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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 ?
The findings of AF Dixon (17) in 1896 that the DSN had cutaneous branches that innervated the skin in the mid-scapular area suggests a possible direct link of NP and DSN neuropathy.
As expected, neuron B19 innervated the Slrt muscles, and similar patterns of connectivity were present in both ipsilateral and contralateral muscle bundles (Fig.
First, the bulk of the muscle is made of extrafusal fibers (synonymous with skeletal muscle fiber), which are innervated by alpha motor neurons; when extrafusal fibers contract, the muscle shortens.
This arrangement may account for clinical observations that focal upper midbrain lesions can cause palsies of just one or a few muscles innervated by the 3rd nerve.
In this way, alterations in RSNA directly influence the function of these innervated renal effector units.
The Pubococcygeus muscle (Pc) is located in the pelvic floor of both males and females, and it is innervated by the somatomotor branch of the pelvic nerve, which originates between the sixth lumbar and the first sacral segments of the spinal cord in rats.
Two-page spreads on outcomes contain information on key innervated muscles, available muscle actions, and functional medical, daily living, mobility, and vocation outcomes, as well as prognosis.
The pupils are innervated by most areas of the brain involved in depression.
While the levator palpebrae superioris and superior rectus muscles were innervated by the upper branch, the medial rectus, the inferior rectus, and the inferior oblique muscles were innervated by the lower branch (2-4).
Golgi ligament receptors are innervated by group I large axons, (2) but not by Ib axons.
Pribyl & Moneim (1994) have reported a case where an anomalous muscle originated on the flexor carpi ulnaris muscle, it was innervated by ulnar nerve, and it joined the flexor digiti minimi muscle distally.