This is a great video of “a zebrafish spinal neuron growth cone in culture loaded with a fluorescent calcium sensor. At time 0, the neuron is depolarized, which elicits a fast calcium signal that is sustained for several minutes.”
What does calcium do in neurons? Well, calcium does a heck of a lot actually. It seems to be involved in synapse strengthening/weakening, the release of vesicles full of neurotransmitters, muscle contraction, and much, more more. I thought this video was particularly great because it shows clearly how quickly calcium can rush into a neuron when it has been depolarized and that it can remain in the cell for a long amount of time (compared to how quick action potentials are anyway)- and this is likely how calcium can enact longer-term changes. Also, I think this video just looks pretty awesome too!
For information about growth cones, go here!