Major Portions of the Brain
The brain is composed of about 100 billion (10¹¹) multipolar neurons and innumerable nerve fibers by which these neurons communicate with one another and with neurons in other parts of the nervous system. The brain can be divided into three major portions - the cerebrum, the cerebellum, and the brain stem. The cerebrum, the largest part, contains nerve centers associated with sensory and motor functions and provides higher mental functions, including memory and reasoning. The cerebellum includes centers that coordinate voluntary muscular movements. Nerve pathways in the brain stem connect various parts of the nervous system and regulate visceral activities.