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see nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
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the cordlike association of nerve tissues that links the brain and nerve ganglia by innervation to the other organs and tissues of the body.

A nerve primarily consists of nerve fibers. In vertebrates many nerves converge to form a bundle that is surrounded by a connective tissue sheath, the perineurium; the thin interstitial layers of connective tissue that separate the individual fibers deep within the bundle constitute the endoneurium. Finally, the entire nerve trunk, comprising several bundles, is covered by an additional sheath, the epineurium.

Nerves can be sensory (also called afferent or centripetal) or motor (also called efferent or centrifugal). Some nerves, for example, those innervating the skeletal muscles, mainly include myelinated, or medullated, fibers; others, for example, the sympathetic nerves, largely consist of unmyelinated, or unmedullated, fibers.

In reptiles, birds, mammals, and man 12 pairs of cranial nerves branch from the brain: the olfactory (cranial nerve I), the optic (cranial nerve II), the oculomotor (cranial nerve III), the trochlear (cranial nerve IV), the trigeminal (cranial nerve V), the abducent (cranial nerve VI), the facial (cranial nerve VII), the acoustic (cranial nerve VIII), the glossopharyngeal (cranial nerve IX), the vagus (cranial nerve X), the accessory (cranial nerve XI), and the hypoglossal (cranial nerve XII). Only the first ten pairs are present in fish and amphibians.

In man there are 31 pairs of spinal nerves: eight cervical, 12 thoracic, five lumbar, five sacral, and one coccygeal. Each pair innervates the effectors and receptors of a certain part of the body. The spinal nerves branch from the spinal cord into two roots—the posterior, or sensory, and the anterior, or motor. Both roots then combine to form a common trunk that consists of both sensory and motor fibers.

Several adjacent nerves can be combined into nerve plexuses, where an exchange of fibers between different nerves can take place. Three large plexuses are distinguished: the cervical, the brachial, and the lumbosacral. Each nerve plexus is the origin of several pairs of nerves; for example, the sacral portion of the lumbosacral plexus gives rise to the sciatic nerves.

Nerves that originate in the ganglia, trunks, and plexuses of the autonomic nervous system constitute a specific group. The optic nerve is remarkable for its large number of fibers; there are more than 1 million in the human optic nerve. Usually, however, there are 103 -104 fibers in a nerve. In invertebrates certain nerves are known to consist of only a few fibers. The peripheral nervous system in animals and man consists of aggregations of nerves.



A bundle of nerve fibers or processes held together by connective tissue.


Any one of the ribs of a groined vault, but esp. a rib which forms one of the sides of a compartment of the groining.


1. any of the cordlike bundles of fibres that conduct sensory or motor impulses between the brain or spinal cord and another part of the body
2. a large vein in a leaf
3. any of the veins of an insect's wing
References in periodicals archive ?
Fernandez-Garza, "Molecular inflammatory mediators in peripheral nerve degeneration and regeneration," Neuroimmunomodulation, vol.
[H.sub.2]S in Peripheral Nerve Degeneration. Based on the degrees of damage in the nerve and surrounding connective tissue, peripheral nerve damage may be classified as neurapraxia, axonotmesis, and neurotmesis, with the latter being a severe type of peripheral nerve injury [86].
The company says the grant will be used to create neural stem cell therapies to restore lost vision in patients with retinal and optic nerve degeneration to improve patient quality of life.
Experiments show that similar genetic variations leave mice vulnerable to the sort of nerve degeneration seen in ALS patients, says Peter Carmeliet of Leuven University in Belgium.
Studies from the Ageing Gerontology Research Center in Baltimore, Maryland, have shown that a diet high in folate lowers your risk of Parkinson's disease which leads to nerve degeneration as we age.
This effort is the likely cause of nerve degeneration and dementia associated with the disease.
Transient ischemia (reduced blood supply) in the vertebrobasilar arterial system often causes episodic vertigo in elderly patients (Baloh, 1996b) and recurrent ischemia could be expected to result in both hair cell and vestibular nerve degeneration. However, vertebrobasilar insufficiency is usually associated with vertigo of abrupt onset and both nausea and vomiting; therefore, the severity of the symptoms would normally result in the patient seeking medical advice.
Adding insult to injury: cochlear nerve degeneration after "temporary" noise-induced hearing loss.
While there are 12 FDA-approved disease-modifying treatments for relapsing MS, these agents work primarily by reducing inflammation in the central nervous system and don't work as well in progressive MS, whose hallmark is nerve degeneration rather than inflammation.
Researchers from Monash University also found a way to block MS nerve degeneration; and Adelaide University is investigating a possible new way of controlling the immune system in MS, Ms Plibersek said.