Ch. 15
The Autonomic
Nervous System
Objectives
• Know the general function of the ANS
• Be able to describe the characteristics of the ANS
• Know the two divisions of the ANS
• Be able to describe the anatomical differences
between the parasympathetic and sympathetic
systems
• Know the role of the adrenal medulla in the
sympathetic system
Divisions of Nervous System
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Autonomic Nervous System
• System of motor neurons that innervates
smooth, cardiac muscle, and glands
• Involuntary nervous system
• General visceral motor system
Characteristics
• Effectors
– Cardiac and smooth muscle
– Glands
• Efferent Pathway
– Involves two neurons
• Ganglia
– Preganglionic neuron > preganglionic axon > ganglionic neuron >
postganglionic axon > effector
• Neurotransmitter
– All preganglionic neurons release acetylcholine
– Norepinephrine, acetylcholine
– Excitatory, inhibitory
Divisions of ANS
• Sympathetic
– Fight or flight
– Norepinephrine
– Adrenergic fibers
• Parasympathetic
– Rest and digest
– Acetylcholine
– Cholinergic fibers
• Dual innervation
– Counterbalance
– Tonic activity
• Ongoing activity of both divisions
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Parasympathetic Division
• Anatomically simpler
• Craniosacral origin
– Cranial nerves III, VII, IX, X
• Oculomotor
– Smooth muscle
• Facial
– Lacrimal and mucus glands
– Salivary glands
• Glossopharyngeal
– Parotid glands
• Vagus
– Innervates thoracic and abdominal
viscera
– Splanchnic nerves S2 - S4
• Innervate pelvic organs
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Sympathetic Division
• Anatomically more complex
– Innervates more organs
• Thoracolumbar origins
– T1 – L2
• Sympathetic trunk ganglia
– Paravertebral ganglia
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Chain Ganglia
• Synapse within
same chain ganglion
• Ascend or descend
then synapse in
chain ganglion
• Pass through chain
ganglion without
synapsing
– Collateral ganglia
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Sympathetic Chain Ganglia
• 22-24 chain ganglia
• Collateral ganglia
– Unpaired
– Only in abdomen and
pelvis
– Lie on abdominal aorta
• Celiac, sup. and inf.
Mesenteric, inf.
hypogastric
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Adrenal Medulla
• Inner portion of the
adrenal gland
• Largest sympathetic
ganglia
– Chromaffin cells
• Secrete
norepinephrine and
epinephrine into
blood stream
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