Sensory Localisation

This is a very clear depiction of the dermatomes and peripheral nerves supplying sensation to the body.

• Testing sensation:
  • Vibration (128Hz tuning fork): dorsal column
  • Touch: dorsal column, diffuse ascending fibres, anterolateral tract
  • Pain and temperature: anterolateral / spinothalamic tract
• Cortical sensation
  • Sensation to pain, vibration intact
  • Loss of two-point discrimination: 3mm at the pump of each finger
  • Agraphia: inability to recognize numbers / letters drawn on pal with eyes closed
  • Stereognosis: inability to identify common objects (e.g. key) using touch only (i.e., by feeling the objects, one hand at a time, with eyes closed)
• Spinal cord: ends at L1. Nerve roots hence take an increasingly long course to reach their respective exit foramina. Spinal cord levels relative to vertebral bodies are:
  • Upper cervical: same level
  • Lower cervical: one level higher
  • Upper thoracic: two levels higher
  • Lower thoracic: two to three levels higher
  • Lumbar: T10 – T12
  • Sacral: T12 – L1
• Dermatomes
  • C4: regimental patch
  • C5: lateral aspect of arm
  • C6: thumb, lateral aspect of forearm
  • C7: middle finger
  • C8: little finger
  • T1: medial aspect of arm
  • L1: anterior aspect of inguinal ligament
  • L2: mid-thigh, especially lateral aspect
  • L3: just proximal to the knee, anterior aspect
  • L4: medial calf
  • L5: lateral calf, dorsal aspect of proximal foot
  • S1: plantar aspect of foot, dorsal aspect of toes
  • S2: posterior aspect of thigh, in the midline
• Peripheral nerve distribution
  • Axillary nerve: lateral aspect of arm, over deltoid
  • Median cutaneous nerve: median aspect of arm
  • Lateral cutaneous nerve of forearm: lateral aspect of forearm
  • Median cutaneous nerve of forearm: median aspect of forearm
  • Median nerve: lateral three-and-a-half digits, palmar aspect
  • Ulnar nerve: median one-and-a-half digits, palmar aspect
  • Radial nerve: anatomical snuffbox / first dorsal web space
  • Lateral femoral cutaneous nerve: lateral aspect of thigh
  • Anterior femoral cutaneous nerve: anterior aspect of thigh (midline)
  • Obturator nerve: medial aspect of upper thigh
  • Posterior femoral cutaneous nerve: posterior aspect of thigh
  • Lateral sural cutaneous nerve: lateral aspect of leg
  • Saphenous nerve: medial aspect of leg
  • Superficial peroneal nerve: dorsal aspect of medial foot, except first web space
  • Deep peroneal nerve: first dorsal web space of foot
  • Sural nerve: dorsal aspect of 5^th toe, posterior aspect of leg (midline)