12. Spine, Rib, Sternum Devo

Question 1

How does sclerotome form?

Answer 1

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

Question 2

How does the sclerotome mesenchyme become a vertebra?

Answer 2

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.

Question 3

What week does scleratome become a vertebrae

Answer 3

4th week

Question 4

During medial displacement/migration, cells in the cranial (anterior) half of the sclerotome remain ______, while those of the caudal (posterior) half become _______

Answer 4

loosely arranged

condensed or tightly packed.

Question 5

How does cranial-caudal compartmentalization of scleratome affect spinal nerve fibers

Answer 5

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.

Question 6

The spinal nerve grows across the

Answer 6

interface between the cranial and caudal compartments.

Question 7

Scleratome tissue forms vertebrae by a process called

Answer 7

Resegmentation

Question 8

How does resegmentation occur

Answer 8

caudal half (compartment) of one sclerotome fuses with the cranial half (compartment) of the sclerotome directly below it. Together they form one vertebra

Question 9

Due to resegmentation… spinal nerves are:

Answer 9

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.

Question 10

Pedicle and proximal rib are from which scleratome compartement?

Answer 10

Central

Question 11

Vertebral body, intervertebral disc are from which scleratome compartement?

Answer 11

Ventral

Question 12

Dorsal part of neural arch, spinous

process are from which scleratome compartement?

Answer 12

Dorsal

Question 13

Distal Rib are from which scleratome compartement?

Answer 13

Lateral

Question 14

Vertebral joints, intervertebral disc,

proximal rib are from which scleratome compartement?

Answer 14

Somatoceal cells

Question 15

What structures allow a vertebra to grow?

Answer 15

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.

Question 16

What controls axial patterning of the vertebrae?

Answer 16

Differential expression of Hox genes along the axis of the embryo mediates regional patterning of the vertebral column in the cranio-caudal axis.

Question 17

Studies show that combinatorial expression of Hox genes in a nested manner is modulated by

Answer 17

retinoic acid.

Question 18

What controls dorsal ventral patterning.

Answer 18

Ventralizing signals from the notochord and the

dorsalizing signals from the spinal ganglia

Question 19

How do the ribs form?

Answer 19

In the thoracic region, the costal processes of the forming vertebra grow ventrolaterally forming the Ribs. Ribs are derived from sclerotome mesenchyme.

Question 20

Ribs are derived from

Answer 20

sclerotome mesenchyme.

Question 21

How does the Sternum form?

Answer 21

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.

Question 22

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

Answer 22

xiphoid process.

Question 23

short neck, a low hairline, and restricted neck
movements. In most cases the number of cervical vertebral bodies is less
than normal.

Answer 23

Klippel Feil sequence

Question 24

Associated anomalies of Klippel Feil sequence

Answer 24

undescended scapula, cervical rib and scoliosis (60%), urinary tract, CNS, cardiopulmonary, hand and
hearing defects.

Question 25

Cause of Kleppel Feil Sequence

Answer 25

defect of abnormal Hox gene expression due to abnormal signaling.

Question 26

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.

Answer 26

Spina Bifida

Question 27

result from the extension of the costal

processes of cervical or lumbar vertebrae.

Answer 27

Accessory Ribs T

Question 28

Accessory Ribs usually don’t cause issues unless a cervical rib on C7 in involved because

Answer 28

can put traction on the lower trunk of the brachial plexus or compress the subclavian artery.

Question 29

Vertebra with a wedge shaped body that sets up an imbalance in the spine often
resulting in scoliosis.

Answer 29

A Hemivertebrae

Question 30

Hemivetebrae results from

Answer 30

results from failure of one of the chondrification centers of the centrum to form.

Question 31

term used when many vertebrae have unfused spinous processes.

Answer 31

Rachischisis

Question 32

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.

Answer 32

Lumbarization

Question 33

The congenital form of scoliosis is often caused by a

Answer 33

hemivertebra.

Question 34

due to abnormal fusion of the sternal bars in the midline. This usually occurs at the inferior end of the
sternum.

Answer 34

Sternal Clefts

Question 35

What do sternal clefts result in:

Answer 35

A concave depression of the sternum is called Precuts

Excavate, while a convex or keel-shaped elevation of the sternum is termed Precuts Cranium.