ANS_Physiology_-_2023 (1).pptx

Autonomic Nervous System Physiology Fight or flight Sympathetic Rest and digest Parasympathetic Gastrointestinal fxn Enteric 1°: Kristin Gosselink, Ph.D. 2°: Tom Eiting, Ph.D. CVS-1 Fall 2023 Learning Objectives: Reading: Guyton and Hall; Chapter 61 • Compare and contrast the innervation a...

Autonomic Nervous System Physiology Fight or flight Sympathetic Rest and digest Parasympathetic Gastrointestinal fxn Enteric 1°: Kristin Gosselink, Ph.D. 2°: Tom Eiting, Ph.D. CVS-1 Fall 2023 Learning Objectives: Reading: Guyton and Hall; Chapter 61 • Compare and contrast the innervation and functions of the sympathetic nervous system with the parasympathetic nervous system • Explain the organization of the autonomic nervous system and the concept of dual innervation • Describe how the enteric nervous system and adrenal medulla are functionally related to the autonomic nervous system • Define the major autonomic nervous system neurotransmitters and where they act COMLEX: • Parasympathetic • Preganglionic ACh activates nAChR • Postganglionic ACh activates mAChR Where is the ANS acting? What’s the neurotransmitter? What’s the receptor / pharmacology? • Sympathetic • Preganglionic ACh activates nAChR • Postganglionic NE activates alpha and beta adrenergic receptors • Control of GI system • ANS branches to include enteric nervous system; activity slowed by symp, promoted by parasymp • Renal control – constriction of afferent arteriole decreases glomerular filtration rate (GFR) and increases filtration fraction ee GI and Renal later…not critical for me on this test, but you should be able to define the “enteric nervou Overview The ANS is an effector/efferent/MOTOR system, with neuronal output to peripheral tissues other than skeletal muscle The ANS controls visceral function; it is constantly active; it integrates behavioral and emotional responses; it receives input from multiple sources The sympathetic and parasympathetic branches of the ANS do not always have opposing effects - there can be dual or single innervation of tissues dual innervation effects can be antagonistic or complimentary the sympathetic nervous system is not always an activator the parasympathetic nervous system is not always an inhibitor In both sympathetic and parasympathetic, there are 2 neurons between the spinal cord and the effector tissue; pre-ganglionic and post-ganglionic neurons that connect at a ganglion - preganglionics are (lightly) myelinated - postganglionics are unmyelinated Autonomic overview Both systems *may* act together - extreme fear - sexual arousal • Regulates glands, smooth muscle, cardiac muscle • Sympathetic • • • • Thoracolumbar Widespread effects through sympathetic Catabolic chains Flight or Flight - paravertebral chain - prevertebral plexus Energy expenditure Preganglionic cell bodies in IML column T1-L2 • Parasympathetic Craniosacral • • • • Anabolic Widespread effects through vagus n. - otherwise fairly localized Rest and Digest Energy conservation Preganglionic cell bodies in S2-S4 plus cranial nerves 3, 7, 9, 10 General organization of the peripheral components of the SYMPATHETIC nervous system Thoraco-Lumbar Paravertebral sympathetic chain of ganglia between spinal nerves and effectors Prevertebral ganglia (4) = peripheral sympathetic ganglia Similar to the paravertebral ganglia in general function. Nerves that synapse in the prevertebral ganglia innervate the pelvic viscera (targets = enteric nervous system, renal system, bladder, other abdominal organs) Preganglionic (red, lightly myelinated) = Acetylcholine (ACh) *Except for sweating = ACh Postganglionic (black, unmyelinated) = Norepinephrine (NE) Paravertebral ganglia chain – look at all the red-to-black connections Preganglionic Neuron (red) Preganglionic Neuron (red) Postganglionic neurons from paravertebral Postganglionic neurons from prevertebral Prevertebral ganglia – look at how the red preganglionic neurons can synapse at the paravertebral AND pass through to synapse General organization of the peripheral components of the PARASYMPATHETIC nervous system Cranio-Sacral In most cases, preganglionic fibers pass uninterrupted to the organ that is to be controlled. Postganglionic neurons are often located in the wall of the target organ and are very short. Preganglionic (blue) & Postganglionic (black) = acetylcholine (Ach) *Vagus nerve Generally has localized responses * aricosities; a modified synapse Most sympathetic postganglionic axons store norepinephrine (NE) in varicosities and release it over the surface of the target tissue. Postganglionic parasympathetic axons store ACh in varicosities and release it onto the target tissue surface I believe you will have seen this elsewhere... Neurotransmi tter synthesis Acetylcholinest erase (AChE) breaks it down This is an important factor in the NMJ rate limiting PNMT TH “Catecholamines” DBH I know you will see this elsewhere...multiple places eceptors for ANS outputs Activates phospholipase C Increases IP3, DAG, PKC, Ca2+ nAChR – a ligand-gated ion channel mAChR – a G-protein-coupled receptor (GPCR) M1,3,5 = Gq; Alpha-adrenergic – GPCR α1 = Gq; α2 = Gi Beta-adrenergic – GPCRβ1 = Gs; β2 = Gs: β3 = Gs Activates adenylyl cyclase Increases cAMP These are sometimes difficult to remember but you’ll see them in multiple systems. You should become familiar with GPCR types and which are used in the various adrenergic pathways. M2,4 = Gi Inhibits adenylyl cyclase Decreases cAMP Contrasting autonomic effects Sympathetic Dilates pupil Parasympathetic Constricts pupil Increases sweat gland secretion --- (cholinergic) --Increases heart rate Increases lacrimation and Dual / Antagonistic salivation (watery) Decreases heart rate Increases ventricular contraction Decreases ventricular contraction - Enteric NS force force Dilates bronchial tubes Constricts bronchial tubes Inhibits GI motility and secretion Simulates GI motility and secretion Contracts GI sphincters Complimentary Relaxes GI sphincters Relaxes bladder/contracts sphincter Contracts bladder/relaxes sphincter (see Table 61-2 in Guyton for Symp/Parasymp contrasting Sympathetic “Tone” Continuous, basal rate of activity Modifiable over time Allows for maintenance of function PLUS ability to respond as needed Note that vasodilation occurs here in response to a withdrawal of sympathetic activation You’ll see more of this in od pressure; flow, pressure, and resistance CV1, and then these Adrenergic β1 same concepts in the respiratory system and at least in part during renal. Adrenergic α1 Central control of the ANS Hypothalamus is the master control for ANS Damage/lesion can have broad effects on thermoregulation, appetite, fear/rage, sexual function Some of the most important factors controlled in the brain stem are arterial pressure, heart rate, and respiratory rate. adrenal medulla as a modified sympathetic ganglion Preganglionic sympathetic nerve fibers pass, without synapsing, all the way from the spinal cord, through the sympathetic chains and splanchnic nerves, into the adrenal medullae. They end directly on modified neuronal cells that secrete epinephrine and norepinephrine into the blood stream. Works with the sympathetic nervous system and can impact tissues that do not have direct sympathetic innervation. Effects last longer because We will see this again in Endo/Repro Responses and the Adrenal Gland (medulla *and* cor Two neuroendocrine responses, both involve the adrenal gland, operate on different time Common ANS misconceptions Misconception – there are only 2 branches of the ANS (Symp/Parasymp) Also ENTERIC Misconception – no voluntary influence or awareness of physiological effects of ANS There *IS* voluntary awareness and influence (e.g., biofeedback training and control of stress) Misconception – activation of parasympathetic to blood vessels dilates them and decreases BP It is withdrawal of sympathetic; effect on penile blood vessels is secondary to parasymp activation – e.g., nitric oxide Misconception – all Symp postganglionics release NE Can release ACh related to sweating Misconception – Symp is always excitatory on its targets Misconception – antagonism = 50:50 balance of symp/para Para dominant at rest, Symp dominant during activation/stress Misconception – Symp always contracts smooth muscle and Para always relaxes Respiratory system it’s the opposite – also gastrointestinal Misconception – the two divisions of the efferent peripheral nervous system (autonomic and somatomotor) always operate independently from one another They work together in micturition, defecation, and sexual function Misconception – activation of parasymp reduces cardiac contractility No – Para innervates atria and reduces atrial contractility but only Symp innervates ventricle Misconception: Vagus nerve = efferent Only 20% of vagus fibers are efferent; 80% are afferent and are responsible for therapeutic effects of vagal nerve stimulation Misconception: Afferent sensory fibers from autonomic effector organs are part of ANS ANS is purely efferent; these are visceral sensory afferents; they *do* travel in same nerve bundle as efferent autonomic fibers Misconception: Baroreceptors are pressure sensors Baroreceptors are actually stretch receptors (vascular wall) Misconception: Baroreceptors are important for long term control of systemic BP Short-term control, prevent large fluctuations during different behaviors (like change in posture) Misconception: Symp NS responds as “all or none” Capable of discrete activation to mediate appropriate responses to specific stimuli Misconception: shivering is the only way to increase heat production in the cold Symp NS innervation of brown adipose tissue is involved in thermogenesis Misconception – vasodilation in skeletal muscle vessels is due to Parasymp activity Local metabolites (NO, K+, ATP, etc.) = “functional sympatholysis”; skeletal muscle vasodilation to counter the effects of increased Symp input Misconception – BP drops during Ex because of vasodilation Systemic responses prevent a drop in MAP