Lecture 15: musculoskeletal development 2

Question 1

Be able to describe each stage in the differentiation of skeletal muscle tissue.

Answer 1

1. myogenic cells: originate in somites and are restricted to muscle forming line; mitotic cells
2. myoblasts: derived from myogenic cells; post mitotic
3. Myotubes: formed after myoblasts line up and adhere to one another; requires calcium dependent CAMs; characterized by appearance of actin, myosin, troponin, tropomyosin, nuclei move to periphery
4. muscle fibers

Question 2

Differentiate between primary and secondary myotyubes.

Answer 2

Primary microbes are formed by fusion of earliest myoblasts; differentiation occurs before innervation

secondary myotubes are smaller than the primary and formed alongside the late myoblasts; contained in basal lamina and are electrically coupled

Question 3

Describe the role of satellite cells.

Answer 3

able to help the muscle fibers with growth by binding to the myotubes

function as stem cells; can become mitotic in times of stress

Question 4

Describe the role/function of each of the following myogenic regulatory factors: Myf-5, Pax-3, Pax-7, FGF, TGF-β, MyoD, Myogenin, Myf-6

Answer 4

Pax-3 and Myf-5 can separately activate MoD and cause myogenic cells to become myoblasts

FGF and TGF-B maintain myogenic cells in the labile state

MyoD is able to convert non muscle cells to cells that can express muscle proteins

Myf-6 leads to the expression of myofiber genes

See L15 S15

Question 5

Describe the origin and characteristics of the following muscle group: trunk muscles

Answer 5

epaxial muscles: dorsal lip of myotome and the tendons are from the syndrome layer within somites

Hypaxial muscles come from the ventral buds of the myotome and the tendons come from the lateral plate mesoderm

Question 6

Describe the origin and characteristics of the following muscle group: limbs

Answer 6

muscles come from the ventrolateral dermomyotome

tendons come from the lateral plate mesoderm

Question 7

Describe the origin and characteristics of the following muscle group: head and neck

Answer 7

derived from the paraxial somitomeres

extra ocular muscles come from the prechordal plate

cranial musculature is from the unsegmented paraxial mesoderm

some of the lower jaw musculature is from the splanchnic mesoderm

Question 8

Describe the origin and characteristics of the following muscle group: cardiac muscle

Answer 8

from the splanchnic mesoderm
both cardiac and skeletal express MADS
cardiac cells contract early and are able to divide