Drugs at synapses

Drugs can affect synaptic transmission. They can do this in various ways...

1. Some drugs are the same shape as neurotransmitters so they mimic their action at receptors (these drugs are called agonists). This means more receptors are activated. Example- Nicotine mimics acetylcholine so binds to nicotinic cholinergic receptors in the brain.             

2. Some drugs block receptors so they can't be activated by neurotransmitters (these drugs are called antagonists). This means fewer receptors are activated. Example- Curare blocks the effects of ACh by blocking nicotinic cholinergic receptors at neuromuscular junctions, so muscle cells can't be stimulated. This results in the muscle being paralysed.                                       

3. Some drugs inhibit the enzyme that breaks down neurotransmitters. This means there are more neurotransmitters in the synaptic cleft to bind to receptors and they're there for longer. Example - nerve gases stop ACh from breaking down. This can lead to loss of muscle control.

4. Some drugs stimulate the release of the neurotransmitters from the presynaptic neurone so more receptors are activated. Example- Amphetamines forces dopamine into the synaptic cleft.                                                                                                                                   5. Some drugs inhibit the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated. Example- opiods block calcium ion channels.