Introduction to Section I
It has been known for almost a century that fine afferent fibres from the skin, muscle and vicera terminate in the superficial dorsal horn of the spinal cord. The close relationship between these afferent fibres and the transmission of nociceptive information gave support to the notion that the superficial dorsal hron plays an important role in the initial modulation and integration of pain-related signals. Recent anatomical and functional studies have, indeed, confirmed that many fine afferent fibres terminate in the superficial layers of the dorsal horn but have also increased our knowledge about the detailed mode of termination of individual afferent fibres and of groups of fibres from skin, muscle and vicea. The papers presented in this section discuss these recent studies and attempt to answer three basic questions: i) do all fine afferent fibres terminate in the superficial dorsal horn? ii) do fine afferent fibres from skin, muscle and vicera show different patterns of termination in the spinal cord? and iii) what are the structure and ultrastructure of the terminals of individual fine afferent fibres in the superficial dorsal horn?