Worrying about the pain that may be experienced after surgery is one of the reasons that causes many people to feel confused and reluctant to go to the hospital for examination and treatment. However, with the development of modern medicine, patients can control their own pain with the PCA method.

Pain has a positive physiological role" because it provides a warning of tissue damage, immobilizing the patient as well as the painful limb for faster recovery. However, pain causes many adverse effects on the patient's recovery process, so what is the mechanism of pain perception and response?