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sympathetic nervous system [‚sim·pə′thed·ik ′nər·vəs ‚sis·təm]
Sympathetic nervous system
The portion of the autonomic nervous system concerned with nonvolitional preparation of the organism for emergency situations. See Autonomic nervous system
The sympathetic nervous system is best understood in mammals. It consists of two neuron chains from the thoracic and lumbar regions of the spinal cord to viscera and blood vessels. The first or preganglionic neuron has its cell body in the spinal cord and sends its axon to synapse with a postganglionic sympathetic neuron, which lies either in a chain of sympathetic ganglia paralleling the spinal cord or in a sympathetic ganglion near the base of the large blood vessels vascularizing the alimentary viscera. The postganglionic axons are longer than the preganglionic axons and extend to glands or smooth muscles of viscera and blood vessels. Sensory visceral nerve fibers innervate blood vessels and viscera and carry sensory information to the spinal cord, thus providing a visceral reflex (see illustration). See Nervous system (vertebrate) See Parasympathetic nervous system
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