From Visual phototransduction - Wikipedia:

When struck by a photon, 11-cis retinal undergoes photoisomerization to all-trans retinal which changes the conformation of the opsin GPCR leading to signal transduction cascades which causes closure of cyclic GMP-gated cation channel, and hyperpolarization of the photoreceptor cell.

From the physics point of view, does this mean the proteins in the eye are combinations of oscillators, each of them in charge for a specific wavelength, so that if one oscillator resonates with the photon, the signal is produced? In general, does all receptors work this way? Note that physical oscillators should have exponential or sinusoid functions. See this Photography question: How to capture a swinging pendulum?

up vote 5 down vote accepted

Photoreceptors themselves dont act as oscilators, a single receptor is either 'on' or 'off' - it does not respond differently to different wavelenghts. Humans have Trichromatic vision, which means that we have 3 different kinds of photo-receptors that respond differently to light of a given wavelength at a given intensity. By combining multiple signals from these 3 different receptor types the brain can translate this to different colors (its actually kind of similar to how RGB color works).

Therefore I would say that even photo-receptors don't work like oscilators, only their specific ligands switch between the 11-cis & trans state, but this is more of a statistical and physico-chemical process (which does involve resonance between the energy of the photons and the electrons in the cis bond)

  • In general, how is a sensory receptor stimulated? I suppose that by the peak of intensity of the signal, right? – Ooker Jun 9 at 10:30

Receptors accept a huge variety of molecules as ligands.
In the example that you outline the receptors are called photoreceptors. The ligands for photoreceptors are generally contain alkene backbones which switch cis and trans forms on exposure to a certain wavelength. The oscillator analogy holds true to a certain extent.
However, not all receptors function similar to photoreceptors. Photoreceptors are designed in a way to sense a wide signal spectrum (the visual spectrum). On the other hand receptors which work on a much local scale e.g. delta receptor for the notch ligand are not similar to oscillators at all i.e. there is no factor of resonance with external stimuli.

  • Do you mean the ligands of photoreceptors switch cis and trans back and forth, which has two and only two configurations? That's not what I mean by oscillators. Physical oscillators should have exponential or sinusoid functions. See this Photography question: How to capture a swinging pendulum – Ooker Feb 20 at 9:15
  • The function will definitely be not exponential as the receptor will be recycled i.e. it will come back to ground state as negative regulation of receptors exists to maintain homeostasis. I think the process can be modeled sinusoidally. However, there will be lag periods between two peaks as the receptor has to be primed to be able to respond to the next stimulus. – Roni Saiba Feb 23 at 8:49

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