Figure 3.

Comparison of action potential kinetics and calcium imaging responses. Calcium indicators are used to measure relative calcium concentration, and this is often used as a proxy for action potential firing. Action potentials consist of an initial depolarization to action potential threshold, which opens voltage-gated sodium channels, causing rapid depolarization of membrane potential. The membrane potential is then rapidly repolarized by the opening of voltage-gated potassium channels. As a result, a typical action potential may only last from 2 to 5 ms. Conversely, observed calcium responses within the somatic cytosol of neurons during action potential firing may require anywhere from 500 to 1000 ms to return to baseline fluorescence (Rahmati et al., 2016). The kinetics of the response is determined in part by the calcium buffering of the neuron itself as well as the affinity and concentration of the calcium indicator present (Borst and Abarbanel, 2007; Hires et al., 2008).