AUTONOMIC AUTONOMIC NERVOUS SYSTEMNERVOUS SYSTEM

Prof. Vajira WeerasingheProf. Vajira Weerasinghe

Professor of PhysiologyProfessor of Physiology

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Autonomic nervous systemAutonomic nervous system

The autonomic nervous system is the The autonomic nervous system is the subdivision of the peripheral nervous subdivision of the peripheral nervous system that regulates body activities system that regulates body activities

that are generally not under that are generally not under conscious controlconscious control

Autonomic (visceral motor)

autonomic

somatic

this dorsal root ganglion is sensory

Somatic motor

Difference between somatic Difference between somatic motor and autonomic motor motor and autonomic motor ► Somatic motor:Somatic motor:

Cell bodies of motor neurons reside in CNS (brain Cell bodies of motor neurons reside in CNS (brain or spinal cord)or spinal cord)

Their axons (sheathed in spinal nerves) extend Their axons (sheathed in spinal nerves) extend all the way to their skeletal musclesall the way to their skeletal muscles

Fast neural transmission Fast neural transmission

► Autonomic system: chains of two neuronsAutonomic system: chains of two neurons 11stst = preganglionic neuron (in brain or cord) = preganglionic neuron (in brain or cord) 22ndnd = postgangionic neuron (cell body in ganglion = postgangionic neuron (cell body in ganglion

outside CNS)outside CNS) Slower because lightly or unmyelinatedSlower because lightly or unmyelinated

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►Axon of 1Axon of 1stst ( (preganglionicpreganglionic) neuron ) neuron leaves CNS to synapse with the 2leaves CNS to synapse with the 2ndnd ((postganglionicpostganglionic) neuron) neuron

►Axon of 2Axon of 2ndnd ( (postganglionicpostganglionic) neuron ) neuron extends to the organ it servesextends to the organ it serves

Diagram contrasts somatic (lower) and autonomic:

autonomic

somatic

Note: the autonomic ganglion is motor

this dorsal root ganglion is sensory

Divisions of the autonomic nervous Divisions of the autonomic nervous systemsystem

►Parasympathetic divisionParasympathetic division►Sympathetic divisionSympathetic division

Serve most of the same organs but Serve most of the same organs but cause opposing or antagonistic effectscause opposing or antagonistic effects

cervical, thoracic, lumbar, sacral

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Where they come fromWhere they come from

Parasympathetic:craniosacral

Sympathetic:thoracolumbar

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Sympathetic nervous systemSympathetic nervous system“fight or flight”“fight or flight”

► Also called Also called thoracolumbarthoracolumbar system: all its system: all its neurons are in lateral horn of gray matter from neurons are in lateral horn of gray matter from T1-L2T1-L2

► Lead to every part of the body (unlike parasymp.) Lead to every part of the body (unlike parasymp.) Easy to remember that when nervous, you sweat; Easy to remember that when nervous, you sweat;

when afraid, hair stands on end; when excited blood when afraid, hair stands on end; when excited blood pressure rises (vasoconstriction): these sympathetic pressure rises (vasoconstriction): these sympathetic onlyonly

Also causes: dry mouth, pupils to dilate, increased Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucosemuscles, and liver to release glucose

►NorepinephrineNorepinephrine (noradrenaline) is (noradrenaline) is neurotransmitter released by most neurotransmitter released by most postganglionic fibers (acetylcholine in postganglionic fibers (acetylcholine in preganglionic): “adrenergic”preganglionic): “adrenergic”

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SympathetiSympathetic c

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Parasympathetic nervous systemParasympathetic nervous system“rest & digest”“rest & digest”

►Also called the Also called the craniosacralcraniosacral system system because all its preganglionic neurons because all its preganglionic neurons are in the brain stem or sacral levels of are in the brain stem or sacral levels of the spinal cordthe spinal cord Cranial nerves III,VII, IX and XCranial nerves III,VII, IX and X In lateral horn of gray matter from S2-S4In lateral horn of gray matter from S2-S4

►Only innervate internal organs (not Only innervate internal organs (not skin)skin)

►AcetylcholineAcetylcholine is neurotransmitter at is neurotransmitter at end organ as well as at preganglionic end organ as well as at preganglionic synapse: “cholinergic”synapse: “cholinergic”

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Parasympathetic continuedParasympathetic continued

► Cranial outflowCranial outflow III - pupils constrictIII - pupils constrict VII - tears, nasal mucus, salivaVII - tears, nasal mucus, saliva IX – parotid salivary glandIX – parotid salivary gland X (Vagus n) – visceral organs of thorax & abdomen:X (Vagus n) – visceral organs of thorax & abdomen:

►Stimulates digestive glandsStimulates digestive glands►Increases motility of smooth muscle of digestive tractIncreases motility of smooth muscle of digestive tract►Decreases heart rateDecreases heart rate►Causes bronchial constrictionCauses bronchial constriction

► Sacral outflow (S2-4): form pelvic splanchnic Sacral outflow (S2-4): form pelvic splanchnic nervesnerves Supply 2Supply 2ndnd half of large intestine half of large intestine Supply all the pelvic (genitourinary) organsSupply all the pelvic (genitourinary) organs

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ParasympathetParasympathetic ic

NeurotransmitterNeurotransmitters s

►Somatic = all motor neurons release Somatic = all motor neurons release ACH which is always stimulatoryACH which is always stimulatory

►Visceral = ACH & norepinephrineVisceral = ACH & norepinephrine All All prepreganglionicganglionic fibers release ACH fibers release ACH AllAll postpostganglionicganglionic PsNSPsNS fibers release ACH fibers release ACH Most postganglionic SNS fibers release Most postganglionic SNS fibers release

norepinorepi

Can be stimulatory or inhibitory based Can be stimulatory or inhibitory based on receptor typeson receptor types

Comparison of Sympathetic and Comparison of Sympathetic and parasympathetic Systemsparasympathetic Systems

Divisions of the ANSDivisions of the ANS

► Sympathetic NSSympathetic NS► Parasymathetic NSParasymathetic NS

► Dual innervationDual innervation Opposing effects on the Opposing effects on the

same organsame organ

► SNS is usually SNS is usually stimulatory (fight or stimulatory (fight or flight)flight)

► PsNS is usually PsNS is usually inhibitory (body maint. inhibitory (body maint. & conservation of E& conservation of E

Sympathetic nervous Sympathetic nervous systemsystem

► The sympathetic division is the The sympathetic division is the “fight-or-flight”“fight-or-flight” systemsystem

► Involves Involves EE activities – exercise, excitement, activities – exercise, excitement, emergency, and embarrassmentemergency, and embarrassment

► Non-essential activities are dampened (GI/urinary)Non-essential activities are dampened (GI/urinary)► Promotes adjustments during exercise – blood flow Promotes adjustments during exercise – blood flow

to organs is reduced, flow to muscles is increasedto organs is reduced, flow to muscles is increased► Its activity is illustrated by a person who is Its activity is illustrated by a person who is

threatenedthreatened Heart rate increases, and breathing is rapid and deepHeart rate increases, and breathing is rapid and deep The skin is cold and sweaty, and the pupils dilateThe skin is cold and sweaty, and the pupils dilate Bronchioles dilate…increasing ventilation, delivering more Bronchioles dilate…increasing ventilation, delivering more

oxygen to cellsoxygen to cells Constriction of visceral & cutaneous bv’s (blood is shunted Constriction of visceral & cutaneous bv’s (blood is shunted

to skeletal mm)to skeletal mm) Liver releases more glucose into blood to provide more Liver releases more glucose into blood to provide more

readily avail. Ereadily avail. E Targets adipocytes for lipolysisTargets adipocytes for lipolysis

Parasympathetic nervous Parasympathetic nervous systemsystem

► Salivation, Lacrimation, Urination, Digestion, Salivation, Lacrimation, Urination, Digestion, DefecationDefecation

►Most active in non-stressful situationsMost active in non-stressful situations► Concerned with keeping body energy use lowConcerned with keeping body energy use low► Lenses of eyes accommodated for near Lenses of eyes accommodated for near

visionvision► Its activity is illustrated in a person who Its activity is illustrated in a person who

relaxes after a mealrelaxes after a meal Blood pressure, heart rate, and respiratory rates Blood pressure, heart rate, and respiratory rates

are loware low Gastrointestinal tract activity is highGastrointestinal tract activity is high The skin is warm and the pupils are constrictedThe skin is warm and the pupils are constricted

Differences Differences

Ach (N)

Ach (N) Ach (M)

Nor

Sympathetic

Parasympathetic

Adre

Neurotransmitters and Neurotransmitters and ReceptorsReceptors

► Acetylcholine (ACh) and norepinephrine (NE) are Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANSthe two major neurotransmitters of the ANS

► ACh is released by all preganglionic axons and all ACh is released by all preganglionic axons and all parasympathetic postganglionic axonsparasympathetic postganglionic axons

► Cholinergic fibersCholinergic fibers – ACh-releasing fibers – ACh-releasing fibers ► Adrenergic fibersAdrenergic fibers – sympathetic postganglionic – sympathetic postganglionic

axons that release NE axons that release NE

► Neurotransmitter effects can be excitatory or Neurotransmitter effects can be excitatory or inhibitory inhibitory depending upon the receptor typedepending upon the receptor type

Cholinergic ReceptorsCholinergic Receptors

►The two types of receptors that The two types of receptors that bind ACh are bind ACh are nicotinicnicotinic and and muscarinicmuscarinic

►These are named after drugs that These are named after drugs that bind to them and mimic ACh bind to them and mimic ACh effectseffects

Nicotinic Receptors Nicotinic Receptors (cholinergic)(cholinergic)

►Nicotinic receptors are found on:Nicotinic receptors are found on: Motor end plates (somatic targets)Motor end plates (somatic targets) All ganglionic neurons of both All ganglionic neurons of both

sympathetic and parasympathetic sympathetic and parasympathetic divisionsdivisions

The hormone-producing cells of the The hormone-producing cells of the adrenal medullaadrenal medulla

►The effect of ACh binding to nicotinic The effect of ACh binding to nicotinic receptors is receptors is always stimulatoryalways stimulatory

Muscarinic Receptors Muscarinic Receptors (cholinergic) (cholinergic)

►Muscarinic receptors occur on all effector cells Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibersstimulated by postganglionic cholinergic fibers

►The effect of ACh binding: The effect of ACh binding: Can be either inhibitory or excitatoryCan be either inhibitory or excitatory Depends on the receptor typeDepends on the receptor type of the target of the target

organorgan

Adrenergic ReceptorsAdrenergic Receptors

► The two types of adrenergic receptors are alpha and betaThe two types of adrenergic receptors are alpha and beta

► Each type has two or three subclasses Each type has two or three subclasses ((11, , 22, , 11, , 2 2 , , 33))

► Effects of NE binding to: Effects of NE binding to: receptors is generally stimulatoryreceptors is generally stimulatory receptors is generally inhibitoryreceptors is generally inhibitory

► A notable exception – NE binding to A notable exception – NE binding to receptors of the heart is receptors of the heart is stimulatorystimulatory

Adrenergic ReceptorsAdrenergic Receptors

►Norepinephrine produces its effects by Norepinephrine produces its effects by combining with adrenergic receptorscombining with adrenergic receptors Alpha Alpha Beta Beta

Adrenergic Receptors Adrenergic Receptors

►Found in:Found in: Cardiovascular Cardiovascular Endocrine Endocrine Gastrointestinal Gastrointestinal Genitourinary Genitourinary Respiratory Respiratory Ocular Ocular

Alpha ReceptorsAlpha Receptors

►Alpha 1: adrenergic receptors located on Alpha 1: adrenergic receptors located on postsynaptic effector cells.postsynaptic effector cells. Smooth muscles of blood vessels: ConstrictionSmooth muscles of blood vessels: Constriction

►Arteriolar constrictionArteriolar constriction

Bladder sphincterBladder sphincter PenisPenis Uterus Uterus Pupillary muscles of irisPupillary muscles of iris

Alpha 2Alpha 2

►Same as the Alpha 1 but are located in Same as the Alpha 1 but are located in the presynaptic nerve terminals.the presynaptic nerve terminals.

Adrenergic ReceptorAdrenergic Receptor

►Beta 1Beta 1►CardiovascularCardiovascular

Cardiac muscle: increased contractilityCardiac muscle: increased contractilityincreased force of contraction increased force of contraction

Atrioventricular node: increased heart Atrioventricular node: increased heart raterate

Sinoatrial node: increase in heart rateSinoatrial node: increase in heart rate

►EndocrineEndocrine PancreasPancreas

Beta 1 DrugsBeta 1 Drugs

►Predominately works on vascular Predominately works on vascular smooth muscle of the heart.smooth muscle of the heart.

Adrenergic ReceptorAdrenergic Receptor

►Beta 2Beta 2►CardiovascularCardiovascular

Dilation of blood vesselsDilation of blood vessels

►EndocrineEndocrine►Uterine relaxationUterine relaxation►Respiratory: dilation of bronchial Respiratory: dilation of bronchial

musclesmuscles

HeartHeart

►Direct stimulation of receptorsDirect stimulation of receptors Alpha 1 – Alpha 1 –

►Vasoconstriction of blood vessels which increases Vasoconstriction of blood vessels which increases blood pressureblood pressure

►Pressor or vasopressor effect to maintain blood Pressor or vasopressor effect to maintain blood pressurepressure

Beta 1Beta 1►Increased force of myocardial contraction Increased force of myocardial contraction ►Increased speed of electrical conduction in the Increased speed of electrical conduction in the

heart.heart.

Sympathetic vs Sympathetic vs parasympathetic parasympathetic

►Distribution on different organsDistribution on different organs►Actions on different organsActions on different organs►Drugs acting on receptors Drugs acting on receptors ►Reflexes in different systems Reflexes in different systems

Sympathetic vs Sympathetic vs parasympathetic parasympathetic

►Distribution on different organsDistribution on different organs

Fig. 9.6Fig. 9.6

Sympathetic (Thoracolumbar) Sympathetic (Thoracolumbar) DivisionDivision

► Preganglionic cell bodies in lateral Preganglionic cell bodies in lateral horns of spinal cord T1-L2: horns of spinal cord T1-L2: thoracolumbarthoracolumbar

► Preganglionic axons pass through Preganglionic axons pass through ventral roots to ventral roots to whitewhite rami rami communicantescommunicantes to the to the retroperitoneal retroperitoneal sympathetic chain sympathetic chain gangliaganglia

Parasympathetic Parasympathetic (Craniosacral) Division(Craniosacral) Division

► Preganglionic cell bodies in Preganglionic cell bodies in nuclei of brainstem or nuclei of brainstem or lateral parts of spinal cord lateral parts of spinal cord gray matter from S2-S4gray matter from S2-S4 Preganglionic axons Preganglionic axons

from brain pass to from brain pass to terminal ganglia through terminal ganglia through cranial nerves III, VII, IX cranial nerves III, VII, IX and Xand X

Preganglionic axons Preganglionic axons from sacral region pass from sacral region pass through through pelvic nervespelvic nerves to terminal gangliato terminal ganglia

► Terminal gangliaTerminal ganglia located located near organ innervated or near organ innervated or embedded in wall of organembedded in wall of organ

Sympathetic vs Sympathetic vs parasympathetic parasympathetic

►Actions on different organsActions on different organs

Sympathetic vs Sympathetic vs parasympathetic parasympathetic

►Drugs acting on receptors Drugs acting on receptors

Parasympathetic

Sympathetic

salbutamol

Sympathetic vs Sympathetic vs parasympathetic parasympathetic

►Reflexes in different systems Reflexes in different systems

ANS reflexesANS reflexes

► CVS: CVS: baroreceptor reflexbaroreceptor reflex Control of heart rateControl of heart rate chemoreceptor reflexchemoreceptor reflex

► GIT: GIT: GIT secretions and motility GIT secretions and motility

► Other:Other: Urinary bladder controlUrinary bladder control Sexual reflexesSexual reflexes SweatingSweating Other visceral reflexes Other visceral reflexes

Exception Exception – –

adrenal medulla adrenal medulla

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Adrenal glandsAdrenal glands

On top of On top of kidneyskidneys

Adrenal Adrenal medulla (inside medulla (inside part) is a major part) is a major organ of the organ of the sympathetic sympathetic nervous systemnervous system

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Adrenal gland is an exceptionAdrenal gland is an exception

►Synapse in glandSynapse in gland►Can cause body-wide Can cause body-wide

release of epinephrine release of epinephrine (adrenaline) and (adrenaline) and norepinephrine norepinephrine (noradrenaline) in an (noradrenaline) in an extreme emergencyextreme emergency

(adrenaline “rush” or (adrenaline “rush” or surge)surge)

Innervation Innervation

Ach

Another exception - Sweat Another exception - Sweat glands glands

► The sweat glands are innervated by the sympathetic The sweat glands are innervated by the sympathetic nervous system (part of the fight or flight response nervous system (part of the fight or flight response system)system)

► Preganglionic neuron is short, originates from the Preganglionic neuron is short, originates from the thoracolumbar region of the spinal cord, uses thoracolumbar region of the spinal cord, uses acetylcholine as its neurotransmitter (nicotinic )acetylcholine as its neurotransmitter (nicotinic )

► Postganglionic neuron for sweat gland innervation differs Postganglionic neuron for sweat gland innervation differs from other sympathetic postganglionic neurons in that it from other sympathetic postganglionic neurons in that it releases acetylcholine to act on muscarinic receptorsreleases acetylcholine to act on muscarinic receptors

Another exception – skeletal Another exception – skeletal muscle blood vessels muscle blood vessels

►These are also innervated by These are also innervated by sympathetic cholinergic fibres sympathetic cholinergic fibres

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Summary