Crossing the Gap

So we have a pretty good picture of how the nervous system fits together and how nerves transmit signals. But there's a third key part of the jigsaw: how signals cross synapses. Back in the 1930s, scientists were divided into two camps: On one side were the 'sparkers' who thought it was electrical, like the nerve impulse itself; on the other side were the 'soupers' who thought the synaptic signal was chemical. Sparkers just couldn't see how chemicals could move fast enough; soupers couldn't see how electricity would work.

The soup idea gained strength in the 1930s through the work of British pharmacologist Henry Dale and German Austrian Otto Loewi, for which they received the Physiology or Medicine Prize in 1936. Loewi's ingenious idea was to collect fluid from around a frog's heart just after the connecting nerve had been stimulated to slow the heart down. He injected the fluid into another frog's heart - and immediately the second frog's heart slowed. No nerve signal had fired - so it was clear some chemical in the fluid was slowing the heart. Dale went on to show that the heart-slowing chemical is acetylcholine. There's also a heart-booster called adrenaline.

Otto Loewi



Otto Loewi with his assistants in his laboratory. Loewi’s ingenious experiment on frog hearts provided the first conclusive proof that chemicals transmit impulses from one nerve cell to another, and from nerve cells to their target organ or gland.
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