Figure 5.

Measuring micron-scale tortuosity in a reconstruction of a 5 × 6 × 6 μm volume of neural tissue. The diffusion of glutamate in the ECS was simulated with MCell to measure the diffusional impedance due to micron-scale geometry of each reconstruction. Seventeen concentric sampling boxes (cyan) recorded the time course of glutamate (white) concentration during diffusion through the reconstructed tissue (not shown). The largest sampling box is 8.5 μm on a side. The glutamate count in each sampling box over time was used to estimate a diminished rate of diffusion (Tao and Nicholson, 2004). The resulting estimate of micron-scale tortuosity (Fig. 8C,D) had a fairly tight confidence interval, suggesting that a tissue volume of 1,000 μm³ would yield similarly well-constrained estimates of tortuosity without mirroring (see Materials and Methods). Reconstructions smaller than this are not representative of the neuropil because the volume is too small to average out the heterogeneity seen in the cellular structure.