Development Of The Nervous System PDF

Development of the Nervous System NPS 5110: Biological Bases of Behavior: Neuroscience Dr. Karla D. Martinez-Casiano, PhD Material by Dr. Juan B. Fernández Pérez Text: Essential Neuroscience...

Development of the Nervous System NPS 5110: Biological Bases of Behavior: Neuroscience Dr. Karla D. Martinez-Casiano, PhD Material by Dr. Juan B. Fernández Pérez Text: Essential Neuroscience Allan Siegel and Sapru, 2006 References: Haines, Nolte y Netter Development of the Neural Tube A. The nervous system develops from ectoderm, the surface layer of embryonic tissue. By the third to fourth week of embryonic development, the notochord, of mesodermal origin, induces the development of the neural plate By the third to fourth week of embryonic development, there is a high rate of cell proliferation. As such, the anterior part of the notochord (of mesodermal origin) begins to thicken, and, thus, the neural plate is formed by the third week of fetal life (Fig. 2.1A). B. The neural plate continues to thicken over the following week and expands laterally. As it expands, the faster growing lateral edges of the plate accumulate in a dorsal position as neural folds (Fig. 2.1B). As this plate grows and widens, it forms a shallow groove along its longitudinal axis known as the neural groove (Fig. 2.1B). Development of the Neural Tube C. The posterior end of the neural plate, which is narrower than the anterior end, will ultimately become the spinal cord, whereas the broader, anterior end will become the brain. The process by which the neural tube is formed from the neural plate is referred to as primary neurulation. As this plate grows and widens, the neural groove becomes deeper. In the process of its forming and deepening, some of the cells located in the lateral margin of the neural groove separate and migrate to a dorsal position to become the neural crest (Fig. 2.1B). As the embryo grows, the neural folds fuse along the midline, thus forming a neural tube (Fig. 2.1C). Development of the Neural Tube D. Neural crest cells will differentiate into separate groups of neurons (Fig. 2.1D). ü One group differentiates into sensory neurons of cranial nerve (CN) ganglia (components of CN V, VII, IX, and X of the head region) and into the dorsal root ganglia (components of the body). ü A second group will differentiate into the autonomic ganglion cells (postganglionic neurons of the paravertebral and prevertebral ganglia of the sympathetic nervous system as well as postganglionic neurons of the parasympathetic nervous system that are located in visceral organs). ü Other neural crest cells will become chromaffin cells (of the adrenal me- dulla), Schwann cells (that are critical for the formation of myelin in peripheral nerves), and melanocytes. ü In addition, groups of mesodermal cells located alongside the neural tube, called somites, will develop into skeletal muscle, vertebrae, and the dermal layer of the skin (Fig. 2.1D). Development of the Nervous System: 18 days (A) and 20 days (B) Neurulation Neural Tube Development and Neural Crests Formation When the anterior neuropore fails to close, the condition of anencephaly results; when the posterior neuropore fails to close, the condition of spina bifida results.  Development of the Neural tube Formación de las vesiculas Tres Vesiculas: caudal to these vesicles are cells from which the spinal cord will develop. Cinco Vesiculas: Development of the Forebrain Forebrain=Cerebro anterior Development of the Ventricular System and Associated Brain Divisions Development of the Ventricles  Alobar and Semilobar Holoprosencephaly Holoprosencephaly (HPE) is a cephalic disorder in which the prosencephalon (the forebrain of the embryo) fails to develop into two hemispheres. Normally, the forebrain is formed and the face begins to develop in the fifth and sixth weeks of human pregnancy. Neural Tube Differentiation  Early Brain Development: 28-day-old Embryo  Early Brain Development: 36-day-old Embryo  Later Brain Development: 49-day-old and 3-month-old Embryos The 6-month and the 9-month Central Nervous System  Early Development of the Cerebral Cortex Later Development of the Cerebral Cortex  Spinal Cord Development The ventricular zone is the major proliferative layer and also the first layer of the forming neural tube to appear. The second layer to form is the marginal layer, followed by the mantle layer.  The Derivatives of the Alar and Basal Plates in the Spinal Cord and Brain Stem Development of the Brainstem In the part of the developing brainstem that contains the fourth ventricle, the roof plate expands greatly so that the alar plate becomes located lateral to the basal plate C. depicts how cranial nerve nuclei are organized in the brainstem in terms of their medial-to-lateral position. Here, it can be seen that motor nuclei (GSE, SVE) are situated medial to the sulcus limitans, sensory nuclei (SSA, GSA) are located lateral to the sulcus limitans, and autonomic nuclei (GVA, SVA, GVE) are found in the region adjoining the sulcus limitans. Panels D and E depict development of cerebellum. Note the development and formation of the cerebellum from the rhombic lips that become fused at the midline. (See text for details.) Development of the Cerebellum  Spina Bifida Occulta and Encephalocele (A) The normal arrangement of the vertebra and associated spinal cord. (B) Figure illustrates a given vertebra and the neural tube where the posterior arch failed to close. It is an example of spina bifida occulta. It is characterized by the absence of the vertebral lamina at a particular level or levels, the effect of which is to allow the meninges to be exposed. (C) An example of an encephalocele, a defect in the cranium in which there is an occipital herniation, causing a protrusion, in this case, of the meninges alone. Spina Bifida Malformations Anencephaly  Occipital Encephalocele A. Meningohydroencephalocele Spina bifida aperta involves the protrusion of either B. Meningocele the meninges alone (called a meningocele) or spinal C. Meningoencephalocele cord together with the meninges (called a meningomyelocele). D. Meningohydroencephalocele  Arnold-Chiari Malformation, Syringobulbia and Syringmyelia Arnold-Chiari malformation. Because the vertebral column grows faster than the spinal cord, the cerebellum and parts of the medulla are displaced and, consequently, pulled through the foramen magnum. Syringo(hydro)myelia. There is a cavitation filled with CSF in the region of the central canal, which damages the crossing fibers of the spinothalamic tract, the net effect of which is to cause segmental loss of pain and temperature. Dandy-Walker syndrome. There is a mnemonic for remembering the components of this syndrome: Dandy- Walker Syn- drome: Dilated fourth ventricle, Water on the brain, Small vermis. The differential Growth of the vertebral Column and Spinal Cord Forms the Cauda Equina