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Studying the Nervous Systems of Humans and Other Animals
Part I
41
Science
Undergraduate 2
08/04/2009

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Term
action potential
Definition
The electrical signal conducted along axons (or muscle fibers) by which information is conveyed from one place to another in the nervous system.
Term
central nervous system (CNS)
Definition
The brain and spinal cord of vertebrates (by analogy, the central nerve cord and ganglia of invertebrates).
Term
axon
Definition
The neuronal process that carries the action potential from the nerve cell body to a target.
Term
dendrite
Definition
A neuronal process arising from the cell body that receives synaptic input.
Term
chemical synapses
Definition
Synapses that transmit information via the secretion of chemical signals (neurotransmitters).
Term
cortex
Definition
The superficial mantle of gray matter covering the cerebral hemispheres and cerebellum, where most of the neurons in the brain are located.
Term
brain-derived neutrophic factor (BDNF)
Definition
One member of a family of neutrophic factors, the best-known constituent of which is nerve growth factor.
Term
convergence
Definition
Innervation of a target cell by axons from more than one neuron.
Term
astrocytes
Definition
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.
Term
cranial nerve ganglia
Definition
The sensory ganglia associated with the cranial nerves; these correspond to the dorsal root ganglia of the spinal segmental nerves.
Term
divergence
Definition
The branching of a single axon to innervate multiple target cells.
Term
dorsal root ganglia (DRG)
Definition
The segmental sensory ganglia of the spinal cord; contain the first-order neurons of the dorsal column/medial lemniscus and spinothalamic pathways.
Term
efferent
Definition
An axon that conducts information away from the central nervous system.
Term
electrical synapses
Definition
Synapses that transmit information via the direct flow of electrical current at gap junctions.
Term
ganglion (ganglia)
Definition
Collections of hundreds to thousands of neurons found outside the brain and spinal cord along the course of peripheral nerves.
Term
gene
Definition
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.
Term
glia
Definition
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). Also known as neuroglia.
Term
gray matter
Definition
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.
Term
interneuron
Definition
Technically, a neuron in the pathway between primary sensory and primary effector neurons; more generally, a neuron whose relatively short axons branch locally to innervate other neurons. Also known as local circuit neuron.
Term
local circuit neuron
Definition
General term referring to neurons whose activity mediates interactions between sensory systems and motor systems; interneuron is often used as a synonym.
Term
microglial cells
Definition
One of the three main types of central nervous system glia; concerned primarily with repairing damage following neural injury.
Term
motor neuron
Definition
By usage, a nerve cell that innervates skeletal muscle. Also called primary or α motor neuron.
Term
motor system
Definition
A broad term used to describe all the central and peripheral structures that support motor behavior.
Term
myelin
Definition
The multilaminated wrapping around many axons formed by oligodendrocytes or Schwann cells.
Term
myotatic reflex
Definition
A fundamental spinal reflex that is generated by the motor response to afferent sensory information arising from muscle spindles. The “knee jerk reaction” is a common example. Also called a stretch reflex.
Term
nerve
Definition
A collection of peripheral axons that are bundled together and travel a common route.
Term
neuron
Definition
Cell specialized for the conduction and transmission of electrical signals in the nervous system.
Term
neuropil
Definition
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.
Term
neurotransmitter
Definition
Substance released by synaptic terminals for the purpose of transmitting information from one nerve cell to another.
Term
nucleus (nuclei)
Definition
Collection of nerve cells in the brain that are anatomically discrete, and which typically serve a particular function.
Term
oligodendrocytes
Definition
One of three classes of central neuroglial cells; their major function is to elaborate myelin
Term
peripheral nervous system
Definition
All nerves and neurons that lie outside the brain and spinal cord.
Term
projection neuron
Definition
A neuron with long axons that project to distant targets.
Term
receptive field
Definition
Region of a receptor surface (e.g., the body surface or the retina) that causes a sensory nerve cell (or axon) to respond.
Term
receptor potential
Definition
The membrane potential change elicited in receptor neurons during sensory transduction.
Term
Schwann cells
Definition
Neuroglial cells in the peripheral nervous system that elaborate myelin (named after the nineteenth-century anatomist and physiologist Theodor Schwann).
Term
sensory system
Definition
Term sometimes used to describe all the components of the central and peripheral nervous system concerned with sensation.
Term
spinal cord
Definition
The portion of the central nervous system that extends from the lower end of the brainstem (the medulla) to the cauda equina.
Term
synaptic cleft
Definition
The space that separates pre- and postsynaptic neurons at chemical synapses.
Term
synaptic vesicle recycling
Definition
A sequence of budding and fusion reactions that occurs within presynaptic terminals to maintain the supply of synaptic vesicles.
Term
white matter
Definition
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.
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