Peripheral Nervous System

Question 1

What is a dermatome?

Answer 1

A region of skin innervated by a specific nerve root

Question 2

Where is the C2 dermatome?

Answer 2

The back of the head and the middle section of the front of the neck

Question 3

Where is the C3 dermatome?

Answer 3

The back of the neck and the bottom of the anterior neck and trapezius muscles

Question 4

Where is the C4 dermatome?

Answer 4

From shoulder to shoulder anteriorly and posteriorly

Question 5

Where is the C5 dermatome?

Answer 5

Along the bicep anteriorly and posteriorly from the shoulder down to the antecubital fossa

Question 6

Where is the C6 dermatome?

Answer 6

The lateral forearm down to the thumb and forefinger

Question 7

Where is C7 dermatome?

Answer 7

The middle finger and the majority of the medial palm and the corresponding back of the hand

Question 8

Where is the C8 dermatome?

Answer 8

The medial palm and the pinky finger and ring finger and the corresponding back of the hand

Question 9

Where is the T1 dermatome?

Answer 9

The medial forearm up to the elbow and antecubital forearm

Question 10

Where is the T2 dermatome?

Answer 10

The tricep, up the medial aspect of the upper arm to cross the chest around the level of the manubriosternal joint and to arch across the back below the C4 dermatome

Question 11

Where is the T3 dermatome?

Answer 11

The armpits and a horizontal strip of the chest and an arch of the back

Question 12

Where is the T4 dermatome?

Answer 12

Just above the nipples across the chest and arching across the back

Question 13

Where are the T5-T12 dermatomes?

Answer 13

They stripe across the chest from the nipples down to below the umbilicus, and arch across the back not as low down

Question 14

Where is the L1 dermatome?

Answer 14

The waist area and the perigenital regions, and arches across the back

Question 15

Where is the L2 dermatome?

Answer 15

L2 innervates a major part of the anterior thigh. It arches posteriorly from the lateral buttocks up to the small of the back

Question 16

Where is the L3 dermatome?

Answer 16

L3 innervates the inferior portion of the anterior thigh, the knee and the area slightly below. Posteriorly, it innervates a small arch above the buttocks as well as the medial thigh

Question 17

Where is the L4 dermatome?

Answer 17

The medial lower leg down below the medial malleolus

Question 18

Where is the L5 dermatome?

Answer 18

The lateral lower leg and the medial 3 toes and superior foot

Question 19

Where is the S1 dermatome?

Answer 19

The lateral 2 toes to the heel and back of the ankle

Question 20

Where is the S2 dermatome?

Answer 20

A major region of the posterior legs

Question 21

Where is the S3 dermatome?

Answer 21

The penis, part of the scrotum, and part of the buttocks

Question 22

Where is the S4 dermatome?

Answer 22

The most distal part of the scrotum, and a small medial region of the buttocks

Question 23

Where is the S5 dermatome?

Answer 23

Perirectal

Question 24

What area of skin is innervated by the median nerve

Answer 24

The palmar. side of the thumb, index finger, middle finger, and the lateral 1/2 of the ring finger, and the radial aspect of the palm (C6 and C7 dermatomes)

Question 25

What area of the skin is innervated by the ulnar nerve?

Answer 25

The anterior and posterior surfaces of the medial one and a half fingers and the associated palm area

Question 26

What area of the skin is innervated by the radial nerve?

Answer 26

The posterior aspect of the hand, except the little finger and medial half of the ring finger

Question 27

What are the 5 modalities of sensation to be checked in a neurological examination?

Answer 27

Light touch (cotton wool)
Pain (pin prick)
Temperature (tuning fork)
Vibration (128 Hz tuning fork)
Joint position sense/proprioception (move their finger)

Question 28

What are the key points for testing light touch?

Answer 28

Use a very small spike of cotton wool and press it against the skin just so it starts to bend. Do 2 quick dabs on the centre of the dermatome

Question 29

What are the key points for testing pain?

Answer 29

Avoid leading questions like ‘is this painful?’. Just press the pin against the skin once. Test like-for-like sides and ask if it feels the same on both sides

Question 30

What are the key points for testing temperature?

Answer 30

Avoid leading questions like ‘does this feel cold?’, instead saying ‘hot or cold?’.

Question 31

What are the key points for testing vibration?

Answer 31

Compare side to side. If impaired, move proximally until they can feel it.

Question 32

What are the key points for testing proprioception?

Answer 32

Hold the finger at the sides rather than holding the nail and the pad. Steady the interphalangeal joint with the other hand. If impaired, move the digit a greater distance, or then test more proximally

Question 33

Where do you test pain sensation?

Answer 33

The most commonly affected areas:
Palmar aspect of index finger (median nerve)
Palmar aspect of pinky finger (ulnar nerve)
Web space between the thumb and index finger on the dorsal surface of the hand (radial nerve)
Lateral surface of the foot (L5)
Posterior aspect of the leg (S1)

Question 34

What is paraesthesia?

Answer 34

Pins and needles

Question 35

What is polyneuropathy?

Answer 35

Damage to multiple peripheral nerves e.g. glove and stocking syndrome