Embryology

Question 1

When do the limb buds start to appear?

Answer 1

End of the 4th week

Question 2

What does the remnant of the notochord become?

Answer 2

Nucleus pulposus

Question 3

What structure contains the nucleus pulposus?

Answer 3

Annulus fibrosus

Question 4

What structure is responsible for ensuring elongation of the limb bud?

Answer 4

AER = apical ectodermal ridge

Keeps the cells close to it undifferentiated

Question 5

How many degrees of asymmetry are there in limbs?

Answer 5

3

Question 6

How do the digits develop?

Answer 6

AER regresses so it is only left over what will be the tips of the digits. Therefore the digits continue to grow leaving gaps/thin tissue between. Webbing left behind is then removed by apoptosis.

Question 7

AER marks which boundary?

Answer 7

Dorsal - ventral

Question 8

What does ZPA stand for?

Answer 8

Zone of polarising activity

Question 9

What is the ZPA?

Answer 9

A signalling centre located on the posterior base of the limb bud. It controls patterning and maintains the AER.

Question 10

Limb defects most commonly affect which limb?

Answer 10

Upper limb

Question 11

Define syndactyly

Answer 11

Fusion of digits

Question 12

Define polydactyly

Answer 12

Extra digits

Question 13

Define amelia

Answer 13

Complete absence of a limb

Question 14

Define meromelia

Answer 14

Partial absence of one or more limb structures

Question 15

Which way do the limbs rotate?

Answer 15

Upper limbs = laterally

Lower limbs = medially

Question 16

Define dermatome

Answer 16

A strip of skin supplied by a single spinal nerve

Question 17

Define myotome

Answer 17

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

Question 18

Where do limb buds appear?

Answer 18

Ventro-lateral body wall

Question 19

Where are the sclerotome and dermatomyotome in relation to one another?

Answer 19

Sclerotome = ventral
Dermatomyotome = dorsal

Question 20

Approximately when do the hand and foot plates form?

Answer 20

6 weeks

Question 21

Approximately when does limb rotation occur?

Answer 21

7 weeks