SNARE Zippering & Fusion Pore Dynamics: Calcium Diffusion Field (2D)

This is the 2D-native counterpart to the 3D orbiting-vesicle SNARE-fusion simulator. Rather than animating individual falling calcium ions above a single, spatially-uniform concentration that decays as one global exponential, this version solves an actual 2D reaction-diffusion field for calcium: a point source at the voltage-gated channel spreads outward across a grid, cleared by a first-order pump term, and each docked SNARE complex on the ring around the release site samples its own local concentration from that field to drive its own Hill-equation zippering kinetics. The result is a genuinely spatial model — a site closer to the channel can zipper meaningfully faster than one further around the ring — feeding into the same fusion-pore nucleation, dilation, and full-fusion-versus-kiss-and-run dynamics as the 3D model, with neurotransmitter release modelled as a real 2D random walk from the vesicle interior, across the cleft, to a postsynaptic receptor ring. A live strip chart tracks zippering percentage, dock-site calcium, pore radius and cumulative release so the causal chain from diffusing field to digital release switch is visible on one timeline.