脑 (traditional 腦) pairs the flesh radical 月 — used for body parts — with a right side that once drew hair above a skull. Flesh + skull-with-hair: the brain inside the head.
脑 is the thinking organ, and Chinese pairs it brilliantly: 电脑 (electric brain — computer) is the everyday star. 脑子 (nǎozi) is the colloquial 'brains/mind': 动脑子 means 'use your head'. 头脑 (with 头 you learned) is one's mind or wits. When Chinese coined a word for computer, it didn't borrow — it imagined a brain made of electricity, and the word stuck.
Flesh radical 月 + a skull full of wiring — the BRAIN.
电脑 'electric brain' beat the loanword for computer in mainland usage — imagination won over transliteration.