Center, Centre, Pivot
noun, の adjective
The middle hinge is the center pivot point.
ちゅうすう
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
どうしてそれが彼女の中枢神経系を刺激したの？
How could it stimulate her central nervous system?