Autonomic Nervous System
After you have completed your study of this material you should be able to:
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2.)
3.)
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6.)
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8.)
9.)
10.)
11.)
State the components of the CNS.
State the organization of the PNS.
Name the effector organs innervated by the ANS.
Describe the location of cell bodies of preganglionic neurons in the sympathetic nervous system.
State the course of the sympathetic preganglionic fiber from the spinal cord to the sympathetic trunk.
State the options for synapse of the sympathetic preganglionic fiber.
State the locations of sympathetic postganglionic neuronal cell bodies.
Describe the course of sympathetic postganglionic fibers.
State the fiber types which compose white and gray rami communicantes.
State with which spinal cord levels white and gray rami communicantes are associated.
State the locations of preganglionic and postganglionic neuronal cell bodies in the cranial and sacral
divisions of the parasympathetic system.
12.) Compare and contrast the functions of the sympathetic and parasympathetic systems.
13.) Discuss how sympathetic innervation is provided to the head.
I.
Introduction
The autonomic nervous system is an efferent system which controls the so called “visceral”
functions of the body and plays an important role in homeostasis.
II.
Nervous System Organization
A. Central Nervous System (CNS)
1. Brain
2. Spinal Cord
B. Peripheral Nervous System (PNS)
1. Afferent fibers
2. Efferent fibers
a. Somatic nervous system (Voluntary)- motor to skeletal muscle
b. Autonomic nervous system (Involuntary)- Motor to smooth muscle,
cardiac muscle and glands (these are the “involuntary effectors”).
III.
Autonomic Nervous System Organization
A. General Organization
1. Consists basically of a two neuron chain
a. Preganglionic neuron- the cell body of this neuron is located within the
CNS (brain or spinal cord).
b. Postganglionic neuron- The cell body of this neuron is located in an
autonomic ganglion outside the CNS.
2. Only three types of structures are innervated by the autonomic nervous system
(ANS).
a. Smooth muscle (viscera, blood vessels, etc.)
b. Cardiac Muscle
c. Glands
d. Note: some research papers suggest that adipose tissue could be
included as a new involuntary effector. However, this is mostly
through hormonal control of the sympathetic nervous system, not
neurotransmitter.
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3. Note that although the ANS is an efferent, or motor system, structures which it
innervates often receive additional afferent innervation. These afferent fibers
are important in reflex autonomic activity (e.g., regulation of blood pressure)
and conscious sensation (discomfort, pain, etc.)
B. Subdivisions of the ANS-Defined by location of cell body of preganglionic neuron
1. Sympathetic system (thoracolumbar). Cell bodies of preganglionic neurons are
located in the intermediolateral cell column of spinal cord segments T1 to L2.
2. Parasympathetic system (craniosacral) - Cell bodies of preganglionic neurons
are located in either brainstem nuclei (associated with cranial nerves III, VII,
IX, and X) or the sacral autonomic nucleus (lateral gray column) of spinal cord
segments S2 to S4.
A. Dorsal Horn
B. Intermediolateral
Cell Column
E. Ventral root
F. Dorsal root ganglion
I. Sympathetic trunk
J. Dorsal
primary
ramus
M. Gray
ramus N. Sympathetic chain
communicans
ganglion
C. Ventral Horn
D. Dorsal Root
G. Spinal nerve
H. Visceral nerve
K. Ventral
primary L. White
ramus
ramus
communicans
O. Prevertebral
P. Splanchnic nerve
ganglion
A.
D.
F.
J.
K.
H.
E.
C.
I.
P.
N.
O.
B.
L.
M.
J.K
G.
K.J
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C. Sympathetic Nervous System
1. Preganglionic and postganglionic neurons.
a. Cell body of preganglionc neuron is located in intermediolateral cell
column of spinal cord T1 to L2.
b. Myelinated axon of preganglionic neuron passes through ventral root,
enters spinal nerve and travels in the ventral primary ramus for a short
distance.
c. The axon of the preganglionic neuron then passes through a white
ramus communicans to enter into a paravertebral (sympathetic)
ganglion of the sympathetic trunk. The sympathetic trunks are paired,
each consisting of a series of ganglia (accumulations of neuronal cell
bodies located outside the CNS) connected by intervening fibers. The
ganglia are roughly segmentally arranged except in the cervical region
where they become fused into larger ganglia (e.g., superior cervical
ganglion (C1, 2, 3, 4).
Options for preganglionic fibers: The fiber of the preganglionic neuron may do one of the
following after passing into a sympathetic trunk ganglion:
OPTION 1
Preganglionic fiber- the preganglionic fiber may synapse in that ganglion. Draw this option here!
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OPTION 2
The preganglionic fiber may pass up or down the trunk to synapse in another ganglion of the
sympathetic chain. Draw this option here:
OPTION 3
Preganglionic fiber-The preganglionic fiber may pass through the sympathetic trunk ganglion and
enter a thoracic or lumbar splanchnic nerve (e.g., the thoracic greater splanchnic nerve). These
splanchnic nerves terminate in nerve plexuses (located around the great vessels) containing collateral
(prevertebral vertebra) ganglia. The preganglionic fiber will synapse in a collateral ganglion (e.g.,
the celiac ganglion). Draw this option here.
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OPTION 4 ( a special case, or is it?)
a. preganglionic fiber- the preganglionic fiber may pass through the sympathetic chain ganglion and
splanchnic nerve to synapse on cells of the adrenal medulla.
b. Postganglionic fiber- the neuroendocrine cells of the adrenal medulla themselves are considered
as modified postganglionic neurons.
Options for postganglionic fibers: When the cell body of the postganglionic fiber is located in the
sympathetic trunk, the unmyelinated postganglionic axon can do one of two things:
1. It can enter a gray ramus communicans and be distributed to a dorsal or ventral primary
ramus. Note that although there are white rami communicantes only at spinal cord levels T1
to L2, there are gray rami communicantes at ALL spinal cord levels. Draw this option with
option 1 of the preganglionic fiber.
2. It can enter a visceral nerve and be distributed to viscera. (Examples of these nerves are the
cardiac nerves branching from the thoracic sympathetic trunk- THESE ARE NOT
SPLANCHNICS- BUT A POSTGANGLIONIC NERVE!!!). Draw this option along with
option 1 of a preganglionic fiber.
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3.
Postganglionic fiber- Cell body of postganglionic neuron is located in a collateral
ganglion. The unmyelinated postganglionic fiber will be distributed to abdominal and
pelvic viscera by following blood vessels. Draw this option here along with option 3 of
the preganglionic fiber.
Visceral afferent fibers: Visceral Afferents associated with autonomic fibers of splanchnic nerves
pass through the sympathetic chain WITHOUT synapse and enter a spinal nerve by passing through a
white ramus communicans. Their cell bodies are located in dorsal root ganglia. Draw an example
coming from the intestines here:
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D. Parasympathetic Nervous System
1.Preganglionic Neuron
a. Cell body in cranial division is located in one brainstem nuclei for cranial
nerves III, VII, IX, and X.The preganglionic efferent fiber leaves the
brainstem in the respective cranial nerves indicated.
b. Cell body in sacral division is located in sacral lateral gray column of spinal
cord levels S2-4. The preganglionic fiber enters the ventral root, passes
through the spinal nerve and enters the ventral primary ramus. It leaves the
ventral primary ramus by passing through a pelvic splanchnic nerve which
passes to the pelvic nerve plexus. Draw this option here:
2. Postganglionic neuron
a. Cell bodies associated with cranial division of this system are located in
the following parasympathetic ganglia. (See table on next page).
b. In sacral division, postganglionic neurons are located in terminal
ganglia, either near to or in the wall of the organs innervated.
(preganglionic neurons, you’ll remember, are in the sacral spinal cord
S2-4). Postganglionic fibers innervated pelvic viscera and the
alimentary canal beyond the splenic flexure.
c. In the parasympathetic system, the cell body of the postganglionic
neuron is usually located close to or in the wall of the structure
innervated. Thus, when the parasympathetic system is compared to the
sympathetic system, preganglionic fibers are, in general, long and
postganglionic fibers short .
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Cell Body Location
Cranial Nerve in which
Preganglionic Fiber
Leaves Brainstem
III
Ganglion
Destination of
Postganglionic Fiber
Ciliary Ganglion
Superior Salivatory
Nucleus
Superior Salivatory
Nucleus
VII
Submandibular Ganglion
VII
Pterygopalatine Ganglion
Inferior Salivatory Nucleus
Dorsal Motor Nucleus
IX
X
Otic Ganglion
Vagal Ganglia (Terminal
Ganglia- located in wall of
visceral organs)
Sphincter pupillae
Ciliary Muscle
Submandibular Gland
Sublingual Gland
Lacrimal Gland
Glands of Palate
Nasal Cavity
Upper Nasopharynx
Parotid Gland
Heart, Bronchi,
Alimentary Canal down to
Splenic Flexure
Edinger Westphal
IV.
Functions and General Principles of the ANS
A. “The most succinct summary of the functions of the sympathetic and
parasympathetic systems is that the sympathetic system is primarily an emergency
one, preparing the body so that the individual can flee or flight, whichever seems
wisest, when faced with danger; the parasympathetic system, in contrast, is primarily
a homeostatic one, tending to promote quiet and orderly processes of the body.”
(Hollinshead and Rosse, p. 63).
B. The sympathetic system often acts en masse while this is generally not true of the
parasympathetic system.
C. Both subdivisions (sympathetic and parasympathetic) can cause excitatory effects in
some organs and inhibitory effects in others.
D. When one division stimulates a particular organ, the other often inhibits it,
illustrating that the two systems can act reciprocally. However, many organs are
dominantly controlled by one division or the other.
E. Effects on specific organs (see table)
F. Note that while sympathetic innervation is distributed throughout the body,
parasympathetic distribution is confined to the head, neck and trunk.
Autonomic Effects on Various Organs of the Body
ORGAN
SYMPATHETIC EFFECTS
PARASYMPATHETIC EFFECTS
Eye: pupil/ciliary muscle
Lacrimal gland
Salivary gland
Heart
Lungs: bronchi
Blood vessels
Gut
Dilation
Vasoconstriction
Scanty, thick secretion
Increased rate and force of contraction
Dilates air passages
Vasoconstriction
Decreased peristalsis and secretion
Constriction/contraction
Secretion
Copious thin secretion
Slowed rate
Constriction
dilation
Increased peristalsis and secretion
Bladder detrusor
Penis
Adrenal medulla
Skin of head, neck, and extremities
Inhibits urination
Ejaculation
Secretion
Vasoconstriction, sweat secretion, piloarrection
Contraction
Erection
None
none
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