13: Dermatomyes, Myotomes, Spinal Nerve Plexuses

Question 1

Trilaminar disc

Answer 1

Mesoderm, endoderm, ectoderm

Question 2

Two things formed by paraxial mesoderm

Answer 2

Head, somites

Question 3

Three things formed by somites

Answer 3

1. Sclerotome (cartilage)
2. Myotome (skeletal muscle)
3. Dermatome (dermis)

Question 4

Where does somatic innervation arise from?

Answer 4

Segmentally along developing CNS in associating with each somite

Question 5

Dermatome

Answer 5

Area of skin supplied with afferent nerve fibers by a single dorsal spinal root

Question 6

Myotome

Answer 6

All muscles innervated by a single efferent anterior root

Question 7

Nerve impingement that effects a single segment vs a single nerve proper

Answer 7

Single segment: can be ascertained by looking at a dermatome map
Single nerve: can be ascertained by looking at a nerve map

Question 8

Do all muscles have just one myotome?

Answer 8

No, most muscles are composed of more than one myotome -> thus, injury to one nerve segment causes weakness, but not typically a complete loss of function