SN7
SHORT NOTE
5M
Describe the cutaneous innervation and dermatomes of the upper limb.
Definition
Cutaneous innervation of the upper limb is derived from the ventral rami C5–T1 through the brachial plexus, and from C4 and T2 at its upper and lower margins.
Dermatomes
| Segment | Area | Landmark |
|---|---|---|
| C4 | Over the shoulder tip | — |
| C5 | Lateral side of the arm | Regimental badge area |
| C6 | Lateral forearm and thumb | Thumb = C6 |
| C7 | Middle finger | Middle finger = C7 |
| C8 | Medial forearm and little finger | Little finger = C8 |
| T1 | Medial side of the arm | — |
| T2 | Axilla and upper medial arm | Intercostobrachial nerve |
- Mnemonic — "C6 grips the thumb, C7 the middle, C8 the little"
- The axial line separates C6 from T1 territory anteriorly — adjacent dermatomes do not overlap across it
Cutaneous Nerves BY Region
| Region | Nerve | Origin |
|---|---|---|
| Shoulder tip | Supraclavicular nerves | Cervical plexus (C3, C4) |
| Upper lateral arm | Upper lateral cutaneous nerve of arm | Axillary |
| Lower lateral arm | Lower lateral cutaneous nerve of arm | Radial |
| Medial arm | Medial cutaneous nerve of arm; intercostobrachial | Medial cord; T2 |
| Posterior arm | Posterior cutaneous nerve of arm | Radial |
| Lateral forearm | Lateral cutaneous nerve of forearm | Musculocutaneous (its terminal branch) |
| Medial forearm | Medial cutaneous nerve of forearm | Medial cord |
| Posterior forearm | Posterior cutaneous nerve of forearm | Radial |
Cutaneous Supply of the Hand
| Surface | Lateral 3½ digits | Medial 1½ digits |
|---|---|---|
| Palmar | Median | Ulnar |
| Dorsal — proximal | Radial | Ulnar |
| Dorsal — nail beds and distal phalanx | Median | Ulnar |
Autonomous Zones
- An autonomous zone is the area supplied by one nerve alone, with no overlap — the only reliable place to test sensation
- Median — pulp of the index finger
- Ulnar — pulp of the little finger
- Radial — first dorsal web space
- Axillary — regimental badge area over the lower deltoid
Applied Aspects
- Distinguishing a dermatomal from a peripheral nerve pattern localises the lesion to the root or to the nerve — the central skill in examining a limb
All questions in Upper Limb
- Q1Describe the formation, parts and branches of the brachial plexus. Add a note on its injuries. ★
- Q2Describe the boundaries and contents of the axilla. Add a note on the axillary artery and the axillary lymph nodes. ★
- Q3Describe the shoulder joint under type, ligaments, movements and stability. Add a note on its dislocation. ★
- Q4Describe the boundaries and contents of the cubital fossa. Add a note on the compartments of the arm and the brachial artery. ★
- Q5Describe the small muscles of the hand with their nerve supply. Add a note on the fascial spaces and the palmar arches. ★
- SN1Write a short note on Erb–Duchenne palsy. ★
- SN2Describe the course of the radial nerve and the effects of its injury at different levels. ★
- SN3Describe the carpal tunnel with its contents. Discuss carpal tunnel syndrome. ★
- SN4Describe the course of the ulnar nerve and the features of its injury. Explain the ulnar paradox. ★
- SN5Describe the anatomical snuffbox with its boundaries and contents. Add a note on scaphoid fracture. ★
- SN6Describe the rotator cuff with its muscles and functions. Add a note on supraspinatus tendinitis. ★
- SN7Describe the cutaneous innervation and dermatomes of the upper limb.