Dermatomes and Myotomes

Question 1

Define dermatome

Answer 1

A patch of skin innervated by a single spinal nerve.

Question 2

Describe how a dermatome is formed.

Answer 2

As a limb bud increases in size, nerves are dragged along with the structures that they innervate.

Question 3

Give the segmental innervation of the following upper limb movements:

• Shoulder abduction
• Elbow flexion
• Elbox extention
• Finger flexion
• Finger ad/abduction

Answer 3

C5
C6
C7
C8
T1

Question 4

Give the segmental innervation of the following lower limb movements:

• Flexion at the hip
• Knee flexion
• Knee extention
• Plantar flexion
• Adduction of the toes

Answer 4

L1/2
L5 to S2
L3/4
S1/2
S2/3

Question 5

Define myotome

Answer 5

All muscles innervated by a single spinal nerve

Question 6

Define motor unit

Answer 6

All muscle fibres innervated by a single motor nerve fibre.

Question 7

Describe the difference in loss of sensation when lesions are close to the spinal cord instead of more distal.

Answer 7

Close - loss of sensation in the dermatomes

Distal - loss of sensation in the peripheral nerve field.