Bioelectricity: A Quantitative Approach
Roger Coke Barr
Nerves, the heart, and the brain are electrical. How do these things work? This course presents fundamental principles, described quantitatively.
Welcome to Bioelectricity Week 4, a week about the Hodgkin-Huxley model of action potentials. This "model" is an integrated set of ideas, computational procedures and experimental data (for squid nerve) that shows how the ionic currents, each one in its own time and sequence, make use of stored energy and membrane capacitance to create action potentials. One could say that everything done in the course so far has been to get ready for Hodgkin-Huxley.
How can a membrane generate these action potentials, a kind of biological voltage pulse? It is not at all obvious A membrane sits at rest. How does the voltage suddenly rise? and then what makes it come down again? All is explained, and precisely so, by the Hodgkin-Huxley model of the sequence of ionic currents and other electrical events within and across the membrane. The train is a good analogy, in the sense that the engine and all the cars have to be lined up and hooked together in just the right way. You will enjoy seeing how it is done.
The importance of the HH model is not because of giant squids, fascinating ugly creatures though they may be. Rather, the importance of HH comes from its use as a powerful core set of ideas, and then as a starting point for model adjustments, extensions and modifications. That power allows descendent models to portray what happens in other kinds of tissues in many other species, including ourselves.
When you have finished this week's work, you will benefit from a mystique about bioelectricity that confers special standing on those who know the Hodgkin-Huxley model. You will know that it's not that hard --- essentially four levels crossed in a certain order, each transit requiring some arithmetic but nothing notably difficulty. However, the mystique is that HH is so deep and so complicated that it can be understood by only a chosen few. Welcome to that inner circle. :)