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
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