## **Core Concept**
The question tests understanding of sensory receptor physiology, specifically the properties of Pacinian corpuscles, which are rapidly adapting mechanoreceptors. These receptors generate receptor potentials in response to changes in pressure or vibration. The relationship between stimulus intensity and receptor potential amplitude is not always linear due to the properties of sensory transduction.

## **Why the Correct Answer is Right**
Pacinian corpuscles exhibit a property known as **sensory transducer saturation**. As the stimulus intensity increases, the receptor potential amplitude also increases but does so in a non-linear fashion. At lower stimulus intensities, the increase in receptor potential amplitude is more pronounced compared to higher stimulus intensities, where the receptor potential approaches its maximum amplitude. This means that as you approach the maximum stimulus intensity, the increase in receptor potential amplitude becomes less significant. Given that an increase from 10% to 30% of maximum stimulus causes a 40% increase in receptor potential amplitude, further increases at higher stimulus levels (e.g., from 70% to 90%) would result in a smaller percentage increase due to saturation. Therefore, the increase in amplitude when going from 70% to 90% of maximum stimulus is expected to be less than 40%, making **C. 10%** a reasonable expectation due to the principle of diminishing returns as the receptor potential approaches its maximum.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A 40% increase would imply a linear relationship or no saturation effect, which contradicts the known physiology of sensory receptors like Pacinian corpuscles.
- **Option B:** A 20% increase might still be considered too high given the saturation effect expected at higher stimulus intensities.
- **Option D:** A 5% increase might be too low and not reflective of the dynamic range of Pacinian corpuscles.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that sensory receptors exhibit **non-linear stimulus-response relationships**, often showing saturation at high stimulus intensities. This property is crucial for understanding how different types of sensory receptors respond to varying levels of stimuli, allowing for a wide dynamic range of detection.

## **Correct Answer:** . 10%