When a nerve cell receives a signal, it creates an electrical impulse (action potential) which travels down the axon to the axon endings. The electrical signal stops here, so how does the signal keep going?

The answer to that question is, chemicals. Neurotransmitters to be exact.

Before we begin discussing how neurotransmitters work, you should familiarise your self with some basic structures and terms.

Observe the image to the right. Scroll over each word.

You will see that the synapse is gap between the axon endings (pre-synaptic neuron) and dendrites (post synaptic neuron).

Neurotransmitters are synthesised in the cell body by the ER and packaged into vesicles by the Golgi Body.

These vesicles are sent down the axon to the axon terminals on microtubules.

These neurotransmitters are receptor specific, and can either excite  or inhibit the opposite neuron.

These receptors can be on the dendrites of neurons, muscles or glands.

Once the signal has reached the end of the axon, it signals a release of the neurotransmitters.

The neurotransmitters are released into the Synapse, through Exocytosis.

Once in the synapse, the neurotransmitters cross via simple diffusion and bind to the appropriate receptors. For example Dopamine can only bind to Dopamine receptors.  

Once bound they open up the protein channels allowing ions to flood into the cell. Starting the next action potential.

But, if we leave these neurotransmitters in the synapse, they neuron will constantly be excited.
So an enzyme comes and breaks down the neurotransmitters bound to the receptors.

Any left over neurotransmitters are re-absorbed into the nerve terminal.

Bellow is the complete animation of what happens. Click the start button to see.

This particular neurotransmitter will excite the opposing neuron.

Many drugs can interfere with this process. Receptors can be blocked preventing the neurotransmitter from binding, either exciting or inhibiting the neuron.

Click here for more information on drugs and their effects on the synapse.

Click here for Questions on the synapse and neurotransmitters

Click here for information on the action potential