Ch. 12: Peripheral Nervous System

Question 1

What is a spinal nerve?

Answer 1

One place where every axon comes together

Question 2

What is the pattern when the “spinal” or “segmental” nerve os damaged?

Answer 2

Myotomal or Dermatomal

Question 3

What nervous system controls peripheral nerves?

Answer 3

Sympathetic

Question 4

What are the parts of peripheral nerves?

Answer 4

• Rami
  
  • Ventral/anterior - front of body + arms & legs
    
    • joint into plexuses
  • Dorsal/posterior - just back of body
  • Communicating
    
    • to and from paravertebral sympathetic ganglia
• Distal axon projections (superficial and deep)
• “Peripheral” pattern when damaged - part of more than one dermatome, myotome

Question 5

What is a Dermatome?

Answer 5

Dermis innervated by a single spinal nerve

Question 6

What is a Myotome?

Answer 6

Muscle innervated by a single spinal nerve

Question 7

How does peripheral nerves get their blood supply?

Answer 7

aterial branches

Question 8

What is the difference between Myelinated and Unmyelinated axons?

Answer 8

Both are myelinated

Myelinated are extra myelinated

Question 9

What are the 3 connective sheaths that surround axons?

Answer 9

• Endoneurium
  
  • Separates individual axons
• Perineurium
  
  • Surrounds bundles of axons (creates “fascicle”)
• Epineurium
  
  • encloses entire nerve trunk

Question 11

How do you classify axons based on Diameter and Conduction speeds?

Answer 11

Question 12

How many Nerve Plexuses are there?

What are they?

Answer 12

1. Cervical plexus (C1-C4): motor, sensory, sympathetic.
2. Brachial plexus (C5-T1): motor, sensory, sympathetic.
   
   • Median nerve shares branches from C5-T1
3. Lumbar plexus (L1-L4): motor, sensory, sympathetic.
4. Sacral plexus (L4-S4): motor, sensory, parasympathetic.

Question 13

What is Convergence in the Afferent Direction?

Answer 13

One peripheral nerve gets axons from many different spinal levels.

Question 14

What is Convergence in the Efferent Direction?

Answer 14

One spinal level sends axons to many different peripheral nerves.

Question 15

What does damage to a peripheral nerve mean for motor output?

Answer 15

Paralysis

or at least major weakness in one or more muscles

Question 16

What does damage to a spinal nerve mean for motor output?

Answer 16

minor weakness in one or more muscles

Question 17

What does damage to a spinal nerve mean for sensory input?

Answer 17

Sensory loss in a dermatomal pattern

(includes some, but not all, of many peripheral nerves)

Question 18

What does damage to a peripheral nerve mean for sensory input?

Answer 18

Sensory loss in a peripheral nerve pattern

(includes some, but not all, on many dermatomes)

Question 19

Why is movement essential for nerve health?

Answer 19

• Movement improves blood flow
• Facilitates gliding of fascicles and nerves
• Facilitates axoplasmic transport
  
  • move nutrients from cell bodies to the end
• “Wrinkling” of axons within endoneurium = neural tension
  
  • Wrinkle in a shortened position - need to be stretched so they do not stick.

Question 20

Are Neuromuscular Junctions excitatory or inhibatory?

Answer 20

Excitatory - EPSP only!

Ach (either release it or don’t) - depolarizes and aids in health

Question 21

What are dysfunctions of peripheral nerves?

Answer 21

• Sensory changes
• Autonomic changes
• Motor changes
• Changes following denervation

Question 22

Changes following denervation:

Fibrillations

Answer 22

• Spontaneous depolarization of single denervated muscle fibers.
  
  • Cannot see or feel
  • Can only exam with a needle detector

Question 23

Changes following denervation:

Trophic Changes

Answer 23

• Degenerative tissue changes that result from lack of muscle depolarization, loss of “trophic” substances from nerves and/or distortion of blood flow.
  
  • Growth, tissue health
  • Atrophy of a muscle

Question 24

Mononeuropathy

Answer 24

1 peripheral nerve, at 1 spot

Question 25

Multiple Mononeuropathy

Answer 25

1+ peripheral nerve, at 1 spot

Question 26

Polyneuropathy

Answer 26

• Multiple nerves effected in multiple locations
• Most common: symmetircal loss of sensory, motor & autonomic function
  
  • starts distal, move prox (stocking & glove)
• Etiologies
  
  • Diabetes
  • Nutritional deficits (secondary to alcoholism)
  • Autoimmune disease (ex: Guillain-Barré)

Question 27

Mononeuropathy

Class I injury: Traumatic Myelinopathy

Answer 27

• Temporary disruption of conduction along axon membrane. Axon remains intact. Demyelination possible.
  
  • Minor = Puts it to sleep
    
    • Ex: crossing legs and foot falls asleep
  • More Major = demyelination possible
• Recovery potential excellent.
• Physical trauma or internal cellular trauma

Question 28

Mononeuropathy

Class II injury: Traumatic Axonopathy

Answer 28

• Axon and myelin degenerate. Connective tissue “tube” remains intact.
  
  • Wallarian Degeneration
• Recovery potential very good (especially for short distances). Axon will likely regrow into connective tissue “tube” at the rate of 1-2 mm/day (or about an inch a month).
  
  • Regenerative sprouting - tube still their to guide them where to grow
• Demyelinated axons will insert modality gated channels and ligand gated channels to try to get signal back
  
  • Modality: touch
  • Ligand: sensitive to SNS neurotransmitters (epi & norepi)

Question 29

Mononeuropathy

Class III injury: Severance

Answer 29

• Axon and myelin degenerate. Connective tissue “tube” is severed or disrupted.
• Recovery potential fair. Axons will attempt to re-grow, but may not find connective tissue “tube” or may grow into “wrong” tube.
  
  • Tube is broken

Question 30

Multiple Mononeuropathy

Answer 30

• Involvement of two or more discrete nerves in different parts of the body.
  
  • Ex: bilateral carpal tunnel syndrome

Question 31

What is Myasthenia Gravis a disorder of?

Answer 31

Disorder of Neuromuscular Junction