Week 1 - MSK development

Question 1

What does the skull develop from?

- What are the two parts of this?

Answer 1

Mesenchyme (developed from neural crest cells) around the brain:

1. Viscerocranium
2. Neurocranium

Question 2

What does each vertebra develop from?

Answer 2

From the sclerotome of 4 somites.

Question 3

What are the two parts of an intervertebral disk?

- and what is their orientation relative to each other?

Answer 3

Nucleus Pulposus - inner center of disk

Annulus Fibrosis - outer ring of disk (fibrous part)

Question 4

What forms the nucleus pulposus of the intervertebral disk?

Answer 4

The notochord

Question 5

What does the annulus fibrosis develop from?

Answer 5

The mesoderm (connective tissue) between the vertebrae.

Question 6

What are the two divisions of the of the myotome (within the thorax and abdominal regions)?

Answer 6

Epaxial division

Hypaxial division

Question 7

What muscles are part of the epaxial division?

Answer 7

Back and neck muscles

Question 8

What innervates the epaxial division?

Answer 8

dorsal rami

Question 9

What muscles are part of the hypaxial division?

Answer 9

Trunk and limb muscles

Question 10

What innervates the hypaxial division?

Answer 10

Ventral rami

Question 11

When does muscle tissue begin to differentiate?

Answer 11

At week 4-5 in development

Question 12

What muscle cell precursors for at 4-5 weeks of development?

Answer 12

Myoblasts

Question 13

What is the embryonic origin of the skull (head mesenchyme)?

Answer 13

Neural crest cells

Question 14

When do muscle cells begin to differentiate?

Answer 14

Week 5-6 in development

Question 15

Describe the process of muscle development after the muscle cells have begun to differentiate.

Answer 15

• myoblasts fuse
• multinucleated myotubes
• more myoblasts added at the ends
• begin synthesizing actin & myosin

Question 16

What is a myotube?

Answer 16

Multi-nucleated, undifferentiated contractile apparatus (sarcomere)

Question 17

What is a myofibre?

Answer 17

Multinucleated differentiated sarcomere

Question 18

What happens between week 9 and 5 months of muscle development?

Answer 18

Nuclei migrate to the outside of the myotube - actin & myosin organized to form contractile elements

Question 19

What is the difference between primary and secondary myotubes?

Answer 19

Primary myotubes do not need nerve cell involvement.

Secondary myotubes need nerve cells present to form.

Question 20

When does development of the limbs begin?

Answer 20

Week 4 of development.

Question 21

What is the primary axial artery in the upper limb?

Answer 21

Brachial artery

Question 22

What gene controls the anterior/posterior axis of limb?

Answer 22

Shh (Sonic Hedgehog gene)

Question 23

What gene controls the dorsal/ventral axis of limb?

Answer 23

Wnt

Question 24

What gene controls the outgrowth (proximal/distal axis) of limb?

Answer 24

Wnt & Shh

Question 25

What is secreted by the mesenchyme in the centre of the deveolping limb?

Answer 25

BMP (Bone Morphogenic Protein)

Question 26

What is the function of Bone Morphogenic Protein?

Answer 26

Necessary for the mesenchyme to develop into cartilage and then bone.

Question 27

What is secreted by the regions where synovial joints will form?

Answer 27

Noggin

Question 28

What does Noggin do on a molecular level?

Answer 28

Antagonizes BMP

Question 29

How does the synovial joint form?

- ie. what happens between bones, on the surface of bones, and around the bones?

Answer 29

There is condensation of mesenchyme in Noggin-rich areas which leads to apoptosis and formation of a fluid filled space between two cartilage rods.
Articular cartilage forms on the ends of these rods where mesenchyme will condense to for m perichondrium which becomes periosteum.
Mesenchyme adjacent to the joint region will form synovium & ligaments of the joint capsule and tendons.

Question 30

What is an Apical Ectodermal Ridge (AER)?

Answer 30

A thickened portion of epithelium at the tip of the limb buds.

Question 31

What is the function of the Apical Ectodermal Ridge (AER)?

Answer 31

It secretes fibroblast growth factors and interacts with the mesenchyme of the limb to promote growth outwards.

Question 32

What does Retinoic Acid do in limb development?

Answer 32

Acts on Zone of Polarizing Activity (ZPA) to induce Shh abd bone morphogenetic proteins.
–> Determines pattern of limb development and programmed cell death (ie. causes apoptosis in areas of tissue between fingers).

Question 33

What is amelia?

Answer 33

Complete failure of limb development

Question 34

What is the term for partial failure of limb development?

Answer 34

Meromelia

Question 35

What is a cause of polydactyly or syndactyly?

Answer 35

Improper gradient of ZPA (zone of proliferating activity) and Shh.