Download Autonomic Nervous System

Pages 264-269
Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves)
Sensory
(afferent)
Sense
organs
Motor
(efferent)
Somatic
(voluntary)
Autonomic
(involuntary)
Skeletal
muscles
Cardiac and
smooth muscle,
glands
Parasympathetic
Sympathetic


ANS function: maintain homeostasis/internal
stability
Involuntary regulation of
◦ Cardiac activity
◦ Smooth muscles/glands

Two subdivisions:
1. Sympathetic division
2. Parasympathetic division
© 2015 Pearson Education, Inc.

The ANS has a chain of two motor neurons
◦ Preganglionic neuron : in CNS (brain/spinal cord)
 Axon is myelinated
◦ Postganglionic neuron: in PNS
 Extends to a specific organ
 Axon is un-myelinated = slower response

This arrangement is different from the
somatic division (voluntary motor division)
which has only one myelinated motor neuron
Central
nervous
system
Peripheral nervous system
Effector organs
Acetylcholine
Somatic nervous
system
Skeletal
muscle
Acetylcholine
Autonomic
nervous
system
Sympathetic
division
Smooth muscle
(e.g., in stomach)
Norepinephrine
Ganglion
Epinephrine and
Acetylcholine
norepinephrine
Blood
vessel
Parasympathetic
division
KEY:
Preganglionic
axons
(sympathetic)
Postganglionic
axons
(sympathetic)
Glands
Acetylcholine
Cardiac
muscle
Ganglion
Myelination
Preganglionic
axons
(parasympathetic)
Postganglionic
axons
(parasympathetic)

Acetylcholine (Ach) is released in both divisions
◦ ACh is released by the Parasympathetic division to
stimulate the effector directly
◦ ACh is released by the Sympathetic division to cause
a release of:
 Epinephrine by the adrenal gland
 Norepinephrine by the postganglionic nerve fibers
 Either of these neurotransmitters will stimulate the
effector (heart, blood vessel, gland…)




PARASYMPATHETIC
Relaxes
Conserves
Neurotransmitter at
work is ACh



SYMPATHETIC
Mobilizes
Triggers:
◦ Fear, exercise, rage

Neurotransmitters at
work are
◦ Epinephrine
◦ Norepinephrine
◦ Acetylcholine
REST/DIGEST
FIGHT/FLIGHT
PNS: Differences Between Somatic
and Autonomic Nervous Systems
Somatic Nervous
System
Autonomic Nervous
System
Nerves
One-neuron system; it
originates in the CNS,
and axons extend to
the skeletal muscles
served
Two-neuron system
consisting of
preganglionic and
postganglionic
neurons
Effector organ
Skeletal muscle
Smooth muscle,
cardiac muscle,
glands
Subdivisions
None
Sympathetic and
parasympathetic
Neurotransmitter
Acetylcholine
Acetylcholine,
epinephrine (adrenaline),
norepinephrine
© 2015 Pearson Education, Inc.