When a receptor is stimulated, it sends a signal to the central nervous system, where the brain co-ordinates the response. But sometimes a very quick response is needed, one that does not need the involvement of the brain. This is a reflex action.
Reflex actions are rapid and happen without us thinking. For example, you would pull your hand away from a hot flame without thinking about it. The animation below allows you to step through each stage of the reflex arc.
This is what happens:
- receptor detects a stimulus - change in the environment
- sensory neurone sends signal to relay neurone
- motor neurone sends signal to effector
- effector produces a response
The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is also a reflex action.
In bright light:
- Radial muscles of the iris relax.
- Circular muscles of the iris contract.
- Less light enters the eye through the contracted pupil.
In dim light:
- Radial muscles of the iris contract.
- Circular muscles of the iris relax.
- More light enters the eye through the dilated pupil.
Cool! 👍
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