1213 Week 14 P

1213 Week 14 P

Nerve Conduction Velocity
1. velocity = distance / time
2. conduction velocity = (x-y)/(a-b)
  1. x-y = the distance the action potential travels
  2. a-b = time it takes for the action potential to travel x-y
3. latency = neuromuscular delay + utilisation time
4. factors that determine velocity
  1. distance
  2. time
  3. myelination
  4. diameter of the axon - the bigger the diameter the less resistance so the faster the conduction
5. synaptic delay - time it takes for the chemical to be released diffuse and elicit the appropriate response in the post synaptic cell
6. acetylcholine is released at the neuromuscular junction
7. examples of substances that effect nerve conduction
  1. botulinum
    1. causes relaxation
    2. blocks the release of acetylcholine by preventing vescular fusion
    3. botox
  2. neostigamine
    1. causes contraction
    2. inhibits acetylcholinesterase so acetylcholine builds up
    3. treats myasthenia gravis
    4. reversible
  3. myasthenia gravis
    1. causes relaxation
    2. the body produces antibodies that attack acetylcholine receptors inhibiting their ability to bind acetylcholine
    3. treated with neostigamine
8. NM delay + utilisation times = total latency response (a > t) – nerve conduction time (a > t).
The Course of the Median Nerve
1. Directional Terms
  1. horizontal plane - parallel to the ground
  2. transverse plane - perpendicular to the longitudinal axis of the structure being considered
2. the nerve starts at the brachial plexus and runs superficially in the axilla
  1. it then descends the brachium deep to the biceps brachii and enters the cubital fossa
    1. the nerve enters the proximal aspect of the cubital fossa, medial to the bicipital aponeurosis
      1. it leaves the fossa lateral to the midline and in the distal portion
        it then descends laterally to the superficial flexor muscles within the anterior compartment
        as it descends the antibrachium it gives off innervating motor branches to all muscles except the deep flexor muscles of digits 4 and 5 and a medial wrist flexor.
        to enter the hand the nerve passes through the carpal tunnel and enters the palm
        here it divides into many branches and provides innervation to the palmar surface and digits 1,2,3 and the lateral aspect of digit 4
        the main motor branch ascends to the thenar eminence to innervate the thumb - the recurrent branch
3. the median nerve doesn't innervate the brachium muscles
4. the 3 muscles of the thumb are the abductor pollicis brevis, opponens pollicis and flexor pollicis brevis
5. Damaging the Median Nerve
  1. if it was damaged at the elbow joint wrist flexion would be seriously impaired - there would be some weak flexion from the deep flexor muscles for digits 4 and 5
  2. if it was damaged at the elbow joint fexion of digits 1,2 and 3 would be absent - flexor muscles of digits 1,2 and 3 are supplied by the median nerve distal to the elbow joint
  3. if the median nerve was damaged at the wrist joint wrist flexion would be normal - wrist flexion is controlled by the median nerve proximal to the wrist
  4. the median nerve was damaged at the wrist joint flexion of digit 1 would be slightly impaired - flexor pollicis brevis doesn't function, felxor pollicis longus originates in the antibrachium so wouldn't be affected

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	Created by 06watkinse over 10 years ago