Musculoskeletal System Development Flashcards
Skele muscle fibers arise from ___
Specific myoblasts lines in paraxial mesoderm
In the head, most skeletal muscles derive from ___
Myoblasts from somitomeres
Skeletal muscles of body wall and limbs derive from ____
Myoblasts of myotomes
Innervation of somites
. Single spinal n. Innervates each somites
. Tissue arising from that somite pulls spinal innervation with it when it migrates
Each myotome splits into ___ components
. Dorsal (epimere)
Ventrolateral (hypomere)
Dorsal myotome cells
. Remain in midline to form intrinsic back mm.
. Innervated by dorsal rami of spinal nn.
Ventrolateral myotome cell path
. 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.
Somitomeres
. In head
. Forms mm. Of mastication, facial expression, palate, pharynx, and larynx
. Extra-ocular eye mm.
Occipital myotomes
Form tongue mm.
Paraxial mesoderm components for skeleton development
. Somitomeres: post. Half of skull from chondroblasts and osteoblasts here
. Sclerotome: vertebrae, ribs, discs, bones of post. Skull from chondroblasts and osteoblasts from here
Somatic later of lat. plate mesoderm components for skeleton development
. Gives rise to chondroblasts that form precursors of bone of shoulder and pelvic girdles, appendicular skeleton, and sternum
Neural crest mesenchyme contribution to skeletal development
. Gives rise to chondroblasts and osteoblasts that form bones of ant. Skull, face, and middle ear cavity
Formation of vertebral column occurs by ____
Resegmentation of the sclerotome
Development of vertebral column
. 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
What occurs with limb buds in week 4 of development?
. 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
Signaling molecule in upper limb development
Tbx-5
Signaling molecules in lower limb development
Thx-4
Hemivertebrae
. Wedge-shaped vertebrae
. Can produce abnormal curvature of the spine
Block vertebrae
. 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
Holt-oram syndrome
. Mutation in tbx-5 gene
. Heart abnormalities and upper limb deformities (finger-like or absent thumbs)
Proximal-distal axis of limb development
. 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
Apical ectodermal ridge
. Ridge of thickening ectoderm located along AP plane of apex of limb bud
Preaxial-postaxial axis in limb development
. 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
Zone of polarizing activity
. 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
Dorsal-ventral axis of limb development
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
Cartilaginous precursors to long bones appear as ____
. Condensations of mesenchyme in central core of prox. Part of limb
. Cartilage will undergo endochondral ossification
Differentiation of cartilaginous skeleton occurs ____
. Proximal to distal
. Postaxial to preaxial
Cartilaginous rods dissolves around ____
Future synovial joints
. In-utero muscular activity is required to maintain integrity of joint
What is derived from somatic lateral plate mesoderm?
Somatic lateral plate mesoderm
Terminal portions of the limb bud flattens to form ____
Hand and foot plates
Digital rays
. Mesenchyme condensations from hand and foot plates
. Precursors to digits
What occurs in digit development in weeks 6-7?
. Selective apoptosis in plates to create 5 separate digits
Absence of interdigital apoptosis results in _____
Syndactyly
Pre-myoblasts from somite pairs ____ migrate into developing upper limb bud
9-13
Pre-myoblasts from somite pairs ____ migrate into developing lower limb bud
26-32
Ventral mass of pre-myoblasts will become ____
Flexor mm. Of limb
In upper limb, flexor mm. Innervated by ____
. Anterior division nn. Of brachial plexus
In lower limb, flexor mm. Are innervated by ___
. Anterior division of lumbosacral plexus
Dorsal mass of pre-myoblasts will become ___
Extensors mm. Of limb
In upper limb, extensor mm. Are innervated by ___
Posterior division of brachial plexus
In lower limb, extensor mm. Are innervated by ___
Posterior division of lumbosacral plexus
Repositioning of limb buds
. 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.
Achondroplasia
. 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
Osteogenesis imperfecta
. Mutations in gene that products type I colllagen
. Results in hypermineralization of bone
. Inc. fractures, shortening and bowing of long bones
Amelia
Absence of limb due to disruption of limb bud development
Meromelia
. Partial absence of limb due to disturbance in differentiation or growth of limb
Phocomelia
. Absence of long bones
. Limbs characterized by ill-formed hands/feet attached to trunk
Hemimelia
. Partial absence of distal part of limb
Clubfoot
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
Cleft hand or foot
. 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
Amniotic band syndrome
. Strands of amnion separate and wrap around digits or other parts of limbs resulting in restriction of movement or amputation of structure
Most sensitive time period for teratogens in limb development?
. Days 24-36 (weeks 4-5)
. More severe effects from exposure at early end of time window
