The mu receptor x

As the diagram in Fig. 12.41 demonstrates, morphine binds to the x receptor and induces a change in shape. This change in conformation opens up an ion channel in the cell membrane and as a result, potassium ions can flow out of the cell. This flow hyperpolarizes the membrane potential and makes it more difficult for an active potential to be reached (see Appendix 2). 

Therefore, the frequency of action potential firing is decreased, which results in a decrease in neurone excitability. 

This increase in potassium permeability has an indirect effect, since it also decreases the influx of calcium ions into the nerve terminal and this in turn reduces neurotransmitter release. 

Both effects, therefore, shut down the nerve and block the pain messages. 

Unfortunately, this receptor is also associated with the hazardous side-effects of 

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