Question:
Hyperpolarization of the receptor cell on stimulation is characteristically seen with which of the following sensory modalities?
Hyperpolarization of the receptor cell on stimulation is characteristically seen with which of the following sensory modalities?
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Think of the receptor that turns off its 'dark current' when stimulated.
Updated On: Jun 25, 2026
- Olfactory
- Visual
- Taste
- Tactile
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The Correct Option is B
Solution and Explanation
Step 1: Identify the unique receptor.
Almost all sensory receptors depolarize when stimulated, generating a depolarizing receptor (generator) potential. The photoreceptors of the retina (rods and cones) are the classic exception.
Step 2: Phototransduction in the dark.
In darkness, cyclic GMP keeps cation (Na⁺/Ca²⁺) channels open, producing a steady inward 'dark current' that keeps the photoreceptor partially depolarized (around −40 mV) and releasing glutamate continuously.
Step 3: Effect of light.
Light activates rhodopsin → transducin → phosphodiesterase, which hydrolyses cGMP. Falling cGMP closes the cation channels, the inward current stops, and the cell hyperpolarizes, reducing glutamate release. Thus the visual receptor responds to its adequate stimulus with hyperpolarization.
Step 4: Why the others are wrong.
Olfactory receptors depolarize via cAMP-gated cation channels; taste receptors depolarize through various transduction routes; tactile (mechanoreceptor) endings depolarize via stretch-activated cation channels. None hyperpolarize on stimulation.
Key fact: Photoreceptors are unique in hyperpolarizing in response to light.
Almost all sensory receptors depolarize when stimulated, generating a depolarizing receptor (generator) potential. The photoreceptors of the retina (rods and cones) are the classic exception.
Step 2: Phototransduction in the dark.
In darkness, cyclic GMP keeps cation (Na⁺/Ca²⁺) channels open, producing a steady inward 'dark current' that keeps the photoreceptor partially depolarized (around −40 mV) and releasing glutamate continuously.
Step 3: Effect of light.
Light activates rhodopsin → transducin → phosphodiesterase, which hydrolyses cGMP. Falling cGMP closes the cation channels, the inward current stops, and the cell hyperpolarizes, reducing glutamate release. Thus the visual receptor responds to its adequate stimulus with hyperpolarization.
Step 4: Why the others are wrong.
Olfactory receptors depolarize via cAMP-gated cation channels; taste receptors depolarize through various transduction routes; tactile (mechanoreceptor) endings depolarize via stretch-activated cation channels. None hyperpolarize on stimulation.
Key fact: Photoreceptors are unique in hyperpolarizing in response to light.
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