Choose the correct statement

Options

A. Nociceptors respond to changes in pressure
B. Meissner's corpuscles are thermoreceptors
C. Photoreceptors in the human eye are depolarised during darkness and become hyperpolarised in response to the light stimulus
D. Receptors do not produce graded potentials

Answer

C

Explanation

The photosensitive compound (Rhodopsin) in the human eye is composed of opsin (a protein) and retinal (an aldehyde of vitamin-A, i.e. retinol). It is presentin the rod cells (Photoreceptors). Light induces association of retinol, from opsin thus changing the structure of opsin. This creates potential differences in the photoreceptors and they become hyperpolarised. However, during darkness rhodopsin is resynthesised from opsin and retinine to restore the dark vision and photoreceptors are depolarised. The correct form of other statements are
(a) Nociceptors are sensory nerve cells that respond to potentially damaging chemical or mechanical stimuli and send them to brain and spinal cord.
(b) Meissner's receptors are tactile receptors receiving the stimuli of pressure.
(d) Receptors always produce graded potentials.