autonomic nervous system

in simple animal autonomic fibers directly originate the segmentally arranged nerve cord and travel to the visceral organ as like peripheral nerves. In higher vertebrate and mammals, there are postganglionic ganglia in the periphery near to the inervated organ. Autonomic nerves innervate involuntary internal organs of the body.

After they emerge from spinal cord, it relays on a ganglia and the postganglionic fibers goes to the organ. When the autonomic nerves of a smooth muscle are cut, the smooth muscle continue to contruct and no athropy seen. But somatic nerve is destroyed, atrophy occur in the innervated organ. Autonomic nervous system is divided into two functional branches: the parasymphatetic branch and symphatetic branch. The preganglionic fibers of the parasymphatetic system exit the central nervous and synapse at the peripheral organs. Nervous system

The preganglionic fibers of symphatetic nerves leave the spinal cord via throracic and lumbar spinal nerves and synaplse on to the ganglia close to the spinal cord or synapse in more peripheral sympathetic ganglia. The symphatetic and parasymphatetic systems have antoganistic actions. In general the symphatetic nervous system preparres the body for response to stressful or dangerous situations; it initiates the fight of flight reactions, elevation of heart rate and increased force of contruction, peripheral vasoconstriction, and sweating.

In contrast, the parasymphatetic nervous system controls general bodily functions such as digestion. The neurotransmitter of postganglionic parasymphatetic synapse is acetylcholine, so the postsynaptyic receptors of these synapses are cholinergic.. http://nervous-system-info.blogspot.com/

The neurotransmitter of the symphatetic postganglionic synapse is usually norepinephrine, so there are adrenergic. The symphatetic neurotransmitter is epinephrine rather than norepinephrine rather than norepnephrine in some vertebrates. The neurotransmitter at the preganglionic synapse of both the parasymphatetic and symphatetic branches is acetylcholine.http://nervous-system-info.blogspot.com/