Nervous System

The nervous system is a system of your body which transmits nervous signals and coordinates your actions and responses.

Sense organs
A sense organ is an organ designed to detect stimuli (changes in your environment which might require a bodily response). Your body needs to monitor its environment constantly so it can respond to stimuli if needed.

Your body has five different sense organs - these are your ears, eyes, tongue, nose and skin. All of these contain different receptors. Receptors are groups of cells which are sensitive to stimuli. They change the energy of a stimulus (such as sound energy carried by noises) into electrical impulses. A stimulus can be sound, light, touch, chemical, or a change in temperature or position.

Sense organs and their receptors

 * The eyes contain light receptors and are sensitive to light.
 * The ears contain sound and balance receptors; they are sensitive to sound and changes in position.
 * The nose contains smell receptors - these are sensitive to chemical stimuli.
 * The tongue contains taste receptors. These are sensitive to bitter, sour, sweet and salty tastes, which are chemical stimuli.
 * The skin is sensitive to touch, pressure, pain and changes in temperature.

Cental nervous system
The central nervous system (CNS) is where information from sense organs is sent, and where reflexes and actions are coordinated. The central nervous system is made up of the brain and spinal cord. Neurones transmit the information as electrical impulses to and from the CNS at a high speed. 'Instructions' from the CNS are sent to the effectors (muscles and glands), which respond accordingly.

Neurones and effectors

 * Sensory neurones are neurones that carry signals as electrical impulses from receptors in sense organs to the central nervous system.
 * Relay neurones are neurones that transfer signals from sensory neurones to motor neurones.
 * Motor neurones are neurones that carry signals from the central nervous system to the effectors
 * Effectors are muscles and glands, and they respond in different ways. Muscles contract in response to nervous impulses whereas glands secrete hormones.