Presentation on theme: "Chapter 14 The Autonomic Nervous System"— Presentation transcript:
1Chapter 14 The Autonomic Nervous System J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
2Autonomic Nervous System Overview automatic, involuntaryprimarily involved in maintaining homeostasis of the internal environmentvisceral efferent neurons innervate visceral effectors: smooth muscle, cardiac muscle, exocrine glands and endocrine glands
3The ANS Is Clinically Significant! If you plan to succeed in a Health-Related Career, you will need to understand the Autonomic Nervous System very well!
4Two Functional Divisions Parasympathetic and Sympathetic DivisionsStructurally, each division consists of nerves, nerve plexuses, and autonomic gangliaEach motor command is carried over a two-cell circuitMost effector organs and tissues receive impulses from both ANS divisions, a dual or parallel innervationThe two divisions often serve as antagonists to each other in adjusting and maintaining internal homeostasisParasympathetic system dominates in sleep and other relaxed or resting statesSympathetic dominates during skeletal muscle activities and various emergency situations (fright, panic, rage, aggression)There is a constant interplay between the two divisions
5Comparison of Somatic to Autonomic somatic: one motor neuron to skeletal muscle effectorsautonomic: two motor neurons to visceral effectors
7Two Types of Autonomic Neurons Preganglionic neuronscell bodies in the CNS (brain or spinal cord)transmit Action Potentials from the CNSPostganglionic neuronscell bodies in autonomic ganglia in the peripherytransmit APs to effectors
8Two Cell Motor Pathways in the ANS preganglionic neuronsin the sympathetic division, the cell body is located in the lateral gray horns (thoraco-lumbar) of the spinal cordin the parasympathetic division, the cell body is located in various nuclei of brain stem or in the lateral gray horns (cranio-sacral)postganglionic neuronsthe postganglionic fiber sends impulses to a target organthe effects at the target organ are due to type of neurotransmitter and specific cell surface receptors on the effector cells
9Dual InnervationThe Sympathetic and Parasympathetic Divisions of the ANS innervate many of the same organsDifferent effects are due to specific molecular differences in the neurotransmitters and in the receptor types on the effectors
10ANS Dual InnervationThe Parasympathetic Division exerts short-lived, highly localized control.The Sympathetic Division exerts long-lasting, diffuse effects.Due to differences in target responsiveness to neurotransmitters
11Parasympathetic Ganglia parasympathetic terminal ganglia = intramural gangliaganglia are located very close to or in the wall of the visceral organseach preganglionic neuron synapses with a only few postganglionic neuronsparasympathetic preganglionic fibers are longparasympathetic postganglionic fibers are short
12Sympathetic Gangliasympathetic trunk = vertebral chain ganglia (paravertebral ganglia)a vertical row on either side of the vertebral columnthese ganglia are interconnectedthoracic and lumbar origineach preganglionic neuron synapses with many postganglionic neuronsother sympathetic ganglia are located in the walls of major abdominal arteriesshort preganglionic fiberslong postganglionic fibers
13ANS Neurotransmitters & Receptors Preganglionic - AcetylcholinePostganglionicParasympathetic - acetylcholineSympathetic – norepinephrine & in a few locations acetylcholineReceptorsParasympatheticnicotinic - excitatorymuscarinic - excitatory or inhibitorySympatheticalpha - excitatorybeta - excitatory or inhibitory
14ANS Neurotransmitters Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANSCholinergic fibers = ACh-releasing fibersACh is released by all preganglionic axons and all parasympathetic postganglionic axonsAdrenergic fibers = NE-releasing fibersMost sympathetic postganglionic axonsNeurotransmitter effects can be excitatory or inhibitory depending upon the receptor type
15Neurotransmitters and Receptors of the Autonomic Nervous System Receptor Class Agonist AntagonistNicotinic Nicotone CurareMuscarinic Muscarine Atropine
16Nicotinic Receptors Nicotinic receptors are found on: Motor end plates (skeletal muscle)All postganglionic neurons of both sympathetic and parasympathetic divisionsThe hormone-producing cells of the adrenal medullaThe effect of ACh binding to nicotinic receptors is always excitatory
17Muscarinic ReceptorsMuscarinic receptors occur on all effector cells stimulated by parasympathetic cholinergic fibers and by those few effectors stimulated by sympathetic cholinergic fibersThe effect of ACh binding at muscarinic receptors:Can be either inhibitory or excitatoryDepends on the receptor type of the target organ
18Adrenergic ReceptorsThe two fundamental types of adrenergic receptors are alpha and betaEach type has subclasses: (1, 2, 1, 2 , 3)Effects of NE binding to: receptors is generally excitatory to effectors receptors is generally inhibitory to effectorsA clinically important exception – NE binding to receptors in the heart is excitatory
19ANS Neurotransmitters & Receptors See Table 14.3 “Cholinergic and Adrenergic Receptors” (p. 543) for all the detailsCholinergic receptors = nicotinic and muscarinicAdrenergic receptors = alpha1,2 and beta1,2,3These details about receptor subtypes will be very important in later courses, such as Pharmacology (in Nursing)
20ANS Neurotransmitter Performance Cholinergic fibers/neurons tend to cause relatively short-lived effects due to the rapid hydrolysis of acetylcholine by cholinesterase in the synapseAdrenergic fibers/neurons tend to cause relatively longer-lived effects due to the slower degradation of norepinephrine by catechol-o-methyltransferase (COMT) and monoamine oxidase (MAO) in the synapse or in body fluidsAdrenergic receptors also respond to the closely-related hormone, epinephrine = adrenalin, secreted by the adrenal medulla
21Drugs Related to ANS Neurotransmitters Drugs which mimic the action of ACh and NE at their receptors are termed cholinergic and adrenergic agonists respectivelyDrugs which block or inhibit the action of ACh and NE at their receptors are termed cholinergic and adrenergic antagonists (or “blockers”) respectivelyDrugs which enhance the action of ACh and NE at their synapses by delaying enzymatic degradation are termed anticholinesterases monoamine oxidase inhibitors (MAO-inhibitors)
22Drugs Related to ANS Neurotransmitters Table 14-3, p. 537, list examples of a number of autonomic drugs classes and some specific examples.Take a look. You’ll probably recognize some. Many are available in over-the-counter preparations. There are many more.Some of the drug classes will be on the examBut no specific drugs will be on the exam
24Autonomic Nervous System Online Review Neuroscience For KidsThis web site has many good reviews and illustrations.
25Autonomic Nervous System Controls Different regions of the CNS have responsibility for different functions.The cerebral cortex, limbic system, hypothalamus, and the brain stem cooperate to initiate autonomic motor commands.
26Autonomic Nervous System Controls Most control is unconscious and originates from the hypothalamusBut strong conscious emotional states can trigger autonomic, usually sympathetic, responses
27Autonomic Nervous System Actions See Table 14.4 (pg. 538) for complete details for the responses of each effector organParasympatheticS(alivation) L(acrimation) U(rination) D(efecation)metabolic “business as usual”“rest and digest” – “feed and breed” – basic survival functionsSympatheticfight or flight = emergency “survival” situationsany increase in skeletal muscular activityfor these activities - increase heart rate, blood flow, breathingdecrease non-survival activities - food digestion, etc.
28Parasympathetic Tone Parasympathetic tone: Slows the heartDirects normal activities of the digestive and urinary systemsThe sympathetic division can override these effects during times of stress or muscular exertionDrugs that block parasympathetic stimuli increase heart rate and interfere with fecal and urinary retention
29Cooperative EffectsANS cooperation is involved in the complex control of the cardiovascular systemANS cooperation is also seen in control of the external genitalia during sexual activitiesParasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitorisSympathetic fibers cause ejaculation of semen in males and reflex peristalsis in the female reproductive tract
30Sympathetic Stimulation Sympathetic stimulation is long-lasting because norepinephrine (NE):NE is inactivated more slowly by MAO and COMTNE is an indirectly acting neurotransmitter, triggering a second-messenger systemNE and epinephrine are released into the blood by the adrenal medulla in certain situations and remain there until inactivated by liver enzymes
31Solitary Sympathetic Stimulation Regulates some effectors not innervated by the parasympathetic divisionTherefore, acting more as an on-off switchThese include the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels
32Solitary Sympathetic Stimulation The sympathetic division controls:Thermoregulatory responses to heatCutaneous vasodilation and sweatingRelease of renin from the kidneysIncreased blood pressure from a complex regulatory responseMetabolic effects (in a complex coordination with the endocrine system)increases the metabolic rate of body cellselevates blood glucose levels for use by nervous tissueshifts cellular metabolism to fats for other tissuesstimulates the reticular activating system (RAS) of the brain, increasing mental alertnessThese actions serve to support the body during strenuous physical activities and emergencies but may contribute to undesirable side effects in cases of long term stress such as illnesses
33Sympathetic ToneThe sympathetic division controls blood pressure, keeping the blood vessels in a continual state of partial constriction (vasomotor tone)Blood pressure rises or falls with sympathetic activityBlood is also diverted to or away from different organ systems depending on the level of muscular activity or the presence of emergency or stressful statesAlpha-blocker drugs inhibit vasomotor tone and are used to treat hypertension
34Autonomic Nervous System Actions StructureSympathetic StimulationParasympathetic Stimulationiris of the eyepupil dilationpupil constrictionsalivary glandsreduce salivationincrease salivationoral/nasal mucosareduce mucus productionincrease mucus productionheartincrease rate and force of contractiondecrease rate and force of contractionlungrelax bronchial smooth muscleconstrict bronchial smooth muscle
35Autonomic Nervous System Actions StructureSympathetic StimulationParasympathetic Stimulationstomachreduce peristalsis; decrease gastric secretionsincrease peristalsis; increase gastric secretionssmall intestinereduce peristalsis; decrease intestinal secretionsincrease peristalsis; increase intestinal secretionslarge intestineliverincrease conversion of glycogen to glucose; release glucose into bloodstreamn/a
36Autonomic Nervous System Actions StructureSympathetic StimulationParasympathetic Stimulationkidneydecrease urinary outputincrease urinary outputurinary bladderwall relaxed; sphincter closedwall contracted; sphincter relaxedadrenal medullasecrete epinephrine and norepinephrinen/asweat glandsincrease sweat secretionblood vesselsincrease supply to skeletal muscles; decrease supply to most visceradecrease supply to skeletal muscles; increase supply to most viscera
37Developmental Aspects of the ANS During youth, ANS impairments are usually due to injuryIn old age, ANS efficiency decreases, resulting in constipation, dry eyes, and orthostatic hypotensionOrthostatic hypotension is a form of low blood pressure that occurs when sympathetic vasoconstriction centers respond slowly to positional changes
38Raynaud’s Diseasecauses sudden severe vasoconstriction in the fingers, toes and, occasionally, the ears and noseduring a Raynaud’s attack, or episode, several skin color changes (pallor, cyanosis, rubor) may occur, which are often accompanied by paresthsias, a throbbing or burning sensation, cold, or numbnessischemia can be so extreme as to cause gangreneThe exact cause of Raynaud’s Disease remains unknown.
39Referred PainVisceral afferents run in the same nerves with somatic afferentsPain in the viscera is transferred or interpreted as if it came from somatic areasHeart attackafferents in T1 - T5pain in the chest, arm, neck or face
40Risk Factors For Hypertension ageheredityracegenderweightdietlifestyle/activity levelstress: overstimulates sympathetic division?alcoholtobacco
41End Chapter 14Some additional information is presented in slides beyond this end point for the lecture. While you will not be tested on this additional material in 2010, you will see it again in some professional courses!
42Structure of the Autonomic Nervous System Preganglionic neuron somata in the thoracic and lumbar spinal cord segments.Preganglionic neurons synapse onto postganglionic neurons in the sympathetic chain ganglia.The postganglionic neurons extend a long distance (usually) to the target organs.Preganglionic neuron somata in the brain and sacral spinal cord.Preganglionic neurons synapse onto postganglionic neuron ganglia near or in the target organs.The postganglionic neurons do not extend a long distance to the target organs.
43Parasympathetic and Sympathetic Divisions Structurally, each division consists of nerves, nerve plexuses, and autonomic gangliaEach motor command is carried in a two-cell circuitMost effector organs and tissues receive impulses from both divisions, a dual or parallel innervationThe two divisions often serve as antagonists to each other in adjusting and maintaining internal homeostasisParasympathetic system dominates in sleep and relaxationSympathetic dominates during vigorous activity/strong emotion
44sympathetic parasympathetic preganglionic fibershort, myelinated, cholinergiclong, myelinated, cholinergicpostganglionic fiberlong,unmyelinated,usually adrenergicshort, unmyelinated, cholinergicgangliasympathetic chain(= paravertebral), collateral(= prevertebral),adrenal medullaeterminal (on or in effector)(= intramural)dominant?fight or flight,“E” situationsrest and relaxation,“SLUD”
45Parasympathetic Pathways Cranial Outflow vial cranial nerves III, VII, IX, and XCranial nerves III, VII, & IX innervate structures in headCranial Nerve X (Vagus) innervates ventral body cavity; carries 90% of parasympathetic fibersSacral OutflowInnervates distal half of large intestine, urinary bladder, ureters, & genitalia
46Sympathetic Gangliasympathetic trunk ( = sympathetic chain or paravertebral) ganglia lateral to vertebraecollateral (=prevertebral) ganglia are located near the major abdominal arteriesadrenal medullae function as sympathetic ganglia, but neurotransmitters released into blood
48Sympathetic PathsAll preganglionic fibers exit spinal cord via ventral root of spinal nerve, travel into ventral ramus, and into sympathetic chain ganglion via white ramus communicansThen, 1 of 4 (sometimes overlapping) possibilities:synapse with postganglionic neurons at that level of sympathetic chaintravel up and/or down sympathetic chain to synapse with postganglionic neurons at other level(s)Pass through sympathetic chain to prevertebral ganglion (via splanchnic nerves) and synapse with postganglionic neurons there(pass through prevertebral ganglion to adrenal medullae)
49Unique Roles of the Sympathetic Division Regulates many functions not subject to parasympathetic influenceThese include the activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vesselsThe sympathetic division controls:Thermoregulatory responses to heatRelease of renin from the kidneysMetabolic effects: increased metabolic rate, increased blood glucose, fat breakdown (lipolysis)
50Interactions of ANS Divisions Antagonistic: most common, organs stimulated by one division inhibited by the otherSympathetic and Parasympathetic ToneSympathetic tone controls most blood vessels (even at rest)Parasympathetic tone controls the normal activity of the heart, digestive, and urinary systemsCooperative EffectsImportant in normal sexual function
51Thermoregulatory Responses to Heat Applying heat to the skin causes reflex dilation of blood vesselsSystemic body temperature elevation results in widespread dilation of blood vesselsThis dilation brings warm blood to the surface and activates sweat glands to cool the bodyWhen temperature falls, blood vessels constrict and blood is retained in deeper vital organs
52Release of Renin from the Kidneys Sympathetic impulses activate the kidneys to release reninRenin is an enzyme that promotes increased blood pressure
53Metabolic EffectsThe sympathetic division promotes metabolic effects that are not reversed by the parasympathetic divisionIncreases the metabolic rate of body cellsRaises blood glucose levelsMobilizes fat as a food sourceStimulates the reticular activating system (RAS) of the brain, increasing mental alertness
54Localized Versus Diffuse Effects The parasympathetic division exerts short-lived, highly localized controlThe sympathetic division exerts long-lasting, diffuse effects because NE:Is inactivated more slowly than AchActs indirectly, using a second-messenger systemAnd epinephrine are released into the blood and remain there until destroyed by the liver
55Localized Versus Diffuse Effects The parasympathetic division exerts localized control becausepreganglionic fiber travels directly to specific targets and synapses with fewer ganglionic neuronsacetylcholine is rapidly degradedThe sympathetic division exerts diffuse effects becausepreganglionic fibers branch and synapse with many ganglionic neuronsstimulation of adrenal medullae causes secretion of epinephrine into bloodslower inactivation of norepinephrine and epinephrine
56Effects of Drugs (see Table 14.4, p. 545) Atropine – blocks parasympathetic effectsNeostigmine – inhibits acetylcholinesterase and is used to treat myasthenia gravisTricyclic antidepressants – prolong the activity of NE on postsynaptic membranesOver-the-counter drugs for colds, allergies, and nasal congestion – stimulate -adrenergic receptorsBeta-blockers – attach mainly to 1 receptors and reduce heart rate and prevent arrhythmias