The body system that gathers and stores information and is in overall control of the body. The brain and spinal cord form the central nervous system (CNS), which consists of billions of interconnected neurons (nerve cells). Input of information to the CNS comes from the sense organs. Motor instructions are sent out to skeletal muscles, the muscles controlling speech, internal organs and glands, and the sweat glands in the skin. This information is carried along nerves that fan out from the CNS to the entire body. Each nerve is a bundle consisting of the axons (filamentous projections) of many individual neurons. In addition to the nervous system’s anatomical divisions, there are various functional divisions. Two of the most important are the autonomic nervous system, concerned with the automatic (unconscious) regulation of internal body functioning, and the somatic nervous system, which controls the muscles responsible for voluntary movement. The overall function of the nervous system is to gather and analyse information about the external environment and the body’s internal state, and to initiate appropriate responses, such as avoiding physical danger. The nervous system functions largely through automatic responses to stimuli (see reflex), although voluntary actions can also be initiated through the activity of higher, conscious areas of the brain. Disorders of the nervous system may result from damage to or dysfunction of its component parts (see brain; spinal cord; neuropathy; nerve injury). They may also be due to impairment of sensory, analytical, or memory functions (see vision, disorders of; deafness; numbness; anosmia; agnosia; amnesia), or of motor functions (see aphasia; dysarthria; ataxia).
Nervous system |
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