Physiology of Physiology of autonomic nervous autonomic nervous

systemsystem

Autonomic Nervous SystemAutonomic Nervous System 2 divisions:2 divisions:

Sympathetic Sympathetic ““Fight or flight”Fight or flight” ““E” divisionE” division

Exercise, Exercise, excitement, excitement, emergency, and emergency, and embarrassmentembarrassment

Parasympathetic Parasympathetic ““Rest and digest”Rest and digest” ““D” divisionD” division

Digestion, Digestion, defecation, and defecation, and diuresisdiuresis

FunctionFunction

Sympathetic and parasympathetic divisions typically function Sympathetic and parasympathetic divisions typically function in opposition to each other. But this opposition is better in opposition to each other. But this opposition is better termed complementary in nature rather than antagonistic. For termed complementary in nature rather than antagonistic. For an analogy, one may think of the sympathetic division as the an analogy, one may think of the sympathetic division as the accelerator and the parasympathetic division as the brake. The accelerator and the parasympathetic division as the brake. The sympathetic division typically functions in actions requiring sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with quick responses. The parasympathetic division functions with actions that do not require immediate reaction. Consider actions that do not require immediate reaction. Consider sympathetic as "fight or flight" and parasympathetic as "rest sympathetic as "fight or flight" and parasympathetic as "rest and digest".and digest".

AutonomicAutonomic nervousnervous systemsystem sympatheticsympathetic nervousnervous systemsystem:: sympatheticsympathetic trunkstrunks ( (whitewhite ramusramus

communicanscommunicans, , graygray ramusramus communicanscommunicans) - ) - collateralcollateral gangliaganglia cavernous plexus - cavernous plexus - cervical ganglia:cervical ganglia: ( (superiorsuperior, , middlemiddle, ,

inferiorinferior) - ) - splanchnic nerves:splanchnic nerves: ( (thoracicthoracic, , lumbarlumbar, , sacralsacral) - ) - ganglionganglion imparimpar

internal carotid - internal carotid - cardiaccardiac celiac:celiac: celiacceliac gangliaganglia - - aorticorenalaorticorenal - - renalrenal - - spermaticspermatic//ovarianovarian

- - superiorsuperior mesentericmesenteric - - aorticaortic plexusplexus - - inferiorinferior mesentericmesenteric - - hepatichepatic - - splenicsplenic - - gastricgastric - - pancreaticpancreatic - - suprarenalsuprarenal

hypogastric:hypogastric: superiorsuperior hypogastrichypogastric - - inferiorinferior hypogastrichypogastric - - vesicalvesical - - prostaticprostatic - - uterovaginaluterovaginal

parasympathetic nervous system:parasympathetic nervous system: ciliaryciliary ganglionganglion ( (shortshort ciliaryciliary nervesnerves) - ) - pterygopalatinepterygopalatine ganglionganglion ( (nervenerve ofof pterygoidpterygoid canalcanal) - ) - submandibularsubmandibular ganglionganglion - - oticotic ganglionganglion - - pelvicpelvic splanchnicsplanchnic

ReceptorsReceptors

The parasympathetic nervous system uses only The parasympathetic nervous system uses only acetylcholineacetylcholine (ACh) as its (ACh) as its neurotransmitterneurotransmitter. The ACh . The ACh acts on two types of receptors, the acts on two types of receptors, the muscarinicmuscarinic and and nicotinicnicotinic cholinergiccholinergic receptors. Most transmissions receptors. Most transmissions occur in two stages: When stimulated, the occur in two stages: When stimulated, the preganglionicpreganglionic nerve releases ACh at the ganglion, nerve releases ACh at the ganglion, which acts on nicotinic receptors of the which acts on nicotinic receptors of the postganglionicpostganglionic nerve. The postganglionic nerve then nerve. The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of releases ACh to stimulate the muscarinic receptors of the target organ.the target organ.

Neurotransmitters and pharmacologyNeurotransmitters and pharmacology At the effector organs, sympathetic ganglionic neurons release At the effector organs, sympathetic ganglionic neurons release

noradrenalinenoradrenaline (norepinephrine) to act on (norepinephrine) to act on adrenergic receptorsadrenergic receptors, , with the exception of the sweat glands and the adrenal with the exception of the sweat glands and the adrenal medulla:medulla:

At At sweat glandssweat glands, the neurotransmitter is acetylcholine, which , the neurotransmitter is acetylcholine, which acts on acts on muscarinic receptorsmuscarinic receptors. .

At the At the adrenal cortexadrenal cortex, there is no postsynapic neuron. Instead , there is no postsynapic neuron. Instead the presynaptic neuron releases acetylcholine to act on the presynaptic neuron releases acetylcholine to act on nicotinic receptorsnicotinic receptors. .

Stimulation of the Stimulation of the adrenal medullaadrenal medulla releases releases adrenalineadrenaline (epinephrine) into the bloodstream which will act on (epinephrine) into the bloodstream which will act on adrenoceptors, producing a widespread increase in adrenoceptors, producing a widespread increase in sympathetic activity. sympathetic activity.

In the parasympathetic system, ganglionic neurons use In the parasympathetic system, ganglionic neurons use acetylcholine as a neurotransmitter, to stimulate acetylcholine as a neurotransmitter, to stimulate muscarinic receptorsmuscarinic receptors..

SympatheticSympathetic ( (adrenergicadrenergic, with , with exceptions)exceptions)

cardiaccardiac outputoutput increasesincreases SA SA nodenode: heart rate (: heart rate (chronotropicchronotropic)β1, β2: increases)β1, β2: increases cardiaccardiac musclemuscle: contractility (: contractility (inotropicinotropic)β1, β2: increases)β1, β2: increases conduction at conduction at AV nodeAV nodeβ1: increasesβ1: increases vascularvascular smoothsmooth musclemuscle M3: contracts; α = contracts; β2 = relaxesM3: contracts; α = contracts; β2 = relaxes smoothsmooth musclesmuscles of of bronchiolesbronchiolesβ2: relaxes (major contribution); α1: β2: relaxes (major contribution); α1:

contracts (minor contribution)contracts (minor contribution) pupilpupil of of eyeeyeα1: relaxesα1: relaxes ciliaryciliary muscle muscleβ2: relaxesβ2: relaxes salivarysalivary glandsglands: secretionsβ: stimulates viscous, : secretionsβ: stimulates viscous, amylaseamylase secretions; α1 = secretions; α1 =

stimulates stimulates potassiumpotassium cation cation smoothsmooth musclesmuscles of of GI GI tracttractα, β2: relaxesα, β2: relaxes sphincterssphincters of of GI tractGI tractα1: contractsα1: contracts glandsglands of of GI GI tracttractinhibitsinhibits

Parasympathetic (muscarinic)Parasympathetic (muscarinic) cardiaccardiac outputoutput M2: decreases M2: decreases SA SA nodenode: heart rate (: heart rate (chronotropicchronotropic) M2: decreases ) M2: decreases cardiaccardiac musclemuscle: contractility (: contractility (inotropicinotropic) M2: decreases () M2: decreases (atriaatria

only) only) conduction at conduction at AV AV nodenode M2: decreases M2: decreases smoothsmooth musclesmuscles of of bronchiolesbronchioles M3: contracts M3: contracts pupilpupil of of eyeeye M3: contracts M3: contracts ciliaryciliary musclemuscle M3: contracts M3: contracts salivarysalivary glandsglands: secretions stimulates watery secretions : secretions stimulates watery secretions GI GI tracttract motility M1, M3: increases motility M1, M3: increases smoothsmooth musclesmuscles of GI tract M3: contracts of GI tract M3: contracts sphincters of GI tract M3: relaxes sphincters of GI tract M3: relaxes glands of GI tract M3: secretes glands of GI tract M3: secretes

Autonomic regulation & stressAutonomic regulation & stress A stressful situation activates three major communication A stressful situation activates three major communication

systemssystems in the brain that regulate bodily functions. in the brain that regulate bodily functions. The first of these systems is the The first of these systems is the voluntary nervous systemvoluntary nervous system,,

which sends messages to muscles so that we may respond to which sends messages to muscles so that we may respond to sensorysensory information. information.

The second communication system is the The second communication system is the autonomic nervousautonomic nervous systemsystem. It combines the . It combines the sympathetic sympathetic or emergency branch, or emergency branch, whichwhich gets us going in emergencies, and the gets us going in emergencies, and the parasympathetic parasympathetic or calmingor calming branch, which keeps the body’s maintenance branch, which keeps the body’s maintenance systems, such assystems, such as digestion, in order and calms the body’s digestion, in order and calms the body’s responses to the emergencyresponses to the emergency branch.branch.

The brain’s third major communication process is the The brain’s third major communication process is the neuroendocrineneuroendocrine systemsystem, which also maintains the body’s , which also maintains the body’s internalinternal functioning.functioning.

Each of these systems has a specific taskEach of these systems has a specific task The emergencyThe emergency branch causes arteries supplying blood to the branch causes arteries supplying blood to the

muscles to relax inmuscles to relax in order to deliver more blood, allowing greater order to deliver more blood, allowing greater capacity to act. Atcapacity to act. At the same time, the emergency system reduces the same time, the emergency system reduces blood flow to theblood flow to the skin, kidneys, and digestive tract and increases skin, kidneys, and digestive tract and increases blood flow to theblood flow to the muscles. muscles.

In contrast, the calming branch helps to regulate bodilyIn contrast, the calming branch helps to regulate bodily functions functions and soothe the body once the stressor has passed, preventingand soothe the body once the stressor has passed, preventing the the body from remaining too long in a state of mobilization.body from remaining too long in a state of mobilization. Left Left mobilized and unchecked, these body functions couldmobilized and unchecked, these body functions could lead to lead to disease. Some actions of the calming branch appear todisease. Some actions of the calming branch appear to reduce the reduce the harmful eharmful effffects of the emergency branch’s response toects of the emergency branch’s response to stress.stress.

Various “stress hormones” travel through the bloodVarious “stress hormones” travel through the blood and stimulate and stimulate the release of other hormones, which athe release of other hormones, which affffect bodilyect bodily processes such processes such as metabolic rate and sexual functions.as metabolic rate and sexual functions.

THE STRESS REACTIONTHE STRESS REACTION When stress occurs, the When stress occurs, the

sympatheticsympathetic nervous system is nervous system is triggered.triggered. Norepinephrine isNorepinephrine is released by nerves, and released by nerves, and epinephrineepinephrine is secreted by theis secreted by the adrenal glands. By activatingadrenal glands. By activating receptors in blood vessels andreceptors in blood vessels and other structures, these other structures, these substancessubstances ready the heart andready the heart and working muscles for action.working muscles for action.

Acetylcholine is released in theAcetylcholine is released in the parasympathetic nervous parasympathetic nervous system,system, producing calming producing calming effects.effects. The digestive tract is The digestive tract is stimulatedstimulated to digest a meal, the to digest a meal, the heart rateheart rate slows, and the pupils slows, and the pupils of theof the eyes become smaller. eyes become smaller. The neuroendocrineThe neuroendocrine system system also maintainsalso maintains the body’s the body’s normalnormal internal functioning.internal functioning.

Chronic stressChronic stress When glucocorticoids or adrenaline are secreted in When glucocorticoids or adrenaline are secreted in

response toresponse to the prolonged psychological stress the prolonged psychological stress commonly encountered bycommonly encountered by humans, the results are not humans, the results are not ideal. Normally, bodily systems gearideal. Normally, bodily systems gear up under stress and up under stress and release hormones to improve memory,release hormones to improve memory, increase immune increase immune function, enhance muscular activity, andfunction, enhance muscular activity, and restore restore homeostasis. If you are not fighting or fleeing, but homeostasis. If you are not fighting or fleeing, but standingstanding frustrated in a supermarket checkout line or frustrated in a supermarket checkout line or sitting in asitting in a tratraffffc jam, you are not engaging in muscular c jam, you are not engaging in muscular exercise. exercise.

Yet theseYet these systems continue to be stimulated, and when systems continue to be stimulated, and when they are stimulatedthey are stimulated chronically, there are dichronically, there are difffferent erent consequences: Memory isconsequences: Memory is impaired, immune function is impaired, immune function is suppressed, and energy is storedsuppressed, and energy is stored as fat.as fat.

Response to stressResponse to stress