The Central Nervous System
The central nervous system functions as a "main switchboard" that controls and coordinates the activities of the entire nervous system. The central nervous system consists of the brain and the spinal cord.
The brain is an extremely complicated organ. It consists of three principal parts, the cerebrum, the cerebellum, and the brain stem.
The cerebrum makes up about 85 per cent of the brain and is the most complex part. It is above the cerebellum and the brain stem and almost surrounds them. Human beings have a highly developed cerebrum that directs their hearing, sight, and touch and their ability to think, use language, and feel emotions. The cerebrum is also the centre of learning.
The cerebellum, which is about the size of an orange, is slightly above the brain stem. It helps maintain the body's sense of balance and coordinates muscular movements with sensory information.
The brain stem is a stalklike structure that is connected to the spinal cord at the base of the skull. The brain stem contains neurons that relay information from the sense organs. Many neurons that regulate automatic functions, such as balance, blood pressure, breathing, and heartbeat, are also in the brain stem.
The spinal cord is a cable of neurons that extends from the neck about two-thirds of the way down the backbone. The backbone surrounds and protects the spinal cord. The spinal cord contains pathways that carry sensory information to the brain. It also has pathways that relay commands from the brain to the motor neurons.