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Lecture 16

DEV2011: Lecture 16 summary

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LECTURE 16 Central Nervous System: The central nervous system (CNS) is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies. It contains the majority of the nervous system and consists of the brain and the spinal cord. Development of the CNS: During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens and the ridges on either side of the groove (the neural folds) become elevated, and ultimately meet, transforming the groove into a closed tube, the ectodermal wall of which forms the rudiment of the nervous system. This tube initially differentiates into three vesicles (pockets): the prosencephalon at the front, the mesencephalon, and, between the mesencephalon and the spinal cord, the rhombencephalon. (By six weeks in the human embryo) the prosencephalon then divides further into the telencephalon and diencephalon; and the rhombencephalon divides into the metencephalon and myelencephalon. Neurulation: Neurulation is the stage of organogenesis in vertebrate embryos, during which the neural tube is transformed into the primitive structures that will later develop into the central nervous system. The process begins when the notochord induces the formation of the central nervous system (CNS) by signaling the ectoderm germ layer above it to form the thick and flat neural plate. 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 central nervous system. Different portions of the neural tube form by two different processes, called primary and secondary neurulation, in different species. Primary Neurulation: In primary neurulation, the neural plate creases inward until the edges come in contact and fuse. Secondary Neurulation: In secondary neurulation, the tube forms by hollowing out of the interior of a solid precursor. Primary Vesicles Secondary Vesicles Adult Structures Forebrain Vesicle Telencephalon Cerebral hemispheres, (Prosencephalon) consisting of the cortex and medullary center, basal ganglia, lamina terminalis, hippocampus, the corpus striatum, and the olfactory system Diencephalon Thalamus, epithalamus, hypothalamus, subthalamus, neurohypophysis, pineal gland, retina, optic nerve, mamillary bodies Midbrain Vesicle Mesencephalon Midbrain (Mesencephalon) Hindbrain Vesicle Metencephalon Pons and Cerebellum (Rhombencephalon Myelencephalon Medulla Telencephalon: Also known as the cerebrum, together with the diencephalon, constitutes the prosencephalon during embryonic development. In humans, the cerebrum is the superior-most region of the vertebrate central nervous system. However, in the majority of animals, the cerebrum is the anterior-most region of the CNS as most animals rarely assume an upright anatomical position. Telencephalon refers to the embryonic structure from which the mature cerebrum develops. During vertebrate embryonic development, the prosencephalon, the most anterior of three vesicles that form from the embryonic neural tube, is further subdivided into the telencephalon and diencephalon. The telencephalon then forms two lateral telencephalic vesicles which develop into the left and right cerebral hemispheres. Spinal Cord: The spinal cord is made from part of the neural tube during development. As the neural tube begins to develop, the notochord begins to secrete a factor known as Sonic hedgehog or SHH. As a result, the floor plate then also begins to secrete SHH, and this will induce the basal plate to develop motor neurons. Meanwhile, the overlying ectoderm secretes bone morphogenetic protein (BMP). This induces the roof plate to begin to secrete BMP, which will induce the alar plate to develop sensory neurons. The alar plate and the basal plate are separated by the sulcus limitans. Neural Tube: The neural tube is the embryo's prec
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