This document provides an overview of pain, including its definition, classification, receptors, pathways and modulation. It discusses how pain is transmitted through nociceptors and sensory neurons from the peripheral nervous system to the central nervous system. Pain is classified based on its origin, quality and location. Various factors can influence pain perception. Diagnosis involves questioning patients and tests, while treatments target different areas along the pain pathways using various medications. Understanding the mechanisms and factors involved in pain is crucial for proper diagnosis and effective treatment.