Question:medium

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

The correct response is the visual system. Sensory transduction normally produces a depolarizing generator potential, but the retinal rod and cone are the textbook outlier. In the dark, a cGMP-gated cationic conductance sustains an inward dark current ($Na^+/Ca^{2+}$), holding the photoreceptor depolarized and tonically secreting glutamate. When a photon strikes, the cascade rhodopsin $\rightarrow$ transducin $\rightarrow$ phosphodiesterase degrades cGMP; the cation channels shut, the dark current collapses, and the membrane potential moves to a more negative value — i.e. it hyperpolarizes — cutting transmitter release. Contrast this with olfaction (cAMP-gated depolarization), gustation (depolarizing receptor potentials), and touch (mechanically gated depolarizing currents), all of which depolarize. The directionality is summarised by the dark-current logic: light $\Rightarrow$ less cGMP $\Rightarrow$ channels close $\Rightarrow$ hyperpolarization.\[\boxed{\text{Visual (photoreceptor) — hyperpolarizes to light}}\]
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