The Autonomic Nervous System

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The Nervous System I:
The Autonomic Nervous System
(ANS)
Anatomy & Physiology
Chapter 16
Autonomic Nervous System (ANS)

The ANS consists of motor neurons that:
◦ Regulate the action of smooth and cardiac
muscle and glands
◦ Make adjustments to ensure optimal support
for body activities
◦ Operate via subconscious control
Motor Divisions: Somatic vs.
Visceral (ANS)
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
Somatic and Autonomic Nervous
Systems

The two systems differ in
◦ Effectors
◦ Efferent pathways (and their neurotransmitters)
◦ Target organ responses to neurotransmitters
Effectors

Somatic nervous system
◦ Skeletal muscles

ANS
◦ Cardiac muscle
◦ Smooth muscle
◦ Glands
Efferent Pathways
 Somatic
nervous system
◦ A, thick, heavily myelinated somatic motor
fiber makes up each pathway from the CNS
to the muscle
 ANS
pathway is a two-neuron chain
1. Preganglionic neuron (in CNS) has a thin,
lightly myelinated preganglionic axon
2. Ganglionic neuron in autonomic ganglion has
an unmyelinated postganglionic axon that
extends to the effector organ
Neurotransmitter Effects
Somatic nervous system
◦ All somatic motor neurons release
acetylcholine (ACh)
◦ Effects are 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

SOMATIC
NERVOUS
SYSTEM
Cell bodies in central
nervous system
Peripheral nervous system
Neurotransmitter
at effector
Effector
organs
Single neuron from CNS to effector organs
Effect
+
ACh
Stimulatory
Heavily myelinated axon
Skeletal muscle
NE
SYMPATHETIC
ACh
Unmyelinated
postganglionic axon
Lightly myelinated Ganglion
Epinephrine and
preganglionic axons
norepinephrine
ACh
Adrenal medulla
PARASYMPATHETIC
AUTONOMIC NERVOUS SYSTEM
Two-neuron chain from CNS to effector organs
Acetylcholine (ACh)
Blood vessel
ACh
ACh
Lightly myelinated
preganglionic axon
Norepinephrine (NE)
Ganglion
+
Unmyelinated
postganglionic
axon
Smooth muscle
(e.g., in gut),
glands, cardiac
muscle
Stimulatory
or inhibitory,
depending
on neurotransmitter
and
receptors
on effector
organs
Divisions of the ANS
Sympathetic division
2. Parasympathetic division
 Dual innervation
1.
◦ Almost all visceral organs are served by both
divisions, but they cause opposite effects
CN III
Ciliary
ganglion
CN VII
CN IX
CN X
Pterygopalatine
ganglion
Submandibular
ganglion
Otic ganglion
Eye
Lacrimal
gland
Nasal
mucosa
Submandibular
and sublingual
glands
Parotid gland
Heart
Cardiac and
pulmonary
plexuses
Celiac
plexus
Lung
Liver and
gallbladder
Stomach
Pancreas
S2
S4
Pelvic
splanchnic
nerves
Inferior
hypogastric
plexus
Genitalia
(penis,
clitoris, and vagina)
Large
intestine
Small
intestine
Rectum
Urinary
bladder
and ureters
Preganglionic
Postganglionic
Cranial nerve
Eye
Lacrimal gland
Nasal mucosa
Pons
Sympathetic trunk
(chain) ganglia
Blood vessels;
skin (arrector pili
muscles and
sweat glands)
Superior
cervical
ganglion
T1
Middle
cervical
ganglion
Inferior
cervical
ganglion
Salivary glands
Heart
Cardiac and
pulmonary
plexuses
Lung
Greater splanchnic nerve
Lesser splanchnic nerve
Celiac ganglion
L2
Liver and
gallbladder
Stomach
White rami
communicantes
Superior
mesenteric
ganglion
Spleen
Adrenal medulla
Kidney
Sacral
splanchnic
nerves
Lumbar
splanchnic
nerves
Inferior
mesenteric
ganglion
Small
intestine
Large
intestine
Rectum
Preganglionic
Postganglionic
Genitalia (uterus, vagina, and
penis) and urinary bladder
Sympathetic nervous system

Thoracolumbar area

Adrenergic system

Activated in the four E’s: excitement,
emergency, embarassment, exercise
Role of the Sympathetic Division

Mobilizes the body during activity; is the
“fight-or-flight” system

Promotes adjustments during exercise, or
when threatened
◦ Blood flow is shunted to skeletal muscles and
heart
◦ Bronchioles dilate
◦ Liver releases glucose
Parasympathetic nervous system

Arise in craniosacral areas

Cholinergic system
Role of the Parasympathetic
Division

Promotes maintenance activities and
conserves body energy

Its activity is illustrated in a person who
relaxes, reading, after a meal
◦ Blood pressure, heart rate, and respiratory
rates are low
◦ Gastrointestinal tract activity is high
◦ Pupils are constricted and lenses are
accommodated for close vision
Sympathetic Effects…












On the iris - Pupillary dilation
On the sweat glands – secretion
On piloerector muscles – hair erection (goose bumps)
On the heart – increased heart rate and force
On blood vessels of skeletal muscle – vasodilation
On blood vessels of skin – vasoconstriction
On the bronchi and bronchioles – bronchodilation
On the kidneys – reduced urine output
On the GI Tract – decreased motility and secretion
On the Liver – glycogen breakdown
On the pancreas – decreased insulin secretion; decreased
digestive enzyme secretion
On the reproductive system – stimulation of orgasm and
relaxation of the uterus
Parasympathetic Effects...

On the iris - Pupillary constriction

On the heart – decreased heart rate and force

On blood vessels of skin – vasodilation

On the bronchi and bronchioles –
bronchoconstriction

On the bladder wall – contraction

On the GI Tract – increased motility and secretion

On the Liver – glycogen synthesis

On the pancreas – increased digestive enzyme
secretion

On the reproductive system – stimulation of
penile and clitoral erection
Autonomic Nervous System
The diagram
shows only one
side of the body
for each
division.
ZOOMING IN
• Which division of the
autonomic nervous
system has ganglia
closer to the effector
organ?
Cellular Receptors

“Docking sites” on postsynaptic cell membranes
Two types:

Cholinergic receptors
◦ Nicotinic (bind nicotine) on skeletal muscle cells
◦ Muscarinic (bind muscarine, a poison) on
effector cells of PNS

Adrenergic receptors
◦ Found on receptor cells of sympathetic nervous
system
◦ Bind norepinephrine, epinephrine
Drugs and 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 interfering with effects of
epinephrine/norepinephrine on heart and blood vessels

parasympathomimetics enhance activity
while parasympatholytics suppress activity
End of Presentation
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