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Collin County Community College
BIOL 2401:
Week 10
Autonomic Nervous
System
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Organization
Central NS
Sensory Division
Visceral Division
Peripheral NS
Motor Division
Somatic Division
Autonomic Division
Enteric
Parasympathetic
Sympathetic
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The Autonomic Nervous System
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Differences between Somatic & Autonomic
Somatic NS
• stimulates skeletal muscles
• referred to as the voluntary system
• heavy, myelinated type A fibers (fast transmission)
Autonomic NS
• stimulates glands, smooth muscle, heart muscle
• referred to as the involuntary system
• light to un - myelinated fibers (slower transmission)
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Important Anatomical Differences
The somatic nervous system is composed of motor neurons that
control the contraction of the skeletal muscles.
The autonomic nervous system is composed of sets of 2 neurons
that control the activities of involuntary processes.
The ganglion is an anatomically visible area where the pre- and
post-ganglionic neurons of the ANS form their synaptic junctions.
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The Autonomic Nervous System
• always a two neuron chain that innervates cardiac,
smooth muscle and glands
• cell body of the first neuron (the pre-ganglionic axon)
resides in the brain or spinal column.
• synapses with a second neuron (ganglionic neuron
with postganglionic axon) in an autonomic ganglion
outside the CNS
• postganglionic axon extends to the effector organ (cell
body of postganglionic neuron is in the ganglion)
• pre-ganglionic neurons are lightly myelinated;
postganglionic ones are thin and unmyelinated
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Anatomical Differences Within ANS
PS - NS
• PS nerves originate from Brain and
Sacral area of the spinal column
• They have long pre-ganglionic fibers,
short postganglionic fibers
S - NS
• Sympathetic fibers originate from
thoraco-lumbar region of SC
• Sympathetic pathways have short
pre-ganglionic fibers, long
postganglionic fibers.
Voluntary
command:
Move!
Involuntary
command:
Rest & digest.
Motor neuron
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Skeletal
muscle
contraction
Heart, smooth
muscle, glands,
many “involuntary”
targets”
Involuntary
command:
Emergency!
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The Sympathetic Nervous System
• All cell bodies of the preganglionic fibers arise in
the SC segments T1-L2
• The nuclei of the preganglionic fibers are located in
the lateral gray horn
• Pre ganglionic fibers leave the SC and enter the
ventral roots of the spinal cord segment
• They form ganglions with postsynaptic neurons in
three major areas, which will innervate the
respective target organs
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Sympathetic Ganglions
Sympathetic Chain Ganglia
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Sympathetic Ganglions
Sympathetic Chain Ganglia
• Although the presynaptic neurons originate from SC
segments T1-L2, this chain of ganglia runs up and down the
spinal cord (remember that the preganglionic neuron is
short ! )
• There are 3 cervical, 12 thoracic , 5 lumbar, 5 sacral and 1
coccygeal ganglion.
• These nerves provide autonomic motor commands for
structures in body wall, thoracic cavity, head, neck or limbs
• The nerves that serve heart and lungs are known as the
sympathetic nerves
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Sympathetic Ganglions
Sympathetic Chain Ganglia
• In general, the preganglionic fibers are
myelinated while the postganglionic fibers
are un-myelinated.
• Because of the chain, every spinal nerve has
a gray ramus that carries sympathetic
postganglionic fibers for distribution
through the body
• If ventral roots of thoracic spinal nerve is
damaged, motor function and sympatetic
function will be lost on that side
• If ventral root of cervical spinal nerve is
damaged, motor function is lost but not
sympathetic function.
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Sympathetic Ganglions
Collateral ganglia
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Sympathetic Ganglions
Collateral ganglia
• These ganglia are formed by presynaptic neurons that
pass through the synaptic chain without forming a
synapse there
• These presynaptic sympathetic fibers are called the
spalnchic nerves
• They form a synapse with postsynaptic neurons in
areas anterior to the vertebral column , known as the
collateral ganglia
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Sympathetic Ganglions
Collateral ganglia
The celiac ganglia (D)
• postganglionic neurons serve the
stomach, liver, spleen
The superior mesenteric ganglia (E)
• postganglionic neurons innervates small
intestine and upper part of large intestine
The inferior mesenteric ganglia (F)
• postganglionic neurons serve the rest of
large intestine, kidneys, urinary bladder
and sex organs
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Sympathetic Ganglions
Adrenal Medullae
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Sympathetic Ganglions
Adrenal Medullae
Preganglionic sympathetic fibers enter the center
area of the adrenal gland, called the adrenal
medulla
In contrast to the other systems discussed, the
postganglionic neurons are very short, modified
neuro-endocrine cells that reside within the
adrenal medulla area
On stimulation, these cells release the
catecholamines epinephrine (80 %) and
norepinephrine into the bloodstream.
They then function similarly as hormones. They
only will have an effect on those target organs
that have receptors for these molecules.
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Sympathetic System
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Sympathetic Ganglions
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The Sympathetic Nervous System
In crises, the entire sympathetic division responds
This is called the Sympathetic activation
• Controlled by centers in the Hypothalamus
• Affects include
• increased alertness, energy and euphoria,
• increased cardiovascular and respiratory activities
• elevation in muscle tone,
• mobilization of energy resources
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The Para Sympathetic Nervous System
• The ParaSympatethic system arises from
preganglionic neurons in the brainstem and sacral
segments of spinal cord
• The preganlionic neurons are long while the
Ganglionic neurons are short and reside in peripheral
ganglia located within or near target organs
• In contrast to SNS, all ganglionic neurons are located
in the same ganglion and influence thus the same
organ; the effect is thus more localized and specific.21
The Para Sympathetic Nervous System
• Preganglionic fibers leave the brain as cranial nerves III, VII,
IX, X
• Those from III, VII and IX synapse in the head ganglia are
known as ciliary, pterygopalatine, submandibular and otic
ganglia.
• The vagus nerve provides innervation in the neck, thorax and
abdominal cavity
• Sacral neurons form the pelvic nerves
• These latter innervate kidneys, urinary bladder, terminal
portion of large intestine, sex organs
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The Para Sympathetic Nervous System
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The Para Sympathetic Nervous System
Effects produced by the PSNS
division
– Secretion of salivary glands,
intestinal glands
– Food processing by
increasing activity of smooth
muscle
– Constriction of respiratory
pathways
– Reduction in heart rate and
contraction
– Sexual arousal
– Energy absorption
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