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Asked by zoeqayum to Aimee, Bridget, Kieran, Mags, Mat on 21 Jun 2011. This question was also asked by hayden, ashley.
Keywords: basic, function, nerve
Hi zoeqayum, a nerve is a specialised type of cell which carries impulses from the body to the brain, or brain to the body. It is also called a neuron. Nerves transmit all the information our brain receives: about light, temperature, touch, pain, movement etc. There are billions of nerves which interconnect throughout our body and a single nerve cell can be up to tens of centimetres long.
Here is a good picture of a nerve: http://user1423300.sites.myregisteredsite.com/ (I don’t know how to link you straight to it, but it’s the yellow thing with the white background near the top right. Looks a bit like a tree)
A nerve has a soma (body) which contains the nucleus, branching dendrites which detect impulses from other nerves, a long axon (tail) which transmits the electrical impulse, and axons which pass the signal on to another nerve or to the muscles. These are all surrounded by a membrane (like a skin) which lets some molecules move through and keeps other molecules out. The axon is surrounded by the myelin sheath, a fatty coating which acts as insulation for faster transmission of the impulse.
Nerves transmit information ‘electrochemically’ meaning that they use chemicals and an electrical impulse. When a nerve is not sending a signal it is at ‘rest’. The inside of the nerve will have a negative charge compared to the outside of the nerve. Usually, the charge would balance itself out by swapping positive and negative molecules, but the membrane prevents this from happening.
When a nerve receives a signal from another nerve, the ‘action potential’ occurs. Chemicals from the first nerve come into contact with the second nerve and cause the membrane to open up. Molecules move through to balance out the negative charge. When this charge gets to a ‘threshold’ (near zero charge) the second nerve starts its action potential. The action potential is a wave of electrical charge which travels down the axon of the nerve, away from the nerve body. Having the myelin sheath means the signal can move quickly though the covered parts, like electricity along a cable. However, if the whole axon was covered the electrical impulse would run out of strength by the time it reached the end. The little spaces between the sheath allow a ‘power up’, strengthening the signal as it moves along.
When the electrical signal reaches the end of the axon it causes the axon terminals to release special chemicals. There is a very small gap between the axon terminals and the dendrites of the next nerve, called a synapse. The chemicals are released into the synapse and travel across this space to bind onto the next nerve. This causes an action potential in the next nerve, repeating the whole cycle until the message is delivered to either the brain or a part of your body.
Wow, long answer. I hope it all makes sense to you.
Aimee’s got this one covered! The nerves are how our bodies are responsive. They’re like our wiring. Though the voltages and stuff are not large, it’s like we’re electrical beings. There’s this constant flickering of charge up and down these billions of wires. It’s all quite breathtaking. All of it done with organic molecules and the movement of metal ions.
And all coordinated by the brain, which makes sense of it all despite signals reaching it at different times. For example: kicking a ball – the feeling of the ball on your foot, and the sound of the impact and the sight of the ball hitting your foot are perfectly coordinated in your mind, even though the touch, sight and sound reach your brain at different times. Nerves carry the messages, the brain makes sense of them.
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