It works on several types of receptors, widely found in nervous tissue. These other opioids may be natural occurring substances, such as morphine, or made in the laboratory such as pethidine. Morphine works on receptors in the cell membranes. These are protein-lipid molecules that alter their shape when stimulated to effect molecular changes within cells. There are thought to be three types of receptors that respond to opioids, mu, kappa and lambda.
Morphine acts mainly on mu receptors to cause a wide variety of effects.
The most important of these are relief of pain and respiratory depression. In anaesthesia morphine is used to relieve pain. This is an effect of its action on the spinal cord to decrease the transmission of painful stimuli from body to brain, and its action within the brain itself. Side Effects Morphine has many side effects. The most dangerous is respiratory depression.