Illustration of Nerve impulses

1952 Nerve impulses

The book of science

Tom Sharp

Alan Lloyd Hodgkin, Andrew Huxley neuroscience Illustration of Nerve impulses

Nerve impulses

Neuron transmit signals along their axons farther and faster than theories could explain. Hodgkin and Huxley made their own equipment to test the giant axon of the squid and found the electrical signal is transmitted by a wave-like exchange of sodium and potassium ions but the signal doesn’t travel through the core; it travels along the surface membrane.

Squid giant axon

The bigger the axon the faster it works. The axon of Atlantic squid, controlling its water-jet propulsion, evolved to increase its chance of escaping predators.


Knee-jerk reactions save effort. At least imitate people you look up to. Sports and war breed snap decisions, but violence is a poor long-term plan. Standing on dry land you might seem as dumb as a fish. The context makes the difference.

Positive-charged sodium ions from outside of the cell membrane exchange positions with negative-charged potassium ions from inside. This exchange propagates in a fraction of a millisecond from the neuron to the axon terminal. Hodgkin and Huxley managed to measure this extremely fast event using voltage clamps on the giant axon of squid. Later, Andrew Huxley was the first to describe how muscles contract.

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