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BIOL 1F25 (223)

System CNS

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Brock University
Daniel Glenday

Central Nervous System CNS develops from NEURAL TUBE (ectodermal) neural tube REGIONALIZATION neural plate = thickened ectoderm anterior to primitive node neural plate forebrain as node migrates caudally (towards posterior) secretes RA forms more neural plate that becomes hindbrain, spinal cord involves HOX gene expression hox mediolateral axis from Shh expression from notochord/floor plate notochord/floor plate neural tube: involves 2 closures 1) tube itself (starts at brain and moves caudally) 2) dorsal surface ectoderm tube closure failure: exencephaly (brain) exencephaly rachishisis (brain + spinal cord) rachishisis spina bifida (spinal cord) spina bifida ANTERIOPOSTERIOR DIVISIONS Forebrain = telencephalon telencephalon diencephalon diencephalon Midbrain = mesencephalon mesencephalon Hindbrain = rhombencephalon rhombencephalon divided into rhombomeres that are defined by Hox expression rhombomeres Spinal Cord: brachial (arms) and lumbar (legs) involves neural crest development DORSOVENTRAL DIVISIONS – due to Shh expression by notochord and floor plate of neural tube dorsal: ALAR plate (sensory processing) alar ventral: BASAL plate (motor/hormonal control) basal simpler patterning in spinal cord than in brain, but similar features Central Nervous System GROWTH AND DIFFERENTIATION Neural tube is single layer of epithelial cells inside = ventricular ventricular outside = pial pial nuclei migrate ventricular to replicate and finish cell cycle at pial surface differentiation occurs at pial end (neuron or glial cell) at cortex, there are several layers of neurons at pial surface LISSENCEPHALY – impaired migration, not enough cells lissencephaly vertical migration common everywhere horizontal migration more common in forebrain horizontal migration Neurons – 1000’s of different types Purkinje – many dendrites (arbors), few axons purkinje Granule – few dendrites, branching axons granule Glial cells – structural scaffolding/ neuronal regulation Astrocytes – blood vessel
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