GCSE biology unit 1 - the nervous system

The nervous system

Its job is to detect stimuli so we can coordinate our behaviour. Stimuli are changes in the environment.
Receptors sense these changes:

• eyes contain light receptors that detect light
• noses contain chemical receptors that detect smells
• mouths contain chemical receptors that detect tastes
• skin has various receptors that are sensitive to touch, temperature, pressure and pain
• ears contain sound receptors and also receptors that detect position (balance)

once the receptor has detected the stimulus, the sensory neurone passes an electrical impulse to the central nervous system (brain + spinal chord), where relay neurones pass the signals from one nerve cell to another. The CNS then passes an impulse through the motor neurone to the effectors  and a response happens.

e.g. sound stimulus - sound receptors - sensory neurone - CNS - motor neurone - effector - response.

The CNS contains synapses which are junctions between the three neurones. that pass the electrical impulses through gaps by using chemical signals.

Reflexes miss out the CNS and go straight through the three neurones. This way they are quicker so protect you. If the brain was involved, there would be a delay.