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Year 10 iGCSE - Biology

The electrical current is sent down the axon and reaches the axon terminals.

Synapse

The synapse is gap between the axon endings (pre-synaptic neuron) and dendrites (post synaptic neuron). The neurons don’t actually touch each other, meaning the signal goes from electrical to chemical.

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.

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

Short answer Questions

1. Explain the steps involved once the electrical impulse reaches the axon endings.


2. Define a neurotransmitter


3. Draw and label the synapse between 2 neurons. Include, post and pre synaptic neuron, dendrites, axon endings, neurotransmitters and synapse.


4.

Click here for a quick activity on synapses