1. The Peripheral Nervous System and Reflex Activity: Part A13
The Peripheral Nervous System and Reflex Activity: Part A

2. Peripheral Nervous System (PNS)
All neural structures outside the brain
Sensory receptors
Peripheral nerves and associated ganglia
Motor endings

3. Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.1

4. 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

5. Sensory Integration
Input comes from exteroceptors, proprioceptors, and interoceptors
Input is relayed toward the head, but is processed along the way

6. Perceptual level (processing in cortical sensory centers)3
Perceptual level (processing in
cortical sensory centers)
Motor
cortex
Somatosensory
cortex
Thalamus
Reticular
formation
Cerebellum
Pons
Medulla 2
Circuit level
(processing in
ascending pathways)
Spinal
cord
Free nerve
endings (pain,
cold, warmth)
Muscle
spindle 1
Receptor level
(sensory reception
and transmission
to CNS)
Joint
kinesthetic
receptor
Figure 13.2

7. Perceptual level (processing in cortical sensory centers)3
Perceptual level (processing in
cortical sensory centers)
Motor
cortex
Somatosensory
cortex
Thalamus
Reticular
formation
Cerebellum
Pons
Medulla 2
Circuit level
(processing in
ascending pathways)
Spinal
cord
Free nerve
endings (pain,
cold, warmth)
Muscle
spindle 1
Receptor level
(sensory reception
and transmission
to CNS)
Joint
kinesthetic
receptor
Figure 13.2

8. Structure of a Nerve
Cordlike organ of the PNS
Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue

9. Connective tissue coverings include:
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

10. Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood
vessels
(b)
Figure 13.3b

11. Regeneration of Nerve Fibers
Mature neurons are amitotic
If the soma of a damaged nerve is intact, axon will regenerate

12. Endoneurium Schwann cells The axon becomes fragmented at1
The axon
becomes
fragmented at
the injury site.
Droplets
of myelin
Fragmented
axon
Site of nerve damage
Figure 13.4 (1 of 4)

13. Macrophages clean out the dead axon distal to the injury. Schwann cell2
Schwann cell
Macrophage
Figure 13.4 (2 of 4)

14. Aligning Schwann cells form regeneration tube Axon sprouts,
or filaments,
grow through a
regeneration tube
formed by
Schwann cells. 3
Fine axon sprouts
or filaments
Figure 13.4 (3 of 4)

15. The axon Schwann cell Site of new regenerates and myelin sheath
a new myelin
sheath forms.
Schwann cell
Site of new
myelin sheath
formation 4
Single enlarging
axon filament
Figure 13.4 (4 of 4)