Chapter 9.1 - Development of the Nervous System & Chapter 11 - Learning, Memory and Amnesia

Chapter 9.1 - Development of the Nervous System & Chapter 11 - Learning, Memory and Amnesia

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(Chapter 9.1) Early phases of neural development (FIG. 9.1). Embryos consit of three layers: ectodem, mesoderm and endoderm. Induction of neural plate (ectodermal tissue) by underlying mesoderm (week 3 after conception). Cells of the neural plate are referred to as embryonic stem cells ( neural and glial stem cells): They have unlimited capacity for self-renewal They have the ability to develop into diferent types of mature cells. The neural plate leads to the formation of the neural tube , from where forebrain, midbrain and hindbrain develop (by 40 days after conception). The inside of the neural tube will eventually become the cerebral ventricles and sopinal canal. Proliferation: cells lining the ventricles divide and form neurons and glial cells. Migration: Movement of cells from ventricular zone to final destination. Radial migration. From the ventricular zone to the to the surface of the neural tube. (Fig. 9.2). Tangential migration. Parallel to the wall of the neural tube (Fig. 9.2). Migration can occur by Somal translocation (caterpillar-like movement, Fig. 9.3, top panel), or Glia-mediated migration (radial glial cells, Fig . 9.3, bottom panel) Cortex develops “inside out” Aggregation. Cells accumulate in certain areas forming nuclei (singular: nucleus). Differentiation Neurons take their adult morphology . Myelination . In humans, starts in spinal cord and progresses toward forebrain. &eural crest.
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Located dorsal to the neural tube (Fig. 9.1). Neural crest cells develop into the neurons and glial cells of the PNS. Axon Growth and Synapse Formation. How do axons make correct connections with appropriate targets? Growth cones and filopodia (Fig. 9.4) Three major mechanisms can guide the process of target finding and synapse formation: 1. Blueprint hypothesis . This hypothesis proposes that there are preformed pathways and tunnels. Pioneer growth cones, guidepost cells. Fasciculation Role of cell-adhesion molecules (NCAMs) Evidence against blueprint hypothesis: Cells with altered locations (transplants) still find targets 2. Chemoaffinity hypothesis : connections are highly specific. Sperry’s eye-rotation experiments (1943). (Fig. 9.5) After cutting optic nerves and rotating eyes 180 deg, the axons of retinal ganglion cells regenerated back to original target regions in the optic tectum (mesencephalon). Frogs whose eyes had been rotated, but without cutting the optic nerves, responded in the same way. How specific are the connections? If half of the retina was distroyed, remaining axons project in an orderly way on the entire tectum (Fig. 9.6, middle panel ). If half of the tectum was destroyed, all of retinal axons accomodated in the remaining tectum and formed appropriate map (Fig. 9.6, bottom panel ).
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This note was uploaded on 04/04/2012 for the course PSYCH 202 taught by Professor Kim during the Fall '06 term at University of Washington.

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Chapter 9.1 - Development of the Nervous System & Chapter 11 - Learning, Memory and Amnesia

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