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CONSTANTS - Space constant(also called length constant or...

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Time and Space Constants PSP's decay with time and with distance. This decay is largely dependent on resistance-capacitance characteristics of the membrane and can be characterized by the rate at which this decay occurs, as shown below. Time constant V T = V max (1-e -T/ τ ) where V T = V at time T, and τ =time constant of circuit. when T = τ , (T = one time constant) V τ = V max (1-e -1 ) V τ = V max (0.63) So, one time constant is the time it takes for the psp to reach 63% of its maximum value. As one moves away from the current source (synapse) the total membrane capacitance increases so the the time to reach peak increases. The larger the time constant of the membrane, more slowly the membrane reaches its peak potential, all else being equal.
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Unformatted text preview: Space constant (also called length constant or characteristic length) V X = V X=0 (e -x/ λ ) where X = distance from source (synapse) λ = (R m /R i ) 1/2 at a distance of one space constant, X = λ thus, V X = V x = 0 (e-1 ) V x = V x=0 (0.37) So, at a distance of one space constant, the PSP has decayed to 37% of its value at the synapse. Or, to put it another way, one space constant is the distance it takes for the PSP to decay to 37% of its initial value. The larger the space constant, the more slowly the PSP decays with distance from the synapse. Note also that as R m increases , the space constant increases; as R i decreases , the space constant increases....
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