Figure 5.18  Decreasing depolarization as a function of distance along a long dendritic cable.  (a) Current is injected into a dendrite, and the depolarization is recorded.  As this current spread down the dendrite, much of it dissipates across the membrane.  Therefore, the depolarization measured at a distance from the site of current injection is smaller than that measured right under it. (b) A plot of membrane depolarization as a function of distance along the dendrite.  At the distance l, one length constant, the membrane depolarization (V_m) is 37% of that at the origin.