Biochemistry - Chemical Reactions in Living Cells, Volume 3 - D. Metzler 1980

Light in Biology
Vision
Nerve Impulse

From the standpoint of nerve impulse initiation, the most crucial consequence of Light absorption is A change in the Membrane Potential at the site of photon absorption, which leads to the initiation of an impulse that propagates toward the synapse along Cell/30.html">The Plasma Membrane like a cable (Chap. 5, Sec. B, 3). The Nature of the transmitted potential change differs between vertebrates and invertebrates. In mammals, the rod outer segment exhibits an extremely high permeability to sodium ions; consequently, a strong inward “dark current” of sodium ions flows through the plasma membrane into The Cell and is pumped back out by sodium pumps. The consequence of light stimulation is a decrease in membrane permeability to Na+ and an increase in its polarization. According to Hagins, it is entirely logical to assume that Calcium Ions serve as the internal messenger in this process, as they effectively block sodium channels and induce the observed hyperpolarization [134]. Hagins estimates that at least 10–20 calcium ions must be released for every absorbed photon. Thus, light absorption opens channels in the disk membranes located within the rods, and the released calcium ions rapidly diffuse to the plasma membrane and block the influx of sodium ions.



Last update: 06/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

  • elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
  • editorial organization of content;
  • standardization of terminology in accordance with academic sources;
  • verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.