This is a visual mnemonic for the nerve arrangement of superficial cervical cutaneous branches of cervical plexus. This mnemonic was created only for the ease to remember and may not resemble exact anatomy.
The site of injection for superior cervical plexus nerve block is the midpoint of posterior border of sternocleidomastoid. Assuming this as a center point, the various position of nerves, from north going anti-clockwise is given by mnemonic "GLAST":
- 1 o' clock: Greater auricular nerve (C2,C3) - Innervates skin over the parotid gland, angle of jaw and posterior ear
- 11 o' clock: Lesser occipital nerve (C2) - Innervates scalp behind and above ear
- 7 o' clock: Spinal accessory nerve (XI) - This doesn't belong to superficial cervical plexus and lies deep to the sternocleidomastoid muscle and innervates sternocleidomastoid and trapezius
- 6 o' clock: Supraclavicular nerve (C3,C4) - Divides into medial, intermediate and lateral branches and supply sensation over shoulder, lateral neck and anterior upper thoracic wall
- 3 o' clock: Transverse cervical nerve (C2, C3) - Innervates skin of front and side of neck (anterior triangle)
All these nerves are also the contents of the occipital triangle of neck. Except spinal accessory nerve, all these nerves crosses superficial to the sternoclediomastoid muscle. In general, the superficial cervical plexus supply the skin of anterolateral neck.