The Nervous System
A stimulus is a change in your environment you may want to react to. You need to be constantly monitoring whats going on so you can respond to it if you wan to. You have five different sense organs and they all contain different receptors. Eyes - Light receptors. Ears - Sound and balance receptors, Nose - Smell receptors (sensitive to chemical stimuli) Tongue - taste receptors (sensitive to chemical stimuli - salt, sweet, sour and savoury and bitter) Skin - sensitive to touch and pressure change. Receptors are a group of cells which are sensitive to a stimulus. They can change stimulus energy to electrical impulses.
When information is detected by receptors in a sense organ the information is sent along neurones to the central nervous system. The central nervous system coordinates a response and then sends instructions along different neurones to the effectors which respond accordingly.
Sensory neurones - The nerve cells that carry electrical impulses from the receptors in the sense organs to the central nervous system.
Motor neurones - The nerve cells that carry electrical impulses from the central nervous system to the effectors.
Effectors - Muscles / glands. Muscles contract in response to the nervous impulse whereas glands secrete a substance.