Neuroanatomy Draw It To Know It

28 Neuroanatomy: Draw It to Know It

Know-It Points

Brachial Plexus

■ R a m i. Th e brachial plexus is most commonly formed
from the C5–T1 ventral rami.
■ Trunks. C7 makes up the middle trunk; C5 and C6
form the upper trunk; and C8 and T1 form the lower
trunk.
■ Divisions & Cords. Th e posterior divisions form the
posterior cord; the anterior division (lower trunk)

forms the medial cord; the anterior division (upper

trunk) and the anterior division (middle trunk) form

the lateral cord.

■ Major terminal nerves. Th e lateral and medial cords

form the median nerve; the medial cord becomes the

ulnar nerve; the posterior cord becomes the radial

n e r v e.

Median Nerve

■ Th e median nerve is formed from the lateral cord
(C6, C7) and the medial cord (C8, T1).
■ Th e superfi cial forearm group comprises pronator
teres and fl exor carpi radialis (C6, C7) and fl exor
digitorum superfi cialis and palmaris longus (C7, C8).
■ Th e anterior interosseous group (C7–T1) comprises
pronator quadratus, fl exor pollicis longus, and fl exor
digitorum profundus 2 and 3.

■ Th e thenar group (C8, T1) comprises abductor

pollicis brevis, opponens pollicis, and fl exor pollicis

brevis.

■ Th e terminal motor group (C8, T1) comprises the

fi rst and second lumbricals.

Ulnar Nerve

■ Th e ulnar nerve is formed from the medial cord
(C8, T1).
■ Th e forearm muscle group comprises fl exor
carpi ulnaris and fl exor digitorum profundus
4 and 5.
■ Th e superfi cial sensory division is purely sensory
except that it provides motor innervation to palmaris
brevis.

■ Th e deep branch is purely motor and innervates

muscle groups across the hand:

• Th e hypothenar group: abductor digiti minimi,
  opponens digiti minimi, and fl exor digiti minimi


• Th e intrinsic hand group: lumbricals 3 and 4,
  palmar interossei, and dorsal interossei


• Th e thenar group: fl exor pollicis brevis and
  adductor pollicis

Radial Nerve

■ Th e radial nerve is formed from the posterior cord
(C5–C8).
■ Th e radial nerve innervates the triceps muscle
(primarily, C6, C7).
■ Th e elbow group comprises brachioradialis
(C5, C6), extensor carpi radialis longus and
brevis (C6, C7), and anconeus (C6–C8).

■ Th e posterior interosseous nerve branch supplies the

supinator muscle (C6, C7), extensor carpi ulnaris

(C7, C8) abductor pollicis longus (C7, C8), and the

fi nger and thumb extensors (C7, C8).