Autonomic Nervous System (ANS) Lecture Notes PDF

Curriculum: Phase 1/ Semester3/ CVS/ Session 4 Lecturer: teacher Dr. Shahlaa khazaal chabuk Degrees: MSc/Ph.D. Phsiology  CVS ‫الجهاز العصبي الالإرادي‬ The Autonomic Nervous System CVS  The Autonomic Nervous System (ANS) Important for regulating many physiolog...

Curriculum: Phase 1/ Semester3/ CVS/ Session 4 Lecturer: teacher Dr. Shahlaa khazaal chabuk Degrees: MSc/Ph.D. Phsiology  CVS ‫الجهاز العصبي الالإرادي‬ The Autonomic Nervous System CVS  The Autonomic Nervous System (ANS) Important for regulating many physiological functions Largely outside voluntary control Exerts control over – smooth muscle (vascular and visceral) ‫إفراز اإلفرازات الخارجية‬ – exocrine secretion ‫معدل وقوة االنقباض في القلب‬ – rate and force of contraction in the heart  Two divisions of the ANS Parasympathetic nervous system Sympathetic nervous system ‫تتضمن بعض الكتب املدرسية قسما ثالثا هو الجهاز العصبي املعوي‬ Some text books include a third division the enteric nervous system ‫شبكة من الخاليا العصبية املحيطة بالجهاز الهضمي‬ – Network of neurones surrounding GI tract ‫عادة ما يتم التحكم فيه عن طريق األلياف املتعاطفة وغير السمبتاوية‬ – Is normally controlled via sympathetic and parasympathetic fibres  ‫تنظيم األنظمة املتعاطفة وغير السمبتاوية‬ Organization of sympathetic and parasympathetic systems ‫اثنان من الخاليا العصبية مرتبة في سلسلة‬ Two neurones arranged in series Central Nervous system Peripheral Nervous Target system cell Preganglionic Postganglionic neuron neuron (‫يتم تنشيط الجهاز العصبي الالإرادي بشكل أساسي عن طريق املراكز املوجودة في الحبل الشوكي وجذع الدماغ وما تحت املهاد )أي يوجد جسم الخلية للعصبون قبل العقدة في الجهاز العصبي املركزي‬ The autonomic nervous system is activated mainly by centers located in the spinal cord, brain stem, and hypothalamus (i.e. Cell body of preganglionic neurone is in the CNS)  ‫تنظيم القسم املتعاطف‬ Organization of the sympathetic ‫أصل الصدر القطني‬ division Thoracolumbar origin (L3 ‫ )أو‬L2 ‫ إلى‬T1 ‫تنشأ الخاليا العصبية قبل العقدية من األجزاء‬ Preganglionic neurones arise from segments T1 to L2 (or L3) (‫معظم املشبك مع الخاليا العصبية بعد العقدية في السلسلة الفقرية للعقد )سلسلة الودي‬ Most synapse with postganglionic neurones in the paravertebral chain of ganglia (sympathetic chain) ‫ العقد املساريقية الدنيا‬،‫ املساريقية العليا‬،‫ االضطرابات الهضمية‬- ‫بعض املشبك في عدد من العقد قبل الفقرية‬ Some synapse in a number of prevertebral ganglia – coeliac, superior mesenteric, inferior mesenteric ganglia ‫عصبون طويل بعد العقدة‬ Long postganglionic neuron  Organization of the parasympathetic division ‫األصل القحفي العجزي‬ Craniosacral origin ‫تنتقل األلياف قبل العقدة في األعصاب القحفية‬ Preganglionic fibres travel in cranial nerves (III, VII, IX & X) S2-S4 ‫أو التدفق العجزي من‬ or sacral outflow from S2-S4 ‫املشبك مع الخاليا العصبية في العقد بالقرب من األنسجة املستهدفة‬ Synapse with neurones in ganglia close to the target tissue ‫الخاليا العصبية القصيرة بعد العقدة‬ Short postganglionic neurones  Arrangement of pre- and postganglionic neurones Sympathetic Preganglionic Postganglionic Target tissue Parasympathetic Postganglionic Preganglionic Target tissue  Preganglionic neurones of both divisions release acetylcholine Preganglionic Postganglionic Acetylcholine (ACh) +K +K ACh acts on nicotinic Ach receptors on the +Na postganglionic cell. Nicotinic ACh receptors have an ion channel.  Neurotransmitters at the postganglionic cell to effector cell synapse Postganglionic sympathetic neurones are usually noradrenergic (use noradrenaline (NA) as a transmitter) Postganglionic parasympathetic neurones are usually cholinergic (have ACh as transmitter) The exceptions of sympathetic innervation include The postganglionic sympathetic nerve fibers to : the sweat glands to the piloerector muscles of the hairs to a very few blood vessels are cholinergic Neurotransmitters in the sympatheticnervous system Adrenergic receptors nicotinic ACh receptors Preganglionic Postganglionic noradrenaline (NA) (norepinephrine) acetylcholine (ACh)  Chromaffin cells of the adrenal medulla are like specialized postganglionic sympathetic neurons Pregangli chromaffin adrenaline onic cell (epinephrine) acetylcholine (ACh) adrenal chromaffin cells release adrenaline which circulates in the blood stream Receptors to noradrenaline and adrenaline adrenoreceptors. G protein-coupled receptors – no integral ion channel Types and subtypes of adrenoreceptors – α-adrenoreceptors α1-adrenoreceptors α2-adrenoreceptors – β-adrenoreceptors β1-adrenoreceptors β2-adrenoreceptors Neurotransmitters in the parasympathetic nervous system nicotinic ACh receptors muscarinic ACh receptors Preganglionic Postganglionic effector cell acetylcholine (ACh) Neurotransmitters in the parasympathetic nervous system parasympathetic postganglionic neurones use ACh as a neurotransmitter ACh acts at muscarinic receptors on the effector cells G protein-coupled receptors (M1, M2 & M3) no integral ion channel What does the autonomic nervous system do? regulates physiological functions where parasympathetic and sympathetic divisions both innervate a tissue they often have opposite effects sympathetic activity is increased under stress parasympathetic system is more dominant under basal conditions both work together to maintain balance note: Sympathetic drive to different tissues is independently regulated eg sympathetic activity to the heart can be increased without increasing activity to GI tract on some occasions (fight or flight) there can be a more co-ordinated sympathetic response Control of the cardiovascular system The ANS controls – heart rate – force of contraction of heart – peripheral resistance of blood vessels Parasympathetic input to the heart preganglionic fibres - 10th (X) cranial nerve VAGUS synapse with postganglionic cells onepicardial surface or within walls of heart at SA and AV node postganglionic cells release ACh acts on M2-receptors – decrease heart rate (-ve chronotropic effect) – decrease AV node conduction velocity Sympathetic input to the heart Postganglionic fibres from the sympathetic trunk Innervate SA node AV node and myocardium Release noradrenaline Acts on β1 adrenoreceptors – increases heart rate (+ve chrontropic effect) – increases force of contraction (+ve inotropic effect) The pacemaker of the heart Cells in the sinoatrial node (SA node) steadily depolarise toward threshold – slow depolarising pacemaker potential – turning on a slow Na+ conductance – opening of Ca2+ channels AP firing in the SA node sets the rhythm of the heart  Effect of ANS on pacemaker potentials sympathetic activity increases slope Parasympathetic activity decreases slope of the Pacemake potential parasympathetic effect sympathetic effect mediated by M2 mediated by β1 receptors receptors G-protein coupled G-protein coupled receptorsIncrease cAMP receptors Increase K+ speads up pacemaker conductanceand potential decrease cAMP How does noradrenaline increase the force of contraction? NA acting on β1 receptors in myocardium causes and increase in cAMP phosphorylation of Ca2+ channels increased Ca2+ entry during AP increased force of contraction also increased uptake of Ca2+ in sarcoplasmic reticulum ANS effects on vasculature most vessels receive sympathetic innervation – exceptions some specialised tissue eg erectile tissue have parasympathetic innervation most arteries and veins have α1-adrenoreceptors – coronary and skeletal muscle vasculature also have β2- receptors Effects of β2 adrenoreceptors and α1 adrenoreceptors on vascular smooth muscle Activating β2 adrenoreceptors causes vasodilation – increases cAMP opens a type of potassium channel relaxation of smooth muscle Activating α1 adrenoreceptors causes vasoconstriction – increase in [Ca2+]in from stores and via influx of extracellular Ca2+ contraction of smooth muscle Role of local metabolites Active tissue produces more metabolites – e.g. adenosine, K+, H+, increase PCO2 Local increases in metabolites have a strong vasodilator effect More important for ensuring adequate perfusion of skeletal and coronary muscle than activation of β2-receptors