Physician Assistant College Admission Test (PA-CAT) 2025 – 400 Free Practice Questions to Pass the Exam

An action potential is characterized by an all-or-nothing response, meaning it either happens fully or not at all. When a neuron reaches a certain threshold of depolarization, voltage-gated sodium channels open, leading to a rapid influx of sodium ions and a change in membrane potential. This initial spike of depolarization initiates the action potential, which then propagates along the axon. Once the threshold is reached, the action potential is generated with a consistent amplitude, regardless of the strength of the stimulus that triggered it, as long as that stimulus is above the threshold.

This characteristic ensures that signals transmitted along neurons are consistent and reliable, preserving the integrity of the information being sent. Subsequent higher or lower intensity stimuli will not affect the amplitude of the action potential, distinguishing it from graded potentials, which vary in magnitude and can be influenced by the strength of the stimulus. The all-or-nothing nature of action potentials is essential for neuronal communication and is a foundational concept in neuroscience.