The potential of an ion

You will write the Nernst equation as a function and use it for the two ions of a nerve cell. The concentrations are the model values of the lesson, in mmol/L, at body temperature.

The idea. For one kind of ion, $E = \dfrac{26.71}{z}\ln\dfrac{[\text{out}]}{[\text{in}]}$ in millivolts, where $z$ is the charge of the ion.

Your tasks.

1. Finish nernst. It gives the potential in millivolts for the concentration outside, the concentration inside and the charge z.
2. Set e_k and e_na to the potentials of K+ and Na+ for the model values, rounded to one decimal place.
3. Finish closer_to. It gives "K" when a voltage is closer to the potassium potential than to the sodium potential, and "Na" otherwise.