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PSY290H1 (52)
Chapter 9

PSY290 Chapter 9

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Junchul Kim

Chapter 9 Development of the Nervous System  3 ideas of neuro development: 1. The amazing nature of neurodevelopment 2. The important role of experience in neurodevelopment 3. The dire consequences of neurodevelopmental errors  Two devastating disorders: Autism and Williams disorder 9.1 Phases of Neurodevelopment  Started with a zygote, the cell that’s formed by amalgamation of an ovum and a sperm  3 things cell multiplication must occur: 1. Cells must differentiate 2. Cells must make their way to appropriate sites and align themselves with the cells around them to form particular structures 3. Cells must establish appropriate functional relations with other cells  5 phases of neuro-development: 1. Induction of the neural plate 2. Neural proliferation 3. Migration and aggression 4. Axon growth and synapse formation 5. Neuron death and synapse rearrangement Induction of the Neural Plate  Neuro Plate: a small patch of ectodermal tissue on the dorsal surface of the developing embryo  The development of the neural plate is the first major stage of neurodevelopment in all vertebrates  Mesoderm Layer: An area that is consequently referred to as an organizer, which seems to induce the development of the neural plate by chemical signals  Totipotent: The earliest cells of the human embryo which have the ability to develop into any type of cell in the body.  Multipotent: The cells of the early neural plate that have ability to develop into most types of mature nervous system cell, but cannot normally develop into other kinds of cells  Stem Cells: cells that meet two specific criteria: 1. Seemingly unlimited capacity for self-renewal if maintained in an appropriate cell culture 2. Have the ability to develop into different types of mature cells  Stem cells have unlimited capacity for self-renewal because when a stem cell divides, two different daughter cells are created, one that eventually develops into some type of body cell and one that develops into another stem cell Neural plate  Neural Groove  Neural Tube  Cerebral ventricles and Spinal canal (after 40 days, the three swellings develop into forebrain, midbrain and hindbrain.) Neural Proliferation  Neural Proliferation: the process that’s done by the cells of the neural tube once it’s created and fused by the lips of the neural groove  It does not occur simultaneously or equally in all parts of the tube  Ventricular Zone: where the most cell division in the neural tube occur, which is the region adjacent to the ventricle (the fluid-filled center of the tube)  Two organizer areas in the neural tube that control the pattern of proliferation: the floor plate (runs along the midline of the anterior surface of the tube) and the roof plate (runs along the midline of the dorsal surface of the tube) Migration and Aggregation  Migration  Migration: The procedure of cell’s movements once they have been created through cell division in the ventricular zone of the neural tube; the cells haven’t developed axons and dendrites at this stage  2 kinds of migrations:  Radial Migration: Cell proceeds from the ventricular zone in a straight line outward toward the outer wall of the tube  Tangential Migration: Cell proceeds at a right angle to radial migration (parallel to the tube’s walls)  2 methods to develop cells migrate:  Somal Translocation: Extension grows from the developing cell in the general direction of the migration, which explores the immediate environment for attractive and repulsive cues as it grows  Glia-mediated Migration: Once the neural proliferation is well underway and the walls of the neural tube are thickening, a temporary network of glial cells (radial glial cells), appears in the developing neural tube which let the cells engaging in radial migration by moving along the radial glial network.  Inside-out pattern: the radial pattern of cortical development  Neural Crest: the structure that is situated just dorsal to the neural tube, which develop into neurons and glial cells of the PNS (therefore, most of them have to do a long-distance migration)  Many guidance molecules (the chemicals that guide the migrating neurons by attracting or repelling) are released by glial cells.  Aggregation  Aggregation: the process about how neurons align themselves with other developing neurons that have migrated to the same area to form the structures of the nervous system  Cell-adhesion molecules (CAMs): What mediate migration and aggregation, which are located on the surfaces of neurons and other cells  CAMs are critical to normal function and development of the brain  Gap junctions are also prevalent in brain development; which plays a role in migration and aggregation as well. Axon Growth and Synapse Formation  Axon Growth  Axons and dendrites begin to grow from the neurons once they have migrated to the appropriate positions and aggregated into neural structures  Growth cone: the amoebalike structure that’s at each growing tip of the axon or dendrite, which extends and retracts fingerlike cytoplasmic extensions: Filopodia  Retinal Ganglion Cells: Roger Sperry’s study (1940)  Optic Tectum  Chemoaffinity Hypothesis of axonal development: Sperry indicates that each postsynaptic surface in the nervous system releases a specific chemical label and that each growing axon is attracted by the label to its postsynaptic target during both neural development and regeneration\  According to revised hypothesis, growth cones seem to be influenced by a series of chemical signals along the route, which (the guidance molecules) are similar to those that guide neural migration in the sense that some attract and others repel the growing axons  Pioneer Growth cones: the first growth cones to travel along a particular route in a developing nervous system, which are presumed to follow the correct trail by interacting with guidance molecules along the route  Fasciculation: the tendency of developing axons to grow along the paths established by preceding axons  Topographic array of neurons to another: the neurons maintain the same topographic relation they had on the first array, which can be evolved as a means of minimizing the volume of neural connections in the brain  Topographic Gradient Hypothesis: axons growing from one topographic surface to another are guided to specific targets that are arranged on the terminal surface in the same way as the axons’ cell bodies are arranged on the original surface; the key is that growing axons are guided to their destinations by two intersecting signal gradients  Ephrins  Synapse Formation  Synaptogenesis: the formation of new synapses depends on the presence of glial cells, particularly astrocytes  Most current studies focus on explaining the chemical signals that must be exchanged between presynaptic and postsynaptic neurons for a synapse to be created Neuron Death and Synapse Rearrangement  Neuron Death  Assume to be passive: the neurons died when they failed to get enough nutrition  However, it is clear now that cell death is usually active.  Necrosis: Passive cell death  Apoptosis: Active cell death  Apoptosis is safer than necrosis because necrosis can be potentially harmful inflammation (the cell spills the contents into extracellular fluid)  Apoptosis can prevent inflammations by attract scavenger microglia and other molecules, which removes excess neurons in a safe, neat and orderly way  However, apoptosis can be cancer if the genetic programs for apoptotic cell death are blocked (and neurodegenerative disease)  2 kinds of triggers of apoptosis: 1. Developing neurons appear to be genetically programmed for an early death (mission completed  died.) 2. Fail to obtain the life-preserving chemica
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