system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is actually happening when you feel your muscles twitch without moving the muscle?

Like when they start to move involuntarily and twitch a few times on your leg muscles, for example.
gpt
What you're referring to is called a fasciculation.

Essentially a motor neuron (one of the neurons that normally transmits the signals for your muscles to contract) is activated (depolarized) spontaneously causing your muscle to contract.

It's essentially the same process that causes your heart to beat but it happens randomly. We aren't really sure why and it's benign in a large majority of people. Not the best answer but we still aren't entirely sure why it happens in healthy individuals.