Download Autonomic Nervous System

Autonomic Nervous System
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.
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.
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A. Dorsal Horn
B. Intermediolateral
Cell Column
F. Dorsal root ganglion
J. Dorsal ramus
N. Sympathetic chain
ganglion
E. Ventral root
I. Sympathetic trunk
M. Gray ramus
C. Ventral Horn
D. Dorsal Root
G. Spinal nerve
K. Ventral ramus
O. Prevertebral
ganglion
H. Visceral nerve
L. White ramus
P. Splanchnic nerve
A.
D.
F.
J.
K.
H.
E.
C.
I.
P.
N.
O.
B.
L.
M.
J.
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G.
K.J
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
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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:
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:
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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 .
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 fight, 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.
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Autonomic Effects on Various Organs of the Body- FOR REFERENCE
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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