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central nervous system
Значение термина central nervous system в knolik
central nervous system - CENTRAL NERVOUS SYSTEM (CNS)
central nervous system - A mass of nervous tissue which co-ordinates the activities of an animal. In vertebrates the Central Nervous System is the brain and spinal cord, which together are basically a single hollow tube with very thick walls, enclosed within skull and backbone. In most invertebrates the Central Nervous System consists of a few solid cords of nervous tissue, often associated with larger masses called ganglia. In some invertebrates however (Coelenterata, Echinodermata) the place of a Central Nervous System in providing co-ordination is taken by a diffuse nerve-net.
The Central Nervous System is in a position to co-ordinate the activities of an animal with each other and with the environment because almost all the messages (impulses) sent from the sense-organs travel straight into the Central Nervous System, and almost all impulses received by the muscles, glands, etc., come out from the Central Nervous System. The Central Nervous System contains many fairly direct nervous pathways between certain sense-organs and certain muscles or glands (See also: Reflex) which ensure that some stimuli are followed rapidly by their appropriate standardized responses. But there is also great opportunity in the Central Nervous System for coordination of a variety of stimuli by interaction between nerve cells, because of the large number of junctions (synapses) between nerve cells which occur there. In vertebrates for instance, the great majority of synapses occurs in the Central Nervous System. The Central Nervous System., however, is not to be regarded simply as a means of reconciling and coordinating the immediate activities of the sense-organs; it has an activity of its own independent of the stimuli of the moment, most obvious in the influence of past experience on present performance. The rest of the nervous system, other than the Central Nervous System, is the peripheral nervous system. See also: Nervous System, Nerve-cell.
Рядом со словом central nervous system в knolik
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