Gesamtheit des Nervengewebes in seiner funktionalen Vernetzung. Nach Lage im Körper wird das Gehirn und das Rückenmark als zentrales N. zusammengefaßt und vom peripheren N. unterschieden, das die zu den einzelnen Organen und Geweben verlaufenden Nerven (z.N. Ischiasnerv) umfaßt. Nach Funktionen trennt man das autonome oder vegetative N. (z.B. Darm- oder Bronchialmuskulatur) mit Sympathikus und Parasympathikus vom animal. oder willkürl. N. z.B. des Bewegungsapparats.
The sensory and control apparatus consisting of a network of nerve cells.
The system of interconnected nerve cells of most invertebrates and all vertebrates. It is composed of the central and autonomic nervous systems. It may be as simple as the nerve net of coelenterates (for example, jellyfishes) or as complex as the mammalian nervous system, with a central nervous system comprising brain and spinal chord and a peripheral nervous system connecting up with sensory organs, muscles, and glands.
human nervous system
The human nervous system represents the product of millions of years of evolution, particularly in the degree of encephalization or brain complexity. It can be divided into central and peripheral parts for descriptive purposes, although there is both anatomical and functional continuity between the two parts. The central nervous system consists of the brain and the spinal cord. The peripheral nervous system is not so clearly subdivided, but its anatomical parts are: (1) the spinal nerves; (2) the cranial nerves; and (3) the autonomic nervous system.
positioning of the nervous system
In the simplest nervous system, found in the coelenterates, certain sensory cells on the surface send signals to deeper muscle cells or glands either directly or via a diffuse network of interconnected nerve cells. A diffuse nervous system lying quite superficially is common to all coelenterates, and it is only in the flatworms that a head ganglion develops which receives information from specialized rather than nonspecific sensory cells. In the higher invertebrates, the diffuse nerve net becomes condensed into longitudinal pathways which lead to the head ganglion. In addition the nervous system retreats from its superficial plane and comes to lie beneath the body musculature; this evolutionary migration of the nervous system is reflected in the development of the human nervous system which is derived from ectodermal (skin) layers of the embryo. In higher animals the sensory cells themselves come to lie close to the central nerve cord and maintain their connection with the skin by fibers with specialized nerv
e endings. In vertebrates, the cephalic or head end of the nervous system undergoes relative expansion to form the brain, which integrates the information received from the multitude of sensory cells via the dorsal nervous trunk or spinal cord.