Squids, Axons, and Action Potentials: Stories of Neurobiological Discovery
Looking for the alphabet of cellular communication in squid axons
In the two connected sections of this exhibit, I’ll explore the history of this last fact: the history of our understanding of how neurons communicate with each other using chemical/electrical signals. Neurophysiology can be an intimidating subject to approach casually. But here, all my attention will be spent presenting the excitement of the process of discovery and on the concepts these scientists helped to illuminate. And while we’ve still yet to break the communicative code neurons use –we don’t always know what one neuron is saying to another- we do know how they say things to each other.
When people, especially people who are not molecular biologists, talk about cell to cell communication we’re often inclined to say things like “the cell perceives the presence” of somethign or “the cell tells its neighbors” and since we presume cells can’t perceive anything in the way we perceive, nor can they tell their neighbors anything in the way we tell our neighbors things, there is something wrong with this picture. We should understand that “talking”, “saying”, and the like, is a metaphor for something subtler: communication. And communication doesn’t need to be verbal or linguistic.
All cells have to communicate with each other. It’s become somewhat common knowledge that diseases like cancer are causally related to errors in cellular communication. We also know that complex signaling systems direct and control the expression of gene networks, which makes molecular communication of central interest to developmental biologists. And we know that somehow the signals that neurons and networks of neurons send and receive result, after an extended chain of causation, in all the motions of our bodies and all the thoughts in our minds.
A good deal of the foundations of our understanding of nervous system signaling came from work done at the MBL, as well as in England at the Plymouth Marine Biological Association laboratory. Alan Hodgkin and Andrew Huxley, working at Plymouth, famously shared the 1963 Nobel Prize in Physiology or Medicine for their detailed studies on the biophysics of nerve cell signals. Less well known outside of the community of scientists who work on these issues is that Hodgkin and Huxley’s biophysical methods were pioneered by Kenneth Cole’s work at the MBL. And that Cole was extending the work John Zachary (JZ) Young had done on the squid giant axon, who was in turn extending work first done by Leonard Worcester (L.W.) Williams at the MBL. Williams’s discovery of the giant axon in the squid, and Young’s rediscovery of it 20 years later, will be our first story. And Hodgkin and Huxley’s biophysical work resulting in the so called Hodgkin-Huxley (conductance-based) model of action potentials in neurons will be our second story.
Hodgkin and Huxley’s discovery, and the later characterization of the biological mechanism involved, are the modern attempt to characterize the alphabet used in the language of neural communication. Of course knowing an alphabet isn’t the same as understanding a language, and knowing how action potentials are generated isn’t the same as understand how that eventuates in all the motions of your body and all the thoughts of your mind. But it is one step in the process. A. And a very exciting step at that.