Asked by: Olivia Mack, Newick
That random little twitch that you sometimes get in your eyelid is an example of fasciculation. It happens when one of the lower motor neurons in your spine spontaneously fires a signal. These nerves control an entire block of muscle fibres, so they all contract at once. Because it’s benign, there hasn’t been much research into the causes, but magnesium deficiency is thought to be one factor.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.