Physiology Of Autonomic Nervous System

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ANS and anaesthesia


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Physiology Of Autonomic Nervous System: 

Physiology Of Autonomic Nervous System Presenter: D r K hushbu goel Moderator; Dr P Saraswathi devi


INTRODUCTION Much of the action of the body in maintaining, cardiovascular, gastrointestinal and thermal homeostasis occurs through the autonomic nervous system (ANS). The ANS is our primary defense against challenges, to maintain homeostasis. It provides involuntary control and organization of both maintenance and stress responses. 2


HISTORY  GALEN - spoke of sympathy & consent of body & was probably 1 st to describe Paravertebral nerve trunks. 3 THOMAS WILLIS(1665) : -notion of involuntary movements -Term SNS


JACOB WINSLOW  coined term ‘SYMPATHETIC ’  ROBERT WHYTT recognized that adequate stimulation is necessary for visceral sensation & that all sympathy must be referred to brain 4

XAVIER BICHAT divided nervous system into 2 parts La vie organique- Visceral nervous system. La vie animal- Somatic nervous system: 

XAVIER BICHAT  divided nervous system into 2 parts La vie organique - Visceral nervous system. La vie animal- Somatic nervous system CLAUDE BERNARD  i ) Theory of chemical synapse transmission. ii) Described fundamental role of ANS in maintaining Homeostasis (la fixite du milieu interior) 5

JOHN LANGLEY i) Mapped 3 distinct divisions in system. ii) Coined term ‘AUTONOMIC’ & declared that it was largely independent from brain. Term PNS : 

 JOHN LANGLEY i ) Mapped 3 distinct divisions in system. ii) Coined term ‘AUTONOMIC’ & declared that it was largely independent from brain. Term PNS  SHERRINGTON initiated systemic study of reflexes & described Characteristics of reflex function. 6

JJ ABEL synthetized Epinephrine: 

 JJ ABEL synthetized Epinephrine SIR HENRY DALE  isolated Choline . 7


FUNCTIONAL ANATOMY Nervous System Central Nervous System Peripheral Nervous System Somatic Autonomic Sympathetic Parasympathetic Enteric Nervous System 8

Difference between : 

Difference between Somatic Autonomic Organ supplied Skeletal muscles All other organs Distal most synapse Within CNS Outside the CNS(i.e . ganglia) Nerve fibers Myelinated Preganglionic - myelinated Postganglionic- non­myelinated Peripheral plexus formation Absent Present Efferent transmitter ACH ACH, Nor-adrenaline Effect of nerve section on organ supplied Paralysis and Atrophy Activity maintained, no A trophy 9


Definition Autonomic - self governing It is network of nerves & ganglia that controls involuntary physiologic parameters & maintains internal homeostasis & stress responses Operates via reflex arc -includes; Autonomic sensory neurons - mostly associate with interceptors such as chemoceptors,mechanocptors Integrating centres in cns Autonomic motor neurons – sympathetic parasympathetic

Visceral sensory neurons: 

11 Visceral sensory neurons Monitor temperature, pain, irritation, chemical changes and stretch in the visceral organs Brain interprets as hunger, fullness, pain, nausea, well-being Receptors widely scattered – localization poor (e.g. which part is giving you the gas pain?) Visceral sensory fibers run within autonomic nerves, especially vagus and sympathetic nerves Visceral pain is induced by stretching, infection and cramping of internal organs but seldom by cutting (e.g. cutting off a colon polyp) or scraping them

Visceral sensory and autonomic neurons participate in visceral reflex arcs: 

12 Visceral sensory and autonomic neurons participate in visceral reflex arcs Many are spinal reflexes such as defecation and micturition reflexes Some only involve peripheral neurons: spinal cord not involved e.g . “enteric” nervous system: neuron reflex arcs entirely within the wall of the gut


CENTRAL AUTONOMIC ORGANIZATION Cerebral cortex is the highest level of ANS integration. The principal ANS organization is the Hypothalamus . SNS functions are controlled by nuclei in the postero -lateral hypothalamus. PNS functions are governed by nuclei in the midline and some anterior nuclei of the hypothalamus. The anterior hypothalamus is involved in regulation of Temperature. The supra-optic hypothalamic nuclei regulates water metabolism. 13

Integrating centre ctd: 

Integrating centre ctd Medulla and pons- integrate momentary hemodynamic adjustments Maintain sequence & automaticity of ventilation NTS located in medulla- relay centre for afferent chemoreceptors & baroreceptors from glosopharyngeal & vagus nerve .

Central control of the Autonomic NS: 

15 Central control of the Autonomic NS Amygdala: main limbic region for emotions -Stimulates sympathetic activity, especially previously learned fear-related behavior -Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala -Some people can regulate some autonomic activities by gaining extraordinary control over their emotions Hypothalamus : main integration center Reticular formation: most direct influence over autonomic function

Autonomic motor pathway/visceral motor: 

Autonomic motor pathway/visceral motor Visceral motor innervates non-skeletal (non-somatic) muscles Composed of Preganglionic neuron from CNS (cell body in brain/spinal cord) Exit as cranial/spinal n & Synapse in autonomic ganglion Post ganglionic neuron Visceral effectors


SYMPATHETIC NERVOUS SYSTEM SNS originates from spinal cord in the thoraco -lumbar region. Efferent SNS originates in the intermedio -lateral gray column of T1-12 and L1-L3 segments of spinal cord. Nerve fibers, extend to three types of ganglia, Paired sympathetic chains, prevertebral ganglia, Terminal ganglia near the target organ. 17

Sympathetic trunk ganglia/ vertebral chain ganglia/ paravertebral ganglia: 

Sympathetic trunk ganglia/ vertebral chain ganglia/ paravertebral ganglia The 22 paired ganglia lie along either side of the vertebral column from base of skull to coccyx Sympathetic trunks connect these ganglia to each other Superior, Middle and Cervico -Thoracic ganglion ( stellate ganglion formed by fusion of inferior cervical and thoracic ganglia). The sympathetic distribution to the head and neck enable and mediate vasomotor , pupillodilator , secretory and pilomotor functions.

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After entering the Paravertebral ganglia of lateral sympathetic chain, the Pre-ganglionic fibres follows 1 of the 3 courses . Synapses with post ganglionic fibres in ganglia at the level of exit . Course upwards or downwards in the trunk of SNS chain to synapse in ganglion at other level . Track for variable distance through the sympathetic chain and exit without synapsing to terminate in an outlying, unpaired, SNS collateral ganglion .

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Unpaired pre-vertebral ganglia/ collateral ganglia Reside in the abdomen and pelvis anterior to the vertebral column. Celiac ganglion  innervated by T5-T12  innervates the liver, spleen, kidney, pancreas and small bowel and proximal colon (many preganglionic fibers from T5 to T12 may pass through the paired paravertebral ganglia to form the splanchnic nerves). Superior mesenteric ganglion  innervates the distal colon. Inferior mesenteric ganglion  innervates the rectum, bladder and genitals. 21

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Terminal ganglia Small, few in no. & near their target organs. E.g Adrenal medulla 22


SYMPATHETIC NERVOUS SYSTEM SNS ganglion are almost always located closer to spinal cord than to organ they innervate. SNS post ganglionic neurons outnumber the pre ganglionic no. in an average ratio of 20:1 to 30:1 Sympathetic response is not confined to segments from which stimulus originates. This allows for a more dramatic response, with diffuse discharge of the SNS


PARASYMPATHETIC NERVOUS SYSTEM Preganglionic fibres Arises from Cranial n. III, VII, IX, X as well as from Sacral segments S2-4. Pre ganglion fibres originate in 3 areas of the CNS. Mid brain, Medulla oblongata and Sacral part of spinal cord 24

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Fibres arising in the Edinger-Westphal nucleus of the Occulomotor nerve course in the mid- brain to synapse in the ciliary ganglion. This pathway innervate the smooth muscle of iris and the ciliary muscle. 25

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In Medulla, the facial nerve gives off parasympathetic fibres to the chorda tympani and greater superficial petrosal nerve These subsequently synapse in the ganglia of the submaxillary or sublingual glands and the pterygopalatine ganglion respectively 26

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Glossopharyngeal nerve synapses in the Otic ganglion. These post ganglionic fibres innervate the parotid, salivary and lacrimal glands. 27

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The Vagus n. transmits fully ¾ of the traffic of the PNS. It supplies heart, tracheobronchial tree, liver, spleen, kidney and all GIT except distal colon. Most vagal fibres synapse at small ganglia on and about thoracic and abdominal viscera PNS may synapse with a 1:1 ratio of nerve to effector cells, the vagal innervations of the Auerbach plexus may connect 1 nerve fibre to 8,000 cells. 28

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The Sacral segments emerges from S 2 -S 4. Innervates organs of the pelvis and lower abdomen Preganglionic cell bodies Located in visceral motor region of spinal gray matter Form pelvic splanchnic nerves/ nervi erigentes 29

parasympathetic terminal ganglia: 

parasympathetic terminal ganglia Ganglia occur proximal to or within the innervated organ. This location of ganglia makes the PNS more targeted and less robust than SNS. Eg . Ciliary ganglion, pterygopalatine ganglion, submandibular ganglion, otic ganglion etc

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Difference between : 

Difference between Sympathetic Parasympathetic Origin Dorso -lumbar (T1 to L2) Craniosacral (III, VII, IX, X, S2-S4) Distribution Wide Limited to head, neck and trunk Ganglia Away from organs On / close to the organ Post- ganglionic fibre Long Short Pre-post ganglionic fibre ratio 1:20 to 1:100 1:1 to 1:2 except in enteric plexus Transmitter Nor-adrenaline (major) Acetylcholine (minor) ACH Stability of transmitter NA stable, differ for wider activity Ach rapidly destroyed locally Imp. Function Tackling stress and emergency Assimilation of food, conservation of energy 32

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FUNCTIONS OF ANS Sympathetic “Fight or flight” “E” division Exercise, excitement, emergency, and embarrassment Parasympathetic “Rest and digest” “D” division Digestion, defecation, and diuresis 34

Antagonistic Control: 

Antagonistic Control Most internal organs are innervated by both branches of the ANS which exhibit antagonistic control A great example is heart rate. An increase in sympathetic stimulation causes HR to increase whereas an increase in parasympathetic stimulation causes HR to decrease 35

Exception to the antagonism rule:: 

Exception to the antagonism rule: Symp and parasymp work cooperatively to achieve male sexual function. Parasymp is responsible for erection while symp is responsible to ejaculation. There’s similar ANS cooperation in the female sexual response

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Exception to the dual innervation rule: Sweat glands and blood vessel smooth muscle are only innervated by symp and rely strictly on up-down control. . 37


ENTERIC NERVOUS SYSTEM ENS is the system of neurons and their supporting cells are found in the walls of GIT, including neurons within the pancreas and gall bladder. It is derived from the neuroblasts of the neural crest that migrate to GIT along the Vagus nerve. ENS having extraordinary degree of local autonomy. Digestion and peristalsis, occurs after spinal cord transaction or during spinal anaesthesia, although sphincter function may be impaired. 38

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It contains Myenteric / Auerbach plexus Submucous / Meissner plexus. Acetylcholine is principle excitatory trigger of non- sphincteric portion of ENS. It causes muscle contraction, activation of motor neurons augmenting secretion of water & electrolytes & stimulation of gastric cells . NE- transmitter of postganglionic sympathetic neuron(T8-L3) to gut-inhibits gut action. ( explains postop ileus) 39

ANS Neurotransmitters: 

ANS Neurotransmitters All autonomic preganglionic neuron release Ach on to cholinergic nicotinic receptors Most post ganglionic sns release NE on to adrenergic receptors except sweat gland & BV (release ach on cholinergic recep ) Most post ganglionic pns release Ach on to cholinergic muscarinic receptors Sns fibres ending in adrenal medulla release Ach as they are preganglionic neurons-ach interacts with chromaffin cells & release EPI(80%) & NE 40

Synthesis & Metabolism of ACH: 

Synthesis & Metabolism of ACH 41


Catecholamines A catecholamine is any compound having a catechol nucleus (a benzene ring with 2 adjacent OH group) and an amine containing side. Endogenous catecholamines in humans are dopamine, NE and EPI. Dopamine is a neurotransmitter in CNS and primarily involved in co- ordinating motor activity in the brain. It is a precursor of NE. NE is synthesized and stored in the nerve endings of postganglionic SNS neurons. Catecholamines are often referred to as adrenergic drugs because their effector action is mediated through receptors specific for the SNS. 42

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Regulation : Increased SNS activity as in chronic stress stimulates the synthesis of tyrosine hydroxylase & dopamine  hydroxylase . Glucocorticoid from the adrenal cortex pass through the adrenal medulla and stimulate increase in phenylethanolamine N methyl transferase that methylates NE to EPI. The release of NE is dependent upon depolarization of the nerve and an increase calcium ion permeability. NE inhibits its own release by stimulating presynaptic prejunctional alpha 2 receptors. 44

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Inactivation : Catcholamine are removed from the synaptic cleft by 3 mechanism. These are (a) reuptake into the presynaptic terminals, (b) extraneuronal uptake, and (c) Diffusion into circulation Termination of NE at the effector site is almost entirely by reuptake of NE into the terminals of presynaptic neurons (uptake 1) and this is stored in the vesicle for reuse. A small amount is deaminated in the cytoplasm of the neuron by MAO to form dihydroxyl mandelic acid. 45

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Uptake 1 is an active energy requiring temperature dependent process that can be inhibited. Extraneuronal uptake (uptake 2) is a minor pathway for inactivation of NE and NE that is taken up by the extraneuronal tissue is metabolized by MAO and COMT to form VMA. The importance of uptake 1 & uptake 2 is diminished when sympathomimetics are given exogenously, diffusion is the predominant pathway for catecholamines given exogenously and is metabolised in liver & kidney. 46



Cholinergic receptors : 

Cholinergic receptors 48

Nicotinic receptors : 

Nicotinic receptors Rossette like Pentameric structure which encloses a ligand gated cation channel Present in; -plasma membrane of preganglionic S&P neurons -adrenal medulla -skeletal muscle motor ending plate Two types: Nm & Nn 49

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Muscarinic receptors These are 7 transmembrane domain, G-protein coupled receptors. M 1, M 3,& M 5 51

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Muscarinic receptors M 2 & M 4 52

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Adrenergic Receptors: 

Adrenergic Receptors 56

α1 Adrenergic receptor: 

α 1 Adrenergic receptor G protein-coupled receptor (GPCR) associated with the G q heterotrimeric G-protein . It consists of 3 highly homologous subtypes, including α 1A , α 1B , and α 1c adrenergic 57

α1 Adrenergic receptor( post synaptic): 

α1 Adrenergic receptor( post synaptic) Present in Smooth muscle fibres of Most arteries-vasoconstriction Myocardium-mediate perhaps as much as 30-50% of the basal ionotrophic tone of the normal heart Splenic capsule- contraction Uterus- contraction Vas deferens- contraction Prostatic capsule- contractin Ureter-contraction Urinary bladder & gi sphincters- contraction(closure of sphincter) Radial muscles of eye-contraction( mydriasis ) Kidney (tubules)- antinatriuresis Salivary gland- increase secretion Sweat gland on palms n soles- sweating Liver- increase glycogenolysis

α2 (pre& post synaptic)Adrenergic receptor : 

α 2 (pre& post synaptic)Adrenergic receptor G protein-coupled receptor (GPCR) associated with the G i heterotrimeric G-protein . It consists of 3 highly homologous subtypes, including α 2A , α 2B , and α 2C adrenergic 59

α2 Adrenergic receptor : 

α2 Adrenergic receptor Prejunctional on nerve endings- inhibit NE transmitter release-vasodilation Post junctional - on posterior pituitary-secrete ADH JG cells kidney- secrete renin Kidney (tubules)- water n na excretion Pancreas- decrease insulin release smooth muscles of most veins- vasoconstriction Platelets- aggregation


α-PERIPHERAL VESSELS Activation of presynaptic  2 vascular receptor inhibit NE release, produces vasodilatation. Whereas postsynaptic  1 and  2 vascular receptors subserve vasoconstriction. Postsynaptic α1 and  2 receptors co-exist in both the arterial and venous sides of the circulation with relative distribution of  2 receptors being greater on the venous side. Nor epinephrine is the most potent venoconstrictor of all the catecholamine 61


 -RECEPTORS IN CNS There is a close association between α and β for BP and HR control. Cerebral and Spinal cord presynpatic  2 receptors also involved in inhibition of presynpatic NE release. Central neuraxial injection of  2 agonists such as clonidine act at these sites to produce analgesia, sedation and CVS depression 62


 -RECEPTORS IN THE KIDNEY The greatest density of adrenergic receptors innervation is present in the thick ascending loop of Henle followed by DCT and proximal tubule. Both α1 and  2 are found but  2 is dominating, a1 receptor predominantes in the renal vasculature and elicits vasoconstriction which modulates renal blood flow. Tubular α1 receptors enhance sodium and water reabsorption leading to anti-natriuresis where as tubular  2 receptors promotes sodium and water excretion. 63

β Adrenergic receptor: 

β Adrenergic receptor It is a G-protein coupled receptor associated with the Gs heterotrimeric G-protein. They are further divided into β 1, β 2 & β 3. 64

Β1 receptor: 

Β 1 receptor Present in heart- increses rate of conduction & Force of contraction JG cells of kidney- increases renin

Β2 receptor: 

Β 2 receptor Presynaptic - increase NE release Post synaptic on Smoot muscles of blood vessels- vasodilation Airways- bronchodilation Ciliary muscles of eye- relaxation Git & detrusor muscle- relaxation Liver hepatocytes- increse glucogenolysis Pancreas- increase glucagon Decrease peripheral sensitivity to insulin-HYPERGLYCEMIA On RBC & muscle cells- intake of k+ -HYPOKALEMIA

-receptors in CVS: 

 -receptors in CVS  1 and  2 receptors are present in myocardium & are functionally coupled to adenyl cyclase . Post synaptic  1 receptors are distributed predominantly to myocardium in SA node and ventricular conduction system.  2 receptors have the same distribution but are presynaptic. Activation of  2 presynaptic receptors accelerates the release of NE into the synaptic cleft. The effect of NE on ionotropism in the normal heart is mediated entirely through the postsynaptic  1 receptors whereas the ionotropic effects of EPI are mediated through both the  1 and  2 receptors.  2 receptors may also mediate the chronotrophic response to EPI because selective  1 antagonists are less effective in suppressing induced tachycardias than the non selective  antagonist propranolol. 67

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Peripheral vessels: 

Peripheral vessels Greatest numbers of DA1-postsynaptic receptors are found on vascular smooth muscle cells of the kidney and mesentery. The vascular receptors are like the  2 receptors linked to adenyl-cyclase and mediate smooth muscle relaxation. Activation of these receptors produces vasodilatation increasing blood flow to the organs. Concurrent activation of vascular presynaptic DA2 receptors also inhibits NE release at the presynaptic  2 receptors. Higher doses of dopamine can mediate vasoconstriction via the postsynaptic 1 and  2 receptors. 71

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Central nervous system: 

Central nervous system Dopamine receptors have been identified in the hypothalamus where they are involved in prolactin release. They are also found in basal ganglia where they coordinate motor function. Central action of dopamine is to stimulate the CTZ of medulla producing nausea and vomiting. 73

GIT, Kidney & Mesentery: 

GIT, Kidney & Mesentery Dopamine receptors are found in the smooth muscle of esophagus, stomach, small intestine  enhance secretion, production & decrease intestinal motility. DA1 receptors are located on renal tubules which inhibits sodium reabsorption with subsequent natriuresis and diuresis. It reduces afterload via dilatation of the renal and mesenteric arterial beds. The natriuresis may be the result of combined renal vasodilatation, improved cardiac output and tubular action of DA1 receptors. JG cells also contain DA2 receptors which increases renin release when activated. This action modulates the diuresis produced by DA1 activation of tubules. 74


AUTONOMIC INNERVATION Heart: The heart is well supplied by SNS and PNS. These nerves affect cardiac pumping is 3 ways - By changing the rate ( Chronotropism ) By changing the strength of contraction ( Inotropism ) Modulating coronary blood flow. The PNS cardiac vagal fibres approaches the stellate ganglion and then join the efferent cardiac SNS fibres . 75

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The PNS fibres are distributed mainly to SA and AV node and to a lesser extent to the atria. The main effect of Vagal cardiac stimulation to the heart is chronotrophic . Vagal stimulation decreases the rate of SA node discharge and decreases the excitability of the AV junction fibers. 76

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SNS has the same supraventricular distribution as the PNS but with strongest representation, to the ventricles. SNS efferents to the myocardium funnel through the paired stellate ganglion. Right stellate distributes primarily to ant epicardial surface & interventricular septum.its stimulation decreases systolic duration and increases the heart rate. Left stellate ganglion supplies posterolateral ventricles & stimulation increases mean arterial pressure & left ventricular contractility without causing a substantial change in the heart rate. 77

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Lungs : Lungs are innervated by both SNS and PNS. Postganglionic SNS fibres from upper thoracic ganglia ( stellate ) pass to the lungs to innervate the smooth muscles of the bronchi and pulmonary blood vessels. PNS innervation of these structures is from the vagus nerve. 78

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Both SNS and the vagus nerve provide active bronchomotor control. SNS stimulation produces bronchodilatation and pulmonary vasoconstriction. Vagal stimulation produces bronchoconstriction & may increase secretion of bronchial glands. 79

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Effector organ Adrenergic response Receptor Cholinergic response Receptor HEART Rate of Contraction Increase β 1 Decrease M2 Force of Contraction Increase β 1 Decrease M2 LUNG Bronchiolar smooth muscle Bronchodilatation β 2 Bronchoconstriction M3 80

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Effector organ Adrenergic response Receptor Cholinergic response Receptor Arteries (most) Vasoconstriction α 1 Veins Vasoconstriction α 1 Skeletal muscle Vasodilatation β 2 Endothelium Release EDRF M3 81

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Effector organ Adrenergic response Receptor Cholinergic response Receptor GENITO-URINARY & SMOOTH MUSCLE. Baldder wall Relaxation β 2 Contraction M3 Ureter Contraction α 1 Relaxation M3 Sphincter Contraction α 1 Relaxation M3 Uterus (pregnant) Relaxation Contraction β 2 α 1 Variable M3 Penis/Vas deferens Ejaculation α 1 Erection M3 82

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Effector organ Adrenergic response Receptor Cholinergic response Receptor Gastro -Intestinal tract Glands Increase secretion α 1 Increased secretion M3 Smooth muscle Walls Sphincters Relaxation Contraction α 2 β 2 α 1 Contraction Relaxation M3 M3 Secretions Increase secretion M3 83

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Effector organ Adrenergic response Receptor Cholinergic response Receptor SKIN Hair follicles Smooth muscles Contraction Piloerection α1 ------ ------ SWEAT GLANDS Thermoregulation Apocrine (stress) ------ Increased secretion --------- α1 Increased secretion M3 84

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Effector organ Adrenergic response Receptor Cholinergic response Receptor EYE Iris Radial muscle Circular muscle Contraction ---------- α1 ----- ------------ Contraction M3 Ciliary muscle Relaxation β 2 Contraction M3 Ciliary epithelium ↑secretion of Aqueous Humour β 2 --------- 85




OCULO-CARDIAC REFLEX (TRIGEMINO-VAGAL REFLEX) Stimulus Traction on Extra ocular muscle. Pressure on eyeball. Increase in intraocular pressure. Afferent Long & short ciliary nerves (branch of Trigeminal nerve) Center Main Sensory nucleus of Trigeminal n. Efferent Vagus n. Effects Sinus bradycardia , Cardiac Dysrhythmias , Ventricular fibrillation & Asystole . Bernard Aschner & Guiseppe first described this reflex in 1908. 87


CAROTID SINUS REFLEX Stimulus ↑BP & HR Afferent Glossopharyngeal n. Center Receptors present in Carotid vessels & Aortic arch. Efferent Vagus n. Effect ↓BP & HR 88


NASOCARDIAC REFLEX Stimulus Irritation of nasal cavity (by nasal specules , nasal retractor or ET tube) when anaesthesia is inadequate. Afferent Maxillary & Ethmoidal division of Trigeminal n. Center Brainstem nuclei. Efferent Vagus n. Effect ↓BP & HR. 89


PHARYNGEAL REFLEX Stimulus An airway introduced in anaesthesia that is too light, irritation by mucus Afferent Glossopharyngeal Efferent Vagus Effect Swallowing followed by Laryngospasm 90


LARYNGEAL REFLEX (THE KRATSCHMER REFLEX) Stimulus Noxious, mechanical or chemical stimulation of laryngeal mucosa. Afferent Superior laryngeal nerve ( br.of Vagus ) Center Receptors of Hypopharynx , Supraglottic & Glottic region. Efferent Recurrent laryngeal nerve (br. of Vagus ) Effect Closure of Vocal cords. Transient check or arrest of respiration. Sensitivity of this reflex is reduced by age, CNS depressant drugs & Anaesthetics . 91


TRACHEAL REFLEX : (VAGO-VAGAL REFLEX) Stimulus ET intubation, cuff inflation, suctioning, foreign body in trachea. Afferent Vagus Center Dorsal nucleus of Vagus Efferent Vagus Effect Laryngospasm, Bronchospasm , bucking. Cardiac – arrhythmias, hypotension. First described by Brace & Reid . 92


ABDOMINAL REFLEX Stimulus During operations within the abdominal cavity autonomic nerves get stimulated by traction pressure on the viscera. Afferent Splanchnic nerves Efferent Vagus Effect Respiration-apnea followed by tachypnea with or without laryngospasm. CVS- Bradycardia , hypotension Peritoneal, mesenteric reflex, & celiac plexus reflex have same effects. 93


TESTS OF AUTONOMIC SYSTEM FUNCTION These tests measure how the various systems in the body, controlled by autonomic nerves, respond to stimulation. The data collected during testing will indicate functioning of ANS. Early autonomic dysfunction is defined as a single abnormal or two borderline-abnormal results on the tests involving changes in heart rate. Definite involvement comes when two of the tests of changes in heart rate are abnormal . Severe dysfunction is defined as abnormalities in the blood pressure assessments. Tests are done to monitor BP, blood flow, heart rate, skin temperature and sweating. 94

Indications for ANS testing: 

Indications for ANS testing Syncope Central autonomic degeneration ex. Parkinsons Pure autonomic failure Postural tachycardia syndrome Autonomic and small fiber peripheral neuropathies ex.- diabetic neuropathy Sympathetically mediated pain Evaluating response to therapy Differentiating benign symptoms from autonomic disorders 95

Parasympathetic function tests: 

Parasympathetic function tests HR response with valsalva manoeuver Valsalva manoeuver : valsalva ratio is an index of HR response to BP changes that occur during valsalva manoeuver resulting from mechanical and cardiovascular effects. Measure baseline HR and BP 3 minutes before this test Patient takes a deep inhalation, a complete exhalation, inhales again and then blows into a mouthpiece for 15 seconds Expiratory pressure is maintained at 40 mm Hg. This pressure can be measured by having the patient to exhale through a mouth piece attached to a transducer 96

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BP and HR are measured throughout the manoeuver for 60 seconds after temination of the manoeuver An average of 2 trials are taken for analysis Caution while performing the test in elderly with pulmonary disease who may not be able to perform the test satisfactorily As intraocular pressure is known to rise, the test must not be performed in those with recent retinal surgery VR values are aggregated. There is a decrease with age. 97

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VR=longest R-R /shortest R-R. a normal VR indicates an intact baroreceptor mediated increase and decrease in HR. a decreased VR reflects baroreceptor and cardiovagal dysfunction. Normal value is a ratio of >1.21 Stimulus Expiration of 40mm Hg for 15sec. Afferent Baroreceptors , Glossopharyngeal & Vagus nerves. Central Nucleus Tractus Solitarus Efferent Vagus & sympathetic nervous system. Response Heart rate response to blood pressure changes Increase/Decrease in BP (phases I-IV) 98

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HR variability with respiration (respiratory sinus arrhythmia) Respiratory sinus arrhythmia is recorded with patient supine & breathing at fixed rate of 6 breaths/min with slow inhalation & exhalation. This provides close to maximum HR variability. 6-8 cycles are recorded with one or two trials being performed. Timed breathing potentiates normal sinus arrhythmia that occurs during the normal respiratory cycles Reduced HR variability with respiration is seen in aging, autonomic peripheral neuropathies and central autonomic degenerations. Other factors which can influence this test are poor respiratory efforts, hypercapnia , salicylates poisoning, obesity 99

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MEAN OF DIFFERENCE(Maximum HR- Minimum HR) during 3 consecutives breath cycles taken Normal value is a mean difference of >15 BPM. Stimulus Deep breathing (6cycles/min) Afferent Pulmonary receptors, Cardiac mechanoreceptors, Vagus & Glossopharyngeal nerves, Respiratory centre . Center Nucleus tractus solitaries Efferent Vagus Response Heart rate increases during Inspiration. Heart rate decreases during Expiration. 100

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The 30:15 ratio (HR response to standing) With patient in supine position baseline HR is measured Patient is asked to quickly stand up HR variability is measured for at least 1 min of active standing A normal ratio is greater than 1 & reflects intact vagally mediated HR changes. An abnormal ratio indicates parasympathetic cardiovagal dysfunction Misinterpretations of this test can occur in hypovolemia , medical deconditioning , and hypothyroidism. 101

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After standing HR ↑ Exercise, reflex/withdrawl of parasympathetic tone. Approx 15sec later HR ↑↑ Compensatory response to decreased venous return, cardiac output & BP. At approx 30 sec Relative bradycardia Stimulus Decreased central blood volume. Afferent Baroreceptors , E rgoreceptors , Vagus & Glossopharyngeal nerves. Center Nucleus tractus solitaries, Rostral ventrolateral medulla. Efferent Vagus Response HR increases at approx 15 sec. HR decreases at approx 30 sec. 102

Sympathetic function tests : 

Sympathetic function tests Blood pressure response to sustained hand grip Sustained hand grip causes reflex increase in heart rate & cardiac output without changing systemic vascular resistance. Diastolic BP thus normally increases. BP is measured every min for 5 min. The initial diastolic BP is substracted from the diastolic BP just before release. The normal value is difference of >16mm Hg. 103

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Blood pressure response to standing The patient moves from resting supine to standing position. The standing Systolic BP is substracted from the supine Systolic BP. The normal value is difference of <10mm Hg. 104

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Head Up Tilt Table Test This test determines BP & HR response to an orthostatic challenge as a measure of sympathetic function. Used to access orthostatic intolerance caused by sympathetic nervous system dysfunction & to detect any predisposition to vasovagal syncope. Patient lies supine on a tilt table & a belt is placed around the waist to secure them in case of syncope. BP & ECG are monitored throughout the tests & recorded. Baseline BP is recorded for atleast 3 min. 105

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Patient is slowly tilted upright to an angle of 60-80°. Patient is asked to report any symptoms. Patient is returned to horizontal supine position. HR & BP are monitored in supine position until it returns to baseline. IV Isoproterenol , a pharmacological measure to potentiate orthostatic challenge to the tilt table test, is frequently used. A normal tilt table test is one in which there are no symptoms & a modest fall in BP. 106

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Stimulus Decreased central blood volume. Afferent Baroreceptors , Vagus & Glossopharyngeal nerves Center Nucleus Tractus Solitarus , Rostral ventrolateral medulla, Hypothalamus. Efferent Sympathetic vasomotor Response Pattern, degree & rate of BP changes. HR increase/decrease. 3 patterns: a) Vasodepression resulting in hypotension without bradycardia . b)Marked bradycardia (<40/min) with or without fall in BP. c)Both bradycardia & Hypotension. 107

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Other tests used are- Sympathetic Cholinergic Sweat Function Quantitative Sudomotor Axon Reflex Test. Silastic Imprint Test. Thermoregulatory Sweat Test. Microneurography . 108


REFERENCES Miller`s Anaesthesia- 7 th ed. Barash Clinical Anesthesia- 6 th ed. Ganong`s Review of Medical Physiology-23 rd ed. ISACON 2009. 109