Mu Opioid Receptors are a type of protein found in the brain and other parts of the body. They play a crucial role in the body's response to pain and are activated by natural substances like endorphins, as well as synthetic drugs such as morphine and fentanyl. When these receptors are activated, they can produce feelings of pain relief, euphoria, and relaxation. These receptors are part of the larger opioid receptor family, which includes delta and kappa receptors. Activation of Mu Opioid Receptors can also lead to side effects, including respiratory depression and addiction, making their study important for understanding pain management and substance use disorders.