Dear Biology Nerd,
THIS VIDEO
WHAT
WHAAAAAAAAT
-Amelia P.
***
Dear Amelia,
For those who can’t (or just didn’t) see the video, it’s somebody sprinkling salt on some frog legs, which jump around and enjoy a dance despite having no body to go with. I have a pretty simple biological theory on why this happens. Let me break it down for you
First of all, table salt is a chemical called sodium chloride. The sodium and the chloride are bonded together, which is why they are totally safe even though on their own large concentrations are explosive or poisonous, respectively. (Go Google sodium and water reactions. Pretty crazy explosions!) When salt is placed in water, the chloride and sodium separate to form charged particles called ions.
The body uses both sodium and chloride all the time as chemical messengers. One way to use them causes electrical impulses in your neurons. Your neurons have long fibers, called axons, that connect one to another like wiring in an electrical system. Where one of the axons “plugs in” to the next neuron, it’s a synapse.
Synapses are cool because they use chemicals to create electricity, sort of like how a battery works. These ions, when separated, have a charge. Sodium’s is positive. A cell will usually pump sodium out to keep the concentration and thus the voltage that it wants.
The voltage is very important, because in neurons it allows for something called an action potential to occur. The synapses have channels in them that are opened or closed depending on the charge of the environment around them. They will open at a certain voltage and let sodium into the cell. Because this sodium has a positive charge, the voltage in the cell skyrockets upward, creating an electrical impulse as little sodiums pour into the cell. And bada-bing bada-boom, these impulses can be used to tell muscles to move.
Unfortunately, funding for our All-Frog-Leg Rockettes startup has so far failed to materialize. (Art credit: The Language Nerd — the Bio Nerd’s in med school, she doesn’t have time to illustrate every brilliant thought she has!)
So, what does this have to do with frog legs? Basically, the salt releases sodium onto the muscles of the frog legs, which causes an action potential. This makes the frog legs jerk even though there is no frog attached!
Yours,
The Biology Nerd
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Because these are fresh frog legs, the cells inside them are all still intact. The biochemical machinery still functions. There is still a source of energy for the muscles in the form of unused ATP molecules stored in the cells. All that the muscles need is something to activate them and they can still contract and relax (until they run out of ATP or something else shuts down the biochemical machinery).
You are correct. The ATP supply continues post mortem until it is used up over a period of time. This process is a lot more complicated than what I explained. In fact, there is all sorts of jazz with calcium ion releases, T-tubules in the myofibers, sarcoplasmic reticulum’s Ca mediated calcium release, Ca binding to the troponin, which moves the tropomyosin, which allows the myosin to bind to the actin causing the power stroke and muscle fiber contraction.
Interestingly, ATP’s role in this whole thing is not the contraction of the muscle itself, but the RELEASE of contraction. The ATP binds to the myosin to allow it to detach from the actin and release the contraction. This process will continue after death until the ATP reserve is completely utilized. This is actually the explanation of rigor mortis, or why things get stiff after they die. The muscles are stuck in a contracted position because of the lack of ATP to release the contraction until they degenerate enough that the contraction is released.
That’s all a little complicated and really beyond the scope of the explanation for why the salt causes the frog legs to dance, but in the interest of science, you are correct in the role of ATP even if it works a little differently than you imply it does.