Chapter 12 - Peripheral Nervous System

Question 1

Endoneurium

Answer 1

separates individual axons

Question 2

Perineurium

Answer 2

surrounds bundles of axons(fascicles)

Question 3

epineurium

Answer 3

encloses the entire nerve trunk

- surrounded by the mesoneurium

Question 4

cervical plexus

Answer 4

• anterior rami of C1-C4
• deep to sternocleidomastoid muscle
• cutaneous sensory of posterior scalp to the clavicle
• innervates neck muscles and diaphragm
• phrenic nerve(C3-C5) to diaphragm

Question 5

brachial plexus

Answer 5

• anterior rami of C5-T1
• from the ant. and middle scalene muscles, deep to clavicle and into the axilla
• radial, axillary, ulnar, median, and musculotaneous
• upper limb

Question 6

lumbar plexus

Answer 6

• anterior rami of L1-L4
• forms in the psoas major muscle
• innervate skin and muscles of the anterior and medial thigh
• saphenous nerve to medial leg and foot

Question 7

sacral plexus

Answer 7

• innervates posterior thigh and most of the leg and foot

- contains parasympathetic axons also

Question 8

retrograde axoplasmic transport

Answer 8

moves chemicals from the axons and surrounding structures to the cell body
- provides information for the genetic machinery to adjust production of ion channels, transmitters, vesicles, and support structures

Question 9

anterograde axoplasmic transport

Answer 9

delivers new structural and signaling components to their proper locations in the neuron

Question 10

signs of sensory changes

Answer 10

decreased or lost sensation and/or abnormal sensations

- hyperalgesia, dysesthesia, paresthesia, and allodynia

Question 11

Signs of autonomic changes

Answer 11

depend on the pattern of axonal dysfunction

• only observed when nerve is completely severed
• lack of sweating
• loss of sympathetic control of smooth muscle fibers in arterial walls
  - causing edema
• if many nerves, difficulty regulating BP, HR, sweating, and bowel functions

Question 12

Signs of motor changes

Answer 12

paresis or paralysis

Question 13

Trophic changes

Answer 13

Denervation

- muscle atrophy, shiny skin, brittle nails, subcutaneous tissue thickens

Question 14

mononeuropathy

Answer 14

single nerve involvement

- focal dysfunction

Question 15

multiple mononeuropathy

Answer 15

several nerves involved

• multifocal
• presents as asymmetric involvement of individual nerves
• common with diabetes
• vasculitis(inflammation of blood vessels) causes ischemia of the nerves

Question 16

polyneuropathy

Answer 16

many nerves involved

• a generalized disorder that typically presents distally and symmetrically
• distal to proximal (feet –> hands)(longest axons)
• caused by toxic, metabolic, or autoimmune reasons
• most common cause = diabetes, nutritional deficiencies secondary to alcoholism, and autoimmune diseases

Question 17

Traumatic myelinopathy

Answer 17

a loss of myelin limited to the site of injury

• interfere with the function of large-diameter axons
  
  • production of motor, discriminative touch, proprioceptive, and phasic stretch reflex deficits
• can be caused by focal compression of nerve
  
  • compression caused by repeated mechanical stimuli(excessive pressure, stretch, vibration, friction)
• recovery tends to be complete because remyelination can occur rapidly

Question 18

nerve entrapment

Answer 18

mechanical constriction of a nerve within an anatomic canal

• causes traumatic myelinopathy
• most common in nerves: median(carpal tunnel), ulnar(ulnar groove), radial(spiral groove), peroneal(fibular head)

Question 19

carpal tunnel syndrome

Answer 19

compression of the median nerve in the space between carpal bones and flexor retinaculum
- sensation decreased in lateral 3.5 digits, adjacent palm of hand, distal halves of same digits on dorsal side
- paresis of the thumb intrinsic muscles
- pain may radiate to forearm and shoulder
Treatment:
- mild cases = 1 month rest, splinting, anti-inflammatory, exercises(improve blood flow and axonal transport)
- severe cases = surgery

Question 20

traumatic axonopathy

Answer 20

axons are damaged by trauma
disrupts axons and wallerian degeneration occurs distal to the lesion
- reflexes, somatosensation, and motor function reduced or absent
- recovery is good since connective tissue and myelin sheaths provide guidance and support for axonal sprouts

Question 21

Severance

Answer 21

nerves are physically divided by excessive stretch or laceration

• immediate loss of sensation and/or muscle paralysis
• recovery can occur, however axon sprouts could reach innappropriate end-organs
• could cause neuroma(tumor of axons and Schwann cells)

Question 22

diabetic plyneuropathy

Answer 22

axons and myelin are damaged

• sensation is mostly affected(stocking/glove distribution)
• 1st sign = impaired vibration sense

Question 23

polyneuropathy and Guillain-Barre syndrome

Answer 23

characterized by more severe effects on motor than sensory

• paresis may be worse proximally
• diagnosis is urgent to prevent respiratory failure

Question 24

Hereditary motor and sensory neuropathy(HMSN)

Answer 24

Charcot-Marie-Tooth disease

• causes paresis of muscles distal to the knee
  
  • foot drop, steppage gait, frequent tripping, muscle atrophy
• progresses to the hands

Question 25

myasthenia gravis

Answer 25

autoimmune disease that damages ACh receptors at the neuromuscular junction
- repeated use of a muscle leads to increasing weakness

Question 26

botulism

Answer 26

ingesting the botulinum toxin from improperly stored foods causes interference with the release of ACh from the motor axon
- produces acute, progressive weakness, with loss of stretch reflexes

Question 27

botox

Answer 27

used therapeutically in people with spasticity or dystonia, to weaken overactive muscles
- does not affect muscle contracture