Channelrhodopsin: a light switch for nerve cells
About this app
The green alga Chlamydomonas swims towards light; its eyespot carries channelrhodopsin. In a nerve cell, blue light opens this ion channel: cations flow in, the voltage jumps above threshold, and each light pulse triggers an action potential. Pulse rate, light intensity and yellow light with halorhodopsin as a brake.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
An ion channel opened by light
Channelrhodopsin is a membrane protein of the single-celled green alga Chlamydomonas. It captures light with the pigment retinal and is an ion channel at the same time. Peter Hegemann suspected this, and Georg Nagel demonstrated it in 2002 (channelrhodopsin-1) and 2003 (channelrhodopsin-2): blue light opens the channel in less than a millisecond and positively charged ions flow in. In 2005 Karl Deisseroth put the gene into nerve cells, and light pulses triggered action potentials. This earned the 2026 Nobel Prize in Physiology or Medicine.
What the app shows
In the alga scenario Chlamydomonas cells swim to the lamp, and the close-up shows the eyespot and channelrhodopsin in the membrane. In the nerve cell scenario you see the membrane with channelrhodopsin-2 and halorhodopsin, a nerve cell with a light guide and the voltage trace over 500 milliseconds. The trace comes from a simplified model with a resting potential of −70 mV and a threshold of −50 mV.
Try it yourself
Switch on the lamp and watch the algae swim to the light. For the nerve cell, play pulses at 5, 10 or 20 Hz: each pulse gives one action potential. Lower the intensity below about 70 percent and the membrane stays below threshold. With spontaneous activity and yellow light you see how halorhodopsin silences the cell.
Frequently asked questions
- What is optogenetics?
- Optogenetics is a method for switching nerve cells on and off with light. Researchers put the gene for a light-sensitive protein such as channelrhodopsin into specific cells. Light then opens their ion channels and triggers action potentials. This shows which cells control a behaviour, a memory or a feeling.
- What was the 2026 Nobel Prize in Medicine awarded for?
- Karl Deisseroth, Peter Hegemann and Georg Nagel received it "for their discoveries concerning light-gated ion channels and optogenetics". Hegemann and Nagel discovered channelrhodopsin in the green alga Chlamydomonas; in 2005 Deisseroth turned it into a light switch for nerve cells.
- How can light inhibit a nerve cell?
- With halorhodopsin from the archaeon Natronomonas pharaonis. Under yellow light it pumps chloride ions into the cell. The membrane becomes more negative than at rest, the threshold is not reached, and the cell does not fire while the light is on.
- What can I try in this app?
- You switch the lamp for the alga, choose pulse rate and intensity for the nerve cell, add yellow light and spontaneous activity and scrub time from 0 to 500 milliseconds. An explain mode guides you step by step through both scenarios.
Subject: Biology & neuroscience
More from Biology & neuroscience
- Aquaporin — water in single file (3D)
- ATP synthase — the cell's motor (3D)
- Eye — eye muscles and vision (3D)
- CRISPR-Cas9 — the gene scissors (3D)
- Fibonacci cactus — one angle, many spirals (3D)
- Gait — walking from real measurements (3D)
- Haemoglobin — cooperativity (3D)
- Explore the heart (3D)
A VisuApp by heyprof: interactive, free in your browser, no sign-up. What is a VisuApp? · All apps