Development of the musculoskeletal system

Question 1

What embryonic germ layer is skeletal muscle derived from?

Answer 1

Paraxial mesoderm

Question 2

Where are the epaxial muscles located and what do they form upon maturation?

Answer 2

They are dorsal to the transverse processes and form the intrinsic muscles of the back

Question 3

What line do myotomes originate from?

Answer 3

Somites

Formed by the cells at the ventrolateral lip (VLL) of the prospective myotome region and by cells from the dorsomedial lip (DML)

Question 4

What portion of the mesoderm do VLL contribute cells to?

Answer 4

Cells at the ventrolateral lip contributes cells to both the primaxial and abaxial domains of the mesoderm

Question 5

What portion of the mesoderm do DML contribute cells to?

Answer 5

Cells at the dorsomedial lip contribute to the primaxial domain of the mesoderm (also includes sclerotome and dermatome cells)

Question 6

What cells does the primaxial domain contain? What does this domain form?

Answer 6

Cells from the paraxial mesoderm.

Forms muscles of the back, shoulder girdle (rhomboids, levator scapulae, and latissimus dorsi), and intercostals

Question 7

What cells form dermis on the back (from dermatomes), vertebrae, and bony parts of the ribs (from sclerotome)?

Answer 7

Paraxial cells

Question 8

What does the abaxial domain form?

Answer 8

Limb and abdominal wall (obliques and transversus abdominus muscles)

Question 9

What do abaxial cells form?

Answer 9

The dermis in the body wall (from lateral plate mesoderm) and rib cartilages (from sclerotome cells that migrate across the lateral somitic frontier)

Question 10

Where do migrating muscle cells receive innervation from?

Answer 10

Their spinal segments of origin - migrating muscle cells carry these spinal nerves with them as they migrate

Question 11

What molecular regulation is important for the formation of skeletal muscle?

Answer 11

WNT, MyoD, BMP4 with low SHH

Question 12

Describe the patterning of the muscles in the head

Answer 12

Head musculature formed by somitomeres - tongue, eye (except those of the iris = pupillary muscles = derived from the optic cup) and pharyngeal arches.

Muscles in the head are patterned by connective tissue that is formed by neural crest

Question 13

Describe the patterning of the muscles of the limb:

Answer 13

Limb muscles formed by VLL cells: patterned by connective tissue formed by lateral plate mesoderm regulated by MyoD genes (transcription factor)

Question 14

Describe the formation of cardiac muscle:

Answer 14

Derived from visceral mesoderm surrounding heart tube
Intercalated discs
Purkinje fibers

Question 15

Describe the formation of smooth muscle:

Answer 15

Embryonic derivative of visceral layer of lateral plate mesoderm, some neural crest cells for sphincter and dilater

Molecular commitment — SRF, MRTFs

Question 16

Paraxial mesoderm forms ________ along the spinal cord and somitomeres in the head.

Answer 16

Somites

Question 17

What are the three components of somites?

Answer 17

Dermatome (skin)

Myotome (muscle)

Sclerotome (bone)

Question 18

What is mesenchyme tissue?

Answer 18

Mesenchyme tissue = any loose connective tissue regardless of origin (i.e. neural crest cells)

Question 19

List the parts of the neurocranium:

Answer 19

Membranous (membranes - intramembranous ossification)

Condrocranium

Sutures

Question 20

List the parts of the viscerocranium

Answer 20

Face

Mostly from the frontonasal prominence and the 1st and 2nd pharyngeal arches - neural crest cells

1st arch = maxilla, mandible, malleus, incus

2nd arch - stapes, part of hyoid bone

Question 21

When do the limb buds form?

Answer 21

During the 4th and 5th weeks

Question 22

What specifies the location and type (forelilmb/hindlimb) of limb budding?

Answer 22

HOX genes location

TBX5 specifies forelimb structures

TBX4 specifies hindlimb structures

Question 23

AER

Answer 23

Apical ectodermal ridge - proximodistal growth - FGF’s maintain a rapidly proliferating population of cells adjacent to the ridge - the progress zone

Question 24

ZPA

Answer 24

Zone of polarizing activity - cranial to caudal (anterior-posterior) patterning, thumb to little finger - SHH and retinoic acid - morphogens

Question 25

How do the digits separate during development?

Answer 25

Cell death in ridge

Question 26

What determines bone patterning

Answer 26

HOX genes

Question 27

What clinical issues are associated with limb development?

Answer 27

Amelia - no limbs Meromelia - short limbs Talidomide - limb defects, now an anticancer and anti AIDS drug so we are seeing these limb defects again syndactyly - fused digits brachydactylly - short digits

Question 28

What is the vertebral column derived from?

Answer 28

Somites (slerotome) and notochord (nucleus pulposus) ## Footnote Caudal part of one clerotome fuses with cranial part of another - intersegmental so that muscles bridge the vertebra to act on them - resegmentation

Question 29

What are the two major parts of the skull?

Answer 29

The viscerocranium (face)/Neurocranium(flat bones of the skull from paraxial mesoderm)

Question 30

What do the hypaxia muscles form?

Answer 30

Muscles in the body wall

Question 31

Anywhere there is segmentation in the embryo there are ____ genes:

Answer 31

HOX

Question 32

What upper limb muscles are derived from the VLL that migrate across the lateral somitic frontier?

Answer 32

All distal limb muscles

Question 33

What muscles do the primaxial cells give rise to?

Answer 33

The extrinsic and intrinsic back muscles

Question 34

What gives rise to the spinal ganglia?

Answer 34

The neural crest cells (ganglia composed of cell bodies)

Question 35

What do abaxial/sclerotome form when they cross the lateral somitic frontier?

Answer 35

The ribs

Question 36

What is the relationship between homebox and HOX genes?

Answer 36

All HOX are homeobox genes, not all homeobox are HOX

Question 37

How do vertebrae form from somites?

Answer 37

The caudal half of one fuses with the cranial half of another. ## Footnote This process is called resegmentation

Question 38

What cell population is responsible form forming the neurocranial region?

Answer 38

Paraxial mesoderm

Question 39

What cell population is responsible for forming the viscerocranial region?

Answer 39

Neural crest cells

Question 40

What cell population is responsible for forming the chordal chondrocranium?

Answer 40

The paraxial mesoderm

Question 41

What cell population is responsible for forming the viscero chondrocranium?

Answer 41

Neural crest cells

Question 42

What causes craniusynostosis and achondroplasia?

Answer 42

Mutations in the fibroblast growth factor receptors (FGFRs)

Question 43

What is SALL4?

Answer 43

Transcription factor that regulates FGF. Drugs that interfere with SALL4 during embryogenesis cause birth defects where the fetus has shortened limbs.

Question 44

What gene misregulation causes polydactyly?

Answer 44

SHH

Question 45

What is responsible form the location of limb bud formation?

Answer 45

The HOX genes ## Footnote FGF 10 is expressed in the lateral mesoderm that induces limb bud growth

Question 46

What growth regulation factors does the apical ectrodermal ridge secrete?

Answer 46

FGF4 and FGF8 ## Footnote The flank mesoderm initiates limb outgrowth and causes the AER

Question 47

Where and what is the zone of polarizing activity?

Answer 47

The ZPA secretes SHH and specifies anterior-posterior patterning (i.e. thumb to little finger)