Coordination is the working together of the various organs of an organism in a systematic manner so as to produce a proper response to the stimuli. Without coordination the body becomes disorderly and it may fail to function properly.
The coordination in simple multicellular animals takes place through nervous systemonly. The control and coordination in higher animals called vertebrates (including humanbeings) takes place through nervous system as well as hormonal system called endocrinesystem. Coordination in plants is under the control of hormones.
All the living organisms (plants and animals) respond and react to changes in the environment around them. The changes in the environment to which the organisms respond and react are called stimuli (singular: stimulus). The living organisms show response to stimuli such as light, heat, cold, sound, smell, taste, touch, pressure, pain,water, and force of gravity, etc. The ability to perceive, interpret and respond to stimuli is called irritability or sensitivity.
There are two types of stimuli: external and internal. External stimuli are associated with the surrounding environment such as wind temperature, light, pressure, touch, water and gravity. Internal stimuli occur within the organism, for example, a decrease or an increase in the amount of water and glucose in the blood.
When an organism detects a stimulus, it initiates a response. A response is a behavioural,physiological or muscular activity initiated by a stimulus. For example, if a man touches a very hot utensil accidentally, he quickly pulls his hand away from the hot utensil. Here,heat is the stimulus and the man reacts (responds) by moving his hand away from the hot utensil.
Similarly, when the sun is bright, we close our eyes. In this case, light is the stimulus and we react by closing our eyes. Likewise, when the amount of water in the blood drops, the pituitary gland secretes an anti-diuretic hormone (ADH) which stimulates the reabsorption of water in the kidneys.
Multicellular organisms detect stimuli through sense organs called receptors. A receptor is a sense organ (e.g. eye) or sensory nerve ending (e.g. in the skin or internal organ) which receives stimuli and sets nervous impulses. Impulses are electrical transmissions or chemical stimuli that are sent from the receptor to the coordinating system in the organism. The organs that respond to the stimuli are called effectors.
A coordinator is an organ (e.g. the brain and spinal cord) that receives messages from the receptors,translates them and sends the information back to an effector for action. An effector is a muscle or gland which receives impulses from nerves, brain or spinal cord and responds to them. Response is the end-action, such as a muscle contracting to cause the movement of the arm. The diagram below illustrates the five components of coordination in mammals.