Session 1

Question 1

When do limb buds first appear and where?

Answer 1

Appear as small projections on the lateral body wall during the fourth week of development

Question 2

What gene do limbs develop against?

Answer 2

Hox genes - determine the type of limb and the different types of vertebrae that will form in a body segment

Question 3

What does the neural tube develop from?

Answer 3

The primitive streak

Question 4

What does the neural tube contain?

Answer 4

Precursor cells of the nervous system

Question 5

What do limb buds consist of?

Answer 5

A mass of mesenchyme covered by a layer of ectoderm. At the tip of the bud the ectodermal cells divide to form an apical ectodermal ridge.

Question 6

How do limb buds elongate?

Answer 6

Proliferation of mesenchyme, influenced by the apical ectodermal ridge

Question 7

How does ossification of long bones begin?

Answer 7

The appearance of primary centres of ossification in the middle of the long bones

Question 8

Why is limb rotation in early development a big deal?

Answer 8

• Because it explains the spiral pattern of dermatomes in the lower limb
• why flex ion of the elbows and flex ion of the knee send the distal limb in different direction
• why sartorious follows an oblique path

Question 9

How do synovial joints develop in an embryo?

Answer 9

• Areas of mesenchyme within the bud begin to differentiate into hyaline cartilage
• Synovial joints form between adjacent cartilage models in an area called the joint inter zone
• cells at the centre of this inter zone will undergo apoptosis to form the joint cavity