Lec 7 - Synaptic Plasticity

Lec 7 - Synaptic Plasticity - How are memories stored? At...

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1 How are memories stored? • At this point, we do not know the answer • However, it is likely that memory involves long-term changes in the strength of synaptic interactions among neurons • So, although we cannot yet say for sure how these changes in synaptic strength produce memories, a great deal is known about molecular mechanisms that can alter synaptic interactions among neurons • Collectively, these alterations in synaptic strength are called synaptic plasticity Short-term changes in synaptic strength Neurons tend to fire action potentials in bursts We have treated the postsynaptic effect of each action potential as a fixed quantity, but usually the synaptic strength changes with time “Synaptic strength” means the amount of change in postsynaptic membrane potential produced by a single presynaptic action potential (bang for buck) Synaptic plasticity refers to these temporal changes in strength, which can last for very short times (tens to hundreds of milliseconds) or for very long times (days, months, or years)
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2 Short-term changes in synaptic strength If each action potential in a burst produces the same postsynaptic effect, the result is simple temporal summation, as we discussed in our synaptic transmission lectures If each action potential within a burst produces progressively greater postsynaptic action, the result is called synaptic enhancement If each action potential within a burst produces progressively smaller postsynaptic action, the result is called synaptic depression Short-term changes in synaptic strength
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3 After a burst of action potentials, short-term synaptic enhancement can last for a second or less (called facilitation ), a few seconds (called augmentation ), or several minutes (called potentiation ). 5 min Short-term synaptic enhancement: residual Ca 2+ • Facilitation, augmentation, and potentiation are thought to be triggered by the buildup of intracellular calcium inside the presynaptic terminal during action potential activity • Ca 2+ promotes vesicle fusion and also triggers biochemical events that potentiate release of neurotransmitter during subsequent action potentials
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4 Short-term synaptic enhancement: residual Ca 2+ Ca 2+ Ca 2+ Short-term synaptic depression: three possible mechanisms Vesicle depletion
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5 Calcium accumulation: activation of potassium channels and/or inactivation of calcium channels Short-term synaptic depression: three possible mechanisms Feedback mechanisms via presynaptic neurotransmitter receptors Short-term synaptic depression: three possible mechanisms
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6 Associative vs. Nonassociative Learning • These short-term changes in synaptic strength are a form of nonassociative learning. That is, they are simply time-dependent and activity-dependent changes in the response to a single stimulus • However, learning is frequently associative , involving the formation of associations between two or more events that occur together in time • An familiar example of associative learning is
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Lec 7 - Synaptic Plasticity - How are memories stored? At...

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