Nerve cells don’t hold their electrical charge by chance. Cupritium sets out the documented contribution potassium makes, under EU regulation, to the normal functioning of the nervous system.
Read the Starter GuidePotassium is involved in virtually every electrical event in a nerve cell — from the quiet baseline state to the return to that baseline after a signal.
Potassium is the most abundant positively charged particle inside a cell. By far the largest share of the body’s total is found not in the blood but within the cell membranes — a ratio that matters for how nerve cells work electrically.
EU-authorized wording · Regulation (EU) No 432/2012
At rest, there’s a voltage difference of roughly −70 to −90 millivolts between the inside and outside of a nerve cell. That’s not a side detail — it’s the precondition for the cell being able to respond to a stimulus at all. How the potassium gradient helps set this value follows below.
Every nerve cell is wrapped in a thin membrane that doesn’t let charged particles pass through freely. Potassium sits at a markedly higher concentration inside the cell than outside it — sodium behaves the other way around. This gradient doesn’t arise on its own; it’s continually defended against the constant pull toward equalization by carrier proteins in the membrane.
Four pieces of this interplay can be looked at separately. They explain why potassium specifically has been studied scientifically in connection with the normal functioning of the nervous system — they’re background knowledge and not themselves part of the official wording.
For a single, freely moving ion, it’s possible to estimate the voltage at which the inward-pulling electrical field and the outward-pushing concentration gradient exactly balance out. This value is called the equilibrium potential, and it’s described by the Nernst equation.
EK = 61 mV × log10 ([K+]out ÷ [K+]in)
Because there’s so much more potassium inside than outside, the concentration gradient pulls potassium ions outward. The negative charge left behind inside the cell then pulls those positive ions back in. The measured resting potential of a nerve cell sits close to this calculated value, because at rest it’s mainly potassium channels that are open.
During an action potential, the charge briefly reverses: sodium flows in first. Shortly afterward, voltage-gated potassium channels open — with a small but important delay relative to the sodium channels. These so-called delayed rectifier potassium channels let potassium flow out and drive the membrane voltage back toward its negative starting value.
Without this outward flow of potassium, the membrane would stay stuck in its positively charged state, and the nerve cell couldn’t form a second signal. This sequence — sodium in first, then potassium out — is what gives the action potential its typical, brief shape.
Right after an action potential comes a phase in which the nerve cell can’t be excited again, or only with difficulty — the refractory period. It’s closely tied to the outward potassium flow just described: as long as the voltage-gated potassium channels are still open, the membrane stays more negatively charged than in its usual resting state, sometimes even briefly beyond it.
This brief but measurable delay makes sure a signal travels in only one direction along the nerve fiber and doesn’t overtake itself. Only once the potassium channels close again and the resting potential is reached can the cell respond fully to a new stimulus.
Alongside the voltage-gated channels, there’s a second, lesser-known group: the two-pore domain potassium channels, or K2P for short. They stay partly open at all times, independent of the membrane voltage, and provide a steady, quiet outward flow of potassium — a so-called leak current.
Precisely because this leak current doesn’t wait for a signal, it helps set the baseline resting voltage before an action potential even begins. Only the interplay of a constantly present potassium gradient, open leak channels, and channels that switch on with a time delay explains why potassium was studied scientifically for the normal functioning of the nervous system:
“Potassium contributes to normal functioning of the nervous system” — EU-authorized wording · Regulation (EU) No 432/2012
Access includes every chapter on this page, the summary table, and the full text of the EU regulation on potassium.
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