2.84 - Receptors and Responses

2.84 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses

Nerve cells are different from other cells, they do have a cell membrane, cytoplasm and nucleus, but they are a different shape. Part of the cell is stretched out to form the axon. The axon can be over a meter long. 

The messages that nerves carry are called nerve impulses. They are electrical signals. They pass very quickly along the axon of the neurone. 

An impulse travels along the axon which each impulse being separate from the next. They travel along one after another. 

Some axons have a fatty sheath around them. This insulates the axon and makes the impulse travel along faster. 

In multiple sclerosis the fatty sheath breaks down. Impulses slow down or may even stop. People with this disease gradually lose the use of their muscles because the messages never reach them. 

Synapses

The end of one neuron is not connected to the next making a small gap between them. This gap is called a synapse. 

When an impulse reaches the end of an axon, a chemical is produced. The chemical diffuses across the gap which starts off an impulse in the next neurone. 

Only one end of a neurone can make this chemical. So synapses make sure an impulse can only travel in one direction.

Synapses have 2 other functions:  

- A resistor: it may take a number of impulses before enough chemical is made to start the impulse in the next neurone. 

- a junction box: one neurone may pass on its impulse to a number of other neurones 

Our synapses are easily affected by drugs. Some drugs can block them whereas others can make them work too quickly. Alcohol is thought to affect synapses in the brain and this can slow down peoples reactions.