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Somite Development - Anatomy & Physiology (view source)
Revision as of 14:28, 29 August 2008
, 14:28, 29 August 2008→Somite Maturation
*Somites are simple at this stage, with epithelial cells surrounding an inner cavity that is filled with mesenchymal pre - somitic mesoderm cells. These cells are called '''somitocoel cells'''.
*Somites are simple at this stage, with epithelial cells surrounding an inner cavity that is filled with mesenchymal pre - somitic mesoderm cells. These cells are called '''somitocoel cells'''.
*All cells are undergoing mitosis.
*All cells are undergoing mitosis.
===Somites IV - X===
*Epithelial cells on the ''dorsal'' aspect of the somite develop into the dermomyotome.
*Epithelial cells of the ''ventral - medial'' portion of the somites develop into the sclerotome.
**Cells undergo an epithelial to mesenchymal transition.
**Somitocoel cells join these new mesenchymal cells to also become part of the sclerotome.
*The prospective sclerotome migrates to surround the notochord and neural tube.
*''The scelerotome needs to be at the midline to form the vertebrae.''
===Somites VI Onward===
*At the dorsal aspect of the somite, some cells of the dermomyotome are ingressing to form a new layer between the dermomytome and sclerotome; the '''myotome'''.
*Ingression occurs at two points; ventral - laterally and dorsal - medially.
:'''Ventral - lateral ingression develops into ''hypaxial muscle''. This forms muscle of the body and limb.'''
:'''Dorsal - medial ingression develops intp the ''epaxial muscle''. This forms the muscles of the dorsum.'''
*Myotomal cells do not have the ability to undergo mitosis. To increase cell numbers, cells are recruited from the dermomyotome.
*After all the myotomal cells have ingressed what remains of the dermomyotome becomes the dermotome.
*''The dermotome, which lies dorsally in the somite, forms the dermis.''
===Somites XI Onward===
*The sclerotome surrounds the notochord and breaks it down.
*''Thus far, somite development has been segmented. Cells need to be adjacent to each other to function appropriately, so the sclerotome, in the ventral part of the somite, resegments.''
#A fissure develops in the middle of the sclerotome, dividing each somite into an anterior and posterior portion.
#The anterior portion of one somite unites with the posterior portion of the adjacent somite - '''resegmentation'''.
#*But; because only the sclerotome resegments, the muscle derived from the myotome remains to unite the original anterior and posterior pairs together.
#The sclerotome surrounds the neural tube and differentiates firstly to cartilage and secondly bone. It forms the vertebrae.
==Species Differences==
==Species Differences==