Figure 2.

Two-dimensional sketch of the bouton model. Region Ω₀ denotes the bouton area in which vesicle motion is governed by diffusion. A cutout region in the center represents space occupied by organelles, such as mitochondria. Ω₁ … Ω₄ define synaptic active zones. In these subdomains, vesicles diffuse and are subject to exocytosis modeled by the term f_syn, that also includes the transition from the continuous to discrete scale in Ω₁ … Ω₄. The organelle as well as bouton boundaries are treated as no-flux boundary conditions.