Reflex actions occur AUTOMATICALLY (they do not require messages being sent to the brain for a decision to be made). Because of this they are much quicker than 'thinking actions'. They are usually a response to danger.
Look at the Reflex Arc below. It is complicated, but follow the numbers around.
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1. The pressure from the pin sticking into the skin is the STIMULUS. |
| 2. Pressure RECEPTORS in the skin detect the STIMULUS. | |
| 3. An electric impulse is passed along the SENSORY NEURONE to the spinal column. | |
| 4. Reaching the spinal column a message is NOT passed up to the brain. Instead a chemical is released into the SYNAPSE (a gap). | |
| 5. The chemical moves across the synapse and triggers the RELAY NEURONE to pass an electric impulse towards the next synapse. | |
| 6. Again a chemical is released into the synapse which triggers an electric impulse to travel down the MOTOR NEURONE to the muscle. | |
| 7. The electric impulse causes the EFFECTOR (the muscle) to contract and move away from the pin (the RESPONSE). |