Chapter 14 The PNS

1
Chapter 14 The PNS

• PNS all nervous structures outside of brain and
  spinal cord

(14.9)
2
Functional organization of the PNS 4 major
categories

• 1. Somatic sensory
• General sensory skin, body wall, limbs
• Special sensory hearing, equilibrium, vision,
  smell
• 2. Visceral sensory
• General sensations from viscera
• Special taste

(see Fig. 14.1)
3
Functional organization of the PNS

• 3. Somatic motor
• General skeletal muscles
• Branchial pharyngeal arch muscles
• 4. Visceral motor
• ANS sympathetic parasympathetic
• Autonomic Nervous System

4
Structural organization of the PNS

• Sensory receptors
• Motor endings
• Nerves bundles of axons
• Ganglia clusters of nerve cell bodies

(14.2)
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Locations of sensory receptors

• Exteroceptors stimuli from outside the body
  (cutaneous receptors and special senses)
• Interoceptors stimuli from internal organs
• Proprioceptors stimuli from the musculoskeletal
  system

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Receptor modalities/stimuli

• Mechanoreceptors stimulus is mechanical force,
  physical deformation of receptor, vibration
  (touch, pressure, hearing, balance)
• Thermoreceptors stimulus is temperature change
  (hot or cold sensation)
• Chemoreceptor stimulus is chemical change,
  e.g., O2 level, or smell or taste
• Photoreceptor stimulus is light
• Nociceptors stimulus is damage or potential
  damage to cells/tissue

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General sensory receptor structure

• Free nerve endings dendrites interspersed among
  other cells/tissues (pain, temperature, touch)

(Table 14.1)
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General sensory receptor structure

• Encapsulated nerve endings dendrites with
  special supporting structures (mechanoreceptors
  and proprioceptors)

(Table 14.1)
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Proprioceptors

• Muscle spindles muscle stretch receptor
• Golgi tendon organ muscle tension receptor
• Numerous joint receptors

(14.4)
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Motor endings The NMJ

• Neuromuscular junction innervation of skeletal
  muscle

(14.5a)
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The NMJ

• Axon terminal
• Mitochondria
• Synaptic vesicles with ACh
• Synaptic cleft
• Motor end plate with AChR

(14.5b)
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Visceral motor endings

• Axon terminals secrete neurotransmitter which
  diffuses to receptors on smooth muscle and glands

14.7
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Cranial nerves (CN)

• Paired R L
• CN generally perform the function of spinal
  nerves for the head and neck
• Know the names/numbers of CN, their location and
  function, and be able to identify them from
  figures.

(14.8)
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CN I Olfactory nerve

• Sensory nerve cell bodies in olfactory epithelium
  in roof of nasal cavity.
• Bundles of axons (CN 1) pass through cribriform
  plate of ethmoid bone to synapse in brain
• Function smell

(Table 14.2)
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CN II Optic nerve
(Table 14.2)

• Cell bodies in retina
• From eye axons travel to optic chiasm for partial
  decussation
• Axons continue as optic tract
• Most axons terminate in thalamus
• Function vision

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CN III-XII

• Review from brainstem lecture.
• You are responsible for the figures used in
  lecture.

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Spinal nerves

• 8C
• 12T
• 5L
• 5S
• 1C
• Spinal nerves
• Dorsal and ventral root
• DRG
• No VRG!

(14.9)
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SKIP Nerve Plexuses

• Pp. 414-422

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Dermatomes

• Definition area of skin innervated by one spinal
  nerves sensory fibers

(14.17a)
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Dermatomes

• Clinical relevance loss of sensations along a
  dermatome(s) can indicate injury to
• Dorsal root or spinal nerve
• Spinal cord (if several dermatomes)
• Herpes zoster virus infection

(14.17b Note S1 dermatome)
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Shingles

• Patient has herpes zoster with the vesicles
  following the path of the S1 dermatome down the
  back of his leg.

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