Neurobiology |
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Principles of Neural Science - Kandel, Schwartz and Jessell: Read pages 1114-1129 for this lecture end |
XV. Synaptic Connections back to XIV. Synapse Formation A. Synapses reflect wiring necessary to process sensory information into coherent activity B. Synaptic connections are refined by Sensory Experience and Social Interaction 1. dependent upon specific interactions with the environment a. learning b. experiences have more profound effects in early postnatal development than adulthood 2. deprivation or isolation result in abnormal development a. therefore abnormal behavior C. Critical Periods 1. at specific points in development neurons become irreversibly differentiated a. results in critical periods for acquisition of behavior i. e.g. sexual identity 2. different regions of the brain have different critical periods of development a. do not have sharp time boundaries 3. sensory deprivation during critical periods result in permanent deficits in perception a. by structural/neuronal changes/loss in cerebral cortex D. Competition and Neuronal selection (synapse formation) 1. neurons from developing organs may compete for synapse space a. intermingled axonal growth i. become arranged in a regular pattern (1) via selective elimination (a) synapse retraction ii. e.g. development of optic innervation 2. random differences in density may confer a competitive advantage a. cooperation between clustered fibers allows growth i. spreading to adjacent cells ii. fibers with the highest density retain connections b. competition segregates fibers i. fibers with less extensive contact retract 3. organization of areas of the brain are derived from competition and cooperation of developing afferent fibers over one set of postsynaptic cells a. e.g. optic tectum E. Cooperation requires Synchronous activity 1. spontaneous activity may have instructive function in development a. resulting synchronous excitation of target strengthens synapses when fibers are active together b. synapses are weakened in inactive fibers 2. Coincident activity in pre- and postsynaptic elements leads to strengthing of the synapse a. Neurons need activity F. Survival of neurons depends upon activity, synaptic connections, postsynaptic activity, target cell production of neurotrophins and growth factors 1. Environmental stimuli are at the root of all those actions
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