Musculoskeletal System Development

Question 1

Skele muscle fibers arise from ___

Answer 1

Specific myoblasts lines in paraxial mesoderm

Question 2

In the head, most skeletal muscles derive from ___

Answer 2

Myoblasts from somitomeres

Question 3

Skeletal muscles of body wall and limbs derive from ____

Answer 3

Myoblasts of myotomes

Question 4

Innervation of somites

Answer 4

. Single spinal n. Innervates each somites

. Tissue arising from that somite pulls spinal innervation with it when it migrates

Question 5

Each myotome splits into ___ components

Answer 5

. Dorsal (epimere)

Ventrolateral (hypomere)

Question 6

Dorsal myotome cells

Answer 6

. Remain in midline to form intrinsic back mm.

. Innervated by dorsal rami of spinal nn.

Question 7

Ventrolateral myotome cell path

Answer 7

. Migrate into somatic layer of lateral plate mesoderm
. Give rise to musculature of the ventrolateral body wall (intercostal and abdominal mm.) and limbs
. Innervated by ventral rami of spinal nn.

Question 8

Somitomeres

Answer 8

. In head
. Forms mm. Of mastication, facial expression, palate, pharynx, and larynx
. Extra-ocular eye mm.

Question 9

Occipital myotomes

Answer 9

Form tongue mm.

Question 10

Paraxial mesoderm components for skeleton development

Answer 10

. Somitomeres: post. Half of skull from chondroblasts and osteoblasts here
. Sclerotome: vertebrae, ribs, discs, bones of post. Skull from chondroblasts and osteoblasts from here

Question 11

Somatic later of lat. plate mesoderm components for skeleton development

Answer 11

. Gives rise to chondroblasts that form precursors of bone of shoulder and pelvic girdles, appendicular skeleton, and sternum

Question 12

Neural crest mesenchyme contribution to skeletal development

Answer 12

. Gives rise to chondroblasts and osteoblasts that form bones of ant. Skull, face, and middle ear cavity

Question 13

Formation of vertebral column occurs by ____

Answer 13

Resegmentation of the sclerotome

Question 14

Development of vertebral column

Answer 14

. Week 4: sclerotome cells surround neural tube and notochord
. Caudal half each sclerotome grows into cranial half of subadjacent one
. Each vertebra from cranial half of one sclerotome and caudal half of another
. R/L vertebral arch cartilages surround neural tube and fuse to form vertebral canal and spinous processes
. Mesenchymal tissue btw caudal and cranial portions of each sclerotome forms intervertebral disc
. Portions of notochord persist as primary nucleus pulposus

Question 15

What occurs with limb buds in week 4 of development?

Answer 15

. Develop as outgrowths of ventrolat. Body wall
. Regulated by biomolecular signaling btw surface ectoderm and underlying mesoderm
. Somatic lat. plate mesoderm proliferates and causes ectoderm to bulge out
. Upper limbs develop 1-2 days earlier than lower limbs

Question 16

Signaling molecule in upper limb development

Answer 16

Tbx-5

Question 17

Signaling molecules in lower limb development

Answer 17

Thx-4

Question 18

Hemivertebrae

Answer 18

. Wedge-shaped vertebrae

. Can produce abnormal curvature of the spine

Question 19

Block vertebrae

Answer 19

. Occur from improper re-segmentation
. Parts of or entire vertebrae fuse together
. Can lead to blocking or stretching of n. Root exiting from that segment and neurological problems
. Sacrum is normal blocked vertebrae

Question 20

Holt-oram syndrome

Answer 20

. Mutation in tbx-5 gene

. Heart abnormalities and upper limb deformities (finger-like or absent thumbs)

Question 21

Proximal-distal axis of limb development

Answer 21

. Apical ectodermal ridge (AER) interacts w/ progress zone (limb bud mesoderm) that promotes outgrowth of limb
. Mesoderm cells further from influence of progress zone (closer to trunk) differentiate into cartilage, muscle, and blood vessels first
. Cells closer to tip of bud remain undifferentiated longer and continue proliferating

Question 22

Apical ectodermal ridge

Answer 22

. Ridge of thickening ectoderm located along AP plane of apex of limb bud

Question 23

Preaxial-postaxial axis in limb development

Answer 23

. Cranial to caudal (digit I to V)
. Preaxial border (digit 1) of each limb faces craniallt and postaxial faces caudally prior to week 7 (AP axis)
. Patterning and growth regulated by zone of polarizing activity

Question 24

Zone of polarizing activity

Answer 24

. Cluster of cells located on post. Border of limb close to trunk
. Express sonic hedgehog (shh) and retinoic acid that identifies nearby cells as posterior
. Cells located farther from ZPA and shh and retinoic acid gradient identify as anterior

Question 25

Dorsal-ventral axis of limb development

Answer 25

Dorsum of hand/foot to palm/sole . Wnt-7a expressed in dorsal ectoderm induces expression of Lmx1 in underlying mesenchyme that identifies cells as dorsal . Ventral limb bud ectoderm produces engrailed-1 which represses Wnt-7a and lmx1 . Apical ectodermal ridge marks border btw dorsal and ventral limb bud ectoderm

Question 26

Cartilaginous precursors to long bones appear as ____

Answer 26

. Condensations of mesenchyme in central core of prox. Part of limb . Cartilage will undergo endochondral ossification

Question 27

Differentiation of cartilaginous skeleton occurs ____

Answer 27

. Proximal to distal | . Postaxial to preaxial

Question 28

Cartilaginous rods dissolves around ____

Answer 28

Future synovial joints | . In-utero muscular activity is required to maintain integrity of joint

Question 29

What is derived from somatic lateral plate mesoderm?

Answer 29

Somatic lateral plate mesoderm

Question 30

Terminal portions of the limb bud flattens to form ____

Answer 30

Hand and foot plates

Question 31

Digital rays

Answer 31

. Mesenchyme condensations from hand and foot plates | . Precursors to digits

Question 32

What occurs in digit development in weeks 6-7?

Answer 32

. Selective apoptosis in plates to create 5 separate digits

Question 33

Absence of interdigital apoptosis results in _____

Answer 33

Syndactyly

Question 34

Pre-myoblasts from somite pairs ____ migrate into developing upper limb bud

Answer 34

9-13

Question 35

Pre-myoblasts from somite pairs ____ migrate into developing lower limb bud

Answer 35

26-32

Question 36

Ventral mass of pre-myoblasts will become ____

Answer 36

Flexor mm. Of limb

Question 37

In upper limb, flexor mm. Innervated by ____

Answer 37

. Anterior division nn. Of brachial plexus

Question 38

In lower limb, flexor mm. Are innervated by ___

Answer 38

. Anterior division of lumbosacral plexus

Question 39

Dorsal mass of pre-myoblasts will become ___

Answer 39

Extensors mm. Of limb

Question 40

In upper limb, extensor mm. Are innervated by ___

Answer 40

Posterior division of brachial plexus

Question 41

In lower limb, extensor mm. Are innervated by ___

Answer 41

Posterior division of lumbosacral plexus

Question 42

Repositioning of limb buds

Answer 42

. Initially limbs project anterolat. From body wall . Flexor surface ventral, extensor dorsal, preaxial cranial, postaxial caudal . Limb buds migrate med. to lie in sagittal plane . Upper limbs rotate 90 degrees lat. along long axis so elbow faces post. And thumb is lat. . Lower limb rotates 90 degrees med. on long axes so knees face ant. And digit 1 is med.

Question 43

Achondroplasia

Answer 43

. Mutation in fibroblasts Roth factor receptor 3 . Causes abnormal cartilage formation that effects endochondral ossification . Results in shortened, bowed limbs and shortened skull base . 1:15,000 births

Question 44

Osteogenesis imperfecta

Answer 44

. Mutations in gene that products type I colllagen . Results in hypermineralization of bone . Inc. fractures, shortening and bowing of long bones

Question 45

Amelia

Answer 45

Absence of limb due to disruption of limb bud development

Question 46

Meromelia

Answer 46

. Partial absence of limb due to disturbance in differentiation or growth of limb

Question 47

Phocomelia

Answer 47

. Absence of long bones | . Limbs characterized by ill-formed hands/feet attached to trunk

Question 48

Hemimelia

Answer 48

. Partial absence of distal part of limb

Question 49

Clubfoot

Answer 49

1 : 1,000 births , cause unknown but may include congenital joint contracture from neurologic or soft tissue defects, bone or cartilage defects, and cramped intrauterine conditions

Question 50

Cleft hand or foot

Answer 50

. Lobster claw deformity . Abnormal cleft btw 2nd and 4th metacarpal bones and soft tissue w/ fusion of digits I/II and IV/V due to molecular signaling errors

Question 51

Amniotic band syndrome

Answer 51

. Strands of amnion separate and wrap around digits or other parts of limbs resulting in restriction of movement or amputation of structure

Question 52

Most sensitive time period for teratogens in limb development?

Answer 52

. Days 24-36 (weeks 4-5) | . More severe effects from exposure at early end of time window