Thank you for the suggestions. My students are familiar with the electrolyte activities because several of them completed similar experiments as part of their science fair projects. We also covered active and passive transport in a unit about cell membranes.

Diana has great advice - I was going to suggest the same demo (http://chemdemos.uoregon.edu/demos/Conductivity-of-Electrolytes). This is also a great time to discuss concentrations and solutions. You can use solid salt, then a solution of salt in water, then just water to show you need a salt solution to pass a current. You could also discuss diffusion/active transport, which is a good mix of chem and bio. For the neurons to work you need sodium to be concentrated outside the cell and potassium to be concentrated inside the cell. How does this work? If the solution were just inside a beaker (like the demo), then the ions would distribute evenly. But human bodies have developed really cool ways to do the chemistry they need - active transport to create the ion gradient. There are also some cool demos that have to go with sports drinks. One (which can be done with a light bulb but is better with a current meter) measures the current through different solutions (water, juice, sports drinks), which can then be compared to the sodium and potassium concentration in the drinks (http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p053.shtml). The Royal Society of chemistry also has a really cool lab developed. It focuses more on the sugar aspect (as well as electrolytes), but I thought I'd attach it anyway.

One of the things that I try to emphasize with my students is the difference between talking about electrolytes in Chemistry and "out in the real world". Electrolytes are by definition 'charged particles', so when in the 'real world' people discuss drinking something like Gatorade for the sodium and potassium, I discuss the fact that these are elemental names and symbols and not really the electrolyte name or symbol. I then show how the elements of sodium and potassium will burn when placed in water and so if they were to actually drink sodium in their Gatorade, it would burst into yellow flames in the bottles. Then we talk about Na ions and K ions and what they do within solutions and the human body. We do a lab that shows how solutions will conduct electricity--light up a light bulb--if there are electrolytes, ions, in the solution. I also mention that they may remember in Biology class how the nerve synapses work with the transfer of that electron and the 'spark' that happens. That is my extent of what I remember about the nervous system and electrolytes. I'm not sure this is helpful or not for what you are looking for. You tube could be helpful in videos of the elements burning or the electrolytic solutions lighting up light bulbs. I also mention how high blood pressure medicine reduces the amount of K ions in the body, so people are instructed to eat bananas to replenish this electrolyte.