Unit 1: Nervous System and Reflexes

Biology AQA Unit 1: Nerves and Hormones

1. The Nervous System

A stimulus is a change in your environment which you may need to react to (eg. a tiger pouncing at you). You need to constantly monitor what is going on in order for you to react if you need to.

You have 5 sensory organs which each contain receptors:

• Eyes - contain light receptors.
• Ears - contain sound receptors.
• Nose - contain smell receptors.
• Tongue - contains taste receptors: sensitive to bitter, salt, sweet, and sour, plus the taste of savoury things.
• Skin - contain touch, pressure and temperature change receptors.

They all contain different receptors. Receptors are groups of cells which are sensitive to stimulus. They change stimulus energy into electrical impulses. A stimulus can be light, sound, touch, pressure, chemical or a change in position or temperature.

The central nervous system consists of the brain and spinal cord only, it coordinates a response to changes. All the information from the sensory…