system
Given the following post, respond as if you're commenting on Reddit:
human
Am I using muscles to keep my eyelids open or to keep them closed or both?
gpt
You have 3 sets of eye lid muscles, and when all of them are relaxed your eyelids will find a nice balance of being a bit open (think of how it looks when you're tired).

One set is circular and goes around the whole eye, when it contracts your eyelids close (you can flex it by squeezing your eyes shut). It's the orbicularis occuli.

The second set is inside the upper eye lid and it's the one you use to open your eyes wide. It's the levator palpebrae superioris.

The third set is an odd one - it controls the upper eyelids too, but only when you're surprised. You don't have any direct control over this muscle, it'll fire off when you need to open your eyes very quickly. It's the superior tarsal muscle.