Endocrine System
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2. THE NERVOUS System
What is Nervous System?
2.1 Your nervous system is made up of billions of special cells called neurons. The neurons have bundles of fibres called nerves. These nerves conduct messages rapidly throughout the body. Nerve impulses travel along nerve fibres at speeds of 1-90 meters per second. The pathways between neurons are called neural circuits. Your nervous system regulates and coordinates your body’s physical and mental activities in response to changes in the internal and external environment. The changes, called stimuli, initiate impulses in millions of sensory receptors spread throughout your body. The most familiar are the sense organs: the eyes, ears, nose, skin and tongue. In addition to these organs, there are other sensory receptors within the body and close to the surface of the skin. The receptors translate events in a person’s surroundings into nerve messages, which are known as impulses. The nervous system is broadly divided into three parts i.e. automatic nervous system, central nervous system and peripheral nervous system.
The Automatic Nervous System
2.2 This part, which is not under your control, regulates such automatic involuntary bodily processes as breathing and digestion. This part includes the lower brain and spinal cord.
The Central Nervous System
2.3 The brain and spinal cord make up the second part of the central nervous system. It acts as a switchboard that controls and coordinates the activities of the entire nervous system. The brain (about 1.4 kg) is the organ responsible for thought, memory, consciousness, creativity and emotion. It also receives sensory impulses, controls and coordinates muscular movements, and regulates vital body processes. The spinal cord is the pathway for sensory and motor nerve impulses traveling to and from the brain. It also processes some information without the aid of the brain, as demonstrated by reflexes such as the withdrawal reflex. Cerebrospinal fluid fills the open spaces in the brain and surrounds the spinal cord. This fluid acts as a shock absorber, protecting the brain and spinal cord from damage. It transports metabolic wastes out of the central nervous system. Nutrients, hormones, and other vital substances are transported throughout the central nervous system by the cerebrospinal fluid.
