Q. It is known that calcium plays diverse roles in cellular processes. Upon increases in cytotoxic calcium concentration, calcium binds to proteins that have calcium binding sites, leading to the conformational change of the protein as well as changes in its biological activity. For in case, it is well established that in presynaptic neurons, the elevation of cytosolic calcium triggers the fusion of exocytotic vesicles that contain neurotransmitters to the plasma membrane.

A.) How does calcium trigger the fusion of exocytotic vesicles to the plasma membrane?

B.) How does the presynaptic neuron transducer an action-potential signal to a postsynaptic neuron?