physiology ans

Autonomic Nervous Autonomic Nervous SystemSystem

Dr Ayyaz AhmedDr Ayyaz AhmedAP PhysiologyAP Physiology

Learning ObjectivesLearning Objectives

• O utline the functions of ANS

• Describe the functions of

Sympathetic Nervous System

All smooth muscles

All Glandular structures Myocardium

General Visceral Efferent

ANSANS

Innervates all innervated

structures in the body except

NMJ of SKM

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Part of nervous system that controls visceral functions• Cardiac muscle, smooth muscle (blood

vessels, GIT, urinary bladder etc) glands (secretions)

Not under voluntary control

Anatomy of the Motor Output in Anatomy of the Motor Output in Sympathetic and Parasympathetic Sympathetic and Parasympathetic

nervesnerves

Autonomic nervous system• Two neuron chain from CNS to effector organ• Pre and postganglionic neurons

Somatic nervous system• Single neuron connects CNS with effector

organ

Neurotransmitters Neurotransmitters involvedinvolved

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Ganglion• Cluster of neurons outside CNS• Autonomic ganglion

oSite of synapse between autonomic pre & post ganglionic fibers

oParavertebral ganglionic chainoPrevertebral (collateral) ganglia

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Cell body of preganlionic neuron• Lies in CNS

oSpinal cord (sympathetic division)oBrain and spinal cord (parasympathetic

division)

Cell body of postganglionic neuron• Lies in autonomic ganglia

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Sympathetic nervouss system• Short preganlionic fibers• Long postganglionic fibers

Parasympathetic nervous system• Long preganlionic fibers• Short postganglionic fibers

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Cholinergic fibers• Fibers releasing acetylcholine

Adrenergic fibers• Fibers releasing noradrenalin

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

All preganlionic fibers are cholinergicAll postganglionic parasympathetic

fibers are cholinergicAlmost all postganglionic

sympathetic fibers are adrenergic• postganglionic sympathetic fibers to

sweat glands and piloerector muscles are cholinergic

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Receptors• Nicotinic receptors -in autonomic ganglia• Muscarinic receptors -in effector organs

stimulated by postganglionic cholinergic fibers

• Adrenergic receptors -in effector organs stimulated by postganglionic adrenergic fibersoα adrenergic receptors (α1 and α2)oΒ adrenergic receptors (β1 and β2)

Muscarinic receptors in the parasympathetic system M1 M3, M5 M2, M5

AcetylcholineAcetylcholine

Neuroscience, Sinauer Asssoc., Inc

Neuroscience, Sinauer Asssoc., Inc

Adrenergic receptors in the sympathetic system

Norepinephrine 1 2

Norepinephrine

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Sympathetic division• Thoracolumbar (T1to L2)

Parasympathetic division• Craniosacral (III, VII, IX, X cranial nerves

& S1to S4)

Sympathetic NS

NE, EPINEPHRINE

Stimulated Inhibited

All the tissuesα1 A.R

ExceptHeart, JGA, LipocytesΒ1 A.R

All the tissuesβ2 A.R

ExceptPresynaptic Nerve EndingsPlatelets, some part of GIT

α2 AR

DP- Alpha 1 Receptors

Cilliaris- Beta 2 Receptors

Skin

Vessels StimulatedAlpha 1 Receptors

Respiratory System

Blood Vesselsα1

Bronchial secretion Decreases

Mast Cellsβ2

Bronchial Smoothβ2

Adrenal medullaStimulation of sympathetic innervation of adrenal medulla causes release of large

quantities of epinephrine (80%) and norepinephrine (20%)

Effect lasts 5-10 times longer

Sympathetic tone caused by basal secretion from adrenal medulla

(.2 µg/kg/min Epinephrine and .05 µg/kg/min of noreepineohrine

Adrenal Medulla Adrenal Medulla • Epinephrine affects

– more on beta – Less on alpha– More metabolic effect

• Adrenal medulla provides back up for sympathetic function in addition to normal channel of sympathetic nerves

Thank You

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Dual supply• All the viscera supplied by both the

divisions of ANS• Sympathovagal balance determines the

ultimate function of the viscera

Functions of ANSFunctions of ANS

Sympathetic and parasympathetic components of ANS function to maintain homeostasis at subconscious level -maintain stable internal environment

1 receptors•vascular smooth muscle, on GI and bladder sphincters and radial muscle of the eye. causes excitation (contraction)2 receptors•presynaptic nerve terminals, platelets, fat cells, walls of GI tract causes inhibition (relaxation, dilation)1 receptors•SA node, AV node, ventricular muscle of heart• produces excitation, increases heart rate, contractility, and conduction velocity2 receptors•vascular smooth muscle of skeletal muscle, bronchioles, walls of GI tract and bladder•produces relaxation: dilation of vascular smooth muscle and relaxation of bladder, bronchioles

Location of specific adrenergic receptors

Co-Transmission

Acetylcholine and Norepinephrine playimportant, but not exclusive, rolesin the autonomic nervous system

Sweat glandsSweat glands• Sympathetic fires supply them. If

stimulated copious sweating

• Acetylcholine is neurotransmiiter except palms and soles which are

adrenergic

• Overall control is parasympathetic via hypothalamus so sweating could be

called parasympathetic function

Stimulus RateStimulus Rate

• Low frequency required to fully activate ANS as compared to

Skeletal nervous system

Sympathetic and parasympathetic tone”

Continual basal activity of the sympathetic

and parasympathetic systems allows either branch

of the ANS to increase or decrease its activity

of a stimulated organ

If tone lost intrinsic compensation in some time

Denervation supersensitivity

Receptor up regulation?

Enteric Nervous SystemGastrointestinal tract nervous system

Myenteric plexus (auberbach’s)

Meissner’s plexus (submucosal)The Enteric Nervous System can function

on its own but is most often controlled by the sympathetic and parasympathetic systems

Contains more neurons than the spinal cord and usesmany different neurotransmitters and neuromodulators,

approaching the complexity of the CNS

Autonomic Reflexes

cardiovascular reflexesgastrointestinal reflexes

bladder emptyingsweating

blood glucose concentrationsexual reflexes

Alarm or Stress responseMass discharge of sympathetic system allowsthe body to make maximal use of its resourcesthereby enhancing its chances for survival•pupilary dilation•increase heart rate and strength of contraction•increase blood pressure•increase blood flow to active muscles•increase rates of metabolism•increased blood glucose concentration•increased muscle strength•increase mental activity

Exceptions of isolated Exceptions of isolated Function in Function in SympatheicSympatheic

• SWEATING• Muscle activiy in animals• Local reflexes (skin heat)• Many GIT reflexes

Parasympathetic System Usually CausesParasympathetic System Usually Causesspecific localized responsesspecific localized responses

Parasympathetic cardiovascular reflexes usuallyact only on the heart to control its rate of beating

Examples:Examples:

Stimulation of secretion in mouth while notaffecting stomach, although sometimes they occurtogether

In Contrast……...

Hypothalamus is criticalfor coordinating autonomicoutput.It projects to several brainstem nuclei and coordinates autonomic function with feeding, thermoreg.,water balance, circadium rhythm, sex drive, etc., and thus plays a dominant role in integrating higher cortical areas and autonomic function.panic attacks, emotional stress,

cognitive activity

Medullary, pontine and mesencephalic Medullary, pontine and mesencephalic control of ANS and their supervision by control of ANS and their supervision by

HYPOTHALAMUSHYPOTHALAMUS

Functions of ANSFunctions of ANSSympathetic nervous system

• Prepares and mobilizes the body in emergency (fright, fear, pain, rage etc)

• Fight or flight reaction

Functions of ANSFunctions of ANSParasympathetic nervous system

• Conserves and stores energy -puts the body in cool and calm state

Functions of ANSFunctions of ANSSympathetic Parasympathetic

Heart↑ heart rate↑ force of contraction

Heart↓ heart rate↓force of contraction

Blood vesselsConstriction

Blood vesselsNo effect

LungsBronchodilation

LungsBronchoconstriction

GIT↓ motilitySphincter contractionDecreased secretions

GIT↑ motilitySphincter relaxationIncreased secretions

Functions of ANSFunctions of ANSSympathetic Parasympathetic

Salivary glands

Stimulates secretionSalivary glands

Stimulates secretionSweat glands

Copious secretionSweat glands

Sweating on palms onlyEye

Papillary dilationFlattening of lens

EyePapillary constrictionThickening of lens

Urinary bladderRelaxation of bladder wallSphincter contraction

Urinary bladderContraction of bladder wallSphincter relaxation

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Mass discharge of sympathetic system• Simultaneous discharge of all portions of

sympathetic nervous system as a unit • Due to activation of hypothalamus as a

result of fright, fear or pain• Also called alarm or stress response of

the body• Prepares the body for ‘emergency’

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Mass discharge of sympathetic system• Increased BP• Increased blood flow to active muscles• Less blood flow to skin and GIT• Increased rate of cellular metabolism• Increased glycogenolysis and lipolysis• Increased muscle strength• Increased mental activity• Papillary dilation• Increased respiratory rate

Autonomic nervous Autonomic nervous system (ANS)system (ANS)

Sympathetic and parasympathetic tone• Basal rate of discharge• Allows single division to adjust

stimulation level of an organoSympathetic tone to blood vessels

Thank You