Dr. Indran Development of Skeletal System Flashcards
What are the sources of origin of the skeltal system
§Paraxial mesoderm
§Somatic layer/parietal layer of lateral plate mesoderm
§Neural crest cells
______ cells become ______, the embryonic connective tissue
Sclerotome
mesenchyme
8.5.6
Mesenchyme in the _______ transforms to form the bony elements of the vertebral column and ribs
Mesenchyme in the _______ will transform to form the pectoral and pelvic girdles, and the bones of the upper and lower limbs
sclerotome
somatic mesoderm
What are the two types of ossification?
Intramembranous:
The mesenchymal tissue will directly transform into bone forming cells to lay down bone
Ex: Skull bones, Bones of the face
**Endochondral:
The mesenchymal tissue will first give rise to a cartilaginous model of the bone:
The cartilage model will then ossify to from bone
Ex: long bones, irregular bones like vertebrae etc
Development of the axial skeleton comes from the paraxial mesoderm except for?
Sternum (lateral)
8.5.6
During 4th week, ______ cells migrate around the spinal cord and notochord to merge with cells from the opposite somite on the other side of neural tube
(blue dots)
How does sclerotome resegment and what regulates it?
The caudal half of each sclerotome grows into and fuses with the cephalic half of each subjacent sclerotome
Thus, each vertebra is formed from combination of caudal half of one sclerotome and cranial half of its neighbor
Hox genes
How do spinal nerves become intrasegmental initially?
With splitting and recombination of sclerotomes the originally segmental (intrasegmental) spinal nerves that sprout from each segmental neural tube, become intersegmental
Mesenchymal cells between cephalic and caudal parts of the original sclerotome segment do not proliferate but fill the space between two vertebral bodies: Fibrous part of the intervertebral disc
As the vertebrae form, two primary curves of the spine are established (thoracic and sacral curvatutures)
The ______ forms the nuleus pulposus, how does that work?
8.5.6
Notochord
Notochord present inside vertebral body degenerates, whereas notochord present between vertebrae persists and forms nucleus pulposus
_____ is when mesenchymal cells from one sclerotome fail to migrate, resulting in lateral curving of the spine (scoliosis)
Hemivertebra
*** _____ occurs due to imperfect fusion or non-union of vertebral arches around a part of the spinal cord
____ is mild and most common
______ is when the posterior neuropore does not close, meninges come out through the gap, but spinal cord lies at its normal position
____ is when meninges and spinal cord both come out through the gap
Spina bifida
Spina Bifida Occulta:
Involve only the bony vertebral arches, leaving the spinal cord intact, Bony defect is covered by skin, A dimple, birthmark or hairy patch covering the area, No neurological deficits occur
Spina bifida cystica (meningocele)
MENINGOMYELOCELE
______ results from fusion and shortening of cervical vertebrae
Klippel-Feil Anomaly
Results in:
Shortening of the neck
Limited movement of the neck
Low hair-line
_____ is classified as dysplasic (congenital), isthmic (stress fracture), degenerative, or traumatic changes of the spine
This defecr may allow anterior (forward) displacement or slippage of the vertebra which is called _______
spondylolysis/spondylolisthesis
spondylolisthesis
A spondylolysis in a child or adolescent most commonly results from a defective formation of the pedicle
Explain the image
Congenital Spondylolisthesis:
Pedicles of vertebral arches fail to fuse with the vertebral body
Vertebral body slips forward with respect to vertebrae below it
Causes lordosis
Most common in lower lumbar region (L5-S1)
_____ is when either a benign or malignant tumor that arises from remnants of notochord
Chordorma
Most of them lie in the base of the skull, extending to nasopharynx
Can occur in lumbosacral region
****______ happens when the nucleus pulposus prolapses into the vertebral canal through the defective annulus fibrosus
Intervertebral Disc Herniation
How doe the ribs develop?
¨Ribs develop from the sclerotome in the thoracic region
¨Bony part is derived from central and lateral sclerotome (costal process) cells
¨Sclerotome cells that migrate into the lateral plate mesoderm form costal cartilages
¨Sternum develops from the ______
somatic mesoderm
¨Two sternal bars form on either side of the midline
¨These later fuse to form the cartilaginous model of the manubrium, sternebrae (body) and the xiphoid process
_____ is a depressed sternum, sunken posteriorly ***
_____ is when the sternum protrudes like a keel
Pectus exacvatum
Pectus Carinatum
8.5.6
Development of the muscle overview
True or False: ¨Each myotome receives its innervation from spinal nerves derived from the same segment as the muscle cells
8.5.6
8.5.6
How does the development of trunk muscles work?
Epaxial Cells:
Form extensor muscles of vertebral column (erector spinae , tranverse spinalis)
Supplied by dorsal rami
Hypaxial Cells:
Form antero-lateral muscles of the body wall and muscles of the limbs
Supplied by ventral rami
_____ is progressive muscle weakness and wasting, X-linked recessive disorder caused by a mutation in the gene for dystrophin on the short arm of chromosome X, Dystrophin attaches actin to laminin in the external lamina, common in males
____ is less severe form compared to DMD, late onset (8 to 25 years of age)
Duchenne muscular dystrophy (DMD)
Becker muscular dystrophy (BMD)
____ is underdevelopment or absence of chest muscles on one side of the body
Poland syndrome
¨Absence of the pectoralis minor and partial loss of the pectoralis major
¨Nipple and areola are absent or displaced
¨Associated with webbing of fingers of the hand on the same side:
¨syndactyly (fused digits)
brachydactyly (short digits
_____ is partial or complete absence of abdominal muscles
Prune belly syndrome
¨Abdominal wall is so thin, organs are visible and easily palpable
¨Associated with malformations of the urinary tract and bladder
¨Caused by non- migration/underdevelop-ment of myoblasts in the hypaxial myotomes
How does limb development occur? ***
8.5.6
How does AER help with limb outgrowth?
Limb outgrowth is initiated by the apical ectodermal ridge (AER) at the tip of the limb buds
Proceeds from proximal (i.e. shoulder or hip) to distal (i.e. hand or foot)
This process is absolutely dependent on FGF signaling from the AER
Any disruption to FGF signaling and/or formation and maintenance of the AER will result in arrested limb development
