Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels. Suggest how cannabinoids could prevent muscles contraction?

This question is asking you to explain how action potentials travel across neuromuscular junctions and how the closure of calcium ion channels would prevent the signal travelling across the junction, so would prevent the action potential reaching the muscle, so it would not contract. If the calcium ions channels on the presynaptic membrane are closed, then there is no influx of calcium ions into the pre-synaptic membrane. This means that the synaptic vesicles will not fuse with the membrane, so the neurotransmitter will not be released from the vesicles into the presynaptic cleft. In muscles this neurotransmitter is called acetylcholine. Acetylcholine will not diffuse across the synapse and will not bind to the receptors on the post-synaptic membrane. This means that there will be no depolarisation of the membrane as the sodium ion channels do not open, so there is no influx of sodium ions, which would normally cause the membrane to depolarise. This means that the action potential is not continued to the next neuron so does not reach the muscle so there is no contraction of the muscle.