keywords: sympathetic nervous system; fighlt or flight response
key words: parasympathetic nervous system; rest and digest system
key words: sympathetic nervous system; parasympathetic nervous system
Autonomic nervous system Physiology
Autonomic Nervous System
Central nervous system• The nervous system with the endocrinesystem controls and coordinates variousfunctions of the body.• The body has to make adjustmentsaccording to the changes in its internaland external environments.• These adjustments are essential for themaintenance of homeostasis, as well asfor existence.
The nervous system can be classified:• Anatomically, according to itsdifferent structures,• Physiologically, according to itsfunctions.Anatomically nervous system formed of(Somatic nervous system, autonomicnervous system and integrative nervoussystem).
Peripheral Nervous System• Handles the CNS’s input and output.• Contains all the portions of the NSoutside the brain and spinal cord.• Contains sensory nerves and motornerves• Divided into autonomic nervoussystem and somatic nervoussystem.
Peripheral Nervous System• Sensory Nerves(to the brain)Carry messages fromreceptors in the skin,muscles, and otherinternal and externalsense organs to thespinal cord and thento the brain• Motor Nerves(from the brain)Carry orders from CNSto muscles, glands tocontract and producechemicalmessengers
• The ANS is part of the peripheral nervoussystem and it controls many organs andmuscles within the body.• In most situations, we are unaware of theworkings of the ANS because it functions inan involuntary, reflexive manner.• For example, we do not notice when bloodvessels change size or when our heart beatsfaster.• However, some people can be trained tocontrol some functions of the ANS such asheart rate or blood pressure.
The ANS is most important in two situations:1- In emergencies that cause stressand require us to "fight" or take"flight" (run away).2- In no emergencies that allow usto "rest" and "digest".
DefinitionDefinitionThe portion of the nervousThe portion of the nervoussystem that controls mostsystem that controls mostvisceral functions of the body isvisceral functions of the body iscalled thecalled the autonomic nervousautonomic nervoussystem (ANS).system (ANS).12:11 email@example.com 11
DefinitionDefinitionOr it is the motor nervousOr it is the motor nervoussystem that controls glands,system that controls glands,cardiac muscle, and smoothcardiac muscle, and smoothmuscle.muscle.12:11 firstname.lastname@example.org 12
The primary target organs of theThe primary target organs of theANSANSThe viscera of the thoracic andThe viscera of the thoracic andabdominal cavities andabdominal cavities andsome structures of the bodysome structures of the bodywall, including cutaneous bloodwall, including cutaneous bloodvessels, sweat glands, andvessels, sweat glands, andpiloerector muscles.piloerector muscles.12:11 email@example.com 13
ControlControlAutonomic literallyAutonomic literallymeans “self-governed.”.means “self-governed.”.TheThe ANS usually carries out itsANS usually carries out itsactions involuntarily, without ouractions involuntarily, without ourconscious intent or awareness, inconscious intent or awareness, incontrast to the voluntary nature ofcontrast to the voluntary nature ofthe somatic motor system.the somatic motor system.12:11 firstname.lastname@example.org 14
Visceral effectorsVisceral effectorsVisceral effectors do not dependVisceral effectors do not dependon the ANS to function, but onlyon the ANS to function, but onlyto adjust their activity to theto adjust their activity to thebody’s changing needs.body’s changing needs.12:11 email@example.com 15
Visceral effectorsVisceral effectorsThe heart, for example, goes onThe heart, for example, goes onbeating even if all autonomicbeating even if all autonomicnerves to it are severed, but thenerves to it are severed, but theANSANS modulates (adjusts) themodulates (adjusts) theheart rate in conditions ofheart rate in conditions of restrestor exercise.or exercise.12:11 firstname.lastname@example.org 16
Visceral effectorsVisceral effectorsIf the somatic nerves to aIf the somatic nerves to askeletal muscle are severed, theskeletal muscle are severed, themuscle exhibits flaccidmuscle exhibits flaccidparalysis—it no longerparalysis—it no longerfunctions.functions.12:11 email@example.com 17
Visceral effectorsVisceral effectorsBut if the autonomic nerves toBut if the autonomic nerves tocardiac or smooth muscle arecardiac or smooth muscle aresevered, the muscle exhibitssevered, the muscle exhibitsexaggerated responsesexaggerated responses(denervation hypersensitivity).(denervation hypersensitivity).12:11 firstname.lastname@example.org 18
striking characteristics of the ANSThe rapidity and intensity.For instance,Within 3 to 5 seconds it can increase the heart rateto twice normal.Within 10 to 15 seconds the arterial pressure canbe doubled.The arterial pressure can be decreased lowenough within 10 to 15 seconds to cause fainting.Sweating can begin within seconds, and theurinary bladder may empty involuntarily, also withinseconds.12:11 email@example.com 20
Autonomic System• Two divisions:– sympathetic– Parasympatheitic• Control involuntary functions– heartbeat– blood pressure– respiration– perspiration– digestion• Can be influenced by thought andemotion
• It is usual to divide the nervoussystem into somatic, autonomic andintegrated systems.• The somatic nervous system providesvoluntary motor control of skeletalmuscle.• The autonomic nervous systemprovides an involuntary control ofinternal environment and the viscera.
12:11 firstname.lastname@example.org 26Comparison of Somatic and ANSComparison of Somatic and ANS
Comparison of Autonomic andSomatic Motor Systems• Autonomic nervous system– Chain of two motor neurons• Preganglionic neuron• Postganglionic neuron– Conduction is slower due to thinly orunmyelinated axonsPre-ganglionicGanglionPost-ganglionic
Sympathetic N.S. Parasympathetic N.S.Like the accelerator ofyour carLike the brakes in your carSlows the body down tokeep its rhythmMobilized the body foractionEnables the body toconserve and store energyPreganglionic: short, synapsewithin the lateral & collateralgangliaPreganglionic: long, synapsewithin the terminal gangliaPostganglionic: long Postganglionic: shortHas a wide distributions Has a restricted distributions
Autonomic Nervous System• Often work inopposition• Cooperate to fine-tune homeostasis• Regulated by thebrain;hypothalamus, ponsand medulla• Can also beregulated by spinalreflexes; no higherorder input• Pathways bothconsist of a twoneuron systemPreganglionic neuron autonomic ganglion postganglionic neuron targetfrom CNS outside CNS
General Organization of the ANSGeneral Organization of the ANSThe EFFERENTEFFERENT autonomic signals aretransmitted to the various organs of thebody through two major subdivisions calledThe sympathetic nervous system.sympathetic nervous system.The parasympathetic nervous parasympathetic nervous systemsystem.12:11 email@example.com 33
12:11 firstname.lastname@example.org 35Physiologic Anatomy of the Sympathetic NSPhysiologic Anatomy of the Sympathetic NS
Each sympathetic pathwaysympathetic pathway from the cordto the stimulated tissue is composed oftwo neuronstwo neurons, a preganglionic neuron preganglionic neuron and a postganglionic neuronand a postganglionic neuron, in contrastto only a single neuron in the skeletalmotor pathway.12:11 email@example.com 36
Physiologic Anatomy of thePhysiologic Anatomy of theParasympathetic Nervous SystemParasympathetic Nervous System Parasympathetic fibers leave the CNSthrough cranial nerves III, VII, IX, and XIII, VII, IX, and X. Additional parasympathetic fibers leavethe lowermost part of the spinal cordthrough the second and third sacralsecond and third sacralspinalspinal nerves and occasionally the firstand fourth sacral nerves.12:11 firstname.lastname@example.org 39
Physiologic Anatomy of thePhysiologic Anatomy of theParasympathetic Nervous SystemParasympathetic Nervous SystemAbout 75 per cent of all parasympatheticnerve fibers are in the vagus nerves vagus nerves (cranial nerve X), passing to the entirethoracic and abdominal regions of thebody.Therefore, a physiologist speaking of theparasympathetic nervous system oftenthinks mainly of the two vagus nerves.12:11 email@example.com 40
Sympathetic• Sometimes called the“thoracolumbar” division• Short preganglionic neurons;long postganglionic neurons;ganglia are called the chainganglia• Preganglionic neurons secreteAch onto nicotinic receptors• Postganglionic neuronssecrete NE on to α or βreceptors• Target tissues are smoothmuscle, cardiac muscle,endocrine glands, brown fat
Parasympathetic•Sometimes called the“cranio-sacral division•Long preganglionicneurons;•short postganglionicneurons (often in thetarget organ)•Preganglionic neuronssecrete Ach on tonicotinic receptors•Postganglionic neuronssecrete Ach on tomuscarinic receptors•Target tissues aresmooth muscle,cardiac muscle,exocrine glands, brownfat
Anatomical Differences in Sympatheticand Parasympathetic Divisions
Anatomical Differences in Sympatheticand Parasympathetic Divisions
Similarities between Sympathetic & ParasympatheticSimilarities between Sympathetic & Parasympathetic• Both are efferent (motor) systems: “visceromotor”• Both involve regulation of the “internal” environmentgenerally outside of our conscious control:“autonomous”• Both involve 2 neurons that synapse in a peripheralganglion and Innervate glands, smooth muscle,cardiac muscleCNS ganglionpreganglionicneuronpostganglionicneuronglandssmoothmusclecardiacmuscle
Differences between Sympathetic & ParasympatheticDifferences between Sympathetic & ParasympatheticLocation of Preganglionic Cell BodiesThoracolumbarT1 – L2/L3 levelsof the spinal cordCraniosacralBrain: CN III, VII, IX, XSpinal cord: S2 – S4Sympathetic Parasympathetic
SympatheticCNS ganglionshort preganglionicneuronlong postganglionicneurontargetParasympatheticCNS ganglionlong preganglionicneurontargetshort postganglionicneuronDifferences between Sympathetic & ParasympatheticDifferences between Sympathetic & ParasympatheticRelative Lengths of Neurons
ParasympatheticOverview of the Autonomic Nervous SystemOverview of the Autonomic Nervous SystemDifferences between Sympathetic & ParasympatheticDifferences between Sympathetic & ParasympatheticNeurotransmittersACh, +NE (ACh at sweat glands),+ / -, α & ß receptorsACh, + / -muscarinic receptors• All preganglionics release acetylcholine (ACh) & are excitatory (+)• Symp. postgangl. — norepinephrine (NE) & are excitatory (+) or inhibitory (-)• Parasymp. postgangl. — ACh & are excitatory (+) or inhibitory (-)Sympathetic• Excitation or inhibition is a receptor-dependent & receptor-mediated responseACh, +
Overview of the Autonomic Nervous SystemOverview of the Autonomic Nervous SystemDifferences between Sympathetic & ParasympatheticDifferences between Sympathetic & ParasympatheticTarget TissuesParasympatheticSympathetic• Organs of head, neck,trunk, & external genitalia• Organs of head, neck,trunk, & external genitalia• Adrenal medulla• Sweat glands in skin• Arrector muscles of hair• ALL vascular smooth muscle» Sympathetic system is distributed to essentially alltissues (because of vascular smooth muscle)» Parasympathetic system never reaches limbs orbody wall (except for external genitalia)
Overview of ANSOverview of ANSFunctional DifferencesSympathetic• “Fight or flight”• Catabolic (expend energy)Parasympathetic• “Feed & breed”, “rest &digest”• Homeostasis» Dual innervation of manyorgans — having a brakeand an accelerator providesmore control
55FUNCTION OF PARASYMPATHETIC & SYMPATHETIC NEVOUS SYSTEM
57Sympathetic Nervous SystemMain functions of the SNS• Regulation of cardiovascular system• Regulation of body temperature• Implementation of “fight or flight” reaction• FIGHT OR FLIGHT RESPONSE• Stressful Situations ----trauma, fear , hypoglycemia.
spinalnervedorsalramusventralramusgray ramuscommunicans white ramuscommunicanssympatheticganglionintermediolateralgray columnStructure of spinal nerves: Sympathetic pathwaysStructure of spinal nerves: Sympathetic pathways
Sympathetic System: Postganglionic Cell BodiesSympathetic System: Postganglionic Cell BodiesParavertebralgangliaPrevertebralganglia• celiac ganglion• sup. mesent. g.• inf. mesent. g.aortasympathetictrunk (chain)1. Paravertebral ganglia• Located along sides of vertebrae• United by preganglionics into Sympathetic Trunk• Preganglionic neurons are thoracolumbar (T1–L2/L3)but postganglionic neurons are cervical to coccyx• Some preganglionics ascend or descend in trunksynapse atsame levelascend tosynapse athigher leveldescend tosynapse atlower level
Sympathetic System: Postganglionic Cell BodiesSympathetic System: Postganglionic Cell BodiesParavertebralgangliaPrevertebralganglia• celiac ganglion• sup. mesent. g.• inf. mesent. g.aortasympathetictrunk (chain)2. Prevertebral (preaortic) ganglia• Located anterior to abdominal aorta, in plexusessurrounding its major branches• Preganglionics reach prevertebral ganglia viaabdominopelvic splanchnic nervesabdominopelvicsplanchnicnerve
1- Cervical divisionOrigin: T1-2Course: preganglionic fibres reach the sympatheticchain and then ascend upwards to relayin the superior cervical ganglion.Postganglionic neuron: pass from ganglionto the following organs:-• EYE: pupil dilatation, widening of palpebral fissure, exophthalmos,Vasoconstriction of eye b.v. and Relaxation of ciliary muscle.• Salivary gland : trophic secretion, Vasoconstriction of its blood vessels andSqueezing of salivary secretion.• Lacrimal gland: Trophic secretion and Vasoconstriction.• Face skin blood vessel: Vasoconstriction of (Pale color).• Sweet secretion: copious secretion.• Hair: erection due to contraction of erector pilae muscles..• Cerebral vessels: Weak vasoconstriction
(2) Cardiopulmonary divisionOrigin: Lateral horn cells of upper 4-5 thoracic segments.Course: Preganglionic neurons reach the sympathetic chain torelay in the three cervical ganglion and upper four thoracicganglion.The postganglionic arise from these ganglia supply thefollowing structures:-• Heart: Increase all properties of cardiac muscle (contraction,rhythmicity, excitability, conductivity.• Coronary vessels, its sympathetic supply. At first itcauses vasoconstriction, and then it causes vasodilatation dueto accumulation of metabolites.• Bronchi: Broncho dilation, decrease bronchial secretions andvasoconstriction of pulmonary blood vessels.
3- Splanchnic divisionOrigin: lateral horn cells of the lower six thoracic and upper four lumber segments.Course: Preganglionic neurons originate from these segments reach the sympatheticchain where they pass without relay, and then they divided into two branches:(1) Greater splanchnic nerve(2) Lesser splanchnic nerve.Greater splanchnic nerve:• Origin: Preganglionic nerves fibers emerge from lateral horn cells of lower sixthoracic segments and then relay in the collateral ganglion in the abdomen.• Course: Postganglionic nerve fibers arise from these ganglia (celiac, superiormesenteric and inferior mesenteric ganglia) and supply the abdominal organscausing the following effects:• Vasoconstriction: of most arteries of stomach, small intestine, proximal part of largeintestine, kidney, pancreas and liver.• Relaxation of the musculature of: stomach, small intestine and proximal part oflarge intestine.• Contraction of sphincters: of the stomach and intestine leading to (food retention).• Contraction of the capsule: of the spleen leading to evacuation of about 200 ml ofblood.• Breakdown of the glucose in the liver: (glycogenolysis) leading to increase ofblood glucose level.• Stimulation of adrenal medulla: Secrete adrenaline and noradrenalin.
The Role of the Adrenal Medullain the Sympathetic Division• Major organ of the sympathetic nervoussystem• Secretes great quantities epinephrine (alittle norepinephrine)• Stimulated to secrete by preganglionicsympathetic fibers
Lesser splanchnic nerveOrigin: Preganglionic nerve fibers originate from the lateral horncells of the 12 thoracic and upper two lumber segments.Course: 2 nerves from both sides unite together forming thepresacral nerve, which proceeds to pelvis and divided into twobranches (hypogastric nerves), then relay in the inferiormesenteric ganglion.Postganglionic nerve fiber supplies the following pelvic viscera:Urinary bladder: Relaxation of its wall.– Contraction of internal urethral sphincter.– Leading to urine retention.Rectum:– Relaxation of the distal part of large intestine.– Relaxation of the rectum wall.– Contraction of the internal anal sphincter.– Leading to feces retention.
Genital organs:- Vasoconstriction of its blood vessels.–Leading to shrinkage of penis andclitoris.Vas deferens:- Contraction of its wall, and wall ofseminal vesicles, ejaculatory ducts andprostate- Leading to ejaculation.
(4) Somatic divisionOrigin: Preganglionic nerve fibers arise from all lateralhorn cells of all sympathetic segments, and then relayin the cervical and sympathetic chain ganglia.Course: Postganglionic nerve fibers emerge from theseganglia proceeds outside the central nervous systemto return back to spinal cord to join the spinal nervewhen it comes out from the anterior horn cells, andsupply the following structures:Skin:• Vasoconstriction giving the pale color of the skin.• Stimulation of the sweet glands, the eccrine glands give copioussecretion, while the apocrine glands give thick odoriferous secretion.• Hair erection.Skeletal muscle:• Its blood vessels show vasodilatation (V.D.) due to cholinergiceffect or vasoconstriction (V.C.) due to a adrenergic effect.• The type of stimulation depends upon the nature of stimulation.• Muscles: its stimulation causing delayed fatigue and early recovery.
4- somatic tissues(body wall, limbs)postganglionicsvia 31 spinal nervesto somatic tissues of neck,body wall, and limbssympathetictrunk
Flight or fight reaction• Acceleration of heart and lung action• Inhibition of stomach and intestinal action• Constriction of blood vessels in many parts ofthe body• Liberation of nutrients for muscular action• Dilation of blood vessels for muscles• Inhibition of tear glands and salivation• Dilation of pupil• Relaxation of bladder• Inhibition of erection
83Parasympathetic NervousSystem (PNS)• Rest & Digest situations.The regulatory functions of PNS affect these sites• Heart rate• Gastric secretions• Bladder and bowel• Vision• Bronchial smooth muscle
Parasympathetic• “ Rest and digest” system• Calms body toconserve andmaintain energy• Lowers heartbeat,breathing rate,blood pressure
ParasympatheticParasympatheticPathwaysPathwaysCranial outflow• CN III, VII, IX, X• Four ganglia in head• Vagus nerve (CN X) is majorpreganglionic parasymp.supply to thorax & abdomen• Synapse in ganglia withinwall of the target organs (e.g.,enteric plexus of GI tract)Sacral outflow• S2–S4 via pelvic splanchnics• Hindgut, pelvic viscera, andexternal genitaliaClinical Relevance» Surgery for colorectal cancerputs pelvic splanchnics at risk» Damage causes bladder &sexual dysfunction
The Parasympathetic Division• Cranial outflow– Comes from the brain– Innervates organs of the head, neck, thorax,and abdomen• Sacral outflow– Supplies remaining abdominal and pelvicorgans
Cranial Outflow• Preganglionic fibers run via:– Oculomotor nerve (III)– Facial nerve (VII)– Glossopharyngeal nerve (IX)– Vagus nerve (X)• Cell bodies located in cranial nerve nucleiin the brain stem
Sacral OutflowOrigin: Preganglionic nerve fibers arise from thelateral horn cells of the 2nd, 3rd and 4th sacralsegments.Course: These preganglionic passes without relay,then the right and left branches unit together to formthe pelvic nerve, the pelvic nerve relay in theterminal ganglia, where the postganglionic nervefibers emerge and supply the following structures:-Urinary bladder: parasympathetic stimulationcauses:- Contraction of the bladder wall- Relaxation of its sphincter.- These responses lead to micturition.
Rectum and descending colon:parasympathetic stimulation causes:- Contraction of its wall.- Relaxation of internal anal sphincter.- These responses lead to defecation.Seminal vesicles and prostate:parasympathetic stimulation -causes:- Secretion of these glands.Erectile tissue: parasympathetic stimulationcauses:- Vasodilatation which lead to erection.
Comparison of sympathetic andParasympathetic Pathways• Neurotransmitters• Receptors
103ACTIONS OF CHOLINERGIC AGONIST• CVS:The action of Ach on heart mimic the effects of VAGALstimulation. The normal vagal activity regulates theheart by• release of Ach at SA node. Vasodilatation Decrease in heart rate ( -ve chronotropic effect). Decrease in force of contraction ( -ve Inotropic• effect). Decrease in rate of conduction in SA & AV• nodes ( -ve dromotropic effect).
104Opposing effects of parasympathetic andsympathetic nerves.