FIGURE 2.

The filling of space by five random trajectories in the spine (a) with no drift, and (b) with drift. Each color corresponds to a trajectory. Proteins are uniformly distributed in the spine head, and are represented by circles and crossed circles, respectively. A trajectory starts at the top of the spine head where channels are located and continues until it is terminated at the dendritic shaft or at an active pump. The parameters for the simulation are δ₁ = 0.02 μm, δ₂ = 0.01 μm, R = 0.5 μm, d/2 = 0.21794 μm, l = 1.5 μm, and N_pumps = 10.