Final answer:
More action potentials at the axon terminal lead to more neurotransmitter molecules being released into the synapse, as each potential triggers calcium influx that facilitates neurotransmitter release.
Step-by-step explanation:
When more action potentials arrive at the axon terminal, there is an increase in the number of neurotransmitter molecules released into the synapse. This occurs because each action potential triggers the opening of voltage-gated calcium channels, allowing calcium ions to enter the axon terminal. This influx of calcium ions initiates a cascade of events that result in synaptic vesicles fusing with the presynaptic membrane and releasing their contents of neurotransmitters into the synaptic cleft.
The correct answer to the question is therefore A) More molecules are released into the synapse. This increase in neurotransmitter release enhances the likelihood of stimulating an action potential in the postsynaptic neuron. It's worth noting that after their release, neurotransmitters bind to receptors on the postsynaptic cell, influence its electrochemical potential, and then are rapidly degraded or reabsorbed by the presynaptic cell to prevent ongoing activation of the postsynaptic neuron.