Visceral sensation, also known as visceral pain, is pain that results from the activation of nociceptors of areas including but not limited to the thoracic, pelvic, or abdominal organs (the viscera). Visceral organs that are most often associated with visceral sensations are the lungs, heart, stomach, kidneys, and bladder. Visceral pain is diffuse and usually very difficult to localize. In fact, visceral pain may have referred sensations that are localized relatively far from the actual cause of the pain or sensation. Symptoms accompanying visceral pain can include but are not limited to nausea, vomiting, and changes in vital signs like blood pressure and heart rate.
Previously, the viscera were considered to be insensitive to pain, but today it is well documented that pain from internal organs is a true sensation. This pain can be widespread and could cause a social burden in one’s life. For example, myocardial (heart muscle) ischemia (death) is the most frequent cause of cardiac pain and is the most common cause of death in the United States. Other conditions that start with visceral pain include but are not limited to appendicitis (inflammation of the appendix), cholecystitis (inflammation of the gallbladder), and nephrolithiasis (kidney stones). Visceral pain from these conditions can be very localized to a specific position and move toward the organ (like that found in appendicitis), or one can experience what is called referred pain. Referred pain is common with presentation of gallstones in the gallbladder. Patients often complain of pain in the right shoulder, which is not near where the gallbladder is located. Another example of referred pain is when one is having a myocardial infarction (heart attack) and experiences pain in the left jaw and pain traveling down the left arm. It is very common that the autonomic nervous system plays a role in visceral sensations.
Transmission of Visceral Sensation in the Body
In the past, there were two ideas of how visceral sensation was transmitted: (1) viscera are innervated by separate classes of sensory receptors including pain receptors, and (2) internal organs are innervated by a single and homogenous class of sensory receptors that at low frequencies of activation send normal regulatory signals and at high frequencies of activation signal pain. High threshold receptors have been found in places including but not limited to the heart, lungs, small intestine, and urinary bladder. Damage to the viscus (singular form of viscera) affects the normal pattern of motility for that organ, and secretion produces drastic changes in the environment that surrounds nociceptor endings.
Two goals in the treatment of visceral sensation are (1) to alleviate pain and (2) to address the underlying pathology of the pain. Sometimes identifying the underlying pathology is not possible. In cases like this, symptomatic treatment can be administered. Symptomatic treatment includes medications like analgesics (NSAIDs and opiates), antidepressants (SSRIs), and antispasmodics (loperamide). Nerve blocks, local anesthetics, and steroid injections are more invasive therapies, but these generally have a limited number of treatments. These injections may only offer temporary relief, but permanent nerve blocks can be done by destruction of nerve tissue.
Research by Drs. Fernando Cervero and Jennifer Laird (2004) describes many aspects of visceral sensation, which includes how visceral pain is transmitted throughout the body, the biochemistry of visceral pain, new techniques used to study visceral pain, and how their research can be integrated into clinical practice. Many specialists still continue to treat visceral pain as just a symptom instead of as a distinct neurological entity. However, Cervero and Laird (2004) have shown that the most effective treatment of visceral pain includes electrophysiological and imaging techniques. For instance, when microstimulation of the thalamus was used to evoke visceral pain experiences like angina or labor pain, it significantly altered the sensation even in individuals who experienced these pains years before. Their research highlights the role of the thalamus in processing memories of pain and the existence of long-lived neural mechanisms that are capable of storing the results of previously painful experiences even for years after the fact.
See also: Autonomic Nervous System; Nociception; Nociceptors; Phantom Pain
Cervero, Fernando, & Jennifer M. A. Laird. (2004). Understanding the signaling and transmission of visceral nociceptive events. Journal of Neurobiology, 61(1), 45—54.
Collett, Beverly. (2013). Visceral pain: The importance of pain management services. British Journal of Pain, 7(1), 6—7. Retrieved from http://bjp.sagepub.com/content/7/1/6.full.pdf+html
International Association for the Study of Pain. (2012). Acute vs. chronic presentation of visceral pain. Retrieved from http://iasp-pain.org/files/Content/ContentFolders/GlobalYearAgainstPain2/VisceralPainFactSheets/3-AcuteVsChronic.pdf