神经 (shén jīng): nerve

He works until early morning every day; the pressure is so great that his nerves are constantly on edge, and even on weekends he can't relax.

Upon hearing that sudden news, her nerves broke down all at once, and she couldn't help but cry.

After the examination, the doctor said that his optic nerve was damaged and required prompt treatment.

The surgery is high-risk because the tumor is too close to the nerve, so the doctor must be extremely careful.

Don't lose your temper over such a small thing; you're too nervous. Just relax a bit.