Neurulation & Folding Handout PDF
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Uploaded by inspireeAcademy
Mansoura University
Dr. Hend M. Hassan
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Summary
This handout (Neurulation and Folding) provides an overview of the third week of development, focusing on neurulation. It details the events, process, and fate of the neural tube and crest along with potential anomalies. Key concepts like primitive streak formation, notochord development, and neural folding are explained, along with the derivatives of the neural tube and neural crest cells, which involve ganglia formation, pia mater, spinal cord development and more.
Full Transcript
Semester 1 Neurulation & Folding Dr. Hend M. Hassan The Third Week of Development Events: 1. Primitive streak formation (15th – 16th days). 2. Gastrulation. 3. Notochord formation. 4. Differentiation of the three germ layers. 5...
Semester 1 Neurulation & Folding Dr. Hend M. Hassan The Third Week of Development Events: 1. Primitive streak formation (15th – 16th days). 2. Gastrulation. 3. Notochord formation. 4. Differentiation of the three germ layers. 5. Neurulation. 5. Neurulation ▪ The process of development of the nervous system. ▪ The notochord is the inducer for neurulation. Process: The central part of the ectoderm (lying above the developing Notochord) thickens to form a neural plate. Elevation of the edges of the neural plate forms neural folds and the central depressed part forms a neural groove. Neural folds start fusion in the craniocaudal direction to form neural tube. The neural crest is a portion of the lateral margins of the neural plate at its junction with the rest of the ectoderm. 1 Semester 1 Neurulation & Folding Dr. Hend M. Hassan Fate: On the 25th day, the cranial neuropore closes, whereas on the 27th day, the caudal neuropore closes. Derivatives: 1. Neural tube: The upper part dilates to form the brain vesicle. The lower part elongates to form the spinal cord. 2. Neural Crest cells: Ganglia: (sensory, sympathetic, parasympathetic & spinal) Pia and arachnoids mater. Schwan cells. Chromaffin cells which give the suprarenal medulla. Melanocytes: pigment cells of the skin. 2 Semester 1 Neurulation & Folding Dr. Hend M. Hassan Anomalies of neural tube (neural tube defects): 1. Anencephaly: Cause: Failure of closure of the cranial neuropore. Features: Absent skull. Absent most of the brain parts. Incompatible with life. 2. Spina bifida: Cause: Incomplete closure of the caudal neuropore. Types: 1. Occulta (asymptomatic). 2. With meningocele. 3. With meningomyelocele. N.B. Neural tube defects are diagnosed by finding elevated levels of alpha-fetoprotein and also by ultrasound. Folic acid (vitamin B9) supplementation during pregnancy prevents 70 % of neural tube defect anomalies. 3 Semester 1 Neurulation & Folding Dr. Hend M. Hassan Embryonic Folding Folding of the trilaminar embryo upon itself ventrally. Time: 4th week. Cause: Rapid growth of the developing neural tube and paraxial mesoderm. Process: The amniotic cavity expands and surrounds the embryo. The Yolk sac is constricted into two parts: 1. Part enclosed within the embryo forms primitive gut. 2. Part outside embryo becomes definitive yolk sac. The connection between them is called the vitello intestinal duct. Results: - The primitive gut differentiates into: 1. Foregut: in the head fold. 2. Midgut: in the lateral fold. 3. Hindgut: in the tail fold. - Definitive yolk sac and Vitello intestinal duct degenerate and disappear. - Lateral body folds fuse to form the ventral abdominal wall. 4 Semester 1 Neurulation & Folding Dr. Hend M. Hassan 5
