Autonomic Nervous System
I. Comparison between somatic and autonomic
nervous system
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A. Effectors differ
1. somatic system
2. ans
B. Number of neurons between CNS and effector
1. somatic
2. ans
C. Location of nerve cell bodies
1. somatic
2. ans
D. Ganglia present
1. somatic
2. ans
• E. Nature of response
• 1. Somatic
• 2. Ans
• F. Presence of myelin
• 1. somatic
• 2. ans
• G. Transmitter substance
• 1. somatic is acetycholine
• 2. ans: acetycholine from preganglionic fiber,
either acetycholine or norepinephrine from
postganglionic fiber
Comparison between somatic and autonomic
nervous systems
II. Structure of the ANSSympathetic Division
• A. Location of
preganglionic nerve
cell bodies
• B. Two ganglia in
system
• 1. sympathetic chain
or paravertebral
ganglia
• 2. collateral ganglia
• C. Relative length of
fibers
D. Outflow from CNS
• 1. Gray ramus
communicans
• 2. sympathetic nerves to
thoracic organs
• 3. splanchnic nerves
• 4. special case of the
adrenal medulla
III. Structure of the parasympathetic division
• A. Location of the
preganganglionic nerve cell
bodies
• B. Craniosacral division
• C. Lengths of fibers
• D. Location of ganglia
• E. Terminal or intramural
ganglia
• F. Very little divergence in
the parasympathetic
division when compared to
the sympathetic
IV. Physiology of ANS
• A. Transmitter
substances
• 1. All presynaptic
fibers-acetycholine
• 2. postsynaptic
fibers of
para=acetycholine
• 3. postsynaptic of
sym=most are
adrenergic but a
few are cholinergic
to sweat glands
B. Receptor sites in the ANS
• 1. Cholinergic receptors
• a. Bind acetycholine
• b. Two categories-nicotinic and muscarinic
• c. Nicotinic sites all postganglionic membranes and skeletal
muscle-possess an excitatory affect
• d. Muscarinic sites- membranes of effectors responding to
acetycholine released from postganglionic fibers of ANSresponse to binding of acetycholine to these receptors may be
inhibitory or excitatory
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e. Effects relatively short-lived because it is destroyed by
cholinesterase
2. Adrenergic receptor sites
• a. Located on membranes of effectors innervated by
sympathetic division
• b. Respond to epinephrine or norepinephrine
• c. May be excitatory or inhibitory depending on effector
• d. These receptors can respond to ANS or to adrenalin
released from the adrenal medulla
• e. Sympathetic stimulations tend to be more widespread
• f. Sympathetic reactions tend to be longer lasting because
transmitter substance is not directly broken down but diffuses
away
V. Generalizations about the ANS
• A. Many organs possess dual innervation
• 1. two divisions will have opposing effects
• 2. if one is stimulatory, other is inhibitory
• 3. parasympathetic is rest and recovery
• 4. sympathetic produces the effects of “fight or
flight”
B. Sympathetic division produces longer lasting and
more widespread effects
• 1. The adrenergic receptor sites of the sympathetic division
can respond to adrenal gland secretions
• 2. if adrenalin is circulating in the blood stream, disperses to
many glands
• 3. one sympathetic preganglionic fiber synapses with multiple
postganglionic fibers travelling to many different effectors
• 4. the transmitter substances of the sympathetic fibers
degrades by diffusing from the receptor site
C. Blood vessel diameter is regulated solely by
the sympathetic division of ANS
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1. always basal level of sympathetic activity
2. if greater sympathetic activity, generally vasoconstriction
3. less sympathetic activity, vasodilation
4. generalizations don’t always hold when considering blood
vessels
• 5. during fight or flight
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a. Blood vessels in skeletal muscle dilate
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b. Blood vessels in digestive system constrict to limit flow