MSK Session 3- Development Of The Limbs Flashcards Preview

SOPHIE'S ESA 2 > MSK Session 3- Development Of The Limbs > Flashcards

Flashcards in MSK Session 3- Development Of The Limbs Deck (25)
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0
Q

What forms limb musculature?

A

Somites

1
Q

What forms the limb skeleton?

A

Mesenchyme within the somatic layer of the lateral mesoderm.

2
Q

When do limb buds begin to appear?

A

End of week 4

3
Q

Which are slightly developmentally ahead, and by how many days?

A

Upper limb buds

Approx 2 days

4
Q

Which way do the limb buds grow?

A

Ventrally

5
Q

What is the structure of a limb bud?

A

Core- mesenchyme

Apex- apical ectodermal ridge (thickened ectoderm)

6
Q

What are the roles of the apical ectodermal ridge (AER)? (3)

A

Signalling role by exerting an influence over mesenchymal cells directly beneath it to read undifferentiated and divide, therefore causing limb growth in a proximal to distal direction.
Induces hand and foot plates to develop digits, before it regresses.
Marks the boundary between the dorsal and ventral limb ectoderm.

7
Q

What happens to mesenchyme that is too proximal compared to the AER?

A

It is no longer influenced by the AER and therefore differentiates into tissues.

8
Q

What is the role of the zone of polarising activity (ZPA) (3) and where is it found?

A

It is a signalling centre located in the posterior base of the limb bud.
It is responsible for generating asymmetry in the limbs, controlling patterning and maintaining the AER.

9
Q

How do the hand and foot plates develop so that digits appear?

A
  • digital Rays appear; which are condensations of mesenchyme within the hand and foot plates. They form cartilaginous models of digital bones.
  • the AER regresses, but remains over the digital Rays to allow digital growth.
  • apoptosis of the interdigital spaces sculpts the hand and foot plates.
10
Q

How do muscles arise?

A
  • Myogenic precursors from somites migrate into the limb buds along with their innervation, and form 2 common muscle masses (ventral/flexor compartment and dorsal/extensor compartment) around the new skeletal elements.
  • individual muscles then arise from these two compartments.
11
Q

Where are flexors located in the upper and lower limb respectively?

A

Upper- anteriorly, lower-posteriorly.

12
Q

Describe rotation of the upper limb.

A

The upper limb rotates laterally so that the thumbs face out and the elbows move down.

13
Q

Describe rotation of the lower limb.

A

The lower limb rotates medially, so the soles move down and the knees move up.

14
Q

What happens to development if the limb buds aren’t innervated early on?

A

Development stalls

15
Q

What cords of the brachial plexus innervate the ventral-anterior compartment?

A

The medial and lateral cords

16
Q

Which cord of the brachial plexus Innervates the dorsal/posterior compartment?

A

Posterior cord

17
Q

Define myotome

A

A muscle/group of muscles supplied by a single spinal nerve.

18
Q

Define dermatome.

A

A strip of skin supplied by a single spinal nerve.

19
Q

Why does the mesoderm layer give rise to the most variety of structures?

A

Because it is the most plastic layer.

20
Q

Which limb defects are more common?

A

Upper limb

21
Q

What is syndactyly?

A

Fusion of digits involving connective tissue or bone.

22
Q

What is polydactyly?

A

Extra digits that usually occur bilaterally.

23
Q

What is Amelia?

A

Complete limb absence

24
Q

What is meromelia?

A

Partial limb structure absence.

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