Transcript Peripheral Nervous System

PERIPHERAL NERVOUS SYSTEM
ϋ Link between neurons of CNS and rest
of body
ϋ All sensory information and motor
commands
ϋ Axons bundled together and wrapped in
Connective Tissue= Peripheral Nerves
ϋ Contains cell bodies (ganglia) and axons
Do you remember the names of the
accessory neuroglia cells of the PNS?
Hint: See page 99
Divisions of PNS
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“Afferent Division”
Sensory
Receives info from:
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1) Somatic Receptors
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“Efferent Division”
Motor
Divided into:
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Monitor environment
1) Somatic NS
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2) Visceral Receptors
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Monitor internal
conditions
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Sends signals to skeletal
muscles
2) Autonomic NS
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Sends signals to smooth
& cardiac muscles,
glands, adipose tissue
Autonomic NS (“Efferent”)
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Divided into:
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1) Sympathetic NS
 “Fight
or Flight” responses
 Stimulates metabolism, ↑ alertness, prepares body for
emergencies
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2) Parasympathetic NS
 “Rest
& Digest”responses
 Conserves energy & promotes sedentary activities
(i.e. digestion)
Reflexes
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A) Simple Reflexes: “monosynaptic”
Sensory neuron synapses directly to motor
neuron
 Almost immediate response
 i.e.: Knee Jerk reflex
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B) Complex Reflexes: “polysynaptic”
Sensory neuron communicates with motor
neuron via interneuron
 Slight delay between stimulus & response
 i.e.: Withdrawl reflex
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Cranial Nerves
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Attach to base of brain & lead to muscles &
sense organs in head & neck
12 pairs in 3 categories:
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A) Sensory: detect stimuli only
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B) Motor: stimulate muscle contraction & provide info
about body position & orientation
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I, II, VIII
III, IV, VI, XI, XII
C) Mixed: Sensory & motor functions are unrelated
(i.e. sense taste but control facial expression)
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V, VII, IX, X
Aging of the Nervous System
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As we age (30+), certain anatomical changes
occur:
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1) ↓ brain size & weight (especially cerebral cortex)
2) ↓ # neurons (do not regenerate)
3) ↓ blood flow to brain as fatty deposits accumulate in
blood vessels
4) Changes in synaptic organization (# dendrite
branches, synapses lost, neurotransmitter production ↓)
5) Cellular changes (accumulation of deposits with cells)
These changes may affect our ability to form new
memories and affect our senses and reactions