Median Nerve

Question 1

Nerve roots and obranch origins?

Answer 1

c5-T1

lateral and medial cords of the brachial plexus

lateral root arises from anterior divisions of superior and middle trunks

medial root arises from anterior division of inferior trunk

Question 2

Course of the nerve?

Answer 2

runs down the arm with the brachial artery: it initially lies lateral to the artery, then crosses over to lie medial to it about halfway down the arm

then passes through the medial part of the antecubital fossa between the two heads of pronator teres muscle

Question 3

it then travels through the anterior forearm between the:

Answer 3

flexor digitorum superficialis and flexor digitorum profundus muscles and gives three main branches:

anterior interosseous nerve – descends along anterior interosseous membrane with anterior interosseous artery

deep branch – enters hand through the carpal tunnel beneath flexor retinaculum of wrist, between flexor carpi radialis and flexor digitorum superficialis tendons

superficial/palmar cutaneous branch – arises just before the wrist and pierces the palmar carpal ligament to enter the palm over the top of the carpal tunnel – this nerve is therefore not affected by carpal tunnel syndrome

Question 4

Sensory supply?

Answer 4

he median nerve does not supply any sensory innervation to the axilla or upper arm

skin over thenar eminence

lateral ⅔ palm of hand

palmar aspect of lateral 3½ fingers

dorsal fingertips of lateral 3½ fingers (thumb, index, middle and half of ring finger)

Question 5

Motor supply?

Answer 5

the median nerve does not supply any motor innervation to the axilla or upper arm

all muscles of anterior compartment of forearm EXCEPT flexor carpi ulnaris and the medial two parts of flexor digitorum profundus

pronator teres and pronator quadratus – pronate forearm

flexor carpi radialis – flexes and abducts wrist

palmaris longus – flexes wrist and tenses palmar aponeurosis

flexor digitorum superficialis – flexes fingers at PIPJs

lateral two parts of flexor digitorum profundus – flex index and middle fingers at DIPJs

flexor pollicis longus – flexes thumb at IPJ
intrinsic muscles of hand – LOAF muscles

lateral two lumbricals – flex MCPJs and extend IPJs of index and middle finger

opponens pollicis – opposes thumb

abductor pollicis brevis – abducts thumb

flexor pollicis brevis – flexes thumb at MCPJ

Question 6

Features of median nerve palsy?

Answer 6

SENSORY LOSS
numbness of skin over thenar eminence and median distribution of hand
NB// in carpal tunnel syndrome, sensation to the palm is usually preserved due to an intact palmar cutaneous branch

MOTOR DEFICIT
paralysis of most of anterior compartment of forearm – weak forearm pronation, wrist flexion and abduction, and weak finger flexion with preservation of DIPJ flexion at ring and little fingers
paralysis of thenar eminence – weak pincer grip and overall grip strength, weak thumb opposition

DEFORMITY
wasting of anterior compartment of forearm and thenar eminence
“HAND OF BENEDICTION” deformity on attempted finger flexion – the patient cannot flex their index or middle fingers, resulting in unopposed extension of those two fingers. They cannot make a fist with all of their fingers.