Zusammenfassung der Ressource
1213 Week 14 P
- Nerve Conduction Velocity
- velocity = distance / time
- conduction velocity = (x-y)/(a-b)
- x-y = the distance the action potential travels
- a-b = time it takes for the action potential to travel x-y
- latency = neuromuscular delay + utilisation time
- factors that determine velocity
- distance
- time
- myelination
- diameter of the axon - the bigger the diameter the less resistance so the faster the conduction
- synaptic delay - time it takes for the chemical to be released diffuse and elicit the appropriate response in the post synaptic cell
- acetylcholine is released at the neuromuscular junction
- examples of substances that effect nerve conduction
- botulinum
- causes relaxation
- blocks the release of acetylcholine by preventing vescular fusion
- botox
- neostigamine
- causes contraction
- inhibits acetylcholinesterase so acetylcholine builds up
- treats myasthenia gravis
- reversible
- myasthenia gravis
- causes relaxation
- the body produces antibodies that attack acetylcholine receptors inhibiting their ability to bind acetylcholine
- treated with neostigamine
- NM delay + utilisation times = total latency response (a > t) – nerve conduction time (a > t).
- The Course of the Median Nerve
- Directional Terms
- horizontal plane - parallel to the ground
- transverse plane - perpendicular to the longitudinal axis of the structure being considered
- the nerve starts at the brachial plexus and runs superficially in the axilla
- it then descends the brachium deep to the biceps brachii and enters the cubital fossa
- the nerve enters the proximal aspect of the cubital fossa, medial to the bicipital aponeurosis
- 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
- the median nerve doesn't innervate the brachium muscles
- the 3 muscles of the thumb are the abductor pollicis brevis, opponens pollicis and flexor pollicis brevis
- Damaging the Median Nerve
- 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
- 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
- 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
- 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