association neuron

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association neuron

Interneuron, internuncial neuron A nerve cell confined to the CNS, which conveys impulses in an arc from sensory to motor neurons


(noo'ron?) [Gr. neuron, nerve, sinew]
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A nerve cell, the structural and functional unit of the nervous system. A neuron consists of a cell body (perikaryon) and its processes, an axon and one or more dendrites. Neurons function in the initiation and conduction of impulses. They transmit impulses to other neurons or cells by releasing neurotransmitters at synapses. Alternatively, a neuron may release neurohormones into the bloodstream. Synonym: nerve cell See: illustrationneuronal (noor''on-al), adjective

afferent neuron

A neuron that conducts sensory impulses toward the brain or spinal cord.
Synonym: sensory neuron

association neuron


associative neuron

A neuron that mediates impulses between a sensory and a motor neuron.

bipolar neuron

1. A neuron that bears two processes.
2. A neuron of the retina that receives impulses from the rods and cones and transmits them to a ganglion neuron. See: retina for illus.

central neuron

A neuron confined entirely to the central nervous system.

commissural neuron

A neuron whose axon crosses to the opposite side of the brain or spinal cord.

efferent neuron

A neuron whose axon carries motor impulses away from the brain or spinal cord.

gamma motor neuron

A small nerve originating in the anterior horns of the spinal cord that transmits impulses through type A gamma fibers to intrafusal fibers of the muscle spindle for muscle control.

ganglion neuron

A neuron of the retina that receives impulses from bipolar neurons. Axons of ganglion neurons converge at the optic disk to form the optic nerve.
See: retina for illus.

internuncial neuron


lower motor neuron

A peripheral motor neuron that originates in the ventral horns of the gray matter of the spinal cord and terminates in skeletal muscles. Lesions of these neurons produce flaccid paralysis of the muscles they innervate. Synonym: lower motoneuron

mirror neuron

Any of a group of neurons that become active both when an animal moves in a certain way and when the animal observes others performing the same action. Learning by simulation or imitation is thought to be a function of the system of mirror neurons in the brain.

motor neuron

A neuron that carries impulses from the central nervous system either to muscle tissue to stimulate contraction or to glandular tissue to stimulate secretion.

multipolar neuron

A neuron with one axon and many dendrites.

peripheral neuron

A neuron whose process constitutes a part of the peripheral nervous system (cranial, spinal, or autonomic nerves).

peripheral motor neuron

A motor neuron that transmits impulses to skeletal muscle. Synonym: peripheral motoneuron

postganglionic neuron

A neuron of the autonomic nervous system whose cell body lies in an autonomic ganglion and whose axon terminates in a visceral effector (smooth or cardiac muscle or glands).

preganglionic neuron

A neuron of the autonomic nervous system whose cell body lies in the central nervous system and whose axon terminates in a peripheral ganglion, synapsing with postganglionic neurons.

sensory neuron

Afferent neuron.

serotonergic neuron

A nerve cell that uses serotonin as its neurotransmitter.

unipolar neuron

A neuron whose cell body bears one process.

upper motor neuron

A motor neuron (actually an interneuron) found completely within the central nervous system that synapses with or regulates the actions of lower motor neurons in the spinal cord and cranial nerves. Lesions of these neurons produce spastic paralysis in the muscles they innervate. Synonym: upper motoneuron


a nerve cell; any of the conducting cells of the nervous system, consisting of a cell body, containing the nucleus and its surrounding cytoplasm, and the axon and dendrites.
Neurons are highly specialized cells having two characteristic properties: irritability, which means that they are capable of responding to stimulation; and conductivity, which means that they are able to conduct impulses. They are composed of a cell body (the neurosome or perikaryon), containing the nucleus and its surrounding cytoplasm, and one or more processes (nerve fibers) extending from the cell body.
The processes are actually extensions of the cytoplasm surrounding the nucleus of the neuron. A nerve cell may have only one such slender fiber extending from its body, in which case it is classified as unipolar. A neuron having two processes is bipolar, and one with three or more processes is multipolar. Most neurons are multipolar, this type of neuron being widely distributed throughout the central nervous system and autonomic ganglia. The multipolar neurons have a long single process called an axon and several branched extensions called dendrites. The dendrites receive stimuli from other nerves or from a receptor organ, such as the skin or ear, and transmit them through the neuron to the axon. The axon conducts the impulses to the dendrite of another neuron or to an effector organ that is thereby stimulated into action.
Many processes are covered with a layer of lipid material called myelin. Peripheral nerve fibers have a thin outer covering called the neurilemma.

adrenergic neuron
nerve cells which secrete norepinephrine as a neurotransmitter; they are mostly sympathetic postganglionic nerves plus some within specific brainstem foci.
association neuron
see internuncial neuron (below).
cholinergic neuron
nerves which synthesize the neurotransmitter acetylcholine in their terminals; they include α-motor neurons of the spinal cord, cranial nerves innervating skeletal muscle, preganglionic sympathetic and postganglionic parasympathetic neurons.
internuncial neuron
neurons found in the brain and spinal cord that conduct impulses between neurons such as from afferent to efferent neurons. Called also association neurons or interneurons.
Golgi n's
lower motor n's
see lower motor neuron.
motor neuron
neurosecretory neuron
neurons of the hypothalamus that receive nervous impulses from higher centers and translate them into the regulation of hormone secretion.
nonadrenergic-noncholinergic (NANC) n's
release nitric oxide as a neurotransmitter.
parvicellular neuron
in the hypothalamus; regulate the secretion of adenohypophyseal hormones via releasing and inhibiting factors.
postganglionic n's
neurons whose cell bodies lie in the autonomic ganglia and which relay impulses beyond the ganglia to the effector organ.
preganglionic n's
neurons whose cell bodies lie in the central nervous system and whose efferent fibers terminate in the autonomic ganglia.
neuron transmission
the transmission of impulses along axons by means of electrical impulses and across synapses by neurotransmitters, especially norepinephrine and acetylcholine.
upper motor n's
see upper motor neuron.
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