Lecture 9-development and hormones

Synapseformation dendrites dendrites and axons grow

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Unformatted text preview: and secretes ‘sonic hedgehog’ secretes Sonic hedgehog is a protein Sonic that allows cells to develop into motor neurons (gold) into Note that no motor neurons Note develop above where a different protein is secreted (blue) (blue) • • • • 4. Synapse Formation Dendrites • Dendrites and axons grow out to make synaptic • connections connections Possess growth cones (comprised of lamellipodia and Possess filopoia), specialized structures that seek out the target filopoia), 4. Synapse Formation Dendrites • Dendrites and axons grow out to make synaptic • connections connections Possess growth cones (comprised of lamellipodia and Possess filopoia), specialized structures that seek out the target filopoia), 4. Synapse Formation Filopodia • Filopodia pull cone towards • • • • target target Target cells secrete Target chemical that guides growth cones (chemotropic guidance) guidance) There both There chemoattractants – attract certain growth cones certain And chemorepellents- repel And certain growth cones certain Synapses formed when Synapses cone contacts target cone Chemorepellent (red) Repels most, but not all, axons. Example from Fruit Fly 5. Cell Death (Apoptosis) Programmed • Programmed cell death is a critical phase of embryonic brain development development In chick spinal cord, more motor In neurons are made that are needed and then over 50% undergo apoptosis apoptosis Specific cellular machinery mediates Specific apoptosis (death genes, caspases) apoptosis Machinery is ancient, present in C. Machinery elegans elegans • • • 5. Cell Death (Apoptosis) Pattern • Pattern of cell death in motor neurons in chicks and humans is very similar and Neural darwinism Neurons are overproduced Neurons compete for connections with target Those that make stable connections survive Those that do not perish Why? Because those without connections don’t get trophic factors Chicks • Humans Neurotrophic factors Neurotropic • Neurotropic factor- is the target derived ch...
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