The central nervous system (CNS) is one of the two parts of the nervous system. The other is the peripheral nervous system which includes nerves in the organs, muscles, arms, and legs. The central nervous system consists of the brain and the spinal cord. The central nervous system is the "control center" for the entire body and regulates how the body will function.

The average brain weighs three pounds (1.3 kg) and contains 100 billion nerve cells, or neurons. The skull encloses the brain in bone. The brain contains three main areas: the cerebrum, the cerebellum, and the medulla oblongata. The cerebrum is the conscious part of the brain, while the cerebellum and the medulla oblongata form the part of the brain that controls unconscious behavior from the central nervous system.

The medulla oblongata, along with the pons, regulates heartbeat, blood pressure, breathing, and reflexes such as swallowing and coughing. The medulla oblongata is in the part of the brain known as the hindbrain and is nearest to the spinal cord. The cerebellum, connected to the back of the brainstem, is also part of the hindbrain in the central nervous system. The cerebellum coordinates fine motor movement and regulates balance and posture.

The cerebrum is in the forebrain and relates to the central nervous system functioning of reasoning, intelligence, learning, and memory. The cerebrum also regulates sensory and motor controls. The cerebrum is the biggest part of the brain and is divided into the left and right hemispheres. The corpus callosum separates the cerebral hemispheres and is made up of nerve fibers.

The cerebral cortex is the covering on the brain's two hemispheres. Much of the sensory and motor control functioning of the central nervous system is located in the four divisions of the cerebral cortex lobes. The four divisions are the occipital, temporal, parietal, and frontal lobes.

The occipital lobe relates to the functioning of the eye and its visual messages. The temporal lobe relates to the ear and its processing of sounds. The parietal lobe relates to sensory messages such as taste, touch, pain, pressure, and temperature sensations such as hot or cold. The frontal lobe relates to thought, speech, and motor skills. All four lobes function together as part of the central nervous system.

The spinal cord section of the central nervous system connects the brain to the body. The spinal cord is enclosed by the backbone, or vertebral column. Nerve cells work two ways between the brain and the spinal cord in the central nervous system: they carry messages to the brain from the rest of the body and they carry messages from the brain to the rest of the body.