Myotomes, dermatomes, peripheral nerves

Question 1

What is the sensory distribution of the Median nerve?

Answer 1

Thumb, index finger, middle finger, lateral aspect of fourth finger and palm.

Question 2

What is the motor distribution of the median nerve?

Answer 2

Thenar muscles, lateral lumbricals, flexion of the elbow, flexion of the wrist (apart from flexor carpi ulnaris), flexion of the fingers. - Basically all flexion in hands and arms.

Question 3

What is the sensory distribution of the ulnar nerve?

Answer 3

Question 4

What is the motor function of the ulnar nerve?

Answer 4

All the intrinsic muscles of the hand except for three thenar muscles, and flexor carpi ulnaris. Also does flexor digitorum superficialis which attaches to DIPs

Question 5

What will an ulnar nerve injury cause?

Answer 5

Clawing of the hand, especially on the ulnar side due to lack of extension muscles. sensory changes over the palmar aspect of the little finger and half of the fourth finger.

Question 6

How can you tell the difference between an ulnar nerve injury at the elbow or the wrist?

Answer 6

Elbow - loss of sensation over the dorsal surface of the hand on the median side, preserved in wrist injury

Question 7

What is the sensory supply of the axillary nerve?

Answer 7

Saergents patch over shoulder

Question 8

What is the motor function of the axillary nerve?

Answer 8

paralysis of deltoid – very weak shoulder abduction from 15-90°; weak shoulder flexion and extension

paralysis of teres minor – weak shoulder external rotation

Question 9

What is the nerve root supply of the axillary nerve?

Answer 9

C5/6

Question 10

What injury is classically associated with damage to axillary nerve and why?

Answer 10

Fractured head of humerus, as axillary nerve wraps around head of humerus

Question 11

What is the nerve root origin of the radial nerve?

Answer 11

C5 to T1

Question 12

What is the sensory function of the radial nerve?

Answer 12

Posterior arm and forearm

lateral ⅔ of dorsum of hand

proximal dorsal aspect of lateral 3 ½ fingers (thumb, index, middle and half of ring finger)

• Basically extensor surfaces of arm and hand

Question 13

What is the motor function of the radial nerve?

Answer 13

posterior compartment of arm

triceps – extends and adducts shoulder, extends elbow

posterior compartment of forearm

brachioradialis – flexes elbow

anconeus – extends elbow, stabilises elbow joint

supinator – supinates forearm

extensor carpi radialis longus and brevis – extend and abduct wrist

extensor carpi ulnaris – extends and adducts wrist

extensor digitorum, extensor pollicis longus and brevis, extensor indicis and extensor digiti minimi – extend thumb and fingers at MCPJs and IPJs

abductor pollicis longus – abducts thumb

Basically all extension of arm and hand

Question 14

What are some common mechanisms of injury to the radial nerve?

Answer 14

Saturday night palsy/crutch palsy - prolonged pressure on inside of arm.

Stab wounds (including venesection!) in antecubital fossa

Question 15

Injury to what nerve causes wrist drop? What is this?

Answer 15

Radial nerve

WRIST DROP” deformity at rest and on attempted wrist extension – the patient cannot extend their wrist/fingers, resulting in unopposed wrist flexion. In the classical description of a radial nerve injury, the forearm is also pronated, the fingers are flexed and the thumb adducted.

Question 16

Which peripheral nerve is affected in carpal tunnel syndome?

Answer 16

Median nerve

Question 17

Hand of benediction sign is associated with which nerve palsy? What is it?

Answer 17

Median nerve

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.

Question 18

why does the patient with median nerve palsy struggle with ok sign?

Answer 18

Because they cannot flex their DIPs due to weakness of flexor digitorum profundus. So ok sign looks like a duck.