17. Dermatomes, Myotomes, & Spinal Nerve Plexuses

Question 1

What does intermediate mesoderm give rise to?

Answer 1

Kidney and Gonads

Question 2

What does chordamesoderm give rise to?

Answer 2

Notochord then nucleus pulposa

Question 3

What does lateral plate mesoderm give rise too?

Answer 3

Splanchnic mesoderm: circulatory system
Somatic mesoderm: body cavity
Extra-embryonic:

Question 4

What does paraxial mesoderm give rise to?

Answer 4

Head 
Somite:
- Sclerotome (cartilage)
- Myotome (skeletal muscle)
- Dermatome (dermis)

Question 5

Injury to a __________ will lead only to sensory deficits/symptoms (_________), while injury to a __________ will lead only to motor deficits and symptoms (________).

Answer 5

Recognize that injury to a dorsal root will lead only to sensory deficits/symptoms (paresthesia), while injury to a ventral root will lead only to motor deficits and symptoms (weakness)

Question 6

In regards to somatic innervation, cells that migrate _______ give rise to muscles of the limbs and trunk (___________) and to the associated dermis

Answer 6

• anteriorly

- hypaxial muscles

Question 7

Cells that migrate _________ give rise to the intrinsic muscles of the back (_________) and the associated dermis

Answer 7

• posteriorly

- epaxial muscles

Question 8

Describe the 3 horns of spinal chord gray matter

Answer 8

• Posterior horn: sensory
• Lateral horn: visceromotor
• Anterior horn: motor

Question 9

When do the limb buds begin to appear?

Answer 9

Week 4

Upper Limb: C5-T1
Lower Limb: L2-S2

Question 10

What is the dermatome?

Answer 10

The area of skin supplied with afferent nerve fibers by a single posterior spinal root

Question 11

Impingement or injury that effects a single segment can be ascertained with some degree of certainty by turning to a _________ map

Answer 11

Dermatome

This applies given one caveat, dermatomes are not as precise as shown on dermatome maps and consist fo segments/nerves with overlapping territories.

Question 12

Impingement or injury that effects a single spinal nerve proper can be ascertained with some degree of certainty by turning to a ______ map

Answer 12

Nerve

This applies given one caveat, dermatomes are not as precise as shown on dermatome maps and consist fo segments/nerves with overlapping territories.

Question 13

What is a myotome?

Answer 13

All the muscles that are innervated by a single efferent anterior root. Most muscles are composed of more than one myotome.

If one goes out, others can take care of it. Redundancy is important!