Stop & Think Question

Question

Why does the stimulus intensity affect the amount of neurotransmitter release at the axon terminal?
• The stimulus intensity directly affects the amount of calcium entering the axon terminal.
The stimulus intensity proportionally affects the number of synaptic vesicles that discharge
• their contents into the synaptic cleft.
• The stimulus intensity directly affects the amount of neurotransmitter released per synaptic
Both "The stimulus intensity directly affects the amount of calcium entering the axon terminal."
O and "The stimulus intensity proportionally affects the number of synaptic vesicles that

Answer 1

The stimulus intensity affects the amount of neurotransmitter release at the axon terminal primarily through two mechanisms:

1. Calcium Influx: When an action potential reaches the axon terminal, voltage-gated calcium channels open, allowing calcium ions (Ca²⁺) to enter the cell. The intensity of the stimulus influences the frequency of action potentials, which can lead to a greater influx of calcium. Higher calcium concentrations inside the axon terminal promote more synaptic vesicles to fuse with the presynaptic membrane and release their neurotransmitter contents into the synaptic cleft.

2. Synaptic Vesicle Mobilization and Release: Higher stimulus intensity can also increase the overall number of synaptic vesicles that are prepared for release. When there is a stronger stimulus, more vesicles may be primed and made ready to discharge their neurotransmitters. This results in a proportional increase in the amount of neurotransmitter released into the synaptic cleft.

In summary, both the influx of calcium and the mobilization of synaptic vesicles in response to the strength of a stimulus contribute to the amount of neurotransmitter that is released at the axon terminal.