Note: This experiment is flawed due to the variability in survival of individual legs. Some legs last for an hour, some last for a day, and often legs have variable rates of drying out. Getting an answer to the hypothesis proposed in this experiment has eluded us. If you have a solution, do let us know!

Background

We previously in lesson 3 talked about the ion channels that allow sodium (Na+) and potassium (K+) to cross the membrance, causing the “spikes” you hear on your SpikerBox.

But how does the sodium get back out of the cell, and potassium back into the cell, resetting the ionic balances for the spikes to continue occurring? The answer:

The Sodium-Potassium Pump!

It moves three sodium ions out of the neuron for every two potassium ions it pumps into the neuron. It works hard for your spikes.

Doing this pumping, as you would expect, takes energy. The energy is stored in a molecule called ATP (Adenosine triphosphate).

When it releases one of its phosphate groups to become ADP (Adenosine Diphosphate) energy is released to power the Sodium-Potassium Pump.

Your body, and the body of all animals, makes the ATP from the carbohydrates (like sugar, bread, and pasta) and fats (like oil, milk, and nuts) that you eat. Your body has a limited supply and constantly needs to remake it.

You have probably noticed that the cockroach leg does not last forever (our record is 3 days). Eventually it no longer produces spikes and dies.

Two of the reasons are 1) it dries out (which can be delayed by applying beeswax or vaseline to the exposed parts), and 2) it has run out of its energy. Let’s test the energy hypothesis!

Procedure

We will need:

You will also need:

We will use the speaker & toothpick to stimulate the cockroach leg and generate more spikes in one of the legs (this is much easier than blowing on the legs as you have done in previous lessons). Hip-Hop and R&B music work best.

If the toothpick is resting on the thorny part of the cockroach leg, and you play music through the speaker, the toothpick should vibrate and cause increased spiking in the nerves of the cockroach leg. If you listen carefully, you should actually hear the spikes modulating to the beat of the music. We prefer to use the Beastie Boys or GZA.

This experiment takes a couple days, so be sure to put beeswax on the wounds of the cockroach legs so that they don’t dry out. The SpikerBoxes don’t need to be on all the time, just the music. Every 6-12 hours, take a recording from each SpikerBox to see which leg is continuing to produce spikes (you can briefly put the toothpick on the control leg to see if it’s responsive during your recordings). Which leg do you think will use up all its energy (use up its ATP) first. What did your results show? What could be an alternative explanation?

Note: This is an ongoing experiment. We do not know the answer either. Let us know your results!