Somites and the Typical Body Segment

Question 1

somites

Answer 1

contain the precursor cells for the vertebrae and parts of ribs, the striated musculatore of the neck, trunk and extremities, and the subcutaneous tissue and skin

Question 2

role of somites

Answer 2

responsible for the segmental organization of the embryo

the correct partitioning of the spine, neural tube, trunk wall, and the thorax (ribs) depends on the orgered arrangement of the somite

Question 3

segmentation

Answer 3

the wall of the abdomen and thorax is organized like a stack of similarly structured circles

this is because embryologically each segment is derived from a somite, a repeating structure of the embryo

Question 4

regionalization

Answer 4

differentiation of body segments through further development

Question 5

elements of TBS

Answer 5

spinal cord and the vertebral column

columns of epaxial and hypaxial muscle

spinal nerves: dorsal and ventral rami

major blood vessels in the dorsal wall of the celom

the gut (and its derivatives) hangs in the middle of the celom suspended by a double fold of celomic lining (dorsal mesentary)

celomic cavity and its linings

Question 6

three divisions of the mesoderm

Answer 6

lateral plate

intermediate

paraxial columns

Question 7

What tissues do somites arise from

Answer 7

paraxial columns

Question 8

order of somites from head to tail

Answer 8

occipital, cervical, thoracic, lumbar, sacral, coccygeal

Question 9

What are two molecular signals that leads to the formation of somites?

Answer 9

Notch pathway and FGF gradient

Question 10

three components of a somite

Answer 10

dermatome, myotome, and sclerotome

Question 11

What does the dermatome become?

Answer 11

becomes the skin

Question 12

What does the myotome become?

Answer 12

becomes the muscles

Question 13

What does the scerotome become?

Answer 13

becomes the bertebrae and parts of the ribs

Question 14

two components of the myotome

Answer 14

epimere (dorsal) and hypomere (ventral)

Question 15

epimere innervation and differentiation

Answer 15

dorsal, innervated by the dorsal ramus of spinal nerve

differentiates into the muscle groups of the back including the erector spinae, slenius, and transversopinalis

Question 16

hypomere innervation and differentiation

Answer 16

ventral, innervated by ventral ramus of spinal nerve

differentiates into the body wall and limb muscles

has three layers that correspond to external, internal, and innermost intercostals (and abdominals)

Question 17

Describe the process of vertebrae formation from the sclerotome.

Answer 17

sclerotome tissue surrounds the neural tube and notochord and ossifies around these structures

the cranial and caudal halves of a sclerotome split and merge with adjacent sclerotomes

the part of the notochord that is captured within the vertebral bodies disappears, and the part that remains between the vertebrae becomes the nucleus pulposus of the intervertebral disc

Question 18

respecification of the sclerotome to form vertebrae

Answer 18

as the spinal nerves grow out to innervate the muscles, the cranial segment of one vertebrae combines with the caudal segment of the vertebrae above to form a vertebra

muscles attach to two adjecent vertebrae which facilitates movement between them

Question 19

scoliosis

Answer 19

abnormal lateral curvature of the spine

Question 20

spondylocostal dysostosis

Answer 20

a group of conditions characterized by abnormal development of bones int he spine and ribs

bones of the spine are mishappen and abnormally joined together

abnormal side-to-side curvature do to malformation of the vertebrae, rib bones fused together or missing, short bodies with normal length arms and legs, called short-trunk dwarfism

Question 21

intervertebral disc

Answer 21

acts as a shock absorber and mediates movement between vertebral bodies

arises from the parts of the notochord caught inbetween the developing vertebrae, which becomes the nucleus pulposus

Question 22

What are the different regions of vertebrae and what are some genes that drive the regionalization?

Answer 22

cervical - high retinoic acid, lof FGF

thoracic - driven by HOX-c6

lumbar - driven by HOX-d10

sacral - Hox-d12

coccygeal - Hox-d12 and high FGF, low retinoic acid