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Four Components of the Brain

The Brain Injury Association's booklet, "Living With Brain Injury: A guide for and about adults with moderate to severe brain injury" contains a diagram of the brain and a description of various portions of the brain.


The brain has three main regions: the cerebellum, the brain stem, and the cerebrum. All three regions work together yet each has its own special functions. Most brain injuries affect several areas of the brain.


The brain stem, about the size of the little finger, sits at the base of the brain and is an extension of the spinal cord. The brain stem has two main functions: control of basic life processes (such as breathing and heart rate) and arousal and consciousness (that is, alerting the thinking part of the brain). As a result, damage to the brain stem may reduce arousal and alertness and impair breathing, heart rate, and sense of touch. Twelve cranial nerves based in the brain stem run through the rest of the brain.


The cerebellum, about the size of two large plums, lies under the lower back of the skull. It has a right and a left side and handles two main functions: maintaining balance and coordinating movement. Damage to the cerebellum may therefore cause difficulties in coordination and balance (for walking and standing).


The cerebrum is the largest part of the brain. It has two regions (or halves), left and right. The left side generally receives messages from and controls the movement of the body. The dominant side, which is usually on the left (for right-handed people), controls speech, understanding, reading, writing, arithmetic, and other language functions. The non-dominant side, usually the right (for right-handed people), processes nonverbal information , including spatial orientation, relationships of objects to each other, and recognition of shapes, forms, and faces. The cerebrum hemispheres are further divided into four sections, or lobes-parietal, frontal, temporal, and occipital.