Calcium is important in the synapse because it

A) is necessary for acetylcholine synthesis.
B) signals the exocytosis of the neurotransmitter.
C) binds to receptors on the postsynaptic cell, opening ion channels, and triggering graded potentials.
D) leaves the axon terminal, hyperpolarizing the cell

B) Signals the exocytosis of the neurotransmitter

Explanation:

Calcium ion (Ca2+) channels are critical during the process of neurotransmission; when these channels are blocked, the neurotransmission is inhibited, it happens because the receptors localized in the postsynaptic membrane are not activated

not always but somethings can be reproduced in a laboratory.