Calcium diffusion models and transmitter release in neurons.

Calcium enters neurons or nerve terminals through the surface membrane, and then diffuses inwardly and is diluted. Calcium acts at membrane sites to release transmitter or modulate channels, or at organelles or the nucleus to regulate metabolism. Thus the average cytoplasmic calcium concentration is a poor predictor of calcium-dependent processes. Solutions of the diffusion equation with appropriate geometries and boundary conditions help considerably in our quantitative understanding of calcium-dependent processes in neurons.