system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Am I keeping my eyes open while I'm awake or am I keeping them closed while I'm sleeping?
gpt
Both!

Most movements in the body are done by two muscles (for example, the biceps flexes/bends your elbow and the triceps straightens/extends it).

There is a muscle in the eyelid which closes the eye, and another which keeps it open. When you sleep, your brain forces the muscle that closes your eye to close it - this also happens involuntarily when you blink. You can also choose to activate a voluntary part of this muscle, like when you think about blinking or wink.

When you open your eye an opposing muscle is active, which you have less control over (when you widen your eyes, as opposed to opening them, a different muscle is activated). This is done an unconscious part of your brain (the basal ganglia).

Summary: three muscles move the eyelid - two that open it and one that closes it. You can consciously or unconsciously control the closing muscle, and your eye is kept open automatically when you're awake by your brainstem, which you can modify by activating another muscle to widen the eyelids.

Edited for "brain" (basal ganglia) instead of brainstem.