominant genetic disorder in which a single gene mutation results in personality changes, progressive loss of the control of voluntary movement, and eventually death. Primary target is the basal ganglia.

hydrocephalus

Enlarged cranium as a result of increased cerebrospinal fluid pressure (typically due to a mechanical outflow blockage).

hyperalgesia

Increased perception of pain.

hyperkinesia

Excessive movement.

hyperpolarization

The displacement of a cell’s membrane potential toward a more negative value.

hypokinesia

A paucity of movement.

hypothalamus

A collection of small but critical nuclei in the diencephalon that lies just inferior to the thalamus; governs reproductive, homeostatic, and circadian functions.

imprinting

A rapid and permanent form of learning that occurs in response to early experience.

inactivation

The time-dependent closing of ion channels in response to a stimulus, such as membrane depolarization.

inducers

Chemical signals originating from one set of cells that influence the differentiation of other cells.

induction

The ability of a cell or tissue to influence the fate of nearby cells or tissues during development by chemical signals.

inferior colliculi (singular, colliculus)

Paired hillocks on the dorsal surface of the midbrain; concerned with auditory processing.

inferior olive (inferior olivary nucleus)

Prominent nucleus in the medulla; a major source of input to the cerebellum.

infundibulum

The connection between the hypothalamus and the pituitary gland; also known as the pituitary stalk.

inhibitory postsynaptic potential (IPSP)

Neurotransmitter-induced postsynaptic potential change that tends to decrease the likelihood of a postsynaptic action potential.

innervate

Establish synaptic contact with a target.

innervation

Referring to all the synaptic contacts of a target.

input

The innervation of a target cell by a particular axon; more loosely, the innervation of a target.

input elimination

The developmental process by which the number of axons innervating some classes of target cells is diminished.

instructive

A developmental influence that dictates the fate of a cell rather than simply permitting differentiation to occur.

insula

The portion of the cerebral cortex that is buried within the depths of the lateral fissure.

integral membrane proteins

Proteins that possess hydrophobic domains that are inserted into membranes.

integration

The summation of excitatory and inhibitory synaptic conductance changes by postsynaptic cells.

integrins

A family of receptor molecules found on growth cones that bind to cell adhesion molecules such as laminin and fibronection.

intention tremor

Tremor that occurs while performing a voluntary motor act. Characteristic of cerebellar pathology.

internal arcuate tract

Mechanosensory pathway in the brainstem that runs from the dorsal column nuclei to form the medial lemniscus.

internal capsule

Large white matter tract that lies between the diencephalon and the basal ganglia; contains, among others, sensory axons that run from the thalamus to the cortex and motor axons that run from the cortex to the brainstem and spinal cord.

interneuron

Technically, a neuron in the pathway between primary sensory and primary effector neurons; more generally, a neuron that branches locally to innervate other neurons.

interstitial nuclei of the anterior hypothalamus (INAH)

Four cell groups located slightly lateral to the third ventricle in the anterior hypothalamus of primates; thought to play a role in sexual behavior.

intrafusal muscle fibers

Specialized muscle fibers found in muscle spindles.

invertebrate

An animal without a backbone (includes about 97% of extant animals).

in vitro

Referring to any biological process studied outside of the organism (literally, “in glass”).

in vivo

Referring to any biological process studied in an intact living organism (literally “in life”).

ion channels

Integral membrane proteins possessing pores that allow certain ions to diffuse across cell membranes, thereby conferring selective ionic permeability.

ion exchangers

Membrane transporters that translocate one or more ions against their concentration gradient by using the electrochemical gradient of other ions as an energy source.

ionotropic (ionotropic receptors)

Receptors in which the ligand binding site is an integral part of the receptor molecule.

ion pumps

see transporters.

ipsilateral

On the same side of the body.

iris

Circular pigmented membrane behind the cornea; perforated by the pupil.

ischemia

Insufficient blood supply.

kinocilium

A true ciliary structure which, along with the stereocilia, comprises the hair bundle of vestibular and fetal cochlear hair cells in mammals (it is not present in the adult mammalian cochlear hair cell).

Korsakoff’s syndrome

An amnesic syndrome seen in chronic alcoholics.

labyrinth

Referring to the internal ear; comprises the cochlea, vestibular apparatus, and the bony canals in which these structures are housed.

lamellipodia

The leading edge of a motile cell or growth cone, which is rich in actin filaments.

laminae (singular, lamina)

Cell layers that characterize the neocortex, hippocampus, and cerebellar cortex. The gray matter of the spinal cord is also arranged in laminae.

laminin

A large cell adhesion molecule that binds integrins.

late outward current

The delayed electrical current, measured in voltage clamp experiments, that results from the voltage-dependent efflux of a cation such as K+. Produces the repolarizing phase of the action potential.

lateral columns

The lateral regions of spinal cord white matter that convey motor information from the brain to the spinal cord.

lateral (Sylvian) fissure

The cleft on the lateral surface of the brain that separates the temporal and frontal lobes.

lateral geniculate nucleus (LGN)

A nucleus in the thalamus that receives the axonal projections of retinal ganglion cells in the primary visual pathway.

lateral olfactory tract

The projection from the olfactory bulbs to higher olfactory centers.

lateral posterior nucleus

A thalamic nucleus that receives its major input from sensory and association cortices and projects in turn to association cortices, particularly in the parietal and temporal lobes.

lateral superior olive (LSO)

The auditory brainstem structure that processes interaural intensity differences and, in humans, mediates sound localization for stimuli greater than 3 kHz.

learning

The acquisition of novel behavior through experience.

lens

Transparent structure in the eye whose thickening or flattening in response to visceral motor control allows light rays to be focused on the retina.

lexical

The quality of associating a symbol (e.g., a word) with a particular object, emotion, or idea.

lexicon

Dictionary. Sometimes used to indicate region of brain that stores the meanings of words.

ligand-gated ion channels

Term for a large group of neurotransmitter receptors that combine receptor and ion channel functions into a single molecule.

limb bud

The limb rudiment of vertebrate embryos.

limbic lobe

Cortex that lies superior to the corpus callosum on the medial aspect of the cerebral hemispheres; forms the cortical component of the limbic system.

limbic system

Term that refers to those cortical and subcortical structures concerned with the emotions; the most prominent components are the cingulate gyrus, the hippocampus, and the amygdala.

lobes

The four major divisions of the cerebral cortex (frontal, parietal, occipital, and temporal).

local circuit neurons

General term referring to neurons whose activity mediates interactions between sensory systems and motor systems; interneuron is often used as a synonym.

locus coeruleus

A small brainstem nucleus with widespread adrenergic cortical and descending connections; important in the governance of sleep and waking.

long-term

Lasting days, weeks, months, or longer.

long-term depression

A persistent weakening of synapses based on recent patterns of activity.

long-term memory

Memories that last days, weeks, months, years, or a lifetime.

long-term potentiation (LTP)

A persistent strengthening of synapses based on recent patterns of activity.

lower motor neuron

Spinal motor neuron; directly innervates muscle (also referred to as α or primary motor neuron).

lower motor neuron syndrome

Signs and symptoms arising from damage to α motor neurons; these include paralysis or paresis, muscle atrophy, areflexia, and fibrillations.

macroscopic

Visible with the naked eye.

macroscopic currents

Ionic currents flowing through large numbers of ion channels distributed over a substantial area of membrane.

macula

The central region of the retina that contains the fovea (the term derives from the yellowish appearance of this region in ophthalmoscopic examination); also, the sensory epithelia of the otolith organs.

magnocellular

A component of the primary visual pathway specialized for the perception of motion; so named because of the relatively large cells involved.

mammal

An animal the embyros of which develop in a uterus and the young of which begin to suckle at birth (technically, a member of the class Mammalia).

mammillary bodies

Small prominences on the ventral surface of the diencephalon; functionally, part of the caudal hypothalamus.

map

The ordered projection of axons from one region of the nervous system to another, by which the organization of the body (or some function) is reflected in the organization of the nervous system.

mechanoreceptors

Receptors specialized to sense mechanical forces.

medial

Located nearer to the midsagittal plane of an animal (the opposite of lateral).

medial dorsal nucleus

A thalamic nucleus that receives its major input from sensory and association cortices and projects in turn to association cortices, particularly in the frontal lobe.

medial geniculate complex

The major thalamic relay for auditory information.

medial lemniscus

Axon tract in the brainstem that carries mechanosensory information from the dorsal column nuclei to the thalamus.

medial longitudinal fasciculus

Axon tract that carries excitatory projections from the abducens nucleus to the contralateral oculomotor nucleus; important in coordinating conjugate eye movements.

medial superior olive (MSO)

The auditory brainstem structure that processes interaural time differences and serves to compute the horizontal location of a sound source.

medium spiny neuron

The principal projection neuron of the caudate and putamen.

medulla

The caudal portion of the brainstem, extending from the pons to the spinal cord.

meduallary pyramids

Longitudinal bulges on the ventral aspect of the medulla that signify the corticospinal tracts at this level of the neuraxis.

Meissner’s corpuscles

Encapsulated cutaneous mechanosensory receptors specialized for the detection of fine touch and pressure.

membrane conductance

The reciprocal of membrane resistance. Changes in membrane conductance result from, and are used to describe, the opening or closing of ion channels.

meninges

The external covering of the brain; includes the pia, arachnoid, and dura mater.

Merkel’s disks

Encapsulated cutaneous mechanosensory receptors specialized for the detection of fine touch and pressure.

mesencephalon

see midbrain.

mesoderm

The middle of the three germ layers; gives rise to muscle, connective tissue, skeleton, and other structures.

mesopic

Light levels at which both the rod and cone systems are active.

metabotropic (metabotropic receptors)

Refers to receptors that are indirectly activated by the action of neurotransmitters or other extracellular signals, typically through the aegis of G-protein activation.

Meyer’s loop

That part of the optic radiation that runs in the caudal portion of the temporal lobe.

microglial cells

One of the three main types of central nervous system glia; concerned primarily with repairing damage following neural injury.

microscopic currents

Ionic currents flowing through single ion channels.

midbrain (mesencephalon)

The most rostral portion of the brainstem; identified by the superior and inferior colliculi on its dorsal surface, and the cerebral penduncles on its ventral aspect.

middle cerebellar peduncle

Large white matter tract that carries axons from the pontine relay nuclei to the cerebellar cortex.

miniature end plate potential (MEPP)

Small, spontaneous depolarization of the membrane potential of skeletal muscle cells, caused by the release of a single quantum of acetylcholine.

mitral cells

The major output neurons of the olfactory bulb.

mnemonic

Having to do with memory.

modality

A category of function. For example, vision, hearing, and touch are different sensory modalities.

molecular layer

The layer of the cerebellar cortex containing the apical dendrites of Purkinje cells, parallel fibers from granule cells, a few local circuit neurons, and the synapses between these elements.

monoclonal antibody

An antibody molecule raised from a clone of transformed lymphocytes.

morphine

A plant alkaloid that gives opium its analgesic properties.

morphogen

A molecule that influences morphogenesis.

morphogenesis

The generation of animal form.

morphology

The study of the form and structure of organisms; or, more commonly, the form and structure of an animal or animal part.

motor

Pertaining to movement.

motor cortex

The region of the cerebral cortex lying anterior to the central sulcus concerned with motor behavior; includes the primary motor cortex in the precentral gyrus and associated cortical areas in the frontal lobe.

motor neuron

By usage, a nerve cell that innervates skeletal muscle. Also called primary or α motor neuron.

motor neuron pool

The collection of motor neurons that innervates a single muscle.

motor system

A broad term used to describe all the central and peripheral structures that support motor behavior.

motor unit

A motor neuron and the skeletal muscle fibers it innervates; more loosely, the collection of skeletal muscle fibers innervated by a single motor neuron.

mucosa

Term referring the mucus membranes lining the nose, mouth, gut, and other epithelial surfaces.

muscarinic receptors

A group of G-protein-coupled acetylcholine receptors activated by the plant alkaloid muscarine.

muscle spindle

Highly specialized sensory organ found in most skeletal muscles; provides mechanosensory information about muscle length.

muscle tone

The normal, ongoing tension in a muscle; measured by resistance of a muscle to passive stretching.

myelin

The multilaminated wrapping around many axons formed by oligodendrocytes or Schwann cells.

myelination

Process by which glial cells wrap axons to form multiple layers of glial cell membrane that increase axonal conduction velocity.

myotatic reflex (stretch reflex)

A fundamental spinal reflex that is generated by the motor response to afferent sensory information arising from muscle spindles.

myotome

The part of each somite that contributes to the development of skeletal muscles.

Na+/K+ transporter (or Na+ pump)

A type of ATPase transporter in the plasma membrane of most cells that is responsible for accumulating intracellular K+ and extruding intracellular Na+.

nasal (nasal division)

Referring to the region of the visual field of each eye in the direction of the nose.

near reflex

Reflexive response induced by changing binocular fixation to a closer target; includes convergence, accommodation, and pupillary constriction.

neocortex

The six-layered cortex that forms the surface of most of the cerebral hemispheres.

Nernst equation

A mathematical relationship that predicts the equilibrium potential across a membrane that is permeable to only one ion.

nerve

A collection of peripheral axons that are bundled together and travel a common route.

nerve growth factor (NGF)

A neurotrophic protein required for survival and differentiation of sympathetic ganglion cells and certain sensory neurons. Preeminent member of the neurotrophin family of growth factors.

netrins

A family of diffusible molecules that act as attractive or repulsive cues to guide growing axons.

neural cell adhesion molecule (N-CAM)

Molecule that helps bind axons together and is widely distributed in the developing nervous system. Structurally related to immunoglobin.

neural crest

A group of progenitor cells that forms along the dorsum of the neural tube and gives rise to peripheral neurons and glia (among other derivatives).

neural plate

The thickened region of the dorsal ectoderm of a neurula that gives rise to the neural tube.

neural tube

The primordium of the brain and spinal cord; derived from the neural ectoderm.

neurite

A neuronal branch (usually used when the process in question could be either an axon or a dendrite, such as the branches of isolated nerve cells in tissue culture).

neuroblast

A dividing cell, the progeny of which develop into neurons.

neurogenesis

The development of the nervous system.

neuroglial cells

see glia.

neuroleptics

A group of antipsychotic agents that cause indifference to stimuli by blocking brain dopamine receptors.

neuromere

A segment of the rhombencephalon (synonym for rhombomere).

neuromuscular junction

The synapse made by a motor axon on a skeletal muscle fiber.

neuron

Cell specialized for the conduction and transmission of electrical signals in the nervous system.

neuronal geometry

The spatial arrangement of neuronal branches.

neuron-glia cell adhesion molecule (Ng-CAM)

A cell adhesion molecule, structurally related to immunoglobin molecules, that promotes adhesive interactions between neurons and glia.

neuropeptides

A general term describing a large number of peptides that function as neurotransmitters or neurohormones.

neuropil

The dense tangle of axonal and dendritic branches, and the synapses between them, that lies between neuronal cell bodies in the gray matter of the brain and spinal cord.

neurotransmitter

Substance released by synaptic terminals for the purpose of transmitting information from one nerve cell to another.

neurotrophic factors

A general term for molecules that promote the growth and survival of neurons.

neurotrophic hypothesis

The idea that developing neurons compete for a limited supply of trophic factors secreted by their targets.

neurotrophins

A family of trophic factor molecules that promote the growth and survival of several different classes of neurons.

neurula

The early vertebrate embryo during the stage when the neural tube forms from the neural plate; follows the gastrula stage.

neurulation

The process by which the neural plate folds to form the neural tube.

nociceptors

Cutaneous and subcutaneous receptors (usually free nerve endings) specialized for the detection of harmful (noxious) stimuli.

nodes of Ranvier

Periodic gaps in the myelination of axons where action potentials are generated.

non-rapid eye movement (non-REM) sleep

Collectively, those phases of sleep characterized by the absence of rapid eye movements.

norepinephrine (noradrenaline)

Catecholamine hormone and neurotransmitter that binds to α- and β-adrenergic receptors, both of which are G-protein-coupled receptors.

notochord

A transient, cylindrical structure of mesodermal cells underlying the neural plate (and later the neural tube) in vertebrate embryos. Source of important inductive signals for spinal cord.

nucleus (nuclei)

Collection of nerve cells in the brain that are anatomically discrete, and which typically serve a particular function.

nucleus proprius

Region of the dorsal horn of the spinal cord that receives information from nociceptors.

nystagmus

Literally, a nodding movement. Refers to repetitive movements of the eyes normally elicited by large-scale movements of the visual field (optokinetic nystagmus). Nystagmus in the absence of appropriate stimuli usually indicates brainstem or cerebellar pathology.

occipital lobe

The posterior lobe of the cerebral hemisphere; primarily devoted to vision.

ocular dominance columns

The segregated termination patterns of thalamic inputs representing the two eyes in primary visual cortex of some mammalian species.

odorants

Molecules capable of eliciting responses from receptors in the olfactory mucosa.

olfactory bulb

Olfactory relay station that receives axons from cranial nerve I and transmits this information via the olfactory tract to higher centers.

olfactory epithelium

Pseudostratified epithelium that contains olfactory receptor cells, supporting cells, and mucus-secreting glands.

olfactory receptor neurons

Bipolar neurons in olfactory epithelium that contain receptors for odorants.

olfactory tracts

see lateral olfactory tract.

oligodendrocytes

One of three classes of central neuroglial cells; their major function is to elaborate myelin.

ontogeny

The developmental history of an individual animal; also used as a synonym for development.

Onuf’s nucleus

Sexually dimorphic nucleus in the human spinal cord that innervates striated perineal muscles mediating contraction of the bladder in males, and vaginal constriction in females.

opioid

Any natural or synthetic drug that has pharmacological actions similar to those of morphine.

opsins

Proteins in photoreceptors that absorb light (in humans, rhodopsin and the three specialized cone opsins).

optic chiasm

The junction of the two optic nerves on the ventral aspect of the diencephalon, where axons from the nasal parts of each retina cross the midline.

optic cup

see optic vesicle.

optic disk

The region of the retina where the axons of retinal ganglion cells exit to form the optic nerve.

optic nerve

The nerve (cranial nerve II) containing the axons of retinal ganglion cells; extends from the eye to the optic chiasm.

optic radiation

Portion of the internal capsule that comprises the axons of lateral geniculate neurons that carry visual information to the striate cortex.

optic tectum

The first central station in the visual pathway of many vertebrates (analogous to the superior colliculus in mammals).

optic tract

The axons of retinal ganglion cells after they have passed through the region of the optic chiasm en route to the lateral geniculate nucleus of the thalamus.

optic vesicle

The evagination of the forebrain vesicle that generates the retina and induces lens formation in the overlying ectoderm.

optokinetic eye movements

Movements of the eyes that compensate for head movements; the stimulus for optokinetic movements is large-scale motion of the visual field.

optokinetic nystagmus

Repeated reflexive responses of the eyes to ongoing large-scale movements of the visual scene.

orbital and medial prefrontal cortex

Division of the prefrontal cortex that lies above the orbits in the most rostral and ventral extension of the sagittal fissure; important in emotional processing and rational decision-making.

order

A taxonomic category subordinate to class; comprises animal families.

orientation selectivity

A property of many neurons in visual cortex in which they respond to edges presented over a narrow range of orientations.

oscillopsia

An inability to fixate visual targets while the head is moving as a result of vestibular damage.

ossicles

The bones of the middle ear

otoconia

The calcium carbonate crystals that rest on the otolithic membrane overlying the hair cells of the sacculus and utricle.

otolithic membrane

The gelatinous membrane on which the otoconia lie and in which the tips of the hair bundles are embedded.

otoliths

Dense calcific structures (literally “ear stones”); important in generating the vestibular signals pertinent to balance.

outer segment

Portion of photoreceptors made up of membranous disks that contain the photopigment responsible for initiating phototransduction.

oval window

Site where the middle ear ossicles transfer vibrational energy to the cochlea.

overshoot

The peak, positive-going phase of an action potential, caused by high membrane permeability to a cation such as Na+ or Ca2+.

oxytocin

A 9-amino-acid neuropeptide that is both a putative neurotransmitter and a neurohormone.

Pacinian corpuscle

Encapsulated mechanosensory receptor specialized for the detection of high-frequency vibrations.

Papez’s circuit

System of interconnected brain structures (mainly cingulate gyrus, hippocampus, and hypothalamus) in the medial aspect of the telencephalon and diencephalon described by James Papez. Participates in emotional processing, short-term declarative memory, and autonomic functions.

paracrine

Term referring to the secretion of hormone-like agents whose effects are mediated locally rather than by the general circulation.

parallel fibers

The bifurcated axons of cerebellar granule cells that synapse on dendritic spines of Purkinje cells.

paralysis

Complete loss of voluntary motor control.

paramedian pontine reticular formation (PPRF)

Neurons in the reticular formation of the pons that coordinate the actions of motor neurons in the abducens and oculomotor nuclei to generate horizontal movements of the eyes; also known as the “horizontal gaze center.”

parasympathetic nervous system

A division of the visceral motor system in which the effectors are cholinergic ganglion cells located near target organs.

paresis

Partial loss of voluntary motor control; weakness.

parietal lobe

The lobe of the brain that lies between the frontal lobe anteriorly, and the occipital lobe posteriorly.

Parkinson’s disease

A neurodegenerative disease of the substantia nigra that results in a characteristic tremor at rest and a general paucity of movement.

parvocellular

Referring to the component of the primary visual pathway specialized for the detection of detail and color; so named because of the relatively small cells involved.

passive current flow

Current flow across neuronal membranes that does not entail the action potential mechanism.

patch clamp

An extraordinarily sensitive voltage clamp method that permits the measurement of ionic currents flowing through individual ion channels.

periaqueductal gray matter

Region of brainstem gray matter that contains, among others, nuclei associated with the modulation of pain perception.

perilymph

The potassium-poor fluid that bathes the basal end of the cochlear hair cells.

perineurium

The connective tissue that surrounds a nerve fascicle in a peripheral nerve.

peripheral nervous system

All nerves and neurons that lie outside the brain and spinal cord.

permissive

An influence during development that permits differentiation to occur but does not specifically instruct cell fate.

phasic

Transient firing of action potentials in response to a prolonged stimulus; the opposite of tonic.

phenotype

The visible (or otherwise discernible) characteristics of an animal that arise during development.

phenotypic sex

The visible body characteristics associated with sexual behaviors.

phospholipase A2A

G-protein-activated enzyme that hydrolizes membrane phospholipids at the inner leaflet of the plasma membrane to release fatty acids such as arachadonic acid.

phospholipase CA

G-protein-activated enzyme that hydrolizes membrane phospholipids at the inner leaflet of the plasma membrane to release a diacylglycerol and an inositol phosphate such as inositol trisphosphate (IP3).

photopic vision

Vision at high light levels that is mediated entirely by cones.

phylogeny

The evolutionary history of a species or other taxonomic category.

phylum

A major division of the plant or animal kingdom that includes classes having a common ancestry.

pia mater

The innermost of the three layers of the meninges, which is closely applied to the surface of the brain.

pigment epithelium

Pigmented coat underlying the retina important in the normal turnover of photopigment in rods and cones.

pineal gland

Midline neural structure lying on the dorsal surface of the midbrain; important in the control of circadian rhythms (and, incidentally, considered by Descartes to be the seat of the soul).

pinna

A component of the external ear.

pituitary gland

Endocrine structure comprising an anterior lobe made up of many different types of hormone-secreting cells, and a posterior lobe that secretes neuropeptides produced by neurons in the hypothalamus.

placebo

An inert substance that when administered may, because of the circumstances, have physiological effects.

planum temporale

Region on the superior surface of the temporal lobe posterior to Heschl’s gyrus; notable because it is larger in the left hemisphere in about two-thirds of humans.

plasticity

Term that refers to structural or functional changes in the nervous system.

polarity

Referring to a continually graded organization along one of the major axes of an animal.

polymodal

Responding to more than one sensory modality.

polyneuronal innervation

A state in which neurons or muscle fibers receive synaptic inputs from multiple, rather than single, axons.

pons

One of the three components of the brainstem, lying between the midbrain rostrally and the medulla caudally.

pontine-geniculate-occipital (PGO) waves

Characteristic encephalographic waves that signal the onset of rapid eye movement sleep.

pontine relay nuclei

Collections of neurons in the pons that receive input from the cerebral cortex and send their axons across the midline to the cerebellar cortex via the middle cerebellar peduncle.

pore

A structural feature of membrane ion channels that allows ions to diffuse through the channel.

pore loop

An extracellular domain of amino acids, found in certain ion channels, that lines the channel pore and allows only certain ions to pass.

postcentral gyrus

The gyrus that lies just posterior to the central sulcus; contains the primary somatic sensory cortex.

posterior

Toward the back; sometimes used as a synonym for caudal or dorsal.

postganglionic

Referring to axons that link visceral motor neurons in autonomic ganglia to their targets.

postsynaptic current (PSC)

The current produced in a postsynaptic neuron by the binding of neurotransmitter released from a presynaptic neuron.

postsynaptic

Referring to the component of a synapse specialized for transmitter reception; downstream at a synapse.

postsynaptic potential (PSP)

The potential change produced in a postsynaptic neuron by the binding of neurotransmitter released from a presynaptic neuron.

post-tetanic potentiation (PTP)

An enhancement of synaptic transmission resulting from high-frequency trains of action potentials.

precentral gyrus

The gyrus that lies just anterior to the central sulcus; contains the primary motor cortex.

prefrontal cortex

Cortical regions in the frontal lobe that are anterior to the primary and association motor cortices; thought to be involved in planning complex cognitive behaviors and in the expression of personality and appropriate social behavior.

preganglionic

Referring to neurons and axons that link visceral motor neurons in spinal cord and brainstem to autonomic ganglia.

premotor cortex

Motor association areas in the frontal lobe anterior to primary motor cortex; thought to be involved in planning or programming of voluntary movements.

pre-proproteins

The first protein translation products synthesized in a cell. These polypeptides are usually much larger than the final, mature peptide, and often contain signal sequences that target the peptide to the lumen of the endoplasmic reticulum.

presynaptic

Referring to the component of a synapse specialized for transmitter release; upstream at a synapse.

pretectum

A group of nuclei located at the junction of the thalamus and the midbrain; these nuclei are important in the pupillary light reflex, relaying information from the retina to the Edinger-Westphal nucleus.

prevertebral (prevertebral ganglia)

Sympathetic ganglia that lie anterior to the spinal column (distinct from the sympathetic chain ganglia).

primary auditory cortex

The major cortical target of the neurons in the medial geniculate nucleus.

primary motor cortex

A major source of descending projections to motor neurons in the the spinal cord and cranial nerve nuclei; located in the precentral gyrus (Brodmann’s area 4) and essential for the voluntary control of movement.

primary neuron

A neuron that directly links muscles, glands, and sense organs to the central nervous system.

primary sensory cortex

Any one of several cortical areas receiving the thalamic input for a particular sensory modality.

primary visual cortex

see striate cortex.

primary visual pathway (retinogenticulocortical pathway)

Pathway from the retina via the lateral genticulate nucleus of the thalamus to the primary visual cortex; carries the information that allows conscious visual perception.

primate

An order of mammals that includes lemurs, tarsiers, marmosets, monkeys, apes, and humans (technically, a member of this order).

priming

A phenomenon in which the memory of an initial exposure is expressed unconsciously by improved performance at a later time.

primitive pit

The thickened anterior end of the primitive streak; an important source of inductive signals during early development.

primitive streak

Axial thickening in the ectoderm of the gastrulas of reptiles, birds, and mammals; the mesoderm forms by the ingression of cells at this site.

procedural memory

Unconscious memories such as motor skills and associations.

production aphasia

Aphasia that derives from cortical damage to those centers concerned with the motor aspects of speech.

promoter

DNA sequence (usually within 35 nucleotides upstream of the start site of transcription) to which the RNA polymerase and its associated factors bind to initiate transcription.

proproteins

Partially processed forms of proteins containing peptide sequences that play a role in the correct folding of the final protein.

proprioceptors

Sensory receptors (usually limited to mechanosensory receptors) that sense the internal forces acting on the body; muscle spindles and Golgi tendon organs are the preeminent examples.

prosencephalon

The part of the brain that includes the diencephalon and telencephalon (derived from the embryonic forebrain vesicle).

prosody (adjective, prosodic)

The emotional tone or quality of speech.

prosopagnosia

The inability to recognize faces; usually associated with lesions to the right inferior temporal cortex.

proteoglycan

Molecule consisting of a core protein to which one or more long, linear carbohydrate chains (glycosaminoglycans) are attached.

proximal

Closer to a point of reference (the opposite of distal).

psychotropic

Referring to drugs that alter behavior, mood, and perception.

pulvinar

A thalamic nucleus that receives its major input from sensory and association cortices and projects in turn to association cortices, particularly in the parietal lobe.

pupil

The perforation in the iris that allows light to enter the eye.

pupillary light reflex

The decrease in the diameter of the pupil that follows stimulation of the retina.

Purkinje cell

The large principal projection neuron of the cerebellar cortex that has as its defining characteristic an elaborate apical dendrite.

putamen

One of the three major nuclei that make up the basal ganglia.

pyramidal tract

White matter tract that lies on the ventral surface of the medulla and contains axons descending from motor cortex to the spinal cord.

pyriform cortex

Component of cerebral cortex in the temporal lobe pertinent to olfaction; so named because of its pearlike shape.

radial glia

Glial cells that contact both the luminal and pial surfaces of the neural tube, providing a substrate for neuronal migration.

ramus

Branch; typically applied to the white and gray communicating rami that carry visceral motor axons to the segmental nerves.

raphe nuclei

A collection of serotonergic nuclei in the brainstem tegmentum; important in the governance of sleep and waking.

rapid eye movement (REM) sleep

Phase of sleep characterized by low-voltage, high-frequency electroencephalographic activity accompanied by rapid eye movements.

receptive field

Region of a receptor surface (e.g., the body surface or the retina) that causes a sensory nerve cell (or axon) to respond.

receptor

A molecule specialized to bind any one of a large number of chemical signals, preeminently neurotransmitters.

receptor neuron

A neuron specialized for the transduction of energy in the environment into electrical signals.

receptor potential

The membrane potential change elicited in receptor neurons during sensory transduction.

5-α-reductase

Enzyme that converts testosterone to dihydrotestosterone.

reflex

A stereotyped (involuntary) motor response elicited by a defined stimulus.

refractory period

The brief period after the generation of an action potential during which a second action potential is difficult or impossible to elicit.

remodeling

Change in the anatomical arrangement of neural connections.

reserpine

An antihypertensive drug that is no longer used due to side effects such as behavioral depression.

resting potential

The inside-negative electrical potential that is normally recorded across all cell membranes.

reticular activating system

Region in the brainstem tegmentum that, when stimulated, causes arousal; involved in modulating sleep and wakefulness.

reticular formation

A network of neurons and axons that occupies the core of the brainstem, giving it a reticulated appearance in myelin-stained material; major functions include control of respiration and heart rate, posture, and state of consciousness.

retina

Laminated neural component of the eye that contains the photoreceptors (rods and cones) and the initial processing machinery for the primary (and other) visual pathways.

retinoic acid

A derivative of vitamin A that acts as an inducer during early brain development.

retinotectal system

The pathway between ganglion cells in the retina and the optic tectum of vertebrates.

retrograde

A movement or influence acting from the axon terminal toward the cell body.

reversal potential

The membrane potential of a post-synaptic neuron (or other target cell) at which the action of a given neurotransmitter causes no net current flow.

rhodopsin

The photopigment found in rods.

rhombencephalon

The part of the brain that includes the pons, cerebellum, and medulla (derived from the embryonic hindbrain vesicle).

rhombomere

Segment of the developing rhombencephalon.

rising phase

The initial, depolarizing, phase of an action potential, caused by the regenerative, voltage-dependent influx of a cation such as Na+ or Ca2+.

rods

Photoreceptors specialized for operating at low light levels.

rostral

Anterior, or “headward.”

rostral interstitial nucleus

Neurons in the midbrain reticular formation that coordinate the actions of neurons in the oculomotor nuclei to generate vertical movements of the eye; also known as the “vertical gaze center.”

saccades

Ballistic, conjugate eye movements that change the point of foveal fixation.

sacculus

The otolith organ that detects linear accelerations and head tilts in the vertical plane.

sagittal

Referring to the anterior-posterior plane of an animal.

saltatory conduction

Mechanism of action potential propagation in myelinated axons; so named because action potentials “jump” from one node of Ranvier to the next due to generation of action potentials only at these sites.

Scarpa’s ganglion

The ganglion containing the bipolar cells that innervate the semicircular canals and otolith organs.

Schaffer collaterals

The axons of cells in the CA3 region of hippocampus that form synapses in the CA1 region.

Schwann cells

Neuroglial cells in the peripheral nervous system that elaborate myelin (named after the nineteenth-century anatomist and physiologist Theodor Schwann).

sclera

The external connective tissue coat of the eyeball.

scotoma

A defect in the visual field as a result of pathological changes in some component of the primary visual pathway.

scotopic

Referring to vision in dim light, where the rods are the operative receptors.

second-order neurons

Projection neurons in a sensory pathway that lie between the primary receptor neurons and the third-order neurons.

segment

One of a series of more or less similar anterior-posterior units that make up segmental animals.

segmentation

The anterior-posterior division of animals into roughly similar repeating units.

semaphorins

A family of diffusible, growth-inhibiting molecules (see also collapsin).

semicircular canals

The vestibular end organs within the inner ear that sense rotational accelerations of the head.

sensitization

Increased sensitivity to stimuli in an area surrounding an injury. Also, a generalized aversive response to an otherwise benign stimulus when it is paired with a noxious stimulus.

sensorineural hearing loss

Diminished sense of hearing due to damage of the inner ear or its related central auditory structures. Contrast with conductive hearing loss.

sensory

Pertaining to sensation.

sensory aphasia

Difficulty in communicating with language that derives from cortical damage to those areas concerned with the comprehension of speech.

sensory ganglia

see dorsal root ganglia.

sensory system

Term sometimes used to describe all the components of the central and peripheral nervous system concerned with sensation.

sensory transduction

Process by which energy in the environment is converted into electrical signals by sensory receptors.

serotonin

A biogenic amine neurotransmitter derived from the amino acid tryptophan.

sexually dimorphic

Having two different forms depending on genotypic or phenotypic sex.

short-term memory

Memories that last from seconds to minutes.

silver stain

A classical method for visualizing neurons and their processes by impregnation with silver salts (the best-known technique is the Golgi stain, developed by the Italian anatomist Camillo Golgi in the late nineteenth century).

size principle

The orderly recruitment of motor neurons by size to generate increasing amounts of muscle tension.

sleep spindles

Bursts of electroencephalographic activity, at a frequency about 10–14 Hz and lasting a few seconds; spindles characterize the initial descent into non-REM sleep.

small molecule neurotransmitters

Referring to the non-peptide neurotransmitters such as acetylcholine, the amino acids glutamate, aspartate, GABA, and glycine, as well as the biogenic amines.

smooth pursuit eye movements

Slow, tracking movements of the eyes designed to keep a moving object aligned with the fovea.

soma (somata)

The cell body.

somatic cells

Referring to the cells of an animal other than its germ cells.

somatic sensory cortex

That region of the cerebral cortex concerned with processing sensory information from the body surface, subcutaneous tissues, muscles, and joints; located primarily in the posterior bank of the central sulcus and on the postcentral gyrus.

somatic sensory system

Components of the nervous system involved in processing sensory information about the mechanical forces active on both the body surface and on deeper structures such as muscles and joints.

somatotopic maps

Cortical or subcortical arrangements of sensory pathways that reflect the organization of the body.

somites

Segmentally arranged masses of mesoderm that lie alongside the neural tube and give rise to skeletal muscle, vertebrae, and dermis.

species

A taxonomic category subordinate to genus; members of a species are defined by extensive similarities, including the ability to interbreed.

specificity

Term applied to neural connections that entail specific choices between neurons and their targets.

spina bifida

A congenital defect in which the neural tube fails to close at its posterior end.

spinal cord

The portion of the central nervous system that extends from the lower end of the brainstem (the medulla) to the cauda equina.

spinal ganglia

see dorsal root ganglia.

spinal nucleus of the bulbocavernosus

Sexually dimorphic collection of neurons in the lumbar region of the rodent spinal cord that innervate striated perineal muscles.

spinal shock

The initial flaccid paralysis that accompanies damage to descending motor pathways.

spinal trigeminal tract

Brainstem tract carrying fibers from the trigeminal nerve to the spinal nucleus of the trigeminal complex (which serves as the relay for painful stimulation of the face).

spinocerebellum

Region of the cerebellar cortex that receives input from the spinal cord, particularly Clarke’s column in the thoracic spinal cord.

spinothalamic pathway

see anterolateral pathway.

spinothalamic tract

Ascending white matter tract carrying information about pain and temperature from the spinal cord to the VP nuclear complex in the thalamus; also referred to as the anterolateral tract.

split-brain patients

Individuals who have had the cerebral commissures divided in the midline to control epileptic seizures.

sporadic

Cases of a disease that apparently occur at random in a population; contrasts with familial or inherited.

stem cells

Undifferentiated cells from which other cells, including neurons, can be derived.

stereocilia

The actin-rich processes that, along with the kinocilium, form the hair bundle extending from the apical surface of the hair cell; site of mechanotransduction.

stereopsis

The perception of depth that results from the fact that the two eyes view the world from slightly different angles.

strabismus

Developmental misalignment of the two eyes; may lead to binocular vision being compromised.

stria vascularis

Specialized epithelium lining the cochlear duct that maintains the high potassium concentration of the endolymph.

striate cortex

Primary visual cortex in the occipital lobe (also called Brodmann’s area 17). So named because the prominence of layer IV in myelin-stained sections gives this region a striped appearance.

striatum (neostriatum)

see corpus striatum.

striola

A line found in both the sacculus and utricle that divides the hair cells into two populations with opposing hair bundle polarities.

subarachnoid space

The cerebrospinal fluid—filled space over the surface of the brain that lies between the arachnoid and the pia.

substance P

An 11-amino acid neuropeptide; the first neuropeptide to be characterized.

substantia nigra

Nucleus at the base of the midbrain that receives input from a number of cortical and subcortical structures. The dopaminergic cells of the substantia nigra send their output to the caudate/putamen, while the GABAergic cells send their output to the thalamus.

subthalamic nucleus

A nucleus in the ventral diencephalon that receives input from the caudate/putamen and participates in the modulation of motor behavior.

sulci (singular, sulcus)

The infoldings of the cerebral hemisphere that form the valleys between the gyral ridges.

summation

The addition in space and time of sequential synaptic potentials to generate a larger than normal post-synaptic response.

superior colliculus

Laminated structure that forms part of the roof of the midbrain; plays an important role in orienting movements of the head and eyes.

suprachiasmatic nucleus

Hypothalamic nucleus lying just above the optic chiasm that receives direct input from the retina; involved in light entrainment of circadian rhythms.

Sylvian fissure

see lateral fissure.

sympathetic nervous system

A division of the visceral motor system in vertebrates comprising, for the most part, adrenergic ganglion cells located relatively far from the related end organs.

synapse

Specialized apposition between a neuron and its target cell for transmission of information by release and reception of a chemical transmitter agent.

synaptic cleft

The space that separates pre- and postsynaptic neurons at chemical synapses.

synaptic depression

A short-term decrease in synaptic strength resulting from the depletion of synaptic vesicles at active synapses.

synaptic vesicle recycling

A sequence of budding and fusion reactions that occurs within presynaptic terminals to maintain the supply of synaptic vesicles.

synaptic vesicles

Spherical, membrane-bound organelles in presynaptic terminals that store neurotransmitters.

syncytium

A group of cells in protoplasmic continuity.

target (neural target)

The object of innervation, which can be either non-neuronal targets, such as muscles, glands, and sense organs, or other neurons.

taste buds

Onion-shaped structures in the mouth and pharynx that contain taste cells.

tectorial membrane

The fibrous sheet overlying the apical surface of the cochlear hair cells; produces a shearing motion of the stereocilia when the basilar membrane is displaced.

tectum

A general term referring to the dorsal region of the brainstem (tectum means “roof”).

tegmentum

A general term that refers to the central gray matter of the brainstem.

telencephalon

The part of the brain derived from the anterior part of the embryonic forebrain vesicle; includes the cerebral hemispheres.

temporal (temporal division)

Referring to the region of the visual field of each eye in the direction of the temple.

temporal lobe

The hemispheric lobe that lies inferior to the lateral fissure.

terminal

A presynaptic (axonal) ending.

tetraethylammonium

A quaternary ammonium compound that selectively blocks voltage-sensitive K+ channels; eliminates the delayed K+ current measured in voltage clamp experiments.

tetrodotoxin

An alkaloid neurotoxin, produced by certain puffer fish, tropical frogs, and salamanders, that selectively blocks voltage-sensitive Na+ channels; eliminates the initial Na+ current measured in voltage clamp experiments.

thalamus

A collection of nuclei that forms the major component of the diencephalon. Although its functions are many, a primary role of the thalamus is to relay sensory information from lower centers to the cerebral cortex.

thermoreceptors

Receptors specialized to transduce changes in temperature.

threshold

The level of membrane potential at which an action potential is generated.

tight junction

A specialized junction between epithelial cells that seals them together, preventing most molecules from passing across the cell sheet.

tip links

The filamentous structures that link the tips of adjacent stereocilia; thought to mediate the gating of the hair cell’s transduction channels.

tonic

Sustained activity in response to an ongoing stimulus; the opposite of phasic.

tonotopy

the topographic mapping of frequency across the surface of a structure, which originates in the cochlea and is preserved in ascending auditory structures, including the auditory cortex.

transcription factors

A general term applied to proteins that regulate transcription, including basal transcription factors that interact with the RNA polymerase to initiate transcription, as well as those that bind elsewhere to stimulate or repress transcription.

transcriptional activator proteins

Proteins that bind DNA and activate the transcription of DNA.

transducin

G-protein involved in the phototransduction cascade.

transduction

see sensory transduction.

transforming growth factor (TGF)

A class of peptide growth factors that acts as an inducer during early development.

transgenderism

Gender identification with the opposite phenotypic sex.

transmitter

see neurotransmitter.

transporters (active transporters)

Cell membrane molecules that consume energy to move ions up their concentration gradients, thus restoring and/or maintaining normal concentration gradients across cell membranes.

trichomatic

Referring to the presence of three different cone types in the human retina, which generate the initial steps in color vision by differentially absorbing long, medium, and short wavelength light.

tricyclic antidepressants

A class of antidepressant drugs named for their three-ringed molecular structure; thought to act by blocking the reuptake of biogenic amines.

trigeminal ganglion

The sensory ganglion associated with the trigeminal nerve (cranial nerve V).

Trk receptors

The receptors for the neurotrophin family of growth factors.

trophic

The ability of one tissue or cell to support another; usually applied to long-term interactions between pre- and postsynaptic cells.

trophic factor (agent)

A molecule that mediates trophic interactions.

trophic interactions

Referring to the long-term interdependence of nerve cells and their targets.

trophic molecules

see trophic factor.

tropic

An influence of one cell or tissue on the direction of movement (or outgrowth) of another.

tropic molecules

Molecules that influence the direction of growth or movement.

tropism

Orientation of growth in response to an external stimulus.

tuning curve

Referring to a common physiological test in which the receptive field properties of neurons are gauged against a varying stimulus such that maximum sensitivity or maximum responsiveness can be defined by the peak of the tuning curve.

tympanic membrane

The eardrum.

undershoot

The final, hyperpolarizing phase of an action potential, typically caused by the voltage-dependent efflux of a cation such as K+.

upper motor neuron

A neuron that gives rise to a descending projection that controls the activity of lower motor neurons in the brainstem and spinal cord.

upper motor neuron syndrome

Signs and symptoms that result from damage to descending motor systems; these include paralysis, spasticity, and a positive Babinski sign.

utricle

The otolith organ that senses linear accelerations and head tilts in the horizontal plane.

vasopressin

A 9-amino-acid neuropeptide that acts as a neurotransmitter, as well as a neurohormone.

ventral

Referring to the belly; the opposite of dorsal.

ventral horn

The ventral portion of the spinal cord gray matter; contains the primary motor neurons.

ventral posterior complex

Group of thalamic nuclei that receives the somatic sensory projections from the dorsal column nuclei and the trigeminal nuclear complex.

ventral posterior lateral nucleus

Component of the ventral posterior complex of thalamic nuclei that receives brainstem projections carrying somatic sensory information from the body (excluding the face).

ventral posterior medial nucleus

Component of the ventral posterior complex of thalamic nuclei that receives brainstem projections related to somatic sensory information from the face.

ventral roots

The collection of nerve fibers containing motor axons that exit ventrally from the spinal cord and contribute the motor component of each segmental spinal nerve.

ventricles

The fluid-filled spaces in the vertebrate brain that represent the lumen of the embryonic neural tube.

ventricular zone

The sheet of cells closest to the ventricles in the developing neural tube.

vergence movements

Disjunctive movements of the eyes (convergence or divergence) that align the fovea of each eye with targets located at different distances from the observer.

vertebrate

An animal with a backbone (technically, a member of the subphylum Vertebrata).

vesicle

Literally, a small sac. Used to refer to the organelles that store and release transmitter at nerve endings. Also used to refer to any of the three dilations of the anterior end of the neural tube that give rise to the three major subdivisions of the brain.

vestibulocerebellum

The part of the cerebellar cortex that receives direct input from the vestibular nuclei or vestibular nerve.

vestibulo-ocular reflex

Involuntary movement of the eyes in response to displacement of the head. This reflex allows retinal images to remain stable while the head is moved.

visceral (noun, viscera)

Referring to the internal organs of the body cavity.

visceral motor system

The component of the motor system (also known as the autonomic nervous system) that motivates and governs visceral motor behavior.

visceral nervous system

Synonymous with autonomic nervous system.

visual field

The area in the external world normally seen by one or both eyes (referred to, respectively, as the monocular and visual binocular fields).

vital dye

A reagent that stains cells when they are alive.

voltage clamp

A method that uses electronic feedback to control the membrane potential of a cell, simultaneously measuring transmembrane currents that result from the opening and closing of ion channels.

voltage-gated

Term used to describe ion channels whose opening and closing is sensitive to membrane potential.

Wallerian degeneration

The process by which the distal portion of a damaged axon segment degenerates; named after Augustus Waller, a nineteenth-century physician and neuroanatomist.

Wernicke’s aphasia

Difficulty comprehending speech as a result of damage to Wernicke’s language area.

Wernicke’s area

Region of cortex in the superior and posterior region of the left temporal lobe that helps mediate language comprehension. Named after the nineteenth-century neurologist, Carl Wernicke.

white matter

A general term that refers to large axon tracts in the brain and spinal cord; the phrase derives from the fact that axonal tracts have a whitish cast when viewed in the freshly cut material.

working memory

Memories held briefly in mind that enable a particular task to be accomplished (e.g., efficiently searching a room for a lost object).

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2001, Sinauer Associates, Inc.
Bookshelf ID: NBK10981

Views

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...