In anatomy, a bundle of fibers that transmits signals in the body; a nerve.
腰の神経を痛めて、足にしびれが出た。
I injured a nerve in my lower back and developed numbness in my leg.
その手術は重要な神経に近いので慎重に行われた。
The surgery was performed carefully because it was close to an important nerve.
Psychological sensitivity or nerves — refers to being easily affected, tense, or touchy (e.g., 'to be thin-skinned').
あの人は神経が細いから、少しのことでも気にする。
That person is sensitive and worries even about small things.
大事な発表の前で神経が高ぶっている。
My nerves are on edge before the important presentation.
彼は図太い神経を持っているので、あまり動じない。
He has thick nerves, so he doesn't get rattled easily.