This channel is then unable to move around and line up with an inner channel, so it cannot transmit sodium ions.

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The first of these to do so let sodium ions in.

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But the right circumstances depend on what is happening in the lipid layers because, by itself, a single gramicidin channel is not long enough to span the membrane and thus let any sodium ions through.

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In the right circumstances these channels will allow the passage of sodium ions (the liquid to be investigated must have these added in the form of sodium chloride, or common salt, if they are not present naturally).

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The number of channel molecules present means that, in normal circumstances, about 70% of the free-floating outer channels are lined up with tethered inner ones at any given time, with each dual channel letting through about 1m sodium ions per second.

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It is the movement of potassium (and also sodium) ions that causes the electrical impulses that nerve cells carry including the impulses found in slow-wave sleep.

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Their main finding was that a nerve impulse, now known as an action potential, is caused by the movement in opposite directions across the axon's surface membrane of sodium and potassium ions.

ECONOMIST: Andrew Huxley

Nerve cells transmit their signals using electrically charged atoms (called ions) of sodium and potassium, which work rather like electrons in a metal wire.

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The second utilizes a highly selective media to capture more radioactive elements in the presence of ions other than sodium, such as potassium, magnesium, and calcium, also through ion exchange process.

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The ions inside the axon are held out of equilibrium with those outside it (there are too many potassium ions within, and too few sodium).

ECONOMIST: Andrew Huxley