Responding to stimuli is a characteristic feature of all living organisms. A stimulus is a change in the environmental condition detected by receptors in the body; the changes in the organism's activities are its responses. The working together of organs in a systematic, controlled and efficient way to produce a proper response is coordination, which maintains physiological balance called homeostasis. The nervous system controls and coordinates the activities of the body.
1. Stimulus, Response and Coordination
- Organisms respond to stimuli such as light, heat, cold, sound, smell, taste, touch, pressure, pain or the force of gravity.
- Examples: withdrawing the hand from a hot object, or closing the eyes in bright light (heat or light is the stimulus).
- A receptor is a cell or group of cells that receives the stimuli.
- An effector is a part of the body which can respond to a stimulus according to the instructions from the brain or the spinal cord.