What is the first way intensity is coded by the sensory system?

• A. Receptor potentials vary with stimulus intensity, the magnitude of the GP determines the frequency of the AP
• B. Absolute number of receptors stimulated
• C. External stimulus excites different receptor types producing a larger qualitative sensation
• D. Sensory adaptation reduces response over time

Answer: (A)

The first way intensity is signaled is through the receptor’s graded depolarization that scales with stimulus strength. As the stimulus becomes stronger, the generator potential (receptor potential) grows larger, pushing the sensory neuron to fire more frequently. This change in firing rate encodes how intense the stimulus is. While recruiting more receptors or different receptor types can contribute to perception, the initial coding of intensity is about how the receptor potential amplitude sets the frequency of action potentials. Sensory adaptation, on the other hand, describes how responses diminish with sustained stimulation, not the initial encoding of intensity.