Neuroembryology Crash Course PDF

Neuroembryo logy A Crash Course Learning Objectives Define the notochord and describe its function in the embryo and adult. Explain the process of neurulation and neural tube closure. Describe the consequences following incomplete closure of the neural tube. Identify the...

Neuroembryo logy A Crash Course Learning Objectives Define the notochord and describe its function in the embryo and adult. Explain the process of neurulation and neural tube closure. Describe the consequences following incomplete closure of the neural tube. Identify the primary and secondary vesicles and their adult structures. Explain the significance of the cephalic flexure and how it influences our use of directional terms in the nervous system. VERY Early Embryology: During/After implantation, gastrulation gives us the three main germ layers: 1. Endoderm – becomes the internal organs and tracts (digestive, urinary, and respiratory) 2. Mesoderm – becomes the musculoskeletal and circulatory system 3. Ectoderm – becomes the integumentary and nervous systems VERY Early Embryology: A collection of cells collect at a place called the primitive streak and later becomes a cylinder called the notochord. The presence of the notochord sets neurulation in motion. Major Structures Notochord: a solid cylinder of tissue that secretes factors that helps to guide the development of the brain and spinal cord Neural plate: thickening of the ectoderm that will join fold inward to become the neural tube and neural crest Somites: segmented mesoderm that secretes factors to organize the body rostrocaudally. 1 2 3 4 5 6  1 Neural Crest Cells The notochord migrates between endo and ectoderm along the center of the embryo rostrocaudally. Neural Tube The ectoderm layer that will eventually become the neural Ectoderm crest and neural tube is called the neural plate. Mesoderm Somite Notochord Somite Endoderm 2 Neural Crest Cells The sides of the neural plate fold upward to form the neural groove. The rest of the neural plate sinks down Neural toward the notochord. Tube 3 Neural Crest Cells The neural plate completely folds inward and joins together in a process called convergence. Neural Tube 4 Neural Crest Cells The neural crest cells fuse together. Neural Tube 5 Neural Crest Cells The neural crest cells separate from the remainder of the ectoderm. The overlying ectoderm will Neural become the epidermis of the skin Tube and the neural crest cells will begin to migrate. 6 Neural Crest Cells The neural crest cells migrate away from the ectoderm. These will become the location of the cell bodies of the peripheral nervous system and spinal ganglia. Neural Tube Somite Somite The notochord will eventually become part of the intervertebral discs. The somites will become the axial MSK system including the Notochord spinal column. This will matter later when we discuss the peripheral nervous system. For Context: The joining of the neural folds to form the neural tube begins at about 22 days and ends by day 28. The last things to close are the anterior and posterior neuropores. If these fail to close, we can end up with significant congenital defects. Clinical Correlation: Spina Bifida Occurs when the caudal/posterior neuropore fails to fully close. The degree of severity ranges from no deficit to fully paralyzed based on how much nervous material grows outside of the vertebral cavity. Normal Occulta Meningocele Myelomeningocele Spina Bifida Development of the Brain Once the anterior neuropore closes, it begins to dilate into three primary vesicles. Prosencephalon Mesencephalon Rhombencephalon Development of the Brain The three primary vesicles further differentiate into five secondary vesicles. Prosencephalon Telencephalon (Cerebral hemispheres) Diencephalon (Thalamus, hypothalamus) Mesencephalon (Midbrain) Rhombencephalon Metencephalon (Pons and Cerebellum) Myelencephalon (Medulla oblongata) Flexure In the fifth week of gestation, two major flexures form, causing the telencephalon s: and diencephalon to angle toward the brain stem. Continued growth Cerebral hemispheres develop and grow posterolaterally (black arrows) to enclose the diencephalon and the rostral brain stem. Adult Structure s Why does it matter to this course? Directional terms vary depending on where we are in relation to the cephalic and cervical flexures. When in doubt, use rostral/caudal and ventral/dorsal when discussing the CNS. Why does it matter to this course? The failure of the caudal neuropore results in which of the following defects? A. Cranioraschisis B. Spina Bifida C. Anencephaly D. Microcephaly Which of the following structures give rise to the adult intervertebral disc? A. Neural crest cells B. Neural tube C. Notochord D. Somites E. Neural groove The neural crest cells will migrate to form important structures in what system? A. Peripheral nervous system B. Central nervous system C. Respiratory system D. Reproductive system E. None of these