These are neurons stained with a calcium indicator FURA PE3 (green) and a mitochondrial indicator TMRM (red).  Neurons are full of calcium, and use it as part of the action potential process amongst other things.  Mitochondria, for those who need a refresher, are the organelles of a cell that make ATP (cell energy).  Neurons need a great deal of these for conduction of action potentials and resetting the membrane potential after an AP goes through. [Image Source]

These are neurons stained with a calcium indicator FURA PE3 (green) and a mitochondrial indicator TMRM (red).  Neurons are full of calcium, and use it as part of the action potential process amongst other things.  Mitochondria, for those who need a refresher, are the organelles of a cell that make ATP (cell energy).  Neurons need a great deal of these for conduction of action potentials and resetting the membrane potential after an AP goes through.

[Image Source]