Nociceptive Pain in Your Body

How Somatic and Visceral Pain Is Detected

Man holding his leg in pain
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Nociceptive pain is the term for pain that is detected by specialized sensory nerves called nociceptors. These nerves are located throughout the soft tissues and the internal organs. They are involved both in acute pain due to tissue injury and chronic pain. Nociceptive pain differs from neuropathic pain, which is caused by nerve damage.

There are two types of nociceptive pain: somatic pain and visceral pain.

Somatic pain comes from the joints, bones, muscles and other soft tissues, while visceral pain comes from the internal organs. Though they are detected in similar ways, somatic pain and visceral pain do not feel the same.

Both somatic pain and visceral pain are detected the same way. Nociceptors, or pain-detecting nerves, send an impulse from the painful site up through the spinal cord and to the brain for interpretation and reaction.

How Nociceptors Work

Nociceptors are how we feel pain. These nerves have specialized nerve endings that are triggered to fire by chemical changes in the body. Nociceptors detect temperature, pressure, and stretching in and around their surrounding tissues. They are located throughout the body in the skin, internal organs, joints, muscles, and tendons.

Nociceptors fire when damage is detected, sending pain signals to the spinal cord and the brain. The pain fibers enter the spinal cord at the dorsal root ganglia and transmit the signals across the synapse in the dorsal horn.

The fibers cross to the other side and continue up the lateral columns to the thalamus and the cerebral cortex.

Damaged tissues release substances that can make the nociceptors in the tissues more sensitive. When a painful condition is prolonged, the repetitive stimulation can sensitize the neurons and it takes less stimulation to cause pain.

The pain signal can be acted on at many points to shorten, lengthen, increase, or reduce the pain sensation. Mediating chemicals include endorphins and monoamines such as serotonin and norepinephrine.

Once the damage has been healed, nociceptors should stop firing. Sometimes even after the initial damage has healed, nociceptors may continue to fire, which can lead to chronic pain. Examples of chronic nociceptive pain include headaches,  arthritisfibromyalgia, and pelvic pain not caused by nerve damage.

Somatic Pain

Somatic pain is detected by the nerves located in the skin, subcutaneous tissues, muscles, and joints. It can be localized and may be a sharp pain, a dull ache, or a burning sensation. It can be due to an acute injury or a chronic process. The pain felt from a cut, bruise, or arthritis is a somatic pain. Often, somatic pain has an inflammatory component and can be treated with NSAIDs.

Visceral Pain

Visceral pain is detected by nociceptors in the body's internal organs. Sensory nerves in the internal organs are not as widespread as they are in the body's muscles and skin. This can make visceral pain feel dull and hard to localize. Unlike somatic pain, visceral pain may be felt further away from its actual origin.

Source:

Markman J. Overview of Pain. Merck Manual Professional Version. http://www.merckmanuals.com/professional/neurologic-disorders/pain/overview-of-pain.

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