S1 Somatic Sensation Practice Test

Receptor potentials are graded changes in membrane potential at the sensory ending that can summate over time or across space. The key idea is that an action potential is fired only when this integrated depolarization reaches a threshold at the trigger zone, activating voltage-gated channels. If the receptor potentials do not reach this threshold, no action potential is produced. Therefore, the generation of action potentials depends on receptor potentials summing to threshold. This captures why summation matters: it’s not just any summation that matters, but reaching the critical threshold that triggers the all-or-none spike. The other statements conflict with this view: action potentials rely on receptor-driven depolarization to reach threshold, receptor potentials can influence CNS signaling by driving these spikes, and relying on summation to reach threshold aligns with how sensory information is encoded and transmitted.