The human brain is a greyish-pink, jelly-like organ with many ridges and grooves on its surface. A newborn baby's brain weighs less than 0.5 kg. By the time a person is 6 years old, the brain reaches its full weight of about 1.4 kg. Most of the brain cells are present at birth, and so the increase in weight comes mainly from growth of the cells.
The human brain uses about 20 percent of the oxygen used by the entire body when at rest.
The cerebrum makes up about 85 percent of the weight of the human brain. A thin layer of nerve cell bodies, called the cerebral cortex or cortex forms the outermost part of the cerebrum.
The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord. The bottom part of the brain stem is called the medulla oblongata.
At the upper end of the brain stem are the thalamus and the hypothalamus.
The hypothalamus regulates body temperature, hunger and other internal conditions. It also controls the activity of the nearby pituitary gland, the master gland of the body.
Surgeons treat some cases of epilepsy by cutting the corpus callosum, which connects the cerebral hemispheres. This operation produces a condition called the split brain, in which no communication occurs between the hemispheres. Studies of split-brain patients suggest that the left hemisphere largely controls our ability to use language, mathematics, and logic. The right hemisphere is the main centre for musical ability, the recognition of faces and complicated visual patterns and the expression of emotion.
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