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Autonomic Nervous System Constitutes efferent division of visceral part of peripheral nerves Exclusively motor system controlling activity of cardiac muscles smooth muscles and glands Maintains stable internal environment by regulating circulation, respiration, digestion and other functions not under conscious control The motor neuron of somatic NS has one neuron linkage while ANS has two neuron linkages

Anatomical Difference b/w the Somatic and Autonomic Nervous system Motor neuron of somatic nervous system as one neuron linkage up to the effector organ CNS  Effector organs Motor neuron of the autonomic nervous system has two neuron linkage up to the effector organ (Viscera) CNS  Preganglionic fiber (Myelineated)  ganglion  post ganglionic fiber (unmyelieneated)  effector organ

Autonomic Nervous System Divisions Sympathetic nervous system Parasympathetic nervous system Neurons Preganglionic Postganglionic

Sympathetic Nervous System Cell bodies of preganglionic nerve fiber is located in lateral grey horn of the spinal cord Involves all thoracic and 2 – 3 lumbar segments of the spinal cord (thoraco lumbar) The myelinated axons of preganglionic neurons emerge from the ventral roots of all thoracic and first 2 or 3 lumbar spinal nerves Axons leave the spinal nerve as a small filament called white ramus communicans and enter the paravertebral sympathetic ganglion

Sympathetic Trunk Series of ganglion present bilaterally along vertebral column Bilateral sympathetic trunks extend from level of first cervical vertebrae to the tip of coccyx Series of ganglion is connected by intervening fibers On entering the sympathetic ganglion, preganglionic fiber (WRC) may take one of the following route

Course of preganglionic fiber 1. Synapse with a post ganglionic neuron in the ganglion at that level 2. Pass up or down to a different level of the sympathetic trunk before synapsing with a post ganglionic neuron 3. The pre ganglionic fiber may traverse the sympathetic chain ganglia without synapsing and leave as splanchnic nerve to synapse with post ganglionic neuron in pre-vertebral ganglion or adrenal medullae

Route of post ganglionic neuron Axons of post ganglionic neurons may pass directly to the effector organ (heart or lungs) Most post ganglionic axons return to spinal nerve as grey rami communicantes and are distributed to effector organ through spinal nerve (sweat glands, smooth muscles of the blood vessels, etc.) Post ganglionic fibers from the cervical sympathetic ganglion form plexus upon the walls of major blood vessels of the neck

Sympathetic chain ganglia

Pre-vertebral sympathetic ganglia Located adjacent to the ventral branches of the Aorta Named after these arteries (celiac, superior mesenteric and inferior mesenteric The post ganglionic fibers from the neurons in these ganglia form plexus around a/m arteries Extended along the vessels these fibers innervate the viscera in the abdominal and pelvic regions

Parasympathetic Nervous System Organized on the basis of preganglionic and post ganglionic neurons Preganglionic neurons constitutes parts of the nuclei of certain cranial nerves (III, VII, IX and X) Also lie in the lateral grey horn of the sacral segments of the spinal cord (Craniosacral) Preganglionic axons emerge as part of cranial nerve or component of ventral route of a sacral nerve

Course of parasympathetic neuron Preganglionic axons leave the nerve and end in ganglia containing cell body of post ganglionic neuron Parasympathetic ganglion are irregularly spaced and widely scattered Parasympathetic ganglion are located very close to the organs which they innervate Cranial parasympathetic preganglionic fibers emerge from the brain stem through cranial nerves

Course of parasympathetic neuron Preganglionic fiber emerge through oculomotor, facial, glossopharyngeal, and vagus nerves Preganglionic fibers from III, VII, and IX CN end by synapsing with post ganglionic neurons in four large parasympathetic ganglia The pre ganglionic fibers of the vagus nerve go beyond the head region to synapse with post ganglionic cell bodies in ganglia adjacent or in the walls of viscera (heart, lungs, stomach and intestine)

Course of the sacral parasympathetic outflow The preganglionic fibers from the sacral part leave the SC through ventral routes of the 3 rd and 4 th sacral nerves From the spinal nerves the separate as pelvic splanchnic nerve Post ganglionic parasympathetic ganglion are located on the surface or in the substance of visceral organ being supplied (lower large intestine, sphincter muscles of the urinary bladder and urethra etc.

Cranial parasympathetic ganglia Ciliary ganglion Oculomotor  Orbit  ciliary muscles and constricter pupili Pterygopalatine ganglion Facial nerves  Pterygopalatine fossa  lacrimal glands, glands of nose, nasopharynx, paranasal sinuses Submandibular ganglion Facial nerve  Submandibular region  submandibular and sublingual salivary glands Otic ganglion glasopharyngal  Infratemporal fossa  parotid salivary glands

Functions of autonomic nervous system

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