The nervous system: sensing and responding — Biology, 11–13 years
The nervous system lets an animal notice changes, decide what they mean and act quickly. It links sense organs, the brain, the spinal cord and nerves.
A fast message network
Your nervous system is a communication network inside your body. Sense organs detect changes, nerves carry electrical signals, and the brain or spinal cord helps organise a response, such as pulling your hand away.
Why signals need a network
An animal that reacts only when a whole body moves would be slow and unsafe. The nervous system solves this problem by sending information to the right place quickly, so an animal can find food, avoid danger and coordinate movement.
From hot cup to moved hand
1. Heat receptors in your fingertips detect a very hot cup. 2. Sensory nerves carry a signal to the spinal cord. 3. The spinal cord sends a signal to arm muscles. 4. The muscles contract, so your hand moves away before you have fully thought about it.
The brain is not the only messenger
A common mistake is to imagine that every response must travel to the brain and back. That seems reasonable because the brain is the control centre, but some urgent actions use the spinal cord first, saving time when a delay could cause injury.
In sport and safety
When you catch a ball, your eyes send information and your brain coordinates your hands. When you step back from a cyclist or touch a hot pan, fast signals help protect you. Training can improve timing, but it cannot remove the need for signals.
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