Amplitude control in synaptic transmission ensures postsynaptic responses scale with what?

• A. Postsynaptic receptor density
• B. Temperature
• C. Membrane cholesterol
• D. Presynaptic activity

Answer: (D)

Amplitude of a postsynaptic response is determined by how much neurotransmitter is released, which directly mirrors presynaptic activity. When an action potential reaches the terminal, voltage-gated calcium channels open and calcium influx triggers vesicle fusion, releasing a quantal amount of transmitter. The more vesicles released (higher presynaptic activity), the more transmitter binds to postsynaptic receptors, opening ion channels to produce a larger postsynaptic current or potential. This dynamic scaling relies on the presynaptic release process, whereas factors like temperature, membrane cholesterol, or postsynaptic receptor density mainly influence the timing, efficiency, or maximum potential, but not the trial-to-trial amplitude control driven by presynaptic input.