| nervous system, autonomic | Part of the nervous system once thought functionally independent of the brain. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: (1) the sympathetic nervous system, which accelerates the heart rate, constricts blood vessels, and raises blood pressure; and (2) the parasympathetic nervous system, which slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. (12 Dec 1998) |
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| neuropathies, hereditary sensory and autonomic | A group of inherited disorders in which there is selective involvement of the peripheral sensory and autonomic neurons and degeneration of fibres by axonal atrophy and degeneration. Five types of disorders have been described and classified type I through type v. (12 Dec 1998) |
| accelerator fibres | Postganglionic sympathetic nerve fibre's originating in the superior, middle, and inferior cervical ganglia of the sympathetic trunk, conveying nervous impulses to the heart that increase the rapidity and force of the cardiac pulsations. Synonym: augmentor fibres. (05 Mar 2000) |
| adrenergic fibres | Nerve fibres liberating catecholamines at a synapse after an impulse. (12 Dec 1998) |
| afferent fibres | Those that convey impulses to a ganglion or to a nerve centre in the brain or spinal cord. (05 Mar 2000) |
| A fibres | Myelinated nerve fibre's in somatic nerves, measuring 1 to 22 um in diameter, conducting nerve impulses at a rate of 6 to 120 m/sec. (05 Mar 2000) |
| alpha fibres | Large somatic motor or proprioceptive nerve fibre's conducting impulses at rates near 100 m/sec. (05 Mar 2000) |
| anastomosing fibres | Anastomotic fibres, individual fibre's passing from one nerve trunk or muscle bundle to another. (05 Mar 2000) |
| arcuate fibres | Nervous or tendinous fibre's passing in the form of an arch from one part to another. See: arcuate fibres of cerebrum, external arcuate fibres, internal arcuate fibres. (05 Mar 2000) |
| arcuate fibres of cerebrum | Short association fibres that connect adjacent gyri in the cerebral cortex. Synonym: fibrae arcuatae cerebri. (05 Mar 2000) |
| association fibres | Nerve fibre's interconnecting subdivisions of the cerebral cortex of the same hemisphere or different segments of the spinal cord on the same side. Synonym: endogenous fibres, intrinsic fibres. (05 Mar 2000) |
| astral fibres | Fibre's (fibrils) radiating from the centrosphere toward the periphery of the cell as seen with a light microscope; revealed as microtubules under the electron microscope. Compare: kinetochore fibres, polar fibres. (05 Mar 2000) |
| augmentor fibres | Postganglionic sympathetic nerve fibre's originating in the superior, middle, and inferior cervical ganglia of the sympathetic trunk, conveying nervous impulses to the heart that increase the rapidity and force of the cardiac pulsations. Synonym: augmentor fibres. (05 Mar 2000) |
| Bergmann's fibres | Filamentous glia fibre's traversing the cerebellar cortex perpendicular to the surface. (05 Mar 2000) |
| beta fibres | Nerve fibre's having conduction velocities of about 40 m/sec. (05 Mar 2000) |