Voltage Regulator

It was Adrian's student Alan Hodgkin who along with Andrew Huxley formulated a theory - termed the 'ionic hypothesis' - to explain how action potentials are generated. Most nerve fibres are so small and fine it is almost impossible to make any measurements inside, but Hodgkin and Huxley hit upon the great idea of experimenting with giant axons in squids. At a whopping millimetre thick, a squid giant axon is about a thousand times as thick as most human axons.

Connecting wires inside and out of the squid axon, Hodgkin and Huxley measured the difference in voltage, in other words the action potential, as a nerve impulse sweeps along the axon. Using clever mathematical models to make sense of the mass of electrical data they collected, Hodgkin and Huxley revealed that in its 'resting' state, some negatively charged potassium ions seep in through the membrane that makes up the nerve cell walls, while positively charged sodium ions leak out, which creates a small but measurable voltage. When a nerve is stimulated, however, Hodgkin and Huxley proposed that 'ion gates' open up in the membrane, allowing sodium ions to flood in to create the upstroke of the nerve signal's spike, and potassium ions to flood out to create the downstroke. The action potential sweeps along the nerve as ion gates open and close in quick succession.

In the 1970s, Erwin Neher and Bert Sakmann revolutionized the field with the development of the patch-clamp technique, an instrument that enabled scientists to study the flow of ions through a single one of these ion gates, or channels - a remarkable achievement for which they received the Physiology or Medicine Prize in 1991. And in 2003, Roderick MacKinnon received a Nobel Prize in Chemistry for his astonishing 3D pictures of ion channels.

Ion channels and nerve impulses. Nerve impulses are generated by charged atoms, or ions, flowing into and out of nerve cells through channels that line the cell membrane. Sodium ions flowing in these ion channels create the rising phase of the nerve signal, while the falling phase is created by potassium ions flowing out. The wave of electric charge moves along the nerve cell as ion channels open and close in quick succession.
Copyright: The Royal Swedish Academy of Sciences.

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