Autonomic Nervous System Autonomic Nervous System

Dr. Zeenat Zaidi

OBJECTIVESOBJECTIVES

At the end of the lecture, students should be able At the end of the lecture, students should be able to:to:

Define the autonomic nervous system.Define the autonomic nervous system. Describe the structure of autonomic nervous Describe the structure of autonomic nervous

systemsystem Trace the preganglionic & postganglionic Trace the preganglionic & postganglionic

neurons in both sympathetic & parasympathetic neurons in both sympathetic & parasympathetic nervous system.nervous system.

Enumerate in brief the main effects of Enumerate in brief the main effects of sympathetic & parasympathetic systemsympathetic & parasympathetic system

Autonomic Nervous SystemAutonomic Nervous System

Concerned with the innervation and control of Concerned with the innervation and control of involuntary structures: visceral organsinvoluntary structures: visceral organs, , smooth & cardiac musclessmooth & cardiac muscles and and glandsglandsAlong with the endocrine system, its primary Along with the endocrine system, its primary functionfunction is is homeostasis of the internal homeostasis of the internal environmentenvironment

LocatedLocated both in the both in the central and peripheral central and peripheral nervous system. nervous system.

Regulated (controlled)Regulated (controlled) by by hypothalamushypothalamus..

Unlike the somatic nervous system, the Unlike the somatic nervous system, the efferentefferent pathway of the pathway of the autonomic nervoussystem is made up of two neurones called autonomic nervoussystem is made up of two neurones called as as preganglionicpreganglionic and and postganglionicpostganglionic neurons neurons

The cell bodies of the The cell bodies of the preganglionicpreganglionic neurons are located in the neurons are located in the brain and spinal cordbrain and spinal cord. Their axons synapse with the . Their axons synapse with the postganglionicpostganglionic neurons whose cell bodies are located in the neurons whose cell bodies are located in the

autonomic ganglautonomic ganglia ia

Autonomic Nervous SystemAutonomic Nervous System

Based on the Based on the anatomicalanatomical, , physiologicalphysiological and and pharmacologicalpharmacological characteristics, characteristics, the autonomic nervous system is the autonomic nervous system is divided into:divided into: SympatheticSympathetic: : Activated Activated

during exercise, excitement, during exercise, excitement, and emergencies. and emergencies. “fight, flight, “fight, flight, or fright”or fright”

ParasympatheticParasympathetic: : Concerned Concerned with conserving energy. with conserving energy. “rest “rest and digest”and digest”

Both divisions operate in conjunction with one another (have antagonistic control over the viscera) to maintain a stable

internal environment

Target organTarget organ

Preganglionic neuron

Postganglionic fiber

Ganglion

Postganglionic neuron

Pretganglionic fiberShort

Short

Long

Long

Parsympathetic Sympathetic

Preganglionic Preganglionic neurons: neurons: located in located in the the lateral gray hornlateral gray horn of of TT11-L-L22 segments of segments of

spinal cord spinal cord ((Thoracolumbar Thoracolumbar outflowoutflow))

Sympathetic DivisionSympathetic Division

Sympathetic GangliaSympathetic Ganglia

Located nearer the central nervous system as: Located nearer the central nervous system as: • Prevertebral: Prevertebral: celiac & mesentericceliac & mesenteric• Paravertebral Paravertebral forming sympathetic chainforming sympathetic chain

Paravertebral GangliaParavertebral Ganglia They are interconnected to They are interconnected to

form 2 form 2 sympathetic chainssympathetic chains, , one on each side of vertebral one on each side of vertebral column.column.

Number of ganglia:Number of ganglia:• ThreeThree in in cervicalcervical part of chain part of chain• Eleven to twelve Eleven to twelve in thoracic in thoracic

partpart• FourFour in in lumbar & sacral lumbar & sacral parts parts

each.each. The chains end into a The chains end into a

common common ‘ganglion impar’ ‘ganglion impar’ in in front of coccyxfront of coccyx

Run in the ventral Run in the ventral roots of the spinal roots of the spinal nervenerve

Travel through the Travel through the spinal nerve, spinal nerve, and and then join the then join the sympathetic chain sympathetic chain via the via the white rami white rami communicans.communicans. (WRC)(WRC)

Preganglionic fibersPreganglionic fibers

Within the sympathetic chain, these fibers may:

1. Ascend, descend or remain at the same level to synapse with neurons (postganglionic) of paravertebral ganglia located in sympathetic chain.

2. Leave the sympathetic chain (without synapse) without synapse) to reach coeliac & mesenteric ganglia (around branches of abdominal aorta) to synapse with their neurons (postganglionic).

From the sympathetic From the sympathetic chain ganglia chain ganglia enter back enter back into the spinal nerve into the spinal nerve throughthrough grey rami grey rami communicantes (GRC)communicantes (GRC) to supply structures in head & thorax + blood vessels & sweat glands

From the cells of coeliac & mesenteric ganglia supply abdominal & pelvic viscera.

Postganglionic fibersPostganglionic fibers

Preganglionic neuronsPreganglionic neurons

Located in:Located in:

Nuclei of the Nuclei of the 33rdrd, 7, 7thth, , 99thth & 10 & 10thth cranial cranial nerves, nerves, in the brain in the brain stem (stem (Cranial outflowCranial outflow))

&&

The The lateral gray horn lateral gray horn of of SS22-S-S44 segments of segments of

spinal cord (spinal cord (Sacral Sacral outflowoutflow))

Parasympathetic DivisionParasympathetic Division

Preganglionic fibersPreganglionic fibers from from cranial outflow cranial outflow are are carried by carried by 33rdrd, 7, 7thth, 9, 9thth & & 1010thth cranial nerves cranial nerves and and terminate in terminate in ciliary, ciliary, pterygopalatine, pterygopalatine, submandibular, otic & submandibular, otic & peripheral ganglia peripheral ganglia

Postganglionic fibers Postganglionic fibers innervate organs of the innervate organs of the head, neck, thorax, and head, neck, thorax, and abdomenabdomen

Parasympathetic DivisionParasympathetic Division

Preganglionic fibersPreganglionic fibers from from sacral outflow sacral outflow are are carried by carried by pelvic pelvic splanchnic nerves splanchnic nerves to to peripheral ganglia in peripheral ganglia in pelvis where they pelvis where they synapse. synapse.

Postganglionic fibers Postganglionic fibers innervate organs of the innervate organs of the pelvis and lower pelvis and lower abdomenabdomen

Parasympathetic DivisionParasympathetic Division