Expansion
C5 lateral arm, C6 thumb, C7 middle finger, C8 little finger, T1 medial arm
Mnemonic
“Regimental badge, thumb, middle finger, little finger, medial arm”:
- C4 - the shoulder tip and over the clavicle
- C5 - the lateral upper arm, the regimental badge area
- C6 - the thumb
- C7 - the middle finger
- C8 - the little finger
- T1 - the medial forearm
- T2 - the medial upper arm and axilla
“6, 7, 8 across the hand from thumb to little finger” is the sequence worth carrying, and it maps directly onto the reflexes: C5, 6 biceps and supinator; C7, 8 triceps.
T4 is the nipple, T10 the umbilicus for the trunk continuation.
Note the gap: C4 sits next to T2 over the upper chest, because the C5 to T1 dermatomes have migrated out into the limb, which is why the anterior chest wall dermatomes appear to skip.
Expansion
- C5 - regimental badge area over the lateral upper arm
- C6 - thumb
- C7 - middle finger
- C8 - little finger
- T1 - medial forearm and arm
Memory hook: make a thumbs-up “six-shooter” for C6, point with the C7 middle finger, and the little finger is C8.