什麼是大腦

腦的最大部分。由大腦半球組成，佔腦總量的2/3。是意識過程進行的處所，內有整合感覺和控制隨意運動及高階智慧功能（包括言語及抽象思維）等的神經中樞。大腦半球的中心是有髓神經纖維，即白質；皮質有很多溝回，即灰質。人類的大腦皮質十分發達，這使人腦不同於其他哺乳動物的大腦。雖然某些白質結構也具有獨立的重要功能，但白質中的神經纖維主要用以聯結大腦皮質各功能區。由前到後有一條深裂溝將大腦分為兩個半球，每個半球調控其對側軀體的活動。其中一個半球在功能上佔優勢，它集中了一些特化的神經中樞，如言語、思維的中樞，決定右利還是左利等決定空間趨向的中樞。另一側半球則支配更微妙、複雜的知覺，如識別不同的面孔。兩側大腦半球由胼胝體連線，它是一塊白質的厚板，可聯絡來自身體兩側的感覺訊息和功能應答。大腦的其他重要結構有下視丘和視丘。下視丘控制代謝和內環境穩定。視丘是一個主要的感覺傳遞中樞，管理情緒和本能。

cerebrum

Largest part of the brain. The two cerebral hemispheres consist of an inner core of myelinated nerve fibers, the white matter, and a heavily convoluted outer cortex of gray matter (see cerebral cortex). Nerve fibers in the white matter connect functional areas of the cortex in the same hemispheres, connect functional areas of the cortex in opposite hemispheres, and connect the cerebral cortex to lower centers (e.g., the spinal cord). A front-to-back fissure divides the cerebrum's two hemispheres. One is dominant, holding speech and thought centers and determining right- or left-handedness. The other handles more complex perceptions, such as face recognition. Each controls the opposite side of the body. The corpus callosum, a thick band of white matter, connects them, allowing integration of sensory data and responses from both sides of the body. Other important cerebral structures include the hypothalamus and the thalamus, a sensory relay center involved with emotions and instincts.