[Biophysics of vision].

Light snesory cells are sensitive photon-counting devices. The mechanism by which the light stimulus is transduced to nervous excitation is described. The absorption of a photon by the visual pigment-rhodopsin, a chromoprotein-causes a photo-chemical reaction, which is followed by a cascade of dark reactions of rhodopsin. One of these reactions triggers conductivity changes in the membrane of the visual cell, which results in a transient voltage impulse across the cell membrane. The magnitude and time course of this electrical signal contain the information of the light stimulus. The molecular mechanism of visual excitation can now be investigated experimentally.