1_29_09_PresynapticMechanisms

1_29_09_PresynapticMechanisms - This circuit’s function...

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Unformatted text preview: This circuit’s function depend on nonlinear synaptic mechanisms. Transmitter release is due to Ca 2+-induced vesicle fusion at the presynaptic terminal. A low [Ca 2+ ] out condition shows that the release of transmitters is quantal and probabilistic. If the number of vesicles is large and the probability of release is low, then one can approximate the quantal release with a Poisson distribution: P ( m ) = λ m m ! e −λ variance m ( ) = P ( m ) m − λ ( ) 2 m = ∞ ∑ = λ mean m ( ) = P ( m ) m m = ∞ ∑ = λ A low [Ca 2+ ] out condition shows that the release of transmitters is quantal and probabilistic. The solid line is the sum of several Gaussian distributions weighed by a Poisson distribution. The value of λ depends on the rate, r, of presynaptic action potentials, as [Ca 2+ ] in takes time to decay to the resting level. Let λ→λ +f F ( λ M- λ ) after an action potential and the decay of λ be of first order: τ F d λ dt = λ − λ In steady state, on average, λ returns to λ = λ + λ + f F λ M − λ ( ) − λ ( ) e − 1 r τ F Solving for...
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1_29_09_PresynapticMechanisms - This circuit’s function...

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