Nerve

When a nerve (. . Latin nervus, abbreviation N., plural nervi, abbreviation Nn, from Greek νεῦρον neuron what "thread", " chord " or " string " means ) is parallel nerve fibers ( cell processes: Axons and dendrites ) with a connective tissue sheath. Nerves are part of the peripheral nervous system and are used to exchange information in the animal organism.

Construction

Each of a nerve axons are surrounded by a connective tissue sheath, which is referred to as the endoneurium. Several axons to nerve fiber bundles, called fascicles, summarized, in turn, of connective tissue ( perineurium ) are covered. The connective tissue around the entire nerve is called the epineurium.

In non- peripheral nerve such as the optic nerve, the outer shell is formed from the meninges. Here the dura mater forms the epineurium; also arachnoid and pia and subarachnoid space surround the optic nerve and form Peri - and endoneurium.

Subdivision

After the origin of the nerves in vertebrates spinal nerves that exit the central nervous system (CNS ) in the area of the spinal cord, and cranial nerves that originate from the brain distinguished. In the area of ​​limbs origins form the spinal nerve plexuses ( brachial plexus ), lumbosacral plexus ), in which the units of various spinal nerves intermingle and form to Plexusnerven.

Following the direction of the excitation line afferents can be distinguished ( in the periphery of the CNS ) ( the central nervous system through ) and efferent fibers. The afferents conduct sensitive or sensory information, so be at the service of perception of internal and external stimuli. The efferent fibers conduct motor or secretory impulses. After the target area, the afferent and efferent nerves are further into somatic ( nerves of the body wall; soma of Greek σῶμα, body ') and visceral ( nerves of the viscera, from Latin visceral, the intestines concerning ') distinguished. Most nerves are mixed nerves, that contain both afferent and efferent projections.

On the way to their target area ( the innervation ), the nerves branch out further and further. The smaller nerve branches are called Rami ( Sg Ramus ) refers.