Somites and the Typical Body Segment Flashcards
somites
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
role of somites
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
segmentation
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
regionalization
differentiation of body segments through further development
elements of TBS
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
three divisions of the mesoderm
lateral plate
intermediate
paraxial columns
What tissues do somites arise from
paraxial columns
order of somites from head to tail
occipital, cervical, thoracic, lumbar, sacral, coccygeal
What are two molecular signals that leads to the formation of somites?
Notch pathway and FGF gradient
three components of a somite
dermatome, myotome, and sclerotome
What does the dermatome become?
becomes the skin
What does the myotome become?
becomes the muscles
What does the scerotome become?
becomes the bertebrae and parts of the ribs
two components of the myotome
epimere (dorsal) and hypomere (ventral)
epimere innervation and differentiation
dorsal, innervated by the dorsal ramus of spinal nerve
differentiates into the muscle groups of the back including the erector spinae, slenius, and transversopinalis
hypomere innervation and differentiation
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)
Describe the process of vertebrae formation from the sclerotome.
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
respecification of the sclerotome to form vertebrae
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
scoliosis
abnormal lateral curvature of the spine
spondylocostal dysostosis
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
intervertebral disc
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
What are the different regions of vertebrae and what are some genes that drive the regionalization?
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
