12. Spine, Rib, Sternum Devo Flashcards
How does sclerotome form?
The base of the neural tube and the notochord produce Shh and + other signal molecules–>induce the cells in the ventral half of the somite to undergo an E–>M transformation
How does the sclerotome mesenchyme become a vertebra?
The Precursor tissue for the vertebrae is derived from Sclerotome mesenchyme of the somites in the trunk of the embryo. During the fourth week of development, scleratome mesenchyme is medially displaced/migrates toward the notochord and the neural tube.
What week does scleratome become a vertebrae
4th week
During medial displacement/migration, cells in the cranial (anterior) half of the sclerotome remain ______, while those of the caudal (posterior) half become _______
loosely arranged
condensed or tightly packed.
How does cranial-caudal compartmentalization of scleratome affect spinal nerve fibers
affects the outgrowth of the spinal nerve fibers and the migration of neural crest cells across the sclerotome. Factors secreted by cells in the densely packed compartment prevent crest cells from migrating across this portion of the sclerotome, so they cross via the cranial compartment.
The spinal nerve grows across the
interface between the cranial and caudal compartments.
Scleratome tissue forms vertebrae by a process called
Resegmentation
How does resegmentation occur
caudal half (compartment) of one sclerotome fuses with the cranial half (compartment) of the sclerotome directly below it. Together they form one vertebra
Due to resegmentation… spinal nerves are:
located between adjacent vertebrae, the intersegmental arteries cross the vertebral body and the
muscles formed by the myotome component of the somite attach to processes of adjacent vertebrae.
Pedicle and proximal rib are from which scleratome compartement?
Central
Vertebral body, intervertebral disc are from which scleratome compartement?
Ventral
Dorsal part of neural arch, spinous
process are from which scleratome compartement?
Dorsal
Distal Rib are from which scleratome compartement?
Lateral
Vertebral joints, intervertebral disc,
proximal rib are from which scleratome compartement?
Somatoceal cells
What structures allow a vertebra to grow?
During ossification of the vertebra, a piece of cartilage remains between each neural arch and the centrum. =neurocentral junction. cartilage
allows for longitudinal growth of the vertebra (in the dorsal-ventral axis). The junctions disappears prior to age 10, though some studies suggest a later age.
Ossification unites the centrum and the neural arch.
What controls axial patterning of the vertebrae?
Differential expression of Hox genes along the axis of the embryo mediates regional patterning of the vertebral column in the cranio-caudal axis.
Studies show that combinatorial expression of Hox genes in a nested manner is modulated by
retinoic acid.
What controls dorsal ventral patterning.
Ventralizing signals from the notochord and the
dorsalizing signals from the spinal ganglia
How do the ribs form?
In the thoracic region, the costal processes of the forming vertebra grow ventrolaterally forming the Ribs. Ribs are derived from sclerotome mesenchyme.
Ribs are derived from
sclerotome mesenchyme.
How does the Sternum form?
Pair of vertically oriented bands of condensed mesenchyme, Sternal Bars, appear in the Somatic Mesoderm forming the ventral body wall of the thorax.
The sternal bars fuse in the midline and develop chondrogenic centers. Additional centers form the manuibrum of the sternum.
Several primary ossification centers form within the cartilage model of the sternum form temporary segments called Sternebrae, the most inferior of which will become
the
xiphoid process.
short neck, a low hairline, and restricted neck
movements. In most cases the number of cervical vertebral bodies is less
than normal.
Klippel Feil sequence
Associated anomalies of Klippel Feil sequence
undescended scapula, cervical rib and scoliosis (60%), urinary tract, CNS, cardiopulmonary, hand and
hearing defects.
Cause of Kleppel Feil Sequence
defect of abnormal Hox gene expression due to abnormal signaling.
family of anomalies featuring defects in
vertebrae and often the nervous system. Failure of fusion of the halves of the vertebral arch is the characteristic vertebral defect.
Spina Bifida
result from the extension of the costal
processes of cervical or lumbar vertebrae.
Accessory Ribs T
Accessory Ribs usually don’t cause issues unless a cervical rib on C7 in involved because
can put traction on the lower trunk of the brachial plexus or compress the subclavian artery.
Vertebra with a wedge shaped body that sets up an imbalance in the spine often
resulting in scoliosis.
A Hemivertebrae
Hemivetebrae results from
results from failure of one of the chondrification centers of the centrum to form.
term used when many vertebrae have unfused spinous processes.
Rachischisis
condition where a sacral vertebra fails to fuse with the sacrum and remains free as a sixth lumbar vertebra. This
increases the lever arm of the spine.
Lumbarization
The congenital form of scoliosis is often caused by a
hemivertebra.
due to abnormal fusion of the sternal bars in the midline. This usually occurs at the inferior end of the
sternum.
Sternal Clefts
What do sternal clefts result in:
A concave depression of the sternum is called Precuts
Excavate, while a convex or keel-shaped elevation of the sternum is termed Precuts Cranium.
