什么是大脑

脑的最大部分。由大脑半球组成，占脑总量的2/3。是意识过程进行的处所，内有整合感觉和控制随意运动及高级智能功能（包括言语及抽象思维）等的神经中枢。大脑半球的中心是有髓神经纤维，即白质；皮质有很多沟回，即灰质。人类的大脑皮质十分发达，这使人脑不同於其他哺乳动物的大脑。虽然某些白质结构也具有独立的重要功能，但白质中的神经纤维主要用以联结大脑皮质各功能区。由前到後有一条深裂沟将大脑分为两个半球，每个半球调控其对侧躯体的活动。其中一个半球在功能上占优势，它集中了一些特化的神经中枢，如言语、思维的中枢，决定右利还是左利等决定空间趋向的中枢。另一侧半球则支配更微妙、复杂的知觉，如识别不同的面孔。两侧大脑半球由胼胝体连接，它是一块白质的厚板，可联系来自身体两侧的感觉讯息和功能应答。大脑的其他重要结构有下视丘和视丘。下视丘控制代谢和内环境稳定。视丘是一个主要的感觉传递中枢，管理情绪和本能。

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.