Final answer:
C) the total number of action potentials. The total amount of neurotransmitter released at the axon terminal is related to the total number of action potentials, because action potentials trigger the opening of voltage-gated Ca2+ channels, leading to the release of neurotransmitters through exocytosis.
Step-by-step explanation:
The total amount of neurotransmitter released at the axon terminal is not related to the amplitude of the action potential, because action potentials operate under the all-or-none principle, meaning that as long as the threshold is reached, the action potential is always the same size. Instead, the total amount of neurotransmitter released is more closely related to the total number of action potentials. When an action potential arrives at the axon terminal, it triggers voltage-gated Ca2+ channels to open, which leads to an influx of calcium ions (Ca2+). This increase in Ca2+ inside the axon terminal causes neurotransmitter-containing vesicles to merge with the pre-synaptic membrane and release their contents into the synaptic cleft through a process known as exocytosis.