University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

344

Pages:

3
Author:

Mariam A.

Vertebrae Embryology          Form from the sclerotome portions of the somites, which are derived from PA mesoderm. Mesenchymal cells migrate around the spinal cord and notochord to merge with cells from the opposing somite on the other side of the neural tube. Each scelerotome level has cranial loose and caudal dense packed layer. Caudal half of one sclerotome grows and fuses with the cranial loose layer of the one below to form the vertebral body (centrum). Mesenchymal cells between the caudal and cranial parts of the original sclerotome segment do not proliferate but fill the space between two precartilagenous vertebral bodies, forming the intervertebral discs. Although notochord regresses in the formation of the final spinal cord, it actually persists and enlarges in the region of the intervertebral discs. Here, it forms the nucleus pulposus which is later surrounded by circular fibres of the annulus fibrosus. Mesenchymal cells around neural tube become neural (vertebral) arch. Mesenchymal cells in body wall become costal process (T1-12) to attach onto the ribs. HOX genes specifically differentiates the somite pattern. Neural tube  Neural plate appears at the beginning of the 3rd week as a slippershaped plate of thickened ectoderm, in the mid-dorsal region in front of the primitive node. Lateral edges elevate to form the neural folds.    With further development, neural folds continue to elevate, approach each other in the midline, and finally fuse to form the neural tube. o Fusion begins in the cervical region and proceeds in cranial and caudal directions. Closure of the neural tube. o Open ends of the neural tubes form the cranial and caudal neuropores that communicate with the overlying amniotic cavity. o Closure of the cranial neurospore proceeds cranially from the initial closure site in the cervical region and from a site in the forebrain that forms later. o This later site proceeds cranially, to close the rostral-most region of the neural tube, and caudally to meet advancing closure from the cervical site. o Closure of the caudal neurospore occurs approximately 3 days after the closure of cranial neurospore (25th day). There are three primary brain vesicles in the cephalic end of the neural tube: o Prosencephalon (forebrain): telencephalon (formed by a midportion and two lateral outpocketings, the primitive cerebral hemispheres) and the diencephalon (characterised by outgrowth of the optic vesicles). o Mesencephalon (midbrain): separated from the rhombencephalon by the rhombencephalic isthmus. o Rhombencephalon (hindbrain): metencephalon (later forms the pons and cerebellum) and the myelencephalon. Boundary between the two portion is marked by the pontine flexure.   Lumen of the spinal cord, the central canal, is continuous with the brain vesicles. Ventricle distribution. o Cavity of the rhombencephalon = 4th ventricle. o Cavity of the diencephalon = 3rd ventricle. o Cavity of cerebral hemispheres = lateral ventricles. o 3rd and 4th ventricles are connected by the lumen of the mesencephalon, which later becomes very narrow as the aqueduct of Sylvius. o Each lateral ventricle communicates with the 3rd ventricle through the interventricular foramina of Monro.