Dermatomes, Myotomes, Segmental innervation of the upper and lower limb

Question 1

What is a dermatome?

Answer 1

An area of skin that is mainly supplied by a single spinal nerve

Question 2

What is a somite?

Answer 2

A division of the embroyo

Question 3

What is sclerotome?

Answer 3

Part of the somite, gives rises to the vertebrae and ribs

Question 4

List the dermatomes of the arm.

Answer 4

C5 - Later arm 
C6 - Thumb 
C7 - Middle finger
C8 - Little finger
T1 - Medial forarm

Question 5

Explain why there is 8 cervical nerves but only 7 cervical vertabrae?

Answer 5

The first 7 cervical nerves emerge from above there associated vertebra, C8 emerges from below C7 vertebrae, all following spinal nerved exit below their corresponding vertebra

Question 6

List the dermatomes of the leg.

Answer 6

L2 - Anterior medial thigh
L3 -  Medial epicondyle of femur 
L4 - Medial malleolus
L5 - Dorsum of foot
S1 -  Lateral calcaneus 
S2 - Popliteal Fossa

Question 7

What is a myotome?

Answer 7

A muscle innervated by a single spinal nerve root, referred to as a myotome

Question 8

What is a motor unit?

Answer 8

A muscle fibre innervated by a single motor nerve fibre

Question 9

What is the clinical relevance of dermatomes?

Answer 9

The viral infection shingles affects the skin of a single dermatome