system
Given the following post, respond as if you're commenting on Reddit:
human
Is the optic nerve stretchy or is there some slack to let your eye move?

When you move your eye to look around, does the optic nerve stretch or is there a little bit of slack inside your skull to allow the nerve to be pulled?
gpt
The optic nerve in an adult has about 8mm of slack to allow the eye to move. 

Nerves in general do not stretch very much, and the optic nerve in particular cannot stretch at all. That's because it is part of the central nervous system. 

Because the nerve connects directly to the brain, it is covered in an extension of the brain's protective membrane envelope. Those membranes are called the "meninges," and consist of three layers: the dura, the arachnoid, and the pia mater. The dura is the outermost layer. It's relatively thick and consists of tough, fibrous, connective tissue, to protect the other membrane layers and the underlying nerve itself. It doesn't stretch significantly, and that means the whole bundle has to stay a pretty much constant length.