Peripheral nerves and nerve lesions in the upper limb

Question 1

segmental innervation

Answer 1

• the distribution of nerves (ie. innervation) to the body according to the spinal cord segment(s) which provide motor and sensory nerve supply (eg. innervation of C5 spinal segment)
• myotome(s)
• dermatome(s), in a dermatomal map

Question 2

Myotomes

Answer 2

• A group of muscles supplied by a single nerve root

- Myotomes are often described according to the movts the actions of these muscles produce

Question 3

Myotome chart

Answer 3

shoulder abduction, lateral rotation: C5
shoulder adduction, medial rotation: C6, 7, 8
elbow flexion: C5, 6
elbow extension: C7, 8
radioulnar supination: C6
radioulnar pronation: C7, 8
Wrist flexion + extension: C6, 7
Digits flexion + extension: C7, 8
Digits abduction, adduction, opposition: C8, T1

Question 4

Dermatomes

Answer 4

• An area of skin supplied by a single nerve root
• dermatomal map: a diagram of dermatomes
• There is variation in specific dermatome regions
• Dermatomes are less clinically reliable than myotomes
  LOOK AT DERMATOME MAP

Question 5

Ulnar nerve lesion at elbow

Answer 5

Motor loss
- 1.5 anterior compartment muscles of forearm: FCU, medial ½ FDP, all intrinsic muscles of hand besides thenar eminence + lateral 2 lumbricals
Sensory loss
- Palmar and dorsal skin of medial 1.5 digits + corresponding palm
Functional loss
- Reduced precision grip from loss of digital sweep (intrinsic muscles affected)
- Reduced power grip (adductor pollicis affected)
- Reduced sensation for all grips on medial side of palmar surface of hand
- Deformity with a complete lesion: “claw hand”, Loss of intrinsic muscles to position MCP for digital sweep, so MCP’s extend. Long finger flexors continue to pull fingers into flexion.

Question 6

Medial nerve lesion: functional loss + deformity

Answer 6

Functional loss

• loss of precision grip
• power grip severely affected
• Deformity: (loss of thenar muscles if lesion is at or above carpal tunnel)

Question 7

Radial nerve lesion

Answer 7

Functional loss
- supination 
- wrist extension
- finger extension
Deformity: wrist drop

Question 8

NEED TO DO RADIAL + MEDIAL + POSSIBLY MUSCULOCUTANEOUS NERVE LESION