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© 2012 Pearson Education, Inc.
17 The Nervous System:
Autonomic Nervous
System
© 2012 Pearson Education, Inc.
Introduction
•The autonomic nervous system:
• Functions outside of our conscious awareness
• Makes routine adjustments in our body’s
systems
•The autonomic nervous system:
• Regulates body temperature
• Coordinates cardiovascular, respiratory,
digestive, excretory, and reproductive
functions
© 2012 Pearson Education, Inc.
Subdivisions of the ANS
• The autonomic nervous
system consists of
two major subdivisions
• Sympathetic division
• Also called the
thoracolumbar division
• Known as the “fight or
flight” system
• Parasympathetic division
• Also called the
craniosacral division
• Known as the “rest and
digest” system
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
A Comparison of the Somatic and
Autonomic Nervous Systems • The autonomic nervous system differs from
the somatic nervous system in the arrangement of the neurons connecting the central nervous system to the effector organs.
• Visceral motor neurons in the CNS, known as preganglionic neurons, send their axons, called preganglionic fibers, to synapse on ganglionic neurons, whose cell bodies are located outside the CNS, in autonomic ganglia.
• Axons from the ganglionic neurons are called postganglionic fibers because they carry impulses away from the ganglion.
• Postganglionic fibers innervate peripheral tissues and organs, such as cardiac and smooth muscle, adipose tissue, and glands.
© 2012 Pearson Education, Inc.
Subdivisions of the ANS
•Sympathetic division
• Thoracic and upper lumbar nerves synapse in
ganglia near the spinal cord
• Sympathetic activation results in:
• Increased metabolism and alertness
•Parasympathetic division
• Synapses are located near the target organ
• Parasympathetic activation results in:
• Energy conservation
© 2012 Pearson Education, Inc.
The Sympathetic Division
•Sympathetic division consists of:
• Preganglionic neurons between T1 and L2
• Two types of ganglionic neurons near the
vertebral columns:
sympathetic chain ganglia also called
paravertebral ganglia
collateral ganglia also known as prevertebral
ganglia
• Specialized neurons in the interior of the
suprarenal gland
© 2012 Pearson Education, Inc.
Figure 17.2 Organization of the Sympathetic Division of the ANS
Preganglionic fibers
Postganglionic fibers
Hormones released
into circulation
KEY
Lateral gray
horns of spinal
segments
T1–L2
Sympathetic
chain ganglia
(paired)
Collateral
ganglia
(unpaired)
Suprarenal
medullae
(paired)
Preganglionic Neurons
Ganglionic Neurons
Innervation by
postganglionic
fibers
Through release of
hormones into
the circulation
Target Organs
Visceral effectors
in thoracic cavity,
head, body wall,
and limbs
Visceral effectors
in abdominopelvic
cavity
Organs and systems
throughout body
Sympathetic Division of ANS
© 2012 Pearson Education, Inc.
Sympathetic division of the ANS
• Sympathetic division
• All preganglionic fibers
release acetylcholine
(Ach)
• Most postganglionic
fibers release
norepinephrine
(adrenergic)
stimulatory effects
© 2012 Pearson Education, Inc.
The Sympathetic Division
• Effects of Sympathetic Chain
Ganglia
• Reduction of circulation to the
skin
• More circulation to skeletal
muscles
• Stimulates more energy
production by skeletal muscles
• Releases stored adipose
• Stimulation of arrector pili
muscles
• Dilation of pupils
• Increased heart rate
• Dilation of respiratory tubes
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
The Sympathetic Division
•Summary of the Sympathetic Division
• Consists of parallel chains on either side of the
spinal cord
• Preganglionic fibers are short and extend
from the spinal cord to the sympathetic chain
• Postganglionic fibers are long and extend
from the spinal cord to the body organs
• All preganglionic neurons release Ach
• Most postganglionic neurons release
norepinephrine
© 2012 Pearson Education, Inc.
Figure 17.4 Anatomical Distribution of Sympathetic Postganglionic Fibers
Superior
Middle
Inferior
PONS
Cervical
sympathetic
ganglia
Gray rami to
spinal nerves
Greater
splanchnic
nerve
Superior
mesenteric
ganglion
Cardiac and
pulmonary
plexuses
Celiac ganglion
Sympathetic nerves
T1 T1
T2 T2
T3 T3
T4 T4
T5 T5
T6 T6
T7 T7
T8 T8
T9 T9
T10 T10
T11 T11
T12 T12
L1 L1
L2 L2
L3 L3
L4 L4
L5 L5 S1 S1 S2 S2
S3 S3 S4 S4
S5 S5
Postganglionic fibers
to spinal nerves
(innervating skin, blood
vessels, sweat glands,
arrector pili muscles,
adipose tissue)
Sympathetic
chain ganglia
Spinal cord
Coccygeal
ganglia (Co1)
fused together
(ganglion impar)
Preganglionic neurons
Ganglionic neurons
KEY
Uterus Ovary
Sacral
splanchnic
nerves
Lesser
splanchnic
nerve
Lumbar
splanchnic nerves Inferior
mesenteric
ganglion
Penis Scrotum Urinary bladder
Kidney
Suprarenal
medulla
Small intestine
Large intestine
Pancreas
Spleen
Stomach
Liver and
gallbladder
Lung
Heart
Eye
Salivary
glands
© 2012 Pearson Education, Inc.
The Parasympathetic Division
•Parasympathetic Division
• Preganglionic neurons are in the brain stem and
sacral segments
• Parasympathetic division is more localized and
specific as compared to the sympathetic division
• Postganglionic neurons are near (terminal) the
target organ or within (intramural) the target
organ
© 2012 Pearson Education, Inc.
Parasympathetic division of the ANS
• Parasympathetic
division
• All preganglionic fibers
release acetylcholine
• Postganglionic fibers
release acetylcholine
(cholinergic)
inhibitory effects
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
The Parasympathetic Division
• Effects of the Parasympathetic Division
• Pupil constriction
• Secretion of digestive enzymes from digestive glands
• Increased smooth muscle activity of the digestive
system
• Stimulation and coordination of defecation
• Contraction of the urinary bladder
• Constriction of respiratory passages
• Reduced heart rate
• Sexual arousal
© 2012 Pearson Education, Inc.
Figure 17.8 Autonomic Distribution of the Parasympathetic Output Pterygopalatine ganglion
PONS
N III
N VII
N IX
N X (Vagus)
Ciliary ganglion
Submandibular
ganglion
Otic ganglion
Autonomic plexuses
(see Figure 17.9)
Pelvic
nerves
Lacrimal gland
Eye
Salivary glands
Heart
Lungs
Liver and
gallbladder
Stomach
Spleen
Pancreas
Large intestine
Small intestine
Rectum
Kidney
Urinary bladder Scrotum Penis Ovary Uterus
S2
S3
S4
Spinal
cord
Preganglionic neurons
Ganglionic neurons
KEY
© 2012 Pearson Education, Inc.
Relationships between the Sympathetic and
Parasympathetic Divisions
•Sympathetic
• Widespread stimulatory effect on visceral organs
•Parasympathetic
• Modifies/inhibits the activity of structures innervated by specific cranial nerves and pelvic nerves
•Most vital organs are innervated by both the sympathetic and parasympathetic nerves
• The two often oppose (antagonistic) each other
© 2012 Pearson Education, Inc.
Figure 17.10 A Comparison of the Sympathetic and Parasympathetic Divisions
Sympathetic Parasympathetic
CNS
PNS
KEY
Sympathetic
ganglion
Circulatory
system
Preganglionic
neuron
Preganglionic
fiber
Ganglionic
neurons
Postganglionic
fiber
TARGET
Parasympathetic
ganglion
Neurotransmitters
Acetylcholine
Norepinephrine
Epinephrine or
© 2012 Pearson Education, Inc.
Relationships between the Sympathetic and
Parasympathetic Divisions
• Dual Innervation • The parasympathetic
fibers accompany the
sympathetic fibers to
the target organ
• The parasympathetic
and sympathetic fibers
mingle together forming
peripheral autonomic
plexuses
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Visceral Reflexes
•All are polysynaptic
•Reflexes can be:
• Long reflexes
• Short reflexes
© 2012 Pearson Education, Inc.
Visceral Reflexes
•Long Reflexes
• Visceral sensory
neurons go to the CNS
via the dorsal roots
• There are interneurons
within the CNS
• Information is
“interpreted” in the
spinal cord or brain
• ANS sends motor
commands to the
visceral organs
© 2012 Pearson Education, Inc.
Visceral Reflexes
• Short Reflexes
• Sensory nerve
impulses go to the
ganglionic neurons
• Motor commands are
distributed by the
postganglionic fibers
• Impulses bypass the
CNS
© 2012 Pearson Education, Inc.
Levels of Somatic Motor Control
•Summary of somatic motor control
• Thalamus
• Controls reflexes associated with visual and
auditory stimuli
• Hypothalamus
• Responds to hunger, thirst, and sexual activity
• Pons
• Regulates the rhythmic breathing patterns
© 2012 Pearson Education, Inc.
Levels of Somatic Motor Control
•Summary of somatic motor control
• Medulla oblongata
• Alters the breathing patterns
• Brain stem
• Controls simple reflexes
• Spinal cord
• Controls simple reflexes