Neurulation and Notogenesis PDF

NEURULATION AND Embryology lec 4 NOTOGENESIS Dr. Eman mohammed Neurulation :is a process in which the embryo develops structures that will.eventually become the nervous system Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural p...

NEURULATION AND Embryology lec 4 NOTOGENESIS Dr. Eman mohammed Neurulation :is a process in which the embryo develops structures that will.eventually become the nervous system Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula. The neural plate folds in upon itself to form the neural tube, which will later differentiate into the spinal cord and the brain, eventually forming the cental nervous system Notogenesis is the development of the notochord by epiblasts that form the.floor of the amnion cavity Notochord development starts during gastrulation (3rd week) by the epiblasts where progenitor cells of notochord are derived start migrating.from the primitive node and pit The notochord is a cellular rod that forms the first longitudinal midline axis around which the vertebral bodies are organized and is the basis for the axial.skeleton It is visible throughout the length of the embryo and around it are layered concentrations of cells, representing the primordia of the future vertebral.bodies : Neurulation occurs in four stages a- transformation of the central portion of the embryonic ectoderm into a thickened neural plate b- shaping and elongation of the neural plate c- bending of the neural plate around a medial groove followed by elevation of the Lateral folds d- closure of the neural tub The process begins when the notochord induces the formation of the central nervous system (CNS) by signaling the ectoderm germ layer above it which thickens and forms the neural plate. Cells of the plate make up the , neuroectoderm and their induction represents the initial event in the process of neurulation , As the neural plate lengthens, its lateral edges elevate to form neural folds. and the depressed midregion forms the neural groove Gradually, the neural folds approach each other in the midline, where they fuse forming the neural tube(the neural tube will later differentiate into the.spinal cord and the brain), eventually forming the central nervous system Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the anterior (cranial) and.posterior (caudal) neuropores respectively  Closure of the cranial neuropores occurs at approximately day 25, whereas the posterior neuropore closes at day 28 Neurulation is then complete, and the central nervous system is represented ,by a closed tubular structure with a narrow caudal portion, the spinal cord and a much broader cephalic portion characterized by a number of dilations which are the brain vesicles Neural crest cells As the neural folds elevate and fuse, cells at the lateral border or crest of the neuroectoderm begin to dissociate from their neighbours.This cell population, the neural crest, will undergo an epithelial-to-mesenchymal transition as it leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm. Neural crest cells are so fundamentally important and contribute to so many organs and tissues that they are sometimes referred to as.the fourth germ layer : Neural crest cells eventually give rise to The dorsal root ganglia- Schwann cells- The autonomic nervous system- Meninges- Sensory ganglia- Bones of the face- Teeth- Lens of the eyes- Melanocytes-.Adrenal medulla &many glands- `