Understanding Nociceptive Pain

How Your Body Detects Somatic and Visceral Pain

Man holding his leg in pain
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Nociceptive pain is pain caused by an injury, physical pressure, or inflammation of some part of the body. There are two types: Somatic pain is the pain you feel in your arms, legs, face, and superficial areas of your body, while visceral pain is the pain you feel from your internal organs. Unlike neuropathic pain, which is caused by nerve hypersensitivity or dysfunction, nociceptive pain involves the activation of pain receptors by a stimulus (think bumping your arm on a table).

Nociceptors

Both somatic pain and visceral pain are detected by nociceptors—sensory nerves that detect acute pain due to tissue injury, as well as chronic pain due to swelling or inflammation. 

Nociceptors both respond to painful stimuli and control how we feel pain. These nerves have tiny specialized nerve endings that are activated by temperature, pressure, and stretching in and around their surrounding tissues. Nociceptors are located throughout the body in the skin, bones, joints, muscles, and tendons, as well as in the internal organs, such as the stomach, bladder, uterus, and colon.

Types

Though somatic and visceral pain are detected by the same types of nerves, and the triggers for both types of pain are similar, they do not feel the same. 

Somatic Pain

Somatic pain is detected by the nerves located in the skin, subcutaneous tissues, muscles, and joints. It can be triggered by an acute injury or by a chronic process. The pain felt from a cut, bruise, or arthritis are examples of somatic pain. It can be localized to a specific area in or on your body and may produce a sharp pain, a dull ache, or a burning sensation.

Visceral Pain

Visceral pain is detected by nociceptors in the body's internal organs. You might feel visceral pain if you have a stomach infection, constipation, or something more serious such as internal bleeding or cancer. 

Unlike somatic pain, you might not feel visceral pain exactly at the area that is injured or inflamed, and visceral pain can be felt further away from its actual origin. There are not as many sensory nerves in the internal organs as there are in the body's muscles and skin, which can make visceral pain feel dull and harder to localize.

Visceral pain may also be associated with nausea, vomiting, or jitteriness, which less commonly occurs with somatic pain.

How You Feel Pain

When nociceptors detect physical damage to your body, they create electrical signals. The signals travel to your spinal cord, which sends the message up toward the brain. 

This process occurs rapidly, involves many complex steps, and is the same for both somatic and visceral nociceptive pain:

  1. Initially, transduction occurs as the nociceptive nerve fibers stimulate your peripheral sensory nerves, which triggers transmission of the sensation by traveling from your skin, bones, joints, or internal organs toward your spine. 
  2. The peripheral sensory nerves merge together to enter the spinal cord at an area called the dorsal root ganglia, which is a bundle of nerves entering the spine at each vertebra (small backbones).
  3. The nerves transmit the electrical signals across the synapse (nerve communication region) in the dorsal horn, which are nerve fibers in the back of the spinal cord.
  4. The nerve fibers in the spinal cord cross to the other side.
  5. The crossed nerves continue up the spinal cord in the lateral columns, which are the nerve bundles within the spinal cord that are located along its sides.
  6. The pain message then travels up the brainstem, up to the thalamus, and finally to the cerebral cortex, where your brain has a "map" that registers the exact location of your pain.   
  7. You become aware of the pain, which is the perception of pain. Often, your body naturally modulates the pain to adjust the intensity and duration.

    Resolution and Persistent Pain

    Most of the time, nociceptors stop firing once the injury or illness has resolved, which may require treatment, healing time, or both, depending on the underlying cause. You have probably noticed this when you have recovered from a cut, a broken bone, or an infection.

    Sometimes, however, the body can release substances that make nociceptors more sensitive even after an injury has healed, causing them to continue to fire. For example, when a painful condition is prolonged, the repetitive stimulation can sensitize the neurons for the long-term, resulting in excessive reactivity to pain. This can lead to chronic pain issues such as headaches, arthritisfibromyalgia, and pelvic pain.

    Usually, conditions that cause neuropathic pain also interfere with your ability to properly detect nociceptive pain, but sometimes, you can feel both types of pain in the same body part.

    The pain signal can be diminished by mediating chemicals such as endorphins and serotonin. Many pain medications work by inhibiting the pain signals that are sent along the nerve pathway. Often, somatic pain has an inflammatory component and can be treated with NSAIDs, which reduce pain-inducing inflammation.

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