READ: Basic Nervous System Anatomy

The Brain

The brain is the most complex organ of the human body and the control center of the nervous system. It contains an astonishing 100 billion neurons! The brain controls such mental processes as reasoning, imagination, memory, and language. It also interprets information from the senses. In addition, it controls basic physical processes such as breathing and heartbeat.

The brain has three major parts: the cerebrum, cerebellum, and brain stem. These parts are shown in Figure below and described in this section. 

You can also take an interactive animated tour of the brain:

• http://www.garyfisk.com/anim/neuroanatomy.swf .

• The cerebrum is the largest part of the brain. It controls conscious functions such as reasoning, language, sight, touch, and hearing. It is divided into two hemispheres, or halves. The hemispheres are very similar but not identical to one another. They are connected by a thick bundle of axons deep within the brain. Each hemisphere is further divided into the four lobes shown in Figure below .
• The cerebellum is just below the cerebrum. It coordinates body movements. Many nerve pathways link the cerebellum with motor neurons throughout the body.
• The brain stem is the lowest part of the brain. It connects the rest of the brain with the spinal cord and passes nerve impulses between the brain and spinal cord. It also controls unconscious functions such as heart rate and breathing.