AUTONOMIC NERVOUS SYSTEM ::
Autonomic nervous system (ANS) acts involuntarily without arousing consciousness unless it is disturbed it governs the activity of the body s visceral organs e.g maintenance of blood pressure secretion of glands activity of the cardiac and smooth muscle it is although independent of the CNS it is connected by afferent and efferent nerves with the CNS (hypothalamus in particular ) ANS differs from the somatic nervous system (SNS) as follows ::
1.ANS is supplied to all the organs except the skeletal muscles which are supplied with SNS
2.Synapses of autonomic nerves lie in the ganglia which lie outside the cerebrospinal axis whereas the synapses of SNS lie within the CNS
3.Autonomic nerves form extensive plexuses whereas somatic nerves form limited plexuses
4. All fibres of SNS are myelinated whereas only preganglionic fibres of ANS are nonmyelinated
5.ANS has regulatory role on the activity of the organs it supplies and it is involuntary in nature the organs supplied with ANS usually possess their own inherent activity whereas the skeletal muscles upplied with SNS contract only if there is voluntary stimulation of the nerves Interruption of the nerve supply to the organs supplied through ANS can only alter functions of the organs
Parasympathetic division of ANS is refered as Cranio-sacral as it is formed by III (Oculomotor) VII (Facial) IX (Glassopharyngeal) and X (Vagus ) cranial nerves and third to fifth sacral (spinal) nerves
ANS has two divisions ::
1.Parasympathetic 2.Sympathetic Anatomically
Sympathetic division of ANS is refered as Thoracico lumbar as it is formed by all the twelve thoracic nerves and the first three lumbar nerves
Each autonomic nerve consists of a ganglion the preganglionic nerve fibre and postganglionic nerve fibre which innervates the organ Ganglia of parasympathetic division lie close to or within the organ supplied whereas the ganglia of the sympathetic division lie near the spinal cord or in otherwords aways from the organ supplied hence the preganglionic nerve fibres of parasympathetic division are longer than the postaganglionic nerve fibres however in sympathetic divission the preganglionic nerve fibres are shorter than the postaganglionic fibres
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