brain

The central organ in the nervous system, protected by the skull. The brain consists of the medulla, which sends signals from the spinal cord to the rest of the brain and also controls the autonomic nervous system; the pons, a mass of nerve fibers connected to the medulla; the cerebellum, which controls balance and coordination; and the cerebrum, the outer layer of which, the cerebral cortex, is the location of memory, sight, speech, and other higher functions.

The cerebrum contains two hemispheres (the left hemisphere and the right hemisphere), each of which controls different functions. In general, the right hemisphere controls the left side of the body and such functions as spatial perception, whereas the left hemisphere controls the right side of the body and functions such as speech.

Under the cerebral cortex are the thalamus, the main relay center between the medulla and the cerebrum; and the hypothalamus, which controls blood pressure, body temperature, hunger, thirst, sex drive, and other visceral functions.

Make a great mental effort to understand, solve, or remember something, as in Joe's beating his brains out to finish this puzzle. Christopher Marlowe used this hyperbolic idiom in The Massacre of Paris (1593): “Guise beats his brains to catch us in his trap.” Also see rack one's brains.

In addition to the idioms beginning with brain

• brain drain
• brain someone
• brain trust

also see:

• beat one's brains out
• blow one's brains out
• on one's mind (the brain)
• pick someone's brains
• rack one's brains