Chapter 15 Lecture Outline Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15-1

Chapter 15Lecture Outline

Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

15-1

15-2

Autonomic Nervous System and Visceral Reflexes

• Autonomic Nervous System (ANS)– general properties

• Autonomic Effects on Target Organs

• Central Control of Autonomic Function

15-3

Autonomic Nervous System

• portion of the nervous system that operates in comparative secrecy

• it manages a multitude of unconscious processes responsible for the body’s homeostasis

• homeostasis cannot be maintained without the ANS

15-4

General Properties of ANS• autonomic nervous system (ANS) – a motor nervous

system that controls glands, cardiac muscle, and smooth muscle – also called visceral motor system– primary organs of the ANS

• viscera of thoracic and abdominal cavities• some structures of the body wall

– cutaneous blood vessels– sweat glands– piloerector muscles

– carries out actions involuntarily

15-5

Visceral Reflexes

• visceral reflexes - unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors

• visceral reflex arc– receptors – nerve endings that detect stretch, tissue

damage, blood chemicals, body temperature, and other internal stimuli

– afferent neurons – leading to the CNS– interneurons – in the CNS– efferent neurons – carry motor signals away from the CNS– effectors – that make adjustments

• ANS modifies effector activity

15-6

Visceral Reflex to High BP

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

• homeostatic negative feedback loop

Figure 15.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2

3

4

1

Glossopharyngealnerve transmits signalsto medulla oblongata

Baroreceptors sense increased blood pressure

Common carotidartery

Vagus nervetransmitsinhibitorysignalsto cardiacpacemaker

Terminalganglion

Heart ratedecreases

15-7

Divisions of ANS• two divisions innervate same target organs

– may have cooperative or contrasting effects

sympathetic division – prepares body for physical activity – exercise,

trauma, arousal, competition, anger, or fear• heart rate, BP, airflow, blood glucose levels, etc.• reduces blood flow to the skin and digestive tract

parasympathetic division – calms many body functions reducing energy

expenditure and assists in bodily maintenance • digestion and waste elimination• “resting and digesting” state

15-8

Divisions of ANS• autonomic tone - normal background rate

of activity that represents the balance of the two systems

– parasympathetic tone• maintains smooth muscle tone in intestines• holds resting heart rate down to about 70 – 80 beats

per minute– sympathetic tone

• keeps most blood vessels partially constricted and maintains blood pressure

• sympathetic division excites the heart but inhibits digestive and urinary function, while parasympathetic has the opposite effect

15-9

Neural Pathways• ANS components are in both the central and peripheral nervous

systems– control nucleus in hypothalamus and other brainstem areas– motor neurons in the spinal cord and peripheral ganglia– nerve fibers that travel through the cranial and spinal nerves

• autonomic pathway– signal must travel across two neurons to get to the target organ– must cross a synapse where these two neurons meet in an

autonomic ganglion– presynaptic neuron – first neuron (soma in the brainstem or

spinal cord)– postganglionic neuron – second neuron (axon extends the rest

of the way to the target cell)

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Somatic versus Autonomic Pathways

ANS – two neurons from CNS to effectors• presynaptic neuron whose cell body is in CNS • postsynaptic neuron cell body in peripheral ganglion


Somatic efferent innervation

Autonomic efferent innervation

ACh

ACh

ACh or NE

Myelinatedfiber

Somatic effectors(skeletal muscles)

Myelinatedpreganglionic fiber

Unmyelinatedpostganglionic fiber

Autonomicganglion

Visceral effectors(cardiac muscle,smooth muscle, glands)

Figure 15.2

15-11

Sympathetic Division: Efferent

Pathways


Salivary glands

Heart

Lung

StomachSpleen

Pancreas

Small intestine

Large intestine

Rectum

Kidney

BladderPenisScrotum

Uterus

Ovary

Pons

Regions of spinal cord

ThoracicCervical

LumbarSacral

Eye

Adrenal medulla

Preganglionic neurons

Postganglionic neurons

Postganglionic fibers toskin, blood vessels,adipose tissue

Sympathetic chainganglia

Liver andgallbladder

Inferiormesenteric

ganglion

Superiormesenteric

ganglion

Celiacganglion

Cardiac andpulmonary plexuses

Figure 15.4

15-12

Preganglionic PathwaysCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Collateral ganglion

Spinal nerve

White ramus

Gray ramus

Sympathetic nerve

Splanchnic nerve

2

2

3

1

Postganglionic neuron

Preganglionic neuron

Somatic neuron

Somaticmotor fiber

To somatic effector(skeletal muscle)

Soma ofsomatic motorneuron

Postganglionicsympathetic fibers

To liver, spleen, adrenal glands,stomach, intestines, kidneys,urinary bladder, reproductive organs

Sympatheticganglion

Sympathetictrunk

Soma ofpostganglionicneuron

Communicatingrami

Postganglionicsympathetic fiber

Preganglionicsympathetic fiber

Soma ofpreganglionicneuron

To sweat glands,piloerector muscles,and blood vesselsof skin andskeletal muscles

To iris, salivary glands,lungs, heart, thoracicblood vessels, esophagus

Figure 15.5

15-13

Adrenal Glands• paired adrenal glands on superior poles of the kidneys

• each is two organs with different functions– adrenal cortex (outer layer)

• secretes steroid hormones– adrenal medulla (inner core)

• essentially a sympathetic ganglion• secretes a mixture of hormones into bloodstream

– catecholamines - 85% epinephrine (adrenaline) and 15% norepinephrine (noradrenaline)

– also function as neurotransmitters

• sympathoadrenal system is the closely related functioning adrenal medulla and sympathetic nervous system


Lacrimal gland

Heart

Lung

Stomach

Pancreas

Small intestineRectum

BladderPenis

ScrotumUterus

Ovary

Ciliary ganglion

Spleen

Descendingcolon

Otic ganglion

Cardiac plexus

Eye

ThoracicCervical

LumbarSacral

Preganglionic neuronsPostganglionic neurons

Pterygopalatineganglion

Oculomotor n.(CN III)

Submandibularganglion

Facial n.(CN VII) Submandibular

salivary gland

Parotidsalivary gland

Glossopharyngeal n.(CN IX)

Vagus n.(CN X)

Pulmonaryplexus

Esophagealplexus

Celiacganglion

Abdominalaortic plexus

Pelvicsplanchnicnerves

Inferiorhypogastricplexus

Liver andgallbladder

Kidney andureter

Pelvicnerves

Regions ofspinal cord

Figure 15.7

15-14

Parasympathetic Division: Efferent

Pathways

15-15

Enteric Nervous System

• enteric nervous system – the nervous system of the digestive tract– does not arise from the brainstem or spinal cord– innervates smooth muscle and glands

• 100 million neurons found in walls of the digestive tract

• no components in CNS

• has its own reflex arcs

• regulates motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid

• normal digestive function also requires regulation by sympathetic and parasympathetic systems

15-16

Megacolon

• Hirschsprung disease – hereditary defect causing absence of enteric nervous system

– no innervation in sigmoid colon and rectum

– constricts permanently and will not allow passage of feces

– feces becomes impacted above constriction

– megacolon – massive dilation of bowel accompanied by abdominal distension and chronic constipation

– maybe colonic gangrene, perforation of bowel, and peritonitis

– usually evident in newborns who fail to have their first bowel movement

15-17

Neurotransmitters and Receptors• how can different autonomic neurons have different effects?

constricting some vessels but dilating others

• 2 fundamental reasons:

– sympathetic and parasympathetic fibers secrete different neurotransmitters

– target cells respond to the same neurotransmitter differently depending upon the type of receptor they have

• all autonomic fibers secrete either acetylcholine or norepinephrine

• there are 2 classes of receptors for each of these neurotransmitters

15-18

Acetylcholine (ACh)• ACh is secreted by all preganglionic neurons in both

divisions and the postganglionic parasympathetic neurons– any receptor that binds it is called cholinergic receptor

• 2 types of cholinergic receptors– muscarinic receptors

• Found in all cardiac muscle, smooth muscle, and gland cells• excitatory or inhibitory due to subclasses of muscarinic receptors

– nicotinic receptors• on all ANS postganglionic neurons, in the adrenal medulla, and at

neuromuscular junctions of skeletal muscle• excitatory when ACh binding occurs

15-19

Norepinephrine (NE)

• NE is secreted by nearly all sympathetic postganglionic neurons– receptors for it called adrenergic receptors

• alpha-adrenergic receptors– usually excitatory

– 2 subclasses (α1 & α2)

• beta-adrenergic receptors– usually inhibitory

– 2 subclasses with different effects (β1 & β2)

15-20

Neurotransmitters and Receptors

Figure 15.8

(b) Sympathetic adrenergic fiber

(c) Sympathetic cholinergic fiber

(a) Parasympathetic fiber

NE

ACh

Adrenergic receptor

ACh

ACh

ACh

Muscarinic receptor

ACh

Nicotinicreceptor

Preganglionicneuron

Nicotinicreceptor

Preganglionicneuron Postganglionic

neuron

Nicotinicreceptor

Preganglionicneuron Postganglionic

neuron

Targetcell

Postganglionicneuron

Targetcell

Targetcell

Muscarinicreceptor

15-21

Overview

• sympathetic effects tend to last longer than parasympathetic effects

– ACh released by parasympathetics is broken down quickly at synapse

– NE by sympathetics is reabsorbed by nerve, diffuses to adjacent tissues, and much passes into bloodstream

• many substances released as neurotransmitters that modulate ACh and NE function

– various hormones, neurotransmitters, and the gas, nitric oxide

15-22

Dual Innervation

• dual innervation - most viscera receive nerve fibers from both parasympathetic and sympathetic divisions– antagonistic effect – oppose each other– cooperative effects – two divisions act on

different effectors to produce a unified overall effect

• both divisions do not normally innervate an organ equally

15-23

Dual Innervation

• antagonistic effects - oppose each other

– exerted through dual innervation of same effector cells

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

– exerted because each division innervates different cells

• pupillary dilator muscle (sympathetic) dilates pupil• constrictor pupillae (parasympathetic) constricts pupil

15-24

Dual Innervation of the Iris

Figure 15.9


Brain

Spinal cord

IrisPupil

Pupil dilated Pupil constricted

Parasympathetic fibersof oculomotor nerve (III)

Sympatheticfibers

Ciliaryganglion

Superiorcervicalganglion

Parasympathetic(cholinergic) effect

Sympathetic(adrenergic) effect

Adrenergicstimulation ofpupillary dilator

Cholinergic stimulationof pupillary constrictor

15-25

Dual Innervation

• cooperative effects - when two divisions act on different effectors to produce a unified effect

– parasympathetics increase salivary serous cell secretion

– sympathetics increase salivary mucous cell secretion

15-26

Without Dual Innervation• some effectors receive only sympathetic fibers

– adrenal medulla, piloerector muscles, sweat glands and many blood vessels

• sympathetic vasomotor tone - baseline firing frequency• keeps vessels in state of partial constriction• increase in firing frequency - vasoconstriction• decrease in firing frequency - vasodilation• shifts blood flow from one organ to another as needed

• sympathetic division acting alone can exert opposite effects on the target organ through control of blood vessels– during stress

• blood vessels to muscles and heart dilate• blood vessels to skin constrict

15-27

Sympathetic 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

Figure 15.10

Artery

1

1

2

3

3

1

2

3

2

2

3

1

Strong sympathetictoneSmooth musclecontraction

Vasoconstriction

Weaker sympathetictone

Smooth musclerelaxation

Vasodilation

Sympatheticnerve fiber

Vasomotortone

(a) Vasoconstriction

(b) Vasodilation


15-28

Control of Autonomic Function

• ANS regulated by several levels of CNS

– cerebral cortex has an influence – anger, fear, anxiety• powerful emotions influence the ANS because of the

connections between our limbic system and the hypothalamus

– hypothalamus - major visceral motor control center• nuclei for primitive functions – hunger, thirst, sex

15-29

Control of Autonomic Function

• ANS regulated by several levels of CNS– midbrain, pons, and medulla oblongata contain:

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

– spinal cord reflexes• defecation and urination reflexes are integrated in spinal

cord• we control these functions because of our control over

skeletal muscle sphincters…but if the spinal cord is damaged, the reflexes will remain

15-30

Drugs and the Nervous System• neuropharmacology – study of effects of drugs on the

nervous system

• sympathomimetics enhance sympathetic activity– stimulate receptors or increase norepinephrine release

• cold medicines that dilate the bronchioles or constrict nasal blood vessels

• sympatholytics suppress sympathetic activity– block receptors or inhibit norepinephrine release

• beta blockers reduce high BP by interfering with effects of epinephrine/norepinephrine on heart and blood vessels

15-31

Drugs and the Nervous System• parasympathomimetics enhance activity while

parasympatholytics suppress activity

• many drugs also act on neurotransmitters in CNS– Prozac blocks reuptake of serotonin to prolong its mood-

elevating effect (SSRI: selective serotonin reuptake inhibitor)– MAOI’s (monoamine oxidase inhibitors) prevent MAO from

breaking down neurotransmitters like NE– caffeine competes with adenosine (the presence of which

causes sleepiness) by binding to its receptors

15-32

Adenosine and Caffeine

Figure 15.11


CaffeineAdenosine

O

OH3C

N

N N

N

CH3

CH3

N N

N

NH2

OOH

OH OH

N

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Chapter 15 Lecture Outline Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15-1