Nerve Fibers
| Definition: |
Slender processes of NEURONS, including the AXONS and their glial envelopes (MYELIN SHEATH). Nerve fibers conduct nerve impulses to and from the central nervous system. |
| Notes: |
do not confuse X ref MOSSY FIBERS, CEREBELLAR with MOSSY FIBERS, HIPPOCAMPAL |
| Also Called: |
Cerebellar Mossy Fibers |
| Previously Indexed: |
Nerve Fibers, Myelinated (1969-1976),Neurons (1966-1976) |
Nerve Fibers Categories.
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Adrenergic Fibers - Nerve fibers liberating catecholamines at a synapse after an impulse. |
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Autonomic Fibers, Postganglionic - Nerve fibers which project from cell bodies of autonomic ganglia to synapses on target organs. |
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Autonomic Fibers, Preganglionic - Nerve fibers which project from the central nervous system to autonomic ganglia. In the sympathetic division most preganglionic fibers originate with neurons in the intermediolateral column of the spinal cord, exit via ventral roots from upper thoracic through lower lumbar segments, and project to the paravertebral ganglia; there they either terminate in synapses or continue through the splanchnic nerves to the prevertebral ganglia. In the parasympathetic division the fibers originate in neurons of the brain stem and sacral spinal cord. In both divisions the principal transmitter is acetylcholine but peptide cotransmitters may also be released. |
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Axons - Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. |
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Cholinergic Fibers - Nerve fibers liberating acetylcholine at the synapse after an impulse. |
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Nerve Fibers, Myelinated - A class of nerve fibers as defined by their structure, specifically the nerve sheath arrangement. The AXONS of the myelinated nerve fibers are completely encased in a MYELIN SHEATH. They are fibers of relatively large and varied diameters. Their NEURAL CONDUCTION rates are faster than those of the unmyelinated nerve fibers (NERVE FIBERS, UNMYELINATED). Myelinated nerve fibers are present in somatic and autonomic nerves. |
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Nerve Fibers, Unmyelinated - A class of nerve fibers as defined by their structure, specifically the nerve sheath arrangement. The AXONS of the unmyelinated nerve fibers are small. The axons to SCHWANN CELLS ratio is greater in the unmyelinated nerve fibers than that in the myelinated fiber (NERVE FIBERS, MYELINATED) which is 1:1. Usually several axons are surrounded by a single Schwann cell in the unmyelinated nerve fibers. Therefore, each unmyelinated fiber is not completely covered by the MYELIN SHEATH formed by the Schwann cell. Unmyelinated nerve fibers conduct impulses at low velocities. They represent the majority of peripheral sensory and autonomic fibers. They are also found in the spinal cord and brain. |
Nerve Fibers Definitions and Terms
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