MSK Development

Question 1

Somites differentiate into…

and which genes encode their fate…?

Answer 1

…sclerotome(bones), syndetome(tendons), myotome and dermatome
..HOX genes

Question 2

somites are produced from the..

Answer 2

..PSM - presomitic mesoderm

Question 3

Neural tube closes about day…

Answer 3

20-22

Question 4

-paraxial mesoderm forms the head and somites, the intermediate mesoderm forms the kidneys and gonads, what does the lateral mesoderm differentiate into?

Answer 4

splanchnic, somatic and extra-embryonic

Question 5

Somites are the precursors of what body parts in the adult?

Answer 5

axial skeleton, and axial muscles, appendicular muscles

appendicular skeleton is from limb buds

Question 6

chondrification (cartilage) begins at about week…

ossification begins at about week…

Answer 6

chondrification. ..week 6

ossification. ..week 9, and primary ossification centres present by week 12

Question 7

Most bones form from cartilage by endochondral ossification.
But, the flat bones of the face, cranial bones and clavicles are made with no cartilage intermediate, via the process:

Answer 7

Intramembranous ossification

Question 8

Name 3 abnormalities of Sclerotome formation.

Answer 8

• hemivertebrae/fused vertebrae
• Klippel-Feil Syndrome/Brevicolis - short neck
• Spina Bifida - failed union of arches

Question 9

What does the myotome’s EPIMERE form?

Answer 9

• epaxial spine extensors

- innervated by dorsal ramus of spinal nerve

Question 10

What does the myotome’s HYPOMERE form?

Answer 10

• spine flexors and external, internal and innermost layer of thorax and abdominal muscles.
• Innervated by ventral ramus of spinal nerve

Question 11

Tendons, ligaments, fascia and dermis of LIMBS form from what embryonically?

Answer 11

Limb Bud Mesenchyme

Question 12

Name 2 signal centres of the developing limb.

Answer 12

• ZPA

- AER - apical ectodermal ridge

Question 13

Cleft hand/foot is due to defects in which genes responsible for establishing the distal limb elements pattern?

Answer 13

HOX a13 genes

Question 14

List 4 stages in the differentiation pathway between

• myotome cells/Muscle progenitor cells…
• …and muscle fibre formation

Answer 14

• dividing myoblasts-migrate to muscle and proliferate
• cell allignment
• primary myotube via myoblast fusion
• secondary myotube/maturation

Question 15

What are resident muscle stem cells called and what do they express?

Answer 15

Satellite Cells

Express Pax 7

Question 16

In developing NMJ’s, what does the growth cone of the axon secrete?
What does this bind to on the myofibre at the NMJ?

Answer 16

Axon secretes Agrin.

Agrin binds to Musk-a transmembrane tyrosine kinase