Unit 1: Nervous System and Reflexes

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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


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