Transcript Part A - FacultyWeb Support Center

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
13
The Peripheral
Nervous
System and
Reflex Activity:
Part A
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Peripheral Nervous System (PNS)
• All neural structures outside the brain
• Sensory receptors
• Peripheral nerves and associated ganglia
• Motor endings
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Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
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Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.1
From Sensation to Perception
• Survival depends upon sensation and
perception
• Sensation: the awareness of changes in the
internal and external environment
• Perception: the conscious interpretation of
those stimuli
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Sensory Integration
• Input comes from exteroceptors,
proprioceptors, and interoceptors
• Input is relayed toward the head, but is
processed along the way
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Perceptual level (processing in
cortical sensory centers)
3
Motor
cortex
Somatosensory
cortex
Thalamus
Reticular
formation
Pons
2 Circuit level
(processing in
Spinal
ascending pathways) cord
Cerebellum
Medulla
Free nerve
endings (pain,
cold, warmth)
Muscle
spindle
Receptor level
(sensory reception Joint
and transmission
kinesthetic
to CNS)
receptor
1
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Figure 13.2
Perceptual level (processing in
cortical sensory centers)
3
Motor
cortex
Somatosensory
cortex
Thalamus
Reticular
formation
Pons
2 Circuit level
(processing in
Spinal
ascending pathways) cord
Cerebellum
Medulla
Free nerve
endings (pain,
cold, warmth)
Muscle
spindle
Receptor level
(sensory reception Joint
and transmission
kinesthetic
to CNS)
receptor
1
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Figure 13.2
Structure of a Nerve
• Cordlike organ of the PNS
• Bundle of myelinated and unmyelinated
peripheral axons enclosed by connective
tissue
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Structure of a Nerve
• Connective tissue coverings include:
• Endoneurium—loose connective tissue that
encloses axons and their myelin sheaths
• Perineurium—coarse connective tissue that
bundles fibers into fascicles
• Epineurium—tough fibrous sheath around a
nerve
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Endoneurium
Axon
Myelin sheath
Perineurium
Epineurium
Fascicle
Blood
vessels
(b)
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Figure 13.3b
Regeneration of Nerve Fibers
• Mature neurons are amitotic
• If the soma of a damaged nerve is intact, axon will
regenerate
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Endoneurium
Schwann cells
Droplets
of myelin
1 The axon
becomes
fragmented at
the injury site.
Fragmented
axon
Site of nerve damage
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Figure 13.4 (1 of 4)
Schwann cell
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Macrophage
2 Macrophages
clean out the
dead axon distal
to the injury.
Figure 13.4 (2 of 4)
Aligning Schwann cells
form regeneration tube
3 Axon sprouts,
or filaments,
grow through a
regeneration tube
formed by
Schwann cells.
Fine axon sprouts
or filaments
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Figure 13.4 (3 of 4)
Schwann cell
Site of new
myelin sheath
formation
4 The axon
regenerates and
a new myelin
sheath forms.
Single enlarging
axon filament
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Figure 13.4 (4 of 4)