LG 6.5 - Embryogenesis Limbs

Question 1

Which week(s) are critical time periods for the upper limbs?

Answer 1

• Weeks 4-5

Question 2

Which week(s) are critical time periods for the lower limbs?

Answer 2

• Shortly after the upper limbs occur in week 4 and a little past when the critical period ends for the upper limbs in week 5.
• Slight delay behind upper limbs

Question 3

Which tissues give rise to limbs?

Answer 3

• Paraxial mesoderm - for the muscles of the upper limbs.
• Neural tube - which will give rise to neural axons in the limbs.
• Neural crest - contribute sensory nerves that will innervate extremities.

Question 4

(5) In a 6-week old embryo, the terminal portion of the limb bud becomes flattened to form what?

Answer 4

• Hand and Footplates

Question 5

(5) What occurs for fingers and toes to arise?

Answer 5

• When cell death occurs in the AER , separates the ridge into parts.

Question 6

(5) During the 7th week what occurs in limb development? Why is this important?

Answer 6

• Limbs rotate in opposite directions.
• Upper limbs rotate laterally through 90 degrees. (extensor muscles on lateral/ posterior aspect of limb).
• Lower limb rotates medially through almost 90 degrees (extensor muscle are on anterior surface).

Question 7

(6) What is achondroplasia? What is it a result of?

Answer 7

• One form of congenital dwarfism resulting from improper development of cartilage at the end of long bones.

Question 8

(7) What is the radial nerve formed by? What does it supply?

Answer 8

• Formed from dorsal segmental branches. (C5, C6, C7, C8, T1)
• Supplies extensor muscles of arm.

Question 9

(7) What is the ulnar nerve and median nerve formed by? Innervation?

Answer 9

• Ular nerve from from ventral branches of (C8, T1).
• Median nerve (C6, C7, C8, T1)
• Supply flexor muscles of arm.

Question 10

(7) What is amelia? Phocomelia?

What are these malformations caused by?

Answer 10

• Amelia: complete absence of one or more limbs.
• Phocomelia: upper portion of limb is absent or poorly developed.
• Caused by genetic factors, some environmental.

Question 11

(7) What is syndactyly? Macrodactyly?

Answer 11

• syndactyly: two or more fused fingers or toes.

- Macrodactyly: enlargement of one or more digits.

Question 12

(7) What is polydactyly? Ectrodactyly?

Answer 12

• Polydactyly: extra digits.

- Ectrodactyly: fewer than normal digits.

Question 13

(7) What is club foot?

Answer 13

• Clubfoot: common 1/5000, abnormal position of the foot, can result from compression of the infant in the uterus.