An animal's response to a stimulus is coordinated by its central nervous system (CNS). A simple reflex is an involuntary response to a stimulus. Humans use reflex actions in only some of their behaviour, for example controlling the eye's pupil size.
Responding to a stimulus.
A stimulus is a change in the environment of an organism.
Animals respond to a stimulus in order to keep themselves in favourable conditions.
Examples of this include:
Moving to somewhere warmer if they are too cold.
Moving towards food if they are hungry.
Moving away from danger to protect themselves.
Animals that do not respond to a stimulus do not survive for long.
Receptors respond to a stimulus and send impulses along sensory neurons to the CNS.
Some receptors are found in the skin. Other receptors can form part of complex organs, such as:
- Light receptor cells in the retina of the eye.
- Hormone-secreting cells in a gland.
- Muscle cells.
- Position receptors in the inner ear.
- Sound receptors in the ear.
- Touch, pressure, temperature and pain receptors in skin.
- Chemical receptors in the nose and tongue.
Simple reflexes produce rapid involuntary responses to a stimulus. This ensures an animal responds in the way most likely to result in its survival.
- Moving towards and finding food
- Moving away and sheltering from predators
- Moving towards and finding a mate
Simple animals use reflex actions for the majority…