Reference
Glossary & Sources
Glossary
- Action potential
- The all-or-nothing voltage spike a neuron fires once its membrane crosses threshold.
- Born–Oppenheimer approximation
- Treating electrons as adjusting instantly to nuclear positions, so each electronic state defines an energy surface.
- Channelrhodopsin-2 (ChR2)
- Light-gated cation channel from the alga Chlamydomonas reinhardtii; the workhorse of optogenetics.
- Chromophore
- The part of a molecule that absorbs visible light; here, retinal.
- Conical intersection
- A point where two electronic energy surfaces touch, acting as a fast funnel between them.
- Conjugation
- Alternating single and double bonds whose π electrons are shared along the chain.
- Franck–Condon principle
- Electronic transitions happen so fast that nuclei do not move during them.
- HOMO / LUMO
- Highest occupied and lowest unoccupied molecular orbitals.
- Nernst potential
- The voltage at which a single ion species is in equilibrium across a membrane.
- Opsin shift
- The change in retinal’s absorption colour caused by its protein environment.
- Quantum yield
- Fraction of absorbed photons that produce the desired reaction.
- Rheobase
- The smallest steady current that can bring a neuron to threshold.
- Reversal potential
- Membrane voltage at which a channel’s net current is zero.
- Schiff base
- The C=N link joining retinal to a lysine of the protein; protonated in the dark state.
- Time constant τ
- RC of the membrane; the time to reach 63% of the final voltage change.
The laureates' key papers
- Nagel G., Ollig D., Fuhrmann M., Kateriya S., Musti A. M., Bamberg E., Hegemann P. “Channelrhodopsin-1: a light-gated proton channel in green algae.” Science 296, 2395–2398 (2002). doi:10.1126/science.1072068
- Nagel G., Szellas T., Huhn W., Kateriya S., Adeishvili N., Berthold P., Ollig D., Hegemann P., Bamberg E. “Channelrhodopsin-2, a directly light-gated cation-selective membrane channel.” PNAS 100, 13940–13945 (2003). doi:10.1073/pnas.1936192100
- Boyden E. S., Zhang F., Bamberg E., Nagel G., Deisseroth K. “Millisecond-timescale, genetically targeted optical control of neural activity.” Nature Neuroscience 8, 1263–1268 (2005). doi:10.1038/nn1525
The prize
- Press release, Nobel Prize in Physiology or Medicine 2026 and popular information, NobelPrize.org.
- 2026 Nobel Prize awarded to scientists behind optogenetics, Scientific American, 5 October 2026.
- Deisseroth, Hegemann, Nagel awarded 2026 Nobel Prize in Medicine, STAT, 5 October 2026.
On the numbers in this course
Values in Parts 1 to 3 are order-of-magnitude teaching estimates, and are labelled as such where they appear: the ChR2 single-channel conductance (~50 fS), the rhodopsin quantum yield (~0.65), retinal's absorption cross-section (~2 × 10⁻¹⁶ cm²), the specific membrane resistance (~15,000 Ω·cm²) and the opsin-shift wavelengths (440 / 470 / 570 nm). Real neurons and expression levels vary widely.
Every derived number is recomputed by the code on the simulations page, which you can run in the browser and check against the text.
Licence and changelog
Text and figures CC BY-SA 4.0. The simulation code is MIT-licensed.
5 October 2026 — first published, the day the prize was announced. A revision is planned for December, when the laureates' Nobel lectures are published.