I was on Facebook the other day when I saw a link to a YouTube video that immediately caught my attention. The video shows a woman preparing a fish to be cooked, when out of the blue the fish starts twitching (even after being beheaded and de-gutted).
Why in the world does a gutless, headless fish still thrash around? Fascinated by this, I had to research the science behind it.
According to IFLScience.com, although the brain and heart are not functioning, there are cells that can still respond to stimuli, for example, added sodium. Immediately after death, muscle motor neurons (the nerves that create movement within the tissue), which are triggered by electrical signals, still contain some membrane potential (difference in ion concentrations).
All cells are polarized, which means that there is a high-to-low gradient of charged atoms, or ions, from inside cells to outside them. The difference between these concentrations is what creates a charge across a membrane.
When not being activated by the nervous system, neurons maintain their membrane potential by pumping out a balance of sodium and potassium ions (both needed to instigate neurons firing). However, when the neuron is activated with an electric signal, specific channels within the cell open up, allowing sodium ions to flood in – and as equilibrium of charge in the cell to its environment is required, potassium channels are, as a result, also opened up, causing them to flood out of the cell.
Eventually the channels close and the neurons work to restore balance between concentrations of sodium and potassium inside and outside them – but not before triggering nearby channels to open, causing a chain reaction within the muscle.
This is basically how neurons create movement within a tissue.
As previously mentioned, immediately after death, motor neurons maintain some membrane potential, or difference in ion charge, which then starts a domino effect down neural pathways causing movement.
Surprisingly, this crazy phenomenon doesn’t just happen to fish. Heres another similar video that shows a man putting salt on (clearly dead) frog legs, only for them to start twitching as if they were still alive. The same thing happens when squids heads are cut off and the lower half of their body continues to crawl around. In fact, human corpses are also known to randomly move and jerk limbs for hours after death – although this is due to a different mechanism from that in the dancing squid.