Transcript Chapter 14 PowerPoint

Chapter 14
Autonomic
Nervous
System
© Annie Leibovitz/Contact Press Images
© 2016 Pearson Education, Inc.
PowerPoint® Lecture Slides
prepared by
Karen Dunbar Kareiva
Ivy Tech Community College
Why This Matters
• Understanding the autonomic nervous system
helps you to anticipate the effects and side
effects of drugs on your patients
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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
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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
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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
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Effectors
• Somatic nervous system innervates skeletal
muscles
• ANS innervates cardiac muscle, smooth
muscle, and glands
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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
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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
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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
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Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems.
SOMATIC
NERVOUS
SYSTEM
Cell bodies in central
nervous system
Neurotransmitter
at effector
Peripheral nervous system
Effector
organs
Effect
Single neuron from CNS to effector organs
ACh
Stimulatory
Heavily myelinated axon
Skeletal muscle
Two-neuron chain from CNS to effector organs
NE
SYMPATHETIC
Lightly myelinated
preganglionic axons
Nonmyelinated
postganglionic axon
Ganglion
ACh
Epinephrine and
norepinephrine
Adrenal medulla
PARASYMPATHETIC
AUTONOMIC NERVOUS SYSTEM
ACh
Acetylcholine (ACh)
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Blood vessel
ACh
ACh
Lightly myelinated
preganglionic axon
Norepinephrine (NE)
Ganglion
Nonmyelinated
postganglionic
axon
Smooth muscle
(e.g., in gut), glands,
cardiac muscle
Stimulatory
or inhibitory,
depending
on neurotransmitter
and receptors
on effector
organs
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
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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
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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
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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
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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
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Figure 14.3 Key anatomical differences between ANS divisions.
Sympathetic
Parasympathetic
Eye
Salivary
glands
Eye
Brain stem
Skin*
Cranial
Sympathetic
ganglia
Heart
Lungs
Stomach
1 Fibers originate
in the brain stem
(cranial fibers) or
sacral spinal cord.
1 Fibers originate
in the thoracic and
lumbar spinal cord.
2a Preganglionic
2a Preganglionic
Liver and
gallbladder
Bladder
Genitals
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Lungs
Heart
fibers are long.
fibers are short.
Stomach
2b Postganglionic
2b Postganglionic
fibers are long.
Pancreas
fibers are short.
Pancreas
T1
Salivary
glands
3 Ganglia are
within or near
visceral effector
organs.
Sacral
3 Ganglia are
close to spinal
cord.
L1
Liver
and gallbladder
Adrenal
gland
Bladder
Genitals
Table 14.1 Anatomical and Physiological Differences between the Parasympathetic and Sympathetic Divisions
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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
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Figure 14.3-1 Key anatomical differences between ANS divisions.
Parasympathetic
Eye
Salivary
glands
Heart
Lungs
Brain stem
Cranial
1
Fibers originate
in the brain stem
(cranial fibers) or
sacral spinal cord.
2a
Preganglionic
fibers are long.
Stomach
Pancreas
Liver and
gallbladder
Bladder
Genitals
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2b
Postganglionic
fibers are short.
3 Ganglia are
within or near
visceral effector
organs.
Sacral
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
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Cranial Part of Parasympathetic Division
(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
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Cranial Part of Parasympathetic Division
(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
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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
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Figure 14.4 Parasympathetic division of the ANS.
Eye
Ciliary
ganglion
Lacrimal
gland
Pterygopalatine
ganglion
Submandibular
ganglion
Nasal
mucosa
Submandibular
and sublingual
glands
Otic ganglion
Parotid gland
Heart
Cardiac and
pulmonary
plexuses
Lung
Celiac
plexus
Liver and
gallbladder
Stomach
Pancreas
S2
Large
intestine
S4
Small
intestine
Pelvic
splanchnic
nerves
Inferior
hypogastric
plexus
Rectum
Urinary
bladder
and ureters
Genitalia (penis, clitoris, and vagina)
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Preganglionic
Postganglionic
Cranial nerve
Sacral nerve
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
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Figure 14.3-2 Key anatomical differences between ANS divisions.
Sympathetic
Eye
Skin*
Sympathetic
ganglia
1 Fibers originate
in the thoracic and
lumbar spinal cord.
T1
Salivary
glands
Lungs
Heart
2a Preganglionic
fibers are short.
Stomach
2b Postganglionic
Pancreas
fibers are long.
3 Ganglia are
close to spinal
cord.
L1
Liver
and gallbladder
Adrenal
gland
Bladder
Genitals
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14.4 Sympathetic Division
• Preganglionic fibers pass through white rami
communicantes and enter sympathetic trunk
(chain or paravertebral) ganglia
• Paravertebral ganglia vary in size, position, and
number
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14.4 Sympathetic Division
• There are 23 paravertebral ganglia in the
sympathetic trunk (chain)
–
–
–
–
–
3 cervical
11 thoracic
4 lumbar
4 sacral
1 coccygeal
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Figure 14.5 Location of the sympathetic trunk.
Spinal cord
Dorsal root
Ventral root
Rib
Sympathetic
trunk ganglion
Sympathetic
trunk
Ventral ramus
of spinal nerve
Gray ramus
communicans
White ramus
communicans
Thoracic
splanchnic nerves
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14.4 Sympathetic Division
• 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
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Table 14.2 Summary of Autonomic Ganglia
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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
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Figure 14.6-1 Three pathways of sympathetic innervation.
Lateral horn
(visceral motor zone)
Dorsal root
Dorsal root ganglion
Dorsal ramus of
spinal nerve
Ventral ramus of
spinal nerve
Ventral root
Sympathetic
trunk ganglion
Sympathetic trunk
Gray ramus
communicans
White ramus
communicans
1 Synapse in trunk ganglion
at the same level
Skin (arrector
pili muscles
and sweat
glands)
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Effectors
Figure 14.6-2 Three pathways of sympathetic innervation.
2 Synapse in trunk ganglion
at a higher or lower level
Skin (arrector
pili muscles
and sweat
glands)
Effectors
Blood vessels
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Sympathetic Pathways with Synapses in
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
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Sympathetic Pathways with Synapses in
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
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Figure 14.7 Sympathetic division of the ANS.
Eye
Lacrimal gland
Nasal mucosa
Pons
Sympathetic trunk
(chain) ganglia
Blood vessels;
skin (arrector pili
muscles and
sweat glands)
Superior
cervical
ganglion
Salivary glands
Middle
cervical
ganglion
Heart
Inferior
cervical
ganglion
T1
Cardiac and
pulmonary
plexuses
Lung
Greater splanchnic nerve
Lesser splanchnic nerve
Celiac ganglion
Liver and
gallbladder
L2
Stomach
White rami
communicantes
Sacral
splanchnic
nerves
Superior
mesenteric
ganglion
Spleen
Inferior
mesenteric
ganglion
Adrenal medulla
Kidney
Lumbar
splanchnic nerves
Small
intestine
Large
intestine
Rectum
Preganglionic
Postganglionic
Genitalia (uterus, vagina, and
penis) and urinary bladder
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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
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Figure 14.6-3 Three pathways of sympathetic innervation.
Splanchnic nerve
Collateral ganglion
(such as the celiac)
3 Pass through sympathetic trunk to
synapse in a collateral ganglion
anterior to the vertebral column
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Abdominal
organs (e.g.,
intestine)
Effectors
Pathways with Synapses in Collateral Ganglia
(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
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Pathways with Synapses in Collateral Ganglia
(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
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Pathways with Synapses in Collateral Ganglia
(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
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Figure 14.7 Sympathetic division of the ANS.
Eye
Lacrimal gland
Nasal mucosa
Pons
Sympathetic trunk
(chain) ganglia
Blood vessels;
skin (arrector pili
muscles and
sweat glands)
Superior
cervical
ganglion
Salivary glands
Middle
cervical
ganglion
Heart
Inferior
cervical
ganglion
T1
Cardiac and
pulmonary
plexuses
Lung
Greater splanchnic nerve
Lesser splanchnic nerve
Celiac ganglion
Liver and
gallbladder
L2
Stomach
White rami
communicantes
Sacral
splanchnic
nerves
Superior
mesenteric
ganglion
Spleen
Inferior
mesenteric
ganglion
Adrenal medulla
Kidney
Lumbar
splanchnic nerves
Small
intestine
Large
intestine
Rectum
Preganglionic
Postganglionic
Genitalia (uterus, vagina, and
penis) and urinary bladder
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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
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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
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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
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Figure 14.8 Visceral reflexes.
Stimulus
1 Receptor in viscera
2 Visceral sensory
Dorsal root ganglion
Spinal cord
neuron
3 Integration center
• May be preganglionic
neuron (as shown)
• May be a dorsal horn
interneuron
• May be within walls
of gastrointestinal
tract
4 Motor neuron
(two-neuron chain)
• Preganglionic neuron
• Postganglionic neuron
5 Visceral effector
Response
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Autonomic ganglion
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
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Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems.
SOMATIC
NERVOUS
SYSTEM
Cell bodies in central
nervous system
Neurotransmitter
at effector
Peripheral nervous system
Effector
organs
Effect
Single neuron from CNS to effector organs
ACh
Stimulatory
Heavily myelinated axon
Skeletal muscle
Two-neuron chain from CNS to effector organs
NE
SYMPATHETIC
Lightly myelinated
preganglionic axons
Nonmyelinated
postganglionic axon
Ganglion
ACh
Epinephrine and
norepinephrine
Adrenal medulla
PARASYMPATHETIC
AUTONOMIC NERVOUS SYSTEM
ACh
Acetylcholine (ACh)
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Blood vessel
ACh
ACh
Lightly myelinated
preganglionic axon
Norepinephrine (NE)
Ganglion
Nonmyelinated
postganglionic
axon
Smooth muscle
(e.g., in gut), glands,
cardiac muscle
Stimulatory
or inhibitory,
depending
on neurotransmitter
and receptors
on effector
organs
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)
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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
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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
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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
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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
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Table 14.3 Cholinergic and Adrenergic Receptors
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Table 14.4 Selected Drug Classes That Influence the Autonomic Nervous System
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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
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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
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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
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Sympathetic and Parasympathetic Tone
(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
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Sympathetic and Parasympathetic Tone
(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
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Sympathetic and Parasympathetic Tone
(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
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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
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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
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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
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Localized Versus Diffuse Effects
• Parasympathetic division tends to elicit shortlived 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
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Table 14.5 -1 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs
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Table 14.5-2 Effects of the Parasympathetic and Sympathetic Divisions on Various Organs (continued)
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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
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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
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14.8 Control of ANS Function
– 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
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14.8 Control of ANS Function
– 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
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14.8 Control of ANS Function
– 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
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Figure 14.9 Levels of ANS control.
Communication at
subconscious level
Cerebral cortex
(frontal lobe)
Limbic system
(emotional input)
Hypothalamus
The “boss”: Overall
integration of ANS
Brain stem
(reticular formation, etc.)
Regulates pupil size, heart,
blood pressure, airflow,
salivation, etc.
Spinal cord
Reflexes for urination,
defecation, erection,
and ejaculation
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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
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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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Developmental Aspects of the Autonomic
Nervous System
• ANS preganglionic neurons derive from neural
tube (as do somatic motor neurons)
• ANS structures in PNS derive from neural crest
– Postganglionic neurons, adrenal medulla, and all
ganglia
• Nerve growth factor and signaling chemicals
aid axons in finding path to target organs
• During youth, ANS impairments are usually due
to injury
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Developmental Aspects of the Autonomic
Nervous System
• ANS efficiency declines in old age, partially
because of structural changes at preganglionic
axon terminals
• Effects of age on ANS
– Constipation
– Dry eyes and frequent eye infections
– Orthostatic hypotension
• Low blood pressure after position change
• Pressure receptors are less responsive to blood
pressure changes
• Cardiovascular centers fail to maintain healthy blood
pressure
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