1. Chapter 11 Autonomic Nervous System (ANS)
Copyright 2010, John Wiley & Sons, Inc.

2. Introduction to the ANS
Somatic nervous system (SNS) + ANS  peripheral nervous system (PNS)
ANS
Not under conscious control
Is regulated by hypothalamus, brainstem
The ANS supplies nerves to viscera
Smooth muscle (stomach, blood vessels)
Cardiac muscle (heart)
Glands (sweat and digestive glands)
Copyright 2010, John Wiley & Sons, Inc.

3. Comparison: SNS vs ANS SNS ANS Controls skeletal muscle
Conscious, voluntary control
Motor pathway: one neuron from CNS to effector
Does include sensory neurons (from skin, skeletal muscles, and special sense organs)
All release the neurotransmitter ACh
ANS
Controls viscera: smooth and cardiac muscle, and glands
Unconscious, involuntary
Motor pathway: series of two neurons from CNS to effector
Does include sensory neurons (monitors viscera)
Two divisions: sympathetic, parasympathetic
Release either ACh or NE
Copyright 2010, John Wiley & Sons, Inc.

4. Somatic Nervous System
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5. ANS Motor Pathways Autonomic motor pathway includes two motor neurons
Preganglionic neuron from CNS to neuron in autonomic ganglion
Postganglionic neuron from cell body in ganglion to effector
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6. ANS Motor Pathways
Copyright 2010, John Wiley & Sons, Inc.

7. Divisions of the ANS
Sympathetic (S) division + parasympathetic (P) division
Most viscera supplied with nerves of both S and P divisions: dual innervation
S and P have opposite (antagonistic) effects
Heart rate: S stimulates, P inhibits
Digestive organs: S inhibit, P stimulate
S: “flight or flight,” P: “rest and digest”
Some viscera receive only S (not P) nerves:
Sweat glands, many blood vessels, hair muscles
Copyright 2010, John Wiley & Sons, Inc.

8. Sympathetic (S) Division
Sympathetic preganglionic neurons
Have cell bodies located in lateral gray of spinal cord segments T1-T12 + L1-L2
So S division is called “thoracolumbar”
Axons pass through ventral roots of spinal nerves
May branch many times
May ascend or descend to many levels of S trunk ganglia (from cervical to sacral)
Can synapse with 20 or more postganglionic neuron cell bodies
Results: widespread S effects (viscera respond “in sympathy with one another”)
Copyright 2010, John Wiley & Sons, Inc.

9. Sympathetic (S) Division
Sympathetic postganglionic neurons
S postganglionic neurons cell bodies located
In S “trunk ganglia” (2 long chains lateral to vertebrae)
From cervical to sacral regions  widespread S effects
Many axons from these cell bodies pass back into spinal nerves to reach viscera in skin (sweat glands, hair muscles, blood vessels)
In S “prevertebral ganglia” anterior to 3 large abdominal arteries
Named celiac, superior and inferior mesenteric ganglia
Supply abdominal viscera: stomach, intestine, kidneys, liver, spleen
Axons pass from ganglia to viscera in S nerves
Copyright 2010, John Wiley & Sons, Inc.

10. Sympathetic (S) Division
Copyright 2010, John Wiley & Sons, Inc.

11. Parasympathetic (P) Division
P preganglionic neurons
Cell bodies located in brainstem + in spinal cord segments S2-S4
Therefore P division is called “craniosacral”
Axons in cranial nerves III, VII, IX and X and in pelvic nerves from S2-S4
Vagus nerves (cranial nerves X) carry 80% of all P nerve impulses.
Vagus nerves carry both motor and sensory neurons to/from viscera within the thorax and most of the abdominal cavity.
P preganglionic axons do not branch or pass though S trunk ganglia but pass directly almost to viscera
Copyright 2010, John Wiley & Sons, Inc.

12. Parasympathetic (P) Division
P postganglionic neurons
Cell bodies lie in terminal ganglia
Located within or near the innervated organ
So P nerves cause precise, localized (not widespread) effects
Because of anatomical arrangement, S nerves supply all viscera but P nerves do not reach some viscera. These include sweat glands, arrector pili muscles of hairs in skin, kidneys, spleen, adrenal medullae, and the walls of most blood vessels.
Axons pass from ganglia to viscera in P nerves
Copyright 2010, John Wiley & Sons, Inc.

13. Parasympathetic (P) Division
Copyright 2010, John Wiley & Sons, Inc.

14. ANS Neurotransmitters: Comparison
Acetylcholine (ACh)
ACh more common; released by:
All S and P preganglionic axons
All P postganglionic axons
Some S postganglionic axons (to sweat glands)
ACh destroyed by enzyme ACh-ase so short-lived response
Norepinephrine (NE)
NE less common; released by:
Almost all S postganglionic axons
NE has longer lasting effects enhanced by epinephrine + NE from adrenal medullae
Copyright 2010, John Wiley & Sons, Inc.

15. Sympathetic Effects Fight-or-flight activities
Increase heart rate and contraction, and blood pressure (BP)
Dilate pupils
Dilate airways
Dilate vessels to skeletal muscles, heart, liver and adipose tissue
Constrict blood vessels to nonessential organs: skin, GI tract, kidneys
Mobilize nutrients for energy: glucose and fats
Copyright 2010, John Wiley & Sons, Inc.

16. Parasympathetic Effects
Rest-and-digest activities
SLUDD
Salivation
Lacrimation
Urination
Digestion
Defecation
Decrease heart rate, airway diameter, pupil diameter
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17. End of Chapter 11
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