Final answer:
An action potential requires a minimum threshold of stimulus to occur, while graded potentials do not have a set threshold. Graded potentials vary in strength and summate to influence the generation of an action potential if they cross the required threshold.
Step-by-step explanation:
The question is asking which type of potential – graded potential or action potential – requires a minimum stimulus to occur. The answer is action potential. An action potential requires a minimum threshold to be reached in order to occur, which is known as the minimum stimulus. In contrast, graded potentials are local changes in membrane potential that vary in magnitude and do not have a set threshold.
Graded potentials occur due to various sensory stimuli that can be either depolarizing or hyperpolarizing and affect the probability of an action potential. When graded potentials reach the initial segment of the axon or the axon hillock and if they are sufficient in strength and duration to reach the threshold of the voltage-gated Na⁺ channels, an action potential is generated. Therefore, while graded potentials can vary, an action potential requires the minimum threshold stimulus, termed threshold, to trigger the all-or-nothing electrical signal.
Both graded potentials like generator potentials and receptor potentials, and action potentials, are critical for neuron functions such as sensory perception and synaptic transmission. Spatial summation and temporal summation are mechanisms by which multiple graded potentials can combine to reach the threshold for an action potential to occur.