Our brain is able to perceive pain in both our superficial structures and internal organs. However, the conditions causing pain in the viscera are not completely comparable to those causing pain in the superficial structures. A laceration of the skin produces a localized pain, but a laceration of the internal organs may strangely, not cause any pain at all. In this video, we will discuss the very foundation of pain perception in visceral structures. Our nervous system is able to detect all kinds of changes in and around the body. To do this, sensory neurons possess receptors at their nerve endings. Most types of receptors respond only to a specific type of stimulus. Various kinds of receptors can be distinguished. For instance, there are receptors for pressure and temperature. Furthermore, there is a specific group of receptors capable of detecting pain. All of these different receptors are located throughout the body. Nociception is the action through which the nervous system detects potential harmful events. We perceive these harmful events as pain. It acts as a protective mechanism, enabling us to avoid potential danger. To perceive pain, sensory nerve cells possess receptors at the nerve endings called nociceptors. These nociceptors are capable of detecting various types of noxious stimuli which are converted into electrical impulses and transported to the brain where we perceive them as pain. Vast amounts of nociceptors are present in the gut and abdominal organs. Not all harmful events will trigger the nociceptors in the abdomen and produce pain sensations. For example, a traumatic laceration of the liver can occur without any immediate pain perception. On the other hand, a cut or burn of the skin immediately causes pain. The explanation for these occurrences lies in the type of stimulus and available nociceptors. The nociceptors that line the abdominal organs can be classified as mechano-nociceptors and chemo-nociceptors. Mechano-nociceptors respond to distention or traction on visceral tissues. Chemo-nociceptors are stimulated by local chemical agents released during inflammation and ischemia. Unlike the skin, visual nociceptors are not triggered by cutting, burning, or crushing stimuli. Also note, that a certain threshold of stimulation must be met in order to trigger the nociceptors. First, a normal distention of the stomach during a meal does not provoke pain. Binge eating, however, can exert sufficient distention of the stomach to produce pain. The distribution of nociceptors among the abdominal organs is not equal. Hollow organs such as the intestine, ureter, and bile duct contain considerable amounts of nociceptors. The capsules of solid organs, such as the liver, contain nociceptors as well. Solid organs themselves, however, such as the liver, spleen, and kidneys, hardly contain any nociceptive innervation. This explains why injury to these organs often does not result in abdominal pain. In summary, the visceral abdominal tissues are sensitive to distention, traction, inflammation, and ischemia through visceral nociceptors. On the other hand, crushing, burning, or cutting stimuli do not provoke pain sensations in the internal organs.