autonomic nervous system - dr. jerry...

PowerPoint® Lecture Slides

prepared by

Karen Dunbar Kareiva

Ivy Tech Community College© Annie Leibovitz/Contact Press Images

Chapter 14

Autonomic

Nervous

System

© 2017 Pearson Education, Inc.

Why This Matters

• Understanding the autonomic nervous system

helps you to anticipate the effects and side

effects of drugs on your patients


Autonomic Nervous System

• Automatic nervous system (ANS) consists of

motor neurons that:

– Innervate smooth muscles, cardiac muscle, and

glands

– Make adjustments to ensure optimal support for

body activities

• Shunts blood to areas that need it and adjusts heart

rate, blood pressure, digestive processes, etc.

– Operate via subconscious control

• Also called involuntary nervous system or

general visceral motor system


Figure 14.1 Place of the ANS in the structural organization of the nervous system.


Central nervous system (CNS) Peripheral nervous system (PNS)

Sensory (afferent)

division

Motor (efferent) division

Somatic nervous

system

Autonomic nervous

system (ANS)

Sympathetic

division

Parasympathetic

division

14.1 ANS versus Somatic Nervous System

• Both have motor fibers but differ in:

– Effectors

– Efferent pathways and ganglia

– Target organ responses to neurotransmitters


Effectors

• Somatic nervous system innervates skeletal

muscles

• ANS innervates cardiac muscle, smooth

muscle, and glands


Efferent Pathways and Ganglia

• SNS: cell body is in CNS, and a single, thick

myelinated group A axon extends in spinal or

cranial nerves directly to skeletal muscle

• ANS: pathway uses a two-neuron chain

1. Preganglionic neuron: cell body in CNS with

thin, lightly myelinated preganglionic axon

extending to ganglion

2. Postganglionic (ganglionic) neuron (outside

CNS): cell body synapses with preganglionic

axon in autonomic ganglion with

nonmyelinated postganglionic axon that

extends to effector organ


Neurotransmitter Effects

• Somatic nervous system

– All somatic motor neurons release acetylcholine

(ACh)

– Effect is always stimulatory

• ANS

– Preganglionic fibers release ACh

– Postganglionic fibers release norepinephrine or

ACh at effectors

– Effect is either stimulatory or inhibitory,

depending on type of receptors


Overlap of Somatic and Autonomic Function

• Higher brain centers regulate and coordinate

both systems

• Most spinal and many cranial nerves contain

both somatic and autonomic fibers

• Adaptations usually involve both skeletal

muscles and visceral organs

– Example: Active muscles require more oxygen

and glucose, so ANS nerves speed up heart rate

and open airways


Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems.


Cell bodies in central

nervous system

SO

MA

TIC

NE

RV

OU

S

SY

ST

EM

Peripheral nervous system

Single neuron from CNS to effector organs

Heavily myelinated axon

Two-neuron chain from CNS to effector organs

Lightly myelinated

preganglionic axonsGanglion

ACh

Epinephrine andnorepinephrine

Adrenal medulla Blood vessel

Lightly myelinated

preganglionic axon

ACh

Ganglion

Nonmyelinatedpostganglionicaxon

Nonmyelinatedpostganglionic axon

AU

TO

NO

MIC

N

ER

VO

US

S

YS

TE

M

SY

MP

AT

HE

TIC

PA

RA

SY

MPA

TH

ET

IC

ACh

NE

AChSmooth muscle(e.g., in gut), glands,cardiac muscle

Stimulatoryor inhibitory,dependingon neuro-transmitterand receptorson effectororgans

Neurotransmitter

at effector

Effector

organs Effect

Stimulatory

Skeletal muscle

Norepinephrine (NE)Acetylcholine (ACh)

ACh

14.2 Divisions of Autonomic Nervous System

• Two arms of ANS:

– Parasympathetic division: promotes

maintenance functions, conserves energy

– Sympathetic division: mobilizes body during

activity

• Dual innervation: all visceral organs are served

by both divisions, but these divisions cause

opposite effects

– Dynamic antagonism between two divisions

maintains homeostasis


Role of the Parasympathetic Division

• Keeps body energy use as low as possible,

even while carrying out maintenance activities

– Directs digestion, diuresis, defecation

• Referred to as “rest-and-digest” system

• Example: person relaxing and reading after a

meal

– Blood pressure, heart rate, and respiratory rates

are low

– Gastrointestinal tract activity is high

– Pupils constricted, lenses accommodated for

close vision© 2017 Pearson Education, Inc.

Role of the Sympathetic Division

• Mobilizes body during activity

• Referred to as “fight-or-flight” system

• Exercise, excitement, emergency,

embarrassment activates sympathetic system

– Increased heart rate; dry mouth; cold, sweaty

skin; dilated pupils

• During vigorous physical activity:

– Shunts blood to skeletal muscles and heart

– Dilates bronchioles

– Causes liver to release glucose


Key Anatomical Differences

• Three main differences between sympathetic

and parasympathetic divisions:

1. Sites or origin

• Parasympathetic fibers are craniosacral; originate in

brain and sacral spinal cord

• Sympathetic fibers are thoracolumbar; originate in

thoracic and lumbar regions of spinal cord


Key Anatomical Differences (cont.)

2. Relative lengths of fibers

• Parasympathetic has long preganglionic and short

postganglionic fibers

• Sympathetic has short preganglionic and long

postganglionic

3. Location of ganglia

• Parasympathetic ganglia are located in or near the

their visceral effector organ

• Sympathetic ganglia lie close to spinal cord


Figure 14.3 Key anatomical differences between ANS divisions.


Parasympathetic Sympathetic

Eye

Salivaryglands

Heart

Lungs

Stomach

Pancreas

Liver andgall-bladder

Bladder

Genitals

Sacral

Ganglia arewithin or nearvisceral effectororgans.

Postganglionicfibers are short.

Preganglionicfibers are long.

Fibers originatein the brain stem(cranial fibers) orsacral spinal cord.

Postganglionicfibers are long.

Preganglionicfibers are short.

Fibers originatein the thoracic andlumbar spinal cord.

Brain stem

CranialSympathetic

ganglia

Eye

Skin*

Salivary

glands

Lungs

Heart

Stomach

Pancreas

Liver

and gall-bladder

Adrenal

gland

Bladder

Genitals

L1

T1

2a

2b

2a

2b

1 1

33 Ganglia are

close to spinalcord.

Table 14.1 Anatomical and Physiological Differences between the Parasympathetic and Sympathetic Divisions


14.3 Parasympathetic Division

• Also called craniosacral division because

fibers originate from brain stem and sacral

regions or cord

• Long preganglionic fibers extend from CNS

almost to target organs

– Synapse with postganglionic neurons in terminal

ganglia that are close to or within target organs

– Short postganglionic fibers synapse with

effectors



Figure 14.3-1 Key anatomical differences between ANS divisions.

Parasympathetic

Eye

Salivaryglands

Heart

Lungs

Stomach

Pancreas

Liver andgall-bladder

Bladder

Genitals

Sacral

Ganglia arewithin or nearvisceral effectororgans.

Postganglionicfibers are short.

Preganglionicfibers are long.

Brain stem

Cranial

2b

2a

1

3

Fibers originatein the brain stem(cranial fibers) orsacral spinal cord.

Cranial Part of Parasympathetic Division

• Cell bodies are located in brain stem

• Preganglionic fibers run in:

– Oculomotor nerves (III): control smooth muscle

of eye, cause pupils to constrict and lenses to

bulge for focusing

• Postganglion cell bodies located in ciliary ganglia

within eye orbitals



(cont.)

– Facial nerves (VII): stimulate large glands in

head

• Fibers that activate nasal and lacrimal glands have

synapse in pterygopalatine ganglia

• Fibers that activate submandibular and sublingual

salivary glands synapse in submandibular ganglia

– Glossopharyngeal nerves (IX): stimulate

parotid salivary glands

• Fibers synapse in otic ganglia



(cont.)

– Vagus nerves (X): account for ~ 90% of all

preganglionic parasympathetic fibers in body

• Serve all thoracic and abdominal viscera

• Preganglionic fibers arise from medulla and synapse

in terminal ganglia (intramural ganglia) in walls of

target organs

• Cardiac plexus: slow heart rate

• Pulmonary plexus: serve lungs and bronchi

• Esophageal plexus: form anterior and posterior

vagal trunks that sends branches to stomach, liver,

gallbladder, pancreas, small intestine, and part of

large intestine


Sacral Part of Parasympathetic Division

• Originates from neurons in S2–S4 and serves

pelvic organs and distal half of large intestine

• Axons travel in ventral root of spinal nerves

– Branch off to form pelvic splanchnic nerves

• Synapse with:

– Ganglia in pelvic floor (inferior hypogastric

[pelvic] plexus)

– Intramural ganglia in walls of distal half of large

intestine, urinary bladder, ureters, and

reproductive organs


Figure 14.4 Parasympathetic division of the ANS.


Ciliary

ganglion

Pterygopalatine

ganglion

Submandibular

ganglion

Otic ganglion

Cardiac and

pulmonary

plexuses

Celiacplexus

Pelvicsplanchnicnerves

Inferiorhypogastricplexus

Genitalia (penis, clitoris, and vagina)

Urinarybladderand ureters

Rectum

Small

intestine

Large

intestine

Pancreas

Stomach

Liver and

gallbladder

Lung

Heart

Parotid gland

Submandibular

and sublingual

glands

Nasal

mucosa

Lacrimalgland

Eye

Preganglionic

Postganglionic

Cranial nerve

Sacral nerve

S2

S4

14.4 Sympathetic Division

• Sympathetic is more complex and innervates

more organs than parasympathetic

– Some structures are innervated only by

sympathetic: sweat glands, arrector pili muscle of

hair follicle, smooth muscles of all blood vessels

• Sympathetic also called thoracolumbar

division

– Preganglionic neurons are in spinal cord

segments T1–L2

– Form lateral horns of spinal cord



Figure 14.3-2 Key anatomical differences between ANS divisions.

Eye

Skin*

Salivary

glands

Lungs

Heart

Stomach

Pancreas

Liverand gall-bladder

Adrenalgland

Bladder

Genitals

Sympathetic

Postganglionicfibers are long.

Preganglionicfibers are short.

Fibers originatein the thoracic andlumbar spinal cord.

Sympatheticganglia

T1

2b

Ganglia areclose to spinalcord.

2a

1

3 L1


• Preganglionic fibers pass through white rami

communicantes and enter sympathetic trunk

(chain or paravertebral) ganglia

• Paravertebral ganglia vary in size, position, and

number



• There are 23 paravertebral ganglia in the

sympathetic trunk (chain)

– 3 cervical

– 11 thoracic

– 4 lumbar

– 4 sacral

– 1 coccygeal


Figure 14.5 Location of the sympathetic trunk.


Spinal cord

Dorsal root

Ventral root

Rib

Sympathetic

trunk ganglion

Sympathetic

trunk

Ventral ramusof spinal nerve

Gray ramus

communicans

White ramus

communicans

Thoracicsplanchnic nerves


• Upon entering sympathetic trunk ganglion, short

preganglionic fiber may follow one of three

pathways:

– Synapse in trunk ganglia:

1. Synapse with ganglionic neuron in same trunk

ganglion

2. Ascend or descend sympathetic trunk to synapse in

another trunk ganglion, or

– Synapse in collateral ganglia

3. Pass through trunk ganglion and emerge without

synapsing in trunk (only in abdomen and pelvis)

– Synapse outside of trunk in collateral ganglia


Table 14.2 Summary of Autonomic Ganglia


Sympathetic Pathways with Synapses in

Trunk Ganglia

• Postganglionic axons enter ventral rami via

gray rami communicantes

– Gray rami communicantes: nonmyelinated

postganglionic fibers

– White rami communicantes: myelinated

preganglionic fibers

– White and gray rami communicantes contain

sympathetic system neurons only

• These fibers innervate sweat glands, arrector

pili muscles, and vascular smooth muscle via

pathways to the head and thorax© 2017 Pearson Education, Inc.


Figure 14.6-1 Three pathways of sympathetic innervation.

Lateral horn(visceral motor zone)

Ventral root

Sympathetic

trunk ganglion

Sympathetic trunk

Synapse in trunk ganglion

at the same level

Dorsal root

Dorsal root ganglion

Dorsal ramus ofspinal nerve

Ventral ramus ofspinal nerve

Gray ramus

communicans

White ramus

communicans

1

Effectors

Skin (arrectorpili musclesand sweatglands)



Synapse in trunk ganglion

at a higher or lower level

2

Effectors

Skin (arrectorpili musclesand sweatglands)

Blood vessels


Trunk Ganglia (cont.)

• Pathways to the head

– Fibers emerge from T1 to T4 and synapse in the

superior cervical ganglion

– These fibers:

• Innervate skin and blood vessels of the head

• Stimulate dilator muscles of the iris

• Inhibit nasal and salivary glands

• Innervate smooth muscle of upper eyelid

• Branch to the heart



Trunk Ganglia (cont.)

• Pathways to the thorax

– Preganglionic fibers emerge from T1 to T6 and

synapse in cervical trunk ganglia

– Postganglionic fibers emerge from middle and

inferior cervical ganglia and enter nerves C4 to

C8

– These fibers innervate:

• Heart via the cardiac plexus

• Thyroid gland and the skin

• Lungs and esophagus


Figure 14.7 Sympathetic division of the ANS.


Pons

Superiorcervical

ganglion

Middlecervicalganglion

Inferiorcervicalganglion

Sympathetic trunk(chain) ganglia

Cardiac andpulmonaryplexuses

Greater splanchnic nerve

Lesser splanchnic nerve

Celiac ganglion

White rami

communicantes

Superiormesentericganglion

Sacralsplanchnicnerves

Inferiormesentericganglion

Lumbar

splanchnic nerves

Preganglionic

Postganglionic

Genitalia (uterus, vagina, and

penis) and urinary bladder

Rectum

Large

intestine

Small

intestine

Kidney

Adrenal medulla

Spleen

Stomach

Liver and

gallbladder

Lung

Heart

Salivary glands

Blood vessels;

skin (arrector pilimuscles andsweat glands)

Nasal mucosa

Lacrimal gland

Eye

T1

L2

Pathways with Synapses in Collateral Ganglia

• Most fibers from T5 to L2 synapse in collateral

ganglia outside of trunk, forming several

splanchnic nerves

– Greater, lesser, and least (thoracic splanchnic)

splanchnic nerves

– Lumbar splanchnic nerve

– Sacral splanchnic nerves




Splanchnic nerve

Collateral ganglion

(such as the celiac)

Pass through sympathetic trunk to

synapse in a collateral ganglion

anterior to the vertebral column

3

Abdominalorgans (e.g.,intestine)

Effectors


(cont.)

• Splanchnic nerves interweave, forming

abdominal aortic plexuses that contain

several important ganglia

– Celiac and superior and inferior mesenteric

ganglia

– Postganglionic fibers from these ganglia then

travel pathways to abdomen and pelvis



(cont.)

• Pathways to the abdomen

– Preganglionic fibers from T5 to L2 travel through

thoracic splanchnic nerves

– Synapses occur in celiac and superior

mesenteric ganglia

– Postganglionic fibers serve the stomach,

intestines, liver, spleen, and kidneys



(cont.)

• Pathways to the pelvis

– Preganglionic fibers originate from T10 to L2 and

travel trunk to lumbar and sacral ganglia

– Some synapse with postganglionic fibers that run

in lumbar and sacral splanchnic nerves

– Others pass directly to plexuses to collateral

ganglia (example: inferior mesenteric)

– Postganglionic fibers serve distal half of large

intestine, urinary bladder, and reproductive

organs

• Primarily inhibit activity of muscles and glands in

abdominopelvic visceral organs© 2017 Pearson Education, Inc.

Figure 14.7 Sympathetic division of the ANS.


Pons

Superiorcervical

ganglion

Middlecervicalganglion

Inferiorcervicalganglion

Sympathetic trunk(chain) ganglia

Cardiac andpulmonaryplexuses

Greater splanchnic nerve

Lesser splanchnic nerve

Celiac ganglion

White rami

communicantes

Superiormesentericganglion

Sacralsplanchnicnerves

Inferiormesentericganglion

Lumbar

splanchnic nerves

Preganglionic

Postganglionic

Genitalia (uterus, vagina, and

penis) and urinary bladder

Rectum

Large

intestine

Small

intestine

Kidney

Adrenal medulla

Spleen

Stomach

Liver and

gallbladder

Lung

Heart

Salivary glands

Blood vessels;

skin (arrector pilimuscles andsweat glands)

Nasal mucosa

Lacrimal gland

Eye

T1

L2

Pathways with Synapses in the Adrenal

Medulla

• Some preganglionic fibers pass directly to

adrenal medulla without synapsing

• Upon stimulation, medullary cells secrete

norepinephrine and epinephrine into blood

– Also called noradrenaline and norepinephrine

• Sympathetic ganglia and adrenal medulla arise

from same tissue

– Adrenal medulla can be considered “misplaced”

sympathetic ganglion


14.5 Visceral Reflexes

• Visceral reflex arcs have same components as

somatic reflex arcs: receptor, sensory neuron,

integration center, motor neuron, and effector

• Two key differences between visceral and

somatic:

– Visceral reflex arc has two consecutive neurons

in the motor pathway

– Afferents fibers are visceral sensory neurons

• Send info about chemical changes, stretch, or irritation

• Cell bodies are located in cranial nerve sensory

ganglia or dorsal root ganglia of cord


14.5 Visceral Reflexes

• Examples of visceral reflex: reflexes that empty

rectum and bladder

• Three neuron reflex arcs exist in walls of

gastrointestinal tract

– Involve enteric nervous system made up of sensory

neurons, interneurons, and motor neurons

• Visceral sensory fibers involved in phenomenon of

referred pain


Figure 14.8 Visceral reflexes.


Stimulus

Dorsal root ganglionReceptor in viscera

Visceral sensoryneuron

Integration center

• May be preganglionicneuron (as shown)

• May be a dorsal horn

interneuron• May be within walls

of gastrointestinal

tract

Motor neuron

(two-neuron chain)• Preganglionic neuron• Postganglionic neuron

Visceral effector

Response

Autonomic ganglion

Spinal cord

1

2

3

4

5

14.6 Neurotransmitters

• Major neurotransmitters of ANS are acetylcholine

(ACh) and norepinephrine (NE)

– Ach (same as ACh used by somatic motor neuron) is

released by cholinergic fibers at:

• All ANS preganglionic axons and

• All parasympathetic postganglionic axons

– NE is released by adrenergic fibers at:

• Almost all sympathetic postganglionic axons, except

those at sweat glands (release ACh)

• Effects of neurotransmitter depends on whether it

binds to cholinergic receptor or adrenergic

receptor© 2017 Pearson Education, Inc.

Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems.


Cell bodies in central

nervous system

SO

MA

TIC

NE

RV

OU

S

SY

ST

EM

Peripheral nervous system

Single neuron from CNS to effector organs

Heavily myelinated axon

Two-neuron chain from CNS to effector organs

Lightly myelinated

preganglionic axonsGanglion

ACh

Epinephrine andnorepinephrine

Adrenal medulla Blood vessel

Lightly myelinated

preganglionic axon

ACh

Ganglion

Nonmyelinatedpostganglionicaxon

Nonmyelinatedpostganglionic axon

AU

TO

NO

MIC

N

ER

VO

US

S

YS

TE

M

SY

MP

AT

HE

TIC

PA

RA

SY

MPA

TH

ET

IC

ACh

NE

AChSmooth muscle(e.g., in gut), glands,cardiac muscle

Stimulatoryor inhibitory,dependingon neuro-transmitterand receptorson effectororgans

Neurotransmitter

at effector

Effector

organs Effect

Stimulatory

Skeletal muscle

Norepinephrine (NE)Acetylcholine (ACh)

ACh

Cholinergic Receptors

• Two types of cholinergic receptors bind ACh

1. Nicotinic receptors

2. Muscarinic receptors

• Named after drugs that bind to them and mimic

ACh effects: nicotine and muscarine (mushroom

poison)


Cholinergic Receptors (cont.)

• Nicotinic receptors

– Found on:

• All postganglionic neurons (sympathetic and

parasympathetic)

• Hormone-producing cells of adrenal medulla

• Sarcolemma of skeletal muscle cells at neuromuscular

junction

– Effect of ACh at nicotinic receptors is always

stimulatory

• Opens ion channels, depolarizing postsynaptic cell


Cholinergic Receptors (cont.)

• Muscarinic receptors

– Found on:

• All effector cells stimulated by postganglionic

cholinergic fibers

– Effect of ACh at muscarinic receptors

• Can be either inhibitory or excitatory

• Depends on receptor type of target organ

– Example: Binding of ACh to cardiac muscle cells slows

heart rate, whereas binding to intestinal smooth muscle

cells increases motility


Adrenergic Receptors

• Two major classes that respond to NE or

epinephrine

– Alpha () receptors

• Divided into subclasses: 1, 2

– Beta () receptors

• Divided into subclasses: 1, 2, 3


Adrenergic Receptors (cont.)

• Effects depend on which subclass of receptor

predominates on target organ

– Example: NE binding to cardiac muscle 1

receptors causes increase in rate, whereas

epinephrine causes bronchial relaxation when

bound to 2 receptors


Table 14.3 Cholinergic and Adrenergic Receptors


Table 14.4 Selected Drug Classes That Influence the Autonomic Nervous System


14.7 Parasympathetic and Sympathetic

Interactions

• Most visceral organs have dual innervation

• Action potentials continually fire down axons of

both divisions, producing a dynamic

antagonistic interaction

– Works to precisely control visceral activity

• Both ANS divisions are partially active, resulting

in a basal sympathetic and parasympathetic

tone

• One division usually predominates, but in a few

cases, divisions have a cooperative effect


Antagonistic Interactions

• Dynamic antagonism allows for precise control

of visceral activity

– Sympathetic division increases heart and

respiratory rates and inhibits digestion and

elimination

– Parasympathetic division decreases heart and

respiratory rates and allows for digestion and

discarding of wastes


Sympathetic and Parasympathetic Tone

• Almost all blood vessel smooth muscle is

entirely innervated by sympathetic fibers only,

so this division controls blood pressure, even at

rest



(cont.)

• Sympathetic tone (vasomotor tone): continual

state of partial constriction of blood vessels

– If blood pressure drops, sympathetic fibers fire

faster than normal to increase constriction of

blood vessels and cause blood pressure to rise

– If blood pressure rises, sympathetic fibers fire

less than normal, causing less constriction

(dilation) of vessels, which leads to decrease in

blood pressure

– Allows sympathetic system to shunt blood where

needed



(cont.)

• Parasympathetic division normally dominates

heart and smooth muscle of digestive and

urinary tract organs, and it activates most

glands except for adrenal and sweat glands

– Slows the heart and dictates normal activity

levels of digestive and urinary tracts

– These organs also exhibit parasympathetic

tone where they are always slightly activated



(cont.)

• The sympathetic division can override these

effects during times of stress

• Drugs that block parasympathetic responses

increase heart rate and cause fecal and urinary

retention


Cooperative Effects

• Best example of cooperation between two

divisions seen in control of external genitalia

• Parasympathetic fibers cause vasodilation and

are responsible for erection of penis or clitoris

• Sympathetic fibers cause ejaculation of semen

in males and reflex contraction of a female's

vagina


Unique Roles of the Sympathetic Division

• Adrenal medulla, sweat glands, arrector pili

muscles, kidneys, and almost all blood vessels

receive only sympathetic fibers

• Other unique functions of sympathetic division

include:

– Thermoregulatory responses to heat

• When body temperatures rise, sympathetic nerves:

1. Dilate skin blood vessels, allowing heat to escape

2. Activate sweat glands

• When body temperatures drop, blood vessels constrict


Unique Roles of the Sympathetic Division

(cont.)

– Release of renin from kidneys

• Sympathetic system causes release of renin from

kidneys that in turn activates a system that increases

blood pressure

– Metabolic effects

• Increases metabolic rates of cells

• Raises blood glucose levels

• Mobilizes fats for use as fuels


Localized Versus Diffuse Effects

• Parasympathetic division tends to elicit short-

lived and highly localized control over effectors

– ACh is quickly destroyed by acetylcholinesterase

• Sympathetic division tends to be longer-lasting

with bodywide effects

– NE is inactivated more slowly than ACh

– NE and epinephrine hormones from adrenal

medulla have prolonged effects that last even

after sympathetic signals stop


Table 14.5 -1 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs



Table 14.5-2 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs (continued)

Clinical – Homeostatic Imbalance 14.1

• Autonomic neuropathy: damage to autonomic

nerves that is a common complication of

diabetes mellitus

• Early signs include sexual dysfunction

• Other frequent symptoms include dizziness after

standing suddenly (poor blood pressure control),

urinary incontinence, sluggish eye pupil

reactions, and impaired sweating

• Best way to prevent diabetic neuropathy is to

maintain good blood glucose levels


14.8 Control of ANS Function

• ANS is under control of CNS centers in:

– Brain stem and spinal cord, hypothalamus,

and cerebral cortex

– Hypothalamus is generally main integrative

center of ANS activity

• Cerebral input may modify ANS but does so

subconsciously

– Works through limbic system structures on

hypothalamic centers



– Brain stem and spinal cord controls

• Brain stem reticular formation appears to exert most

direct influence over ANS

• Medullary centers regulate heart rate and blood vessel

diameter, as well as gastrointestinal activities

• Midbrain controls muscles of pupil and lens

• Spinal cord controls defecation and micturition but are

subject to conscious override



– Hypothalamic controls

• Anterior regions direct parasympathetic functions;

posterior region directs sympathetic

• Control may be direct or indirect through reticular

system or spinal cord

• Centers of hypothalamus controls:

– Heart activity, blood pressure, temperature of body,

water balance, and endocrine activity

– Emotional responses (rage, fear, pleasure) activated

through limbic system signal hypothalamus to activate

fight-or-flight system



– Cortical controls

• Connections of hypothalamus to limbic lobe allow

cortical influence on ANS

• Voluntary cortical control of some visceral activities is

possible

– Biofeedback

» Awareness of physiological conditions with goal of

consciously influencing them

» Biofeedback training allows some people to control

migraines and manage stress


Figure 14.9 Levels of ANS control.


Communication atsubconscious level

Cerebral cortex(frontal lobe)

Limbic system(emotional input)

Hypothalamus

Brain stem

(reticular formation, etc.)

Spinal cord

Regulates pupil size, heart,blood pressure, airflow,

salivation, etc.

The “boss”: Overallintegration of ANS

Reflexes for urination,defecation, erection,

and ejaculation

14.9 Disorders of the ANS

• Many ANS disorders involve deficient control of

smooth muscle activity

– Hypertension (high blood pressure)

• Overactive sympathetic vasoconstrictor response to

stress

• Heart must work harder, and artery walls are subject

to increased wear and tear

• Can be treated with adrenergic receptor-blocking

drugs


14.9 Disorders of the ANS

– Raynaud’s disease

• Painful, exaggerated vasoconstriction in fingers and

toes

– Digits turn pale, then cyanotic

– Treated with vasodilators

– Autonomic dysreflexia

• Life-threatening, uncontrolled activation of autonomic

neurons in quadriplegics and people with spinal cord

injuries above T6

• Blood pressure skyrockets, posing increased risk for

stroke


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