Nerves
There are two main parts to the nervous system:
- the central nervous system (CNS) is composed of the spinal cord and the brain
- the peripheral nervous system refers to the collection of nerve fibres which are connected to it
Both these parts work together in collecting external information from the body’s surroundings via receptor cells. Each one of these cells responds to a particular stimulus.
The nervous system is made up of billions of nerve cells known as neurones. The neurones are able to receive the information from the receptor cells as electrical impulses.
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Receptor cells
Receptor cells are a form of nerve cell but their role is to react to stimulus. As you can see from the table below, each receptor is design to respond to a particular stimulus.
| Receptor location | Stimulus |
| EyesEarsEarsTongue
Nose Skin |
LightSoundPositioning (e.g. for balance)Taste and smell
Taste and smell Touch (e.g. pain, pressure and temperature) |
Like other cells in an animal’s body, light receptor cells are made up of a cell membrane, nucleus and cytoplasm.
NOTE: You don’t need to know the structure and the function of sense organs, like the eye and ear, or the functions of cell components.