Neurotransmitters
The gap between the axon endings of one nerve cell and the membrane of the neighbouring cell is called a synapse. The signal travels along the axon of the cell as an electrical impulse. Click to see how the impulse travels along the axon. When it arrives at the nerve endings it triggers the release of chemicals, known as neurotransmitters, into the synapse. Synapses also exist at the junctions between nerve cells and muscles, nerve cells and glands.
The gap under the axon ending is called a synapse. The gap under the axon ending is called a synapse. The gap under the axon ending is called a synapse.
Neurotransmitters are synthesized in the cell body and transported in vesicles to the axon endings by microtubules. Electrical impulses arriving at the axon ending cause the release of the neurotransmitters into the synapse, as shown in the diagram on the left. The neurotransmitter travels quickly across the gap and binds with molecules (receptors) found on the surface of the neighbouring cell. The neurotransmitters have a specific shape that fit perfectly onto the receptors. Once the receptors are occupied they cause a change in the membrane of the cell which generates an electrical signal that travels along the neighbouring cell. The neurotransmitter is then quickly removed. Nerve activity therefore can be considered as a repeated pattern of electrical-chemical signalling.

There are many neurotransmitters active in the brain. Each neuron uses only one or two of the main neurotransmitters.

Once the neurotransmitter is released into the synapse and activates the signal, it is either reabsorbed into the nerve cell or destroyed by special chemicals. If the neurotransmitter is allowed to persist in the synapse, constant excitation of the nerve takes place. Consider the video on the right.
1) A signal travelling down a nerve is called an

2) One nerve communicates with another nerve

3) When an action potential reaches the pre synaptic membrane vesicles containing fuse with the membrane and empty their contents into the

4) Receptors are

5) What binds together in a lock and key type fit?

6) What happens to the neurotransmitter once it is released into the synapse?

7) What triggers an action potential in the postsynaptic neuron?

 

 

 

 
As we shall see on the next page, some drugs can interfere with the action of neurotransmitter. Curare was a poison used by South American Indians to kill animals. The poison was placed on the tips of arrows and would cause paralysis. Curare actually blocked the receptors that lined the membrane of the muscle cells. When neurotransmitter arrived at the synapse it could not bind to the receptors and cause the muscle to contract. As no communication could reach the muscles the animal was totally paralysed.
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