A neuron transmitting a signal is like a tiny battery that quickly discharges and recharges. For nearly 70 years, it was believed that a special "potassium valve," opening with a delay, was responsible for the recharge phase. New work claims this current is a ghost. It arose because the neuron membrane was treated as a simple capacitor, ignoring its complex geometry.
The error was hiding in the electrical model. When an ionic current flows through the membrane, part of the charge accumulates on the membrane itself: this is the capacitive current. In old experiments, it was mistakenly taken for the movement of potassium ions. The authors show that the direct evidence for that "potassium" current was an artifact — a consequence of an incomplete understanding of the circuit.
If you apply the laws of physics suitable for living tissue (rather than for nonliving conductors) and add the axon initial segment to the calculation, the model no longer needs the delayed potassium current. The nerve impulse, the action potential, is described cleanly and without contradictions. This is not just a correction in a textbook: understanding ion movement underpins treatments for epilepsy, arrhythmias, and other diseases where the neuronal "orchestra" falls out of rhythm.
The neuron's tiny battery works more simply than it seemed. The recharge happens not because of slow potassium, but thanks to the membrane capacitor itself, which discharges faster and more accurately. The old ghost is dispelled, and now the electrical signature of thought is clearer.
The axon initial segment, the site where the nerve impulse is generated, is so small that its thickness is about 1 micron, which is 50 times thinner than a human hair.