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Sympathetic nervous system |
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sympathetic nervous system: see nervous system nervous system, network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system. ..... Click the link for more information. . 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 ) The visceral reflex arc and the sympathetic chain How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| There might also be impingement of the plexus of the carotid sheath that produces irritation of the sympathetic nerves. However, the time constant for activation of sympathetic fibers[18,29,30] and for vasoconstriction following direct stimulation of sympathetic nerves is known to be less than 10 seconds. The results of these studies may explain the efficacy of beta-blockers, drugs that block the activity of sympathetic nerves, in the prevention of sudden cardiac death," Chen says. |
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Sympathetic nerves
