Pages 264-269

Central Nervous System(brain and spinal cord)

Peripheral Nervous System(cranial and spinal nerves)

Somatic(voluntary)

Autonomic(involuntary)

Sensory(afferent)

Motor(efferent)

Senseorgans

Skeletalmuscles

Cardiac andsmooth muscle,

glands

Parasympathetic Sympathetic

The relative stability of our internal environment depends largely on ANS function

Involuntary regulation of◦ Cardiac activity◦ Smooth muscles/glands

Two subdivisions:1.Sympathetic division2.Parasympathetic division

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The ANS has a chain of two motor neurons◦ Preganglionic neuron : exists in brain or spinal cord

Axon is myelinated◦ Postganglionic neuron:

outside the CNS 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 motor neuron

Centralnervoussystem Peripheral nervous system Effector organs

Acetylcholine

Skeletalmuscle

Acetylcholine

Norepinephrine

Ganglion

Acetylcholine Epinephrine andnorepinephrine

Bloodvessel

Acetylcholine

Ganglion

Smooth muscle(e.g., in stomach)

Glands

Cardiacmuscle

Somatic nervoussystem

Autonomicnervoussystem

Sympatheticdivision

Para-sympathetic

division

KEY:Preganglionicaxons(sympathetic)

Postganglionicaxons(sympathetic)

Myelination Preganglionicaxons(parasympathetic)

Postganglionicaxons(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…)

Eye Eye

Salivaryglands

Heart

Lungs

Stomach

Pancreas

Liver andgall-bladder

Bladder

Genitals

Cervical

T1

Thoracic

L1

Lumbar

Brain stem

Cranial

Sympatheticganglia

Sacralnerves(S2–S4)

Parasympathetic Sympathetic

Skin

Salivaryglands

Heart

Lungs

Stomach

Pancreas

Liver and gall-bladder

Bladder

Genitals

Adrenalgland

REST/DIGEST FIGHT/FLIGHT

PARASYMPATHETIC Relaxes Conserves Neurotransmitter at

work is ACh

SYMPATHETIC Mobilizes Triggers:

◦ Fear, exercise, rage Neurotransmitters at

work are◦ Epinephrine◦ Norepinephrine◦ Acetylcholine

PNS: Differences Between Somatic and Autonomic Nervous Systems

© 2015 Pearson Education, Inc.

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