The Nervous System and Neurones
Ever wondered how you pull your hand away from something hot before you even think about it? That's your nervous system in action, using specialised cells called neurones to send electrical messages around your body.
Neurones are basically biological electrical cables with three main jobs. Sensory neurones carry signals from your sense organs (like eyes and skin) to your central nervous system (CNS) - that's your brain and spinal cord. Motor neurones do the opposite, carrying messages from your CNS to muscles and glands called effectors. Relay neurones work as connectors inside your CNS, linking sensory and motor neurones together.
Each neurone has a cell body containing the nucleus and main organelles, plus long, thin fibres called axons that carry the electrical impulses. Many axons are wrapped in a fatty myelin sheath that acts like insulation on electrical wire - it speeds up the impulse and stops electrical energy from leaking out.
Quick Tip: Think of neurones like a relay race - sensory neurones detect the stimulus, relay neurones pass the message, and motor neurones make something happen!
The gaps between neurones are called synapses, where electrical impulses trigger the release of chemical messengers called neurotransmitters. These chemicals diffuse across the gap and trigger a new electrical impulse in the next neurone - it's like passing the baton in that relay race.
Reflex Arcs - Your Body's Emergency Response
Reflex arcs are your body's way of keeping you safe without waiting for your brain to think things through. When you touch something sharp, receptor cells detect this stimulus and fire an electrical impulse along a sensory neurone straight to your spinal cord - completely bypassing your brain for speed.
In your spinal cord, a relay neurone picks up the signal and passes it to a motor neurone, which rushes the message to your muscles. Your hand jerks away before you've even consciously felt the pain - that's an automatic response that could save you from serious injury.
This whole process happens in milliseconds because it's such an efficient system. The effectors (usually muscles) contract to move you away from danger, or sometimes glands release hormones if needed.