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Chapter 15Chapter 15

Lecture OutlineLecture Outline

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Autonomic Nervous System Autonomic Nervous System and Visceral Reflexesand Visceral Reflexes

Autonomic nervous system (ANS)Autonomic nervous system (ANS) general propertiesgeneral properties anatomyanatomy

Autonomic effects on target organsAutonomic effects on target organs Central control of autonomic functionCentral control of autonomic function

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ANS - General PropertiesANS - General Properties Motor nervous system controls glands, cardiac Motor nervous system controls glands, cardiac

and smooth muscle and smooth muscle also called visceral motor systemalso called visceral motor system

Regulates unconscious processes that Regulates unconscious processes that maintain homeostasismaintain homeostasis BP, body temperature, respiratory airflowBP, body temperature, respiratory airflow

ANS actions are automaticANS actions are automatic biofeedback techniquesbiofeedback techniques

• train people to control hypertension, stress and migraine train people to control hypertension, stress and migraine headachesheadaches

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Visceral ReflexesVisceral Reflexes Unconscious, automatic responses to stimulation of Unconscious, automatic responses to stimulation of

glands, cardiac or smooth muscleglands, cardiac or smooth muscle1.1. Receptors Receptors

detect internal stimuli -- stretch, blood chemicals, etc.detect internal stimuli -- stretch, blood chemicals, etc.

2.2. Afferent neurons Afferent neurons connect to interneurons in the CNSconnect to interneurons in the CNS

3.3. Efferent neurons Efferent neurons carry motor signals to effectorscarry motor signals to effectors ANS is the efferent neurons of these reflex arcsANS is the efferent neurons of these reflex arcs

4.4. Effectors Effectors glands, smooth or cardiac muscleglands, smooth or cardiac muscle

ANS modifies effector activityANS modifies effector activity

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Visceral Reflex to High BPVisceral Reflex to High BP

High blood High blood pressure detected pressure detected by arterial stretch by arterial stretch receptors (1), receptors (1), afferent neuron (2) afferent neuron (2) carries signal to carries signal to CNS, efferent (3) CNS, efferent (3) signals travel to signals travel to the heart (4), heart the heart (4), heart slows reducing BPslows reducing BP

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Divisions of ANSDivisions of ANS Two divisions innervate same target organsTwo divisions innervate same target organs

may have cooperative or contrasting effectsmay have cooperative or contrasting effects

1.1. Sympathetic division Sympathetic division prepares body for physical activityprepares body for physical activity

• increases heart rate, BP, airflow, blood glucose levels, etcincreases heart rate, BP, airflow, blood glucose levels, etc

2.2. Parasympathetic division Parasympathetic division calms many body functions and assists in bodily calms many body functions and assists in bodily

maintenancemaintenance digestion and waste eliminationdigestion and waste elimination

Autonomic tone is the normal rate of activity that Autonomic tone is the normal rate of activity that represents the balance of the two systemsrepresents the balance of the two systems

Effects of each depend upon neurotransmitters Effects of each depend upon neurotransmitters releasedreleased

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Somatic versus Autonomic PathwaysSomatic versus Autonomic Pathways

ANS = 2 neurons from CNS to effectors• presynaptic neuron cell body in CNS • postsynaptic neuron cell body in peripheral ganglion

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Origin of presynaptic neuronsOrigin of presynaptic neurons lateral horns of spinal cord (T1-L2)lateral horns of spinal cord (T1-L2)

Sympathetic chain ganglia (paravertebral)Sympathetic chain ganglia (paravertebral) 3 cervical, 11 thoracic, 4 lumbar, 4 sacral and 1 3 cervical, 11 thoracic, 4 lumbar, 4 sacral and 1

coccygeal gangliacoccygeal ganglia white and gray communicating rami suspend white and gray communicating rami suspend

ganglia from spinal nerveganglia from spinal nerve pathways of preganglionic fiberspathways of preganglionic fibers

1.1. enter ganglia and synapse on postganglionic cellenter ganglia and synapse on postganglionic cell2.2. travel to higher or lower ganglia and synapsetravel to higher or lower ganglia and synapse3.3. pass through chain without synapsing to reach pass through chain without synapsing to reach

collateral ganglia via splanchnic nervescollateral ganglia via splanchnic nerves

Sympathetic Nervous SystemSympathetic Nervous System

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Neuronal divergence predominates Neuronal divergence predominates each preganglionic cell branches and synapses each preganglionic cell branches and synapses

on multiple postganglionic cellson multiple postganglionic cells produces widespread effects on multiple organsproduces widespread effects on multiple organs

Sympathetic Nervous SystemSympathetic Nervous System

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Efferent PathwaysEfferent Pathways

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Preganglionic PathwaysPreganglionic Pathways

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Ganglia and Abdominal Aortic PlexusGanglia and Abdominal Aortic Plexus

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Sympathetic InnervationSympathetic Innervation

Effectors in body wall are innervated by Effectors in body wall are innervated by sympathetic fibers in spinal nervessympathetic fibers in spinal nerves

Effectors in head and thoracic cavity are Effectors in head and thoracic cavity are innervated by fibers in sympathetic nervesinnervated by fibers in sympathetic nerves

Effectors in abdominal cavity are innervated by Effectors in abdominal cavity are innervated by sympathetic fibers in splanchnic nervessympathetic fibers in splanchnic nerves celiac, superior and inferior mesenteric ganglionceliac, superior and inferior mesenteric ganglion

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Adrenal GlandsAdrenal Glands

Paired glands sit on superior pole of each kidneyPaired glands sit on superior pole of each kidney Cortex (outer layer)Cortex (outer layer)

secretes steroid hormonessecretes steroid hormones

Medulla (inner core)Medulla (inner core) a modified sympathetic ganglion a modified sympathetic ganglion

• stimulated by preganglionic sympathetic neurons stimulated by preganglionic sympathetic neurons secretes neurotransmitters (hormones) into bloodsecretes neurotransmitters (hormones) into blood

• catecholamines (85% epinephrine and 15% norepinephrine)catecholamines (85% epinephrine and 15% norepinephrine)

Sympathoadrenal system is the closely related Sympathoadrenal system is the closely related functioning adrenal medulla and symphathetic functioning adrenal medulla and symphathetic nervous systemnervous system

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Parasympathetic Nervous SystemParasympathetic Nervous System

Origin of preganglionic fibersOrigin of preganglionic fibers pons and medulla (for cranial nerve nuclei)pons and medulla (for cranial nerve nuclei) sacral spinal cord segments S2-S4sacral spinal cord segments S2-S4

Pathways of preganglionic fibersPathways of preganglionic fibers cranial nerves III, VII, IX and Xcranial nerves III, VII, IX and X arising from sacral spinal cordarising from sacral spinal cord

• pelvic splanchnic nerves and inferior hypogastric plexuspelvic splanchnic nerves and inferior hypogastric plexus

Terminal ganglia in/near target organs Terminal ganglia in/near target organs long preganglionic, short postganglionic fiberslong preganglionic, short postganglionic fibers

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Efferent PathwaysEfferent Pathways

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Parasympathetic Cranial NervesParasympathetic Cranial Nerves

Oculomotor nerve (III) Oculomotor nerve (III) narrows pupil and focuses lensnarrows pupil and focuses lens

Facial nerve (VII)Facial nerve (VII) tear, nasal and salivary glandstear, nasal and salivary glands

Glossopharyngeal (IX)Glossopharyngeal (IX) parotid salivary glandparotid salivary gland

Vagus nerve (X)Vagus nerve (X) viscera as far as proximal half viscera as far as proximal half

of colonof colon Cardiac, pulmonary, and Cardiac, pulmonary, and

esophageal plexusesophageal plexus

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Enteric Nervous SystemEnteric Nervous System

Nervous system of the digestive tractNervous system of the digestive tract Composed of 100 million neurons found in Composed of 100 million neurons found in

the walls of the digestive tract (no the walls of the digestive tract (no components in CNS)components in CNS)

Has its own reflex arcsHas its own reflex arcs Regulates motility of viscera and secretion Regulates motility of viscera and secretion

of digestive enzymes and acid in concert of digestive enzymes and acid in concert with the ANSwith the ANS

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Neurotransmitters and ReceptorsNeurotransmitters and Receptors Effects of ANS Effects of ANS

determined by types of neurotransmitters determined by types of neurotransmitters released and types of receptors on target cellsreleased and types of receptors on target cells

Sympathetic has longer lasting effectsSympathetic has longer lasting effects neurotransmitters persist in synapse and some neurotransmitters persist in synapse and some

reach the bloodstreamreach the bloodstream Many substances released as Many substances released as

neurotransmittersneurotransmitters enkephalin, substance P, neuropeptide Y, enkephalin, substance P, neuropeptide Y,

neurotensin, nitric oxide (NO)neurotensin, nitric oxide (NO)• NO inhibits muscle tone in BV walls (vasodilation)NO inhibits muscle tone in BV walls (vasodilation)

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Neurotransmitters and ReceptorsNeurotransmitters and Receptors

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Cholinergic Receptors for AChCholinergic Receptors for ACh

Acetylcholine (Ach) binds to 2 classes of Acetylcholine (Ach) binds to 2 classes of receptorsreceptors

1.1. nicotinic receptorsnicotinic receptors• on all ANS postganglionic neurons, in the adrenal on all ANS postganglionic neurons, in the adrenal

medulla, and at neuromuscular junctions (skeletal medulla, and at neuromuscular junctions (skeletal muscle)muscle)

• excitatory when ACh binding occursexcitatory when ACh binding occurs

2.2. muscarinic receptorsmuscarinic receptors• on all gland, smooth muscle and cardiac muscle on all gland, smooth muscle and cardiac muscle

cells that receives cholinergic innervationcells that receives cholinergic innervation• excitatory or inhibitory due to subclasses of excitatory or inhibitory due to subclasses of

muscarinic receptorsmuscarinic receptors

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Adrenergic Receptors for NEAdrenergic Receptors for NE Norepinephrine binds to 2 classes of Norepinephrine binds to 2 classes of

receptors receptors alpha adrenergic receptors (often excitatory)alpha adrenergic receptors (often excitatory) beta adrenergic receptors (often inhibitory)beta adrenergic receptors (often inhibitory)

ExceptionsExceptions existence of subclasses of each receptor typeexistence of subclasses of each receptor type

• alpha 1 and 2; beta 1 and 2alpha 1 and 2; beta 1 and 2

Function by means of 2nd messengersFunction by means of 2nd messengers cyclic AMP and alpha 1 receptorscyclic AMP and alpha 1 receptors

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Dual InnervationDual Innervation Most of viscera receive nerve fibers from both Most of viscera receive nerve fibers from both

parasympathetic and sympathetic divisionsparasympathetic and sympathetic divisions Both divisions do not normally innervate an Both divisions do not normally innervate an

organ equallyorgan equally

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Dual InnervationDual Innervation Antagonistic effects Antagonistic effects

oppose each otheroppose each other exerted through dual innervation of same effectorexerted through dual innervation of same effector

• heart rate decreases (parasympathetic)heart rate decreases (parasympathetic)• heart rate increases (sympathetic)heart rate increases (sympathetic)

exerted because each division innervates different exerted because each division innervates different cellscells• pupillary dilator muscle (sympathetic) dilates pupilpupillary dilator muscle (sympathetic) dilates pupil• constrictor pupillae (parasympathetic) constricts pupilconstrictor pupillae (parasympathetic) constricts pupil

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Dual InnervationDual Innervation Cooperative effects seen when 2 divisions act Cooperative effects seen when 2 divisions act

on different effectors to produce a unified on different effectors to produce a unified effecteffect parasympathetics increase salivary serous cell parasympathetics increase salivary serous cell

secretionsecretion sympathetics increase salivary mucous cell sympathetics increase salivary mucous cell

secretionsecretion

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Dual Innervation of the IrisDual Innervation of the Iris

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Without Dual InnervationWithout Dual Innervation Some effectors receive only sympatheticSome effectors receive only sympathetic

adrenal medulla, arrector pili muscles, sweat adrenal medulla, arrector pili muscles, sweat glands and many blood vesselsglands and many blood vessels

Sympathetic tone Sympathetic tone a baseline firing frequencya baseline firing frequency vasomotor tone provides partial constrictionvasomotor tone provides partial constriction

• increase in firing frequency = vasoconstrictionincrease in firing frequency = vasoconstriction• decrease in firing frequency = vasodilationdecrease in firing frequency = vasodilation• can shift blood flow from one organ to another as can shift blood flow from one organ to another as

neededneeded sympathetic stimulation increases blood to skeletal and cardiac sympathetic stimulation increases blood to skeletal and cardiac

muscles -- reduced blood to skinmuscles -- reduced blood to skin

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Sympathetic and Vasomotor ToneSympathetic and Vasomotor Tone

Sympathetic division prioritizes blood vessels to skeletal muscles and heart in times of emergency.

Blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise.

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Control of Autonomic FunctionControl of Autonomic Function ANS regulated by several levels of CNSANS regulated by several levels of CNS

cerebral cortex has an influencecerebral cortex has an influence hypothalamus (major visceral motor control center)hypothalamus (major visceral motor control center)

• nuclei for primitive functions – hunger, thirstnuclei for primitive functions – hunger, thirst midbrain, pons, and medulla oblongatamidbrain, pons, and medulla oblongata

• nuclei for cardiac and vasomotor control, salivation, nuclei for cardiac and vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary swallowing, sweating, bladder control, and pupillary changeschanges

spinal cord reflexesspinal cord reflexes• defecation and micturition reflexes integrated in corddefecation and micturition reflexes integrated in cord• brain can inhibit these responses consciouslybrain can inhibit these responses consciously

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DrugsDrugs Sympathomimetics enhance sympathetic activitySympathomimetics enhance sympathetic activity

stimulate receptors or stimulate receptors or norepinephrine releasenorepinephrine release Sympatholytics suppress sympathetic activitySympatholytics suppress sympathetic activity

block receptors or inhibit norepinephrine releaseblock receptors or inhibit norepinephrine release Parasympathomimetics enhance activity while Parasympathomimetics enhance activity while

parasympatholytics suppress activityparasympatholytics suppress activity Management of clinical depressionManagement of clinical depression

Prozac blocks reuptake of serotonin to prolong its mood-Prozac blocks reuptake of serotonin to prolong its mood-elevating effectelevating effect

MAO inhibitors interfere with breakdown of monoamine MAO inhibitors interfere with breakdown of monoamine neurotransmittersneurotransmitters

Caffeine competes with adenosine (inhibitory; causes Caffeine competes with adenosine (inhibitory; causes sleepiness) by binding to its receptorssleepiness) by binding to its receptors