Lecture 17 Autonomic Nervous System PDF

Autonomic Nervous System (ANS) Dr. Elita Partosoedarso Links to segment recordings: Part A, Part B, Part C  ANS overview Reflexes...

Autonomic Nervous System (ANS) Dr. Elita Partosoedarso Links to segment recordings: Part A, Part B, Part C  ANS overview Reflexes Overview The Autonomic Nervous System Long reflex arc Acetylcholine (ACh) Neurotransmitters Norepinephrine Parasympathetic (NE) division Sympathetic Division Dual innervation Referred pain  Overall function: Involuntary control of cardiac, respiratory, digestive, urinary, metabolic systems Main divisions autonomic nervous 1._______________: “rest and digest” Dominant Overview of the controller of most autonomic effectors most of the system (ANS) time 2._______________: “fight or flight” or “emergency” system 3._______________NS: contained entirely within the gut walls _______________ nerves ○Sensory (afferent) function: monitors internal and external environment in the periphery and sends it to the CNS ○Motor function: response to environmental changes so that homeostasis is maintained Enteric NS (ENS) _______________ innervation Entirely within the gut ▪ Regulates digestive function ○ Most organs and organ systems receive inputs from involuntarily both parasympathetic and sympathetic divisions ○ Homeostasis is the balance between the two systems 3 3  Reflexes and Homeostasis Reflex arc: automatic responses to a stimulus that bypasses conscious perception and thought.They are sensory-integrative- motor pathway Components of a reflex arc A. Sensory (afferent) pathway: detects stimuli (change in internal/external environment) and sends a signal to the CNS ○Stimulus can be the same for both somatic and visceral Efferent (autonomic) reflexes pathway for B. Interneuron: not always present. Processes information in somatic reflexes the CNS from various neurons C. Motor (efferent) pathway: receives instructions from the Efferent CNS and sends a signal to the effector cells in the periphery pathway for ○Somatic reflexes: Efferent pathway consist of a single visceral reflexes neuron projecting to skeletal muscles ○Visceral (autonomic) reflexes typically two neurons projecting to cardiac and smooth muscle and glands. All 4 autonomic neurons function in reflex arcs which ultimately Reflexes & the 3rd division of the ANS 11.Long reflexes Involves the CNS 1 Parasympathetic and sympathetic divisions: Preganglion communicates with the ENS Postganglio ic neuron nic neuron Two neuron efferent pathway Preganglionic neuron with cell body in brainstem nuclei or lateral horn of spinal cord 2 Postganglionic neuron with cell body in 2 peripheral ganglia 2. Short Reflexes Does not involve the CNS: Located completed within the peripheral NS Enteric nervous system: located entirely within walls of digestive system organized in two plexuses Myenteric plexus involved in coordinating smooth muscle contraction and relaxation in the digestive tract 5 Submucosal plexus involved in gland secretion  Components of Long Reflex Arc of 1. Afferent (sensory) neuron Conducts impulses FROM peripheral ANS sensory receptor TO CNS (either brain or spinal cord) 1 2. Preganglionic (efferent, motor) neuron Conducts impulses FROM CNS TO an autonomic ganglion 2 3 4 3. Autonomic ganglion Location of cell bodies of postganglionic neurons and their synapse with the preganglionic neuron Nuclei/nucleus: group of neuronal cell bodies in central NS Ganglia/ganglion: group of neuronal cell bodies in 4. Postganglionic (efferent, motor) peripheral NS neuron Conducts impulses FROM autonomic ganglion TO effector6 tissue in the periphery ANS Divisions Nuclei/nucleus: group of neuronal cell bodies in central NS Ganglia/ganglion: group of neuronal cell bodies in peripheral NS 1 2 Location of Length of Location of Length of Degree of preganglion preganglio postganglionic cell postganglio divergence ic cell nic axon bodies nic axon bodies 1 paravertebral (chain) lateral horn 1 ganglia: next to of thoraco- Nerves diverge & Sympathetic vertebral column; lumbar Short Long spread out to nervous connected to other spinal different locations 2 system ipsilateral collateral nerves ganglia brainstem 7 2 or lateral Receptors & neurotransmitters of There are only two neurotransmitters of the sympathetic and parasympathetic divisions of the ANS Cholinergic 1.Acetylcholine (ACh ) is released by presynaptic Presynaptic neuron neuron cholinergic neurons. Cholinergic neurons are found in both parasympathetic ACh and sympathetic divisions of the ANS Cholinergic ACh binds to specific cholinergic receptors on receptor postsynaptic cells Main cholinergic receptor subtypes: nicotinic the ANS Postsynaptic cholinergic receptors located on postganglionic cell neurons and muscarinic cholinergic receptors located on effector cells Adrenergic Presynaptic neuron neuron 2. Norepinephrine (NE ) is released by presynaptic NE adrenergic neurons. Adrenergic Adrenergic neurons are found ONLY in the sympathetic receptor division of the ANS NE (and epinephrine) binds to specific adrenergic Postsynaptic cell receptors on postsynaptic cells Main adrenergic receptor subtypes: alpha (α) and 8 beta (β) adrenergic receptors. Both subtypes are  Duration of Action and Termination of ACh and NE 1.Acetylcholine(ACh) Each vesicle of ACh contains 1000–50 000 ACh molecules. When an action potential reaches the nerve terminal of the presynaptic nerve, it causes the exocytosis of 30-300 vesicles of ACh. This releases 30, 000-3 million ACh molecules into synaptic cleft. Duration of action of ACh: 1-2 msec: need constant release of ACh to have sustained effect Termination: Enzymatic degradation by acetylcholinesterase (AChE) which is located on the postsynaptic membrane 2.Norepinephrine (NE) and epinephrine (Epi) Duration of action of NE and Epi: longer than ACh because Epi is a hormone that travels through blood 9 9 Termination: NE returns to neuron that released it (reuptake by presynaptic neuron) What is the difference between NE and Epi? Both Epi and NE are released when the sympathetic NS is stimulated bind to adrenergic receptors to activate them 1. Norepinephrine (NE) is released as both a neurotransmitter AND a hormone 2. Epinephrine (Epi) is only released as a hormone by adrenal medulla Neurotransmitters travel ____________, have a ________ duration of action and causes ___________ changes. Hormones travel ____________, have a ________ duration of action and causes ___________ changes. 10  1.Referred to craniosacral system: preganglionic Parasympathetic Division of the neurons are located in nuclei of the brain stem and the lateral horn of the sacral spinal cord. 2.Does not diverge: each nerve projects to a single location 3.Cell bodies of preganglionic neuron are located in lateral horn of cranial and sacral portion of spinal nerves Cranial nerves III, VII, IX provide output to extraocular muscles, pupil size, production of ANS tears and saliva Cranial nerve X (vagus) provide output to cardiovascular, respiratory and digestive systems Sacral portion of spinal nerves provide output to urinary, reproductive and digestive systems 4.Cell bodies of postganglionic neuron are located in terminal ganglia, located near or even within target effector. 5.Axons of preganglionic neurons are LONG and those of postganglionic neurons are SHORT 11  Effect of parasympathetic NS Parasympathetic NS Rest and digest Dominant controller of most autonomic effectors most of the Targe central 1 Ganglio 2 t time NS n effect Resting heart rate (HR) preganglioni postganglion or Resting force of ventricular c neuron ic neuron contraction No effect: blood pressure (BP) is normal 1 2 Encourages digestion & absorption. Increases salivary and other digestive secretions In the parasympathetic nervous system, No effect on sweat secretion 1 1.The preganglionic neuron is a(n) ____________ neuron Normal rate and depth of breathing which releases ACh as its neurotransmitter. The ACh binds airways (bronchioles) are narrower: to and activates nicotinic receptors located on dendrites of normal amount of air exchange No effect on renin release or on BP the postganglionic neuron. The effect of ACh binding to Encourages activity of the urinary 2 its receptor is always stimulatory system, including urination 2.The postganglionic neuron is a(n) ____________ neuron No effect on epinephrine or norepinephrine release which releases ACh as its neurotransmitter. The ACh binds to and activates muscarinc receptors located on of the target effector. The effect of ACh binding to its receptor canNote: be either when theinhibitory or stimulatory neurotransmitter binds to adepending on type receptor, it ALWAYS & activates the receptor. location of receptor 12 BUT receptor activation can either excite or inhibit the effector tissue, depending on the 12 receptor and the tissue  1.Referred to thoracolumbar system: emerges centrally Sympathetic Division of the from thoracic and upper lumbar spinal cord 2.Diverges extensively single preganglionic sympathetic neuron may have 10–20 targets 3.Cell bodies of preganglionic neuron are located in lateral horn of thoraco-lumbar spinal nerves 4.Cell bodies of postganglionic neuron are located in ganglia sympathetic chain ganglia: network of ganglia ANS located along vertebral column (23 pairs: 3 cervical, 12 thoracic, four lumbar, four sacral). Thoracic and lumbar pairs connect directly through spinal roots while cervical and sacral pairs connect through ascending or descending connections within the chain. paravertebral ganglia: adjacent to prevertebral ganglia in the sympathetic chain, eg superior cervical ganglion Collateral (prevertebral) ganglia: anterior to vertebral column and receive inputs from splanchnic and sympathetic neurons, eg celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion 13 Axons of preganglionic neurons are SHORT and those Divergence of sympathetic efferent neurons 1.Divergence exists within the sympathetic system because many A single preganglionic sympathetic different effector organs are activated together for a common neuron may have 10–20 targets purpose (fight or flight). Requires coordinated network of neurons that project simultaneously to many effector organs. Neurons in the same nerve may form synapses inside different ganglia Activates respiratory system to increase O2 intake and CO2 outtake Activates cardiovascular system to increase blood flow to 1 skeletal muscles 1 Activates sweat glands to reduce excess heat produced by 2 muscle contraction Inhibits digestive system to maximize blood delivery to skeletal muscles. 2 1. Synapse with sympathetic postganglionic neuron at level of 3 spinal nerve, eg T1 spinal nerve synapses with T1 chain ganglion to innervate trachea 2. Send ascending or descending branches through the sympathetic trunk to synapse with chain ganglia superior or 3 inferior to level of spinal nerve, respectively, eg spinal nerve T1 ascends to superior cervical ganglion to innervate the eye. 14 14 3. Pass through one or more chain ganglia without synapsing in  Sympathetic NS Effect of sympathetic NS Targe “fight-or-flight” response central 1 Ganglio 2 t Active during “E” situations: exercise, NS n effect emergency, excitement, preganglioni postganglion or embarrassment c neuron ic neuron heart beats faster (↑ HR) Increased force of ventricular contraction: ↑ blood flow 1 2 Vasoconstriction: ↑ BP Inhibits digestion & absorption. In the sympathetic nervous system, Inhibits salivary and other digestive 1 1.The preganglionic neuron is a(n) ____________ neuron secretions Activates sweat secretion which releases ACh as its neurotransmitter. The ACh binds Breathing becomes faster and deeper to and activates nicotinic receptors located on dendrites of airways (bronchioles) are open wider: the postganglionic neuron. The effect of ACh binding to more air exchange 2 its receptor is always stimulatory Releases renin to ↑ BP 2.The postganglionic neuron is a(n) ____________ neuron Inhibits activity of the urinary system in order to conserve fluid and ↑ BP which releases NE as its neurotransmitter. The NE binds to Release Epinephrine and and activates adrenergic (alpha or beta) receptors located Norepinephrine as hormones on of the target effector. The effect of NE binding to its receptor can the Note: when be neurotransmitter either inhibitory or to binds stimulatory a receptor, itdepending ALWAYS activates the receptor. on BUT typereceptor & location of receptor 15 activation can either excite or inhibit the effector tissue, depending on the 15 receptor and the tissue  An organ or system that has dual innervation receives inputs from both the parasympathetic and sympathetic divisions of the autonomic nervous system Concept of dual Most systems affected by BOTH divisions of the ANS: innervation One division always stimulates (accelerator) and the other one inhibits (brake), allowing for precise control of effector tissue Example #1: the parasympathetic division __________ digestion while the sympathetic division __________ digestion Example #2: the parasympathetic division __________ heart rate while the sympathetic division __________ heart rate What organ(s) are innervated only by the sympathetic NS? 16  Balance in Competing Autonomic Reflex Arcs: dual innervation Syste Effect of parasympathetic Effect of sympathetic NS m NS Rest and digest “fight-or-flight” response Dominant controller of most Active during “E” situations: Overall autonomic effectors most of exercise, emergency, the time excitement, embarrassment Resting heart rate (HR) heart beats faster (↑ HR) Heart Resting force of ventricular Increased force of ventricular contraction contraction: ↑ blood flow Blood No effect: Resting blood Vasoconstriction: ↑ BP vessels pressure (BP) Encourages digestion & Digesti Inhibits digestion & absorption. absorption. ve Inhibits secretions (saliva, Increases secretions (saliva, system enzymes) enzymes) Sweat No effect Activates sweat secretion glands Resting rate and depth of Breathing becomes faster and Respira breathing deeper tory airways (bronchioles) are airways (bronchioles) are open system narrower: Resting amount of wider: more air exchange air exchange No effect on renin release or Releases renin to ↑ BP on BP Inhibitory or no effect Stimulatory effect Urinary Ke Eg ↓ muscleactivity contraction Inhibits activity of the (relaxation or dilation), eg ↑ urinary muscle contraction (constriction), 17 system y Encourages of urinary ↓ secretion system in order to conserve ↑ rate fluid system, including urination and ↑ BP  Balance in Competing Autonomic Reflex Autonomic neurotransmitters andArcs receptors may influence different types of presynaptic and postsynaptic receptors at synapses with dually innervated effectors; this summation of effects increases precision of control. The overall effect on the effector cell depends on the balance of activity of the sympathetic NS and the parasympathetic NS 1.Control of pupillary size Afferent input from light on retina →activate photoreceptors →activate retinal ganglion cells to send signal via optic nerve to diencephalon Low light levels activates the sympathetic division to cause pupil dilation High light levels activates the parasympathetic division to cause pupil constriction 2.Control of heart rate by cardiovascular center in medulla (brainstem) Afferent input on blood pressure and cardiac function travels through glossopharyngeal and vagus nerves to nucleus of the solitary tract Sympathetic division can increase heart rate via cardiac accelerator nerves 18 Sympathetic division can constrict blood vessels to increase  Classic example: referred pain often associated with a heart attack. Referred Pain Sensation from different locations travel along T1-T5 spinal cord skin on the chest over the heart from the tissue of the heart itself skin areas over the left shoulder and inner surface of the left arm. Result: Brain registers pain of a heart attack in left shoulder/arm/chest 1.Definition: stimulation of pain receptors in deep structures may be felt as pain in the skin that lies over the affected organ or in an area of skin on the body surface far removed from the site of disease or injury. 2.Cause: convergence (mixing) of sensory nerve impulses from both diseased organ and skin in the area of referred pain. 3.Misinterpretation in the brain in regard to the true location of sensory neurons being stimulated causes referred pain. 19 4.Clinical importance: important in correct diagnosis of disease