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Writer's pictureDaniel Selin

Pain pathways and pain regulation

Pain, Pain Regulation, Pain Mechanisms, Ascending and Descending Pain Pathways, Pain Perception, Nociceptive Pain, Neuropathic Pain, Nociplastic Pain, Pain Relief, Pain Management

Pain and the pain experience involves a complex series of electrical and chemical events that we can influence through our actions and the way we think about pain. To understand how we feel pain, it is essential to examine the ascending and descending pain pathways through which the pain signal is transmitted, amplified, or diminished. These pathways not only define how we perceive pain but offers an opportunity to manage and alter the pain experience.

 

Ascending pain pathways

The primary function of pain is to warn the body of ongoing tissue damage or to signal that damage has already occurred. The pain signal originates when specialized nerve endings, called nociceptors, detect a harmful stimulus. This stimulus could be, for example, intense pressure, a significant change in temperature or a chemical irritant.


This activation prompts the nociceptors to send electrical signals along the peripheral nerves toward the spinal cord. In the spinal cord, the incoming signals synapse (i.e., connect) with second-order neurons located in the dorsal horn. Following this, the pain signals travel upwards through the ascending pathways, primarily via the spinothalamic tract, toward the brain.


Upon reaching the brain, the signal continues its journey through the thalamus to the somatosensory cortex. In this cortical area, the brain interprets the location, intensity, and nature of the pain, transforming these into a conscious experience.


This process is not straightforward; emotional and cognitive interpretations of pain and its nature significantly influence the pain experience. These interpretations can greatly affect the type of pain that is perceived.


Various factors impact the transmission of signals along the ascending pain pathways, which is why each of us has a slightly different way of feeling and experiencing pain.

 

Descending pain pathways

While ascending pain pathways are crucial for transmitting pain signals upward to the brain, descending pain pathways are essential for regulating and modulating the pain experience.


Descending pain pathways originate from various brain areas, and their primary function is to inhibit or dampen pain signals before they reach the brain's higher processing centers.

When descending pain pathways are activated, they release neurotransmitters such as serotonin, norepinephrine and endogenous opioids, which can alter the function of second-order neurons in the spinal cord. As a result of this change, the transmission of pain signals along the ascending pathways may decrease or even be blocked, leading to a reduction or cessation of the perceived pain.


The effectiveness of descending pain pathways can vary based on numerous factors, including emotional state, previous pain experiences, and psychological context.

 

The functioning of the ascending and descending pain pathways is similar regardless of the type of pain, but their mechanisms may vary depending on the underlying pain mechanism. Below is a brief description of how pain mechanisms affect the functioning of the ascending and descending pain pathways. If you want to read more about pain mechanisms, you can explore the topic further here.


Nociceptive pain

Nociceptive pain arises when pain-sensitive nerve endings are activated due to actual or potential tissue damage. Nociceptive pain is experienced, for example, as a result of sprains, bruises, inflammation or other injuries.


Ascending pain pathways: Operate fairly straightforward by transmitting the pain message from the peripheral nervous system through the spinal cord to the brain. The pain message originates from the activation of nerve endings in the peripheral nervous system, which carry the message forward and synapse in the dorsal horn of the spinal cord. From there the message is relayed toward the brain via the spinothalamic tract. Ultimately, the message reaches the somatosensory cortex through the thalamus, transforming the message into a conscious experience.


Descending pain pathways: The brain can modulate nociceptive pain signals through descending pain pathways. When the brain detects pain, it can manage this by releasing neurotransmitters such as opioids, serotonin or norepinephrine to inhibit the upward transmission of the pain message.


Neuropathic pain

Neuropathic pain arises as a result of injury or dysfunction in the nervous system. In neuropathic pain, nociceptive nerve endings may become sensitized or exhibit ectopic activity, causing the pain message and pain experience to intensify without any harmful stimuli to the tissues.


Ascending pain pathways: In neuropathic pain, ascending pain pathways can change, leading to increased sensitivity and atypical pain processing in both the peripheral and central nervous systems.


Descending pain pathways: The effectiveness of the descending pain pathways may diminish in neuropathic pain due to changes in pain processing. Treatment methods that activate descending pain pathways and relieve nociceptive pain do not typically work as effectively in neuropathic pain. This type of pain does not seem to respond as well to the activation of the descending pain pathways.


Nociplastic Pain

Nociplastic or central pain is pain that is felt and transmitted even when there is no clear evidence of actual or imminent tissue damage or dysfunction in the somatosensory system. Chronic pain often involves nociplastic pain or at least part of the pain can be explained through nociplastic mechanisms. Nociplastic pain often shows changes at the central nervous system level in the processing of the pain messages, resulting in pain that is typically vague and widespread.


Ascending pain pathways: Ascending pain pathways can still transmit nociceptive signals, but these signals are now interpreted differently. A stimulus that previously would not have caused a pain response can now feel painful. This so-called sensitization can occur at the level of the peripheral nervous system, spinal cord or brain.


Descending pain pathways: In nociplastic pain, descending pain pathways may be in a state of dysfunction, preventing them from inhibiting or calming incoming pain messages. Psychological factors, such as stress, anxiety or previous chronic pain experiences, can further weaken the functioning of the descending pain pathways.


Summary

In conclusion, while the fundamental mechanisms of the ascending and descending pain pathways are consistent regardless of the pain mechanism, their functioning may vary slightly depending on the origin of the pain:

  • Nociceptive pain is typically directly related to the activation and modulation of pain pathways.

  • Neuropathic pain may lead to changes in sensitivity and impaired regulation of descending pain pathways.

  • Nociplastic pain is characterized by dysfunction in both ascending and descending mechanisms, often requiring a multidisciplinary approach for management.


Understanding these differences is essential for effective pain management and treatment. Pain behaves differently depending on its origin and not all pain is treated the same way.

 

Activation of the descending pain athways

Activating the descending pain pathways can reduce perceived pain and provide significant relief for those suffering from pain. There are several ways to activate and enhance the effects of the descending pain pathways. Below are a few methods to try for alleviating pain by activating pain-inhibiting or calming descending pathways:


Pharmacological interventions: Medications such as opioids and antidepressants can stimulate the descending pathways. Opioids activate the brain's opioid receptors, resulting in reduced pain perception. Antidepressants, which increase the levels of serotonin and norepinephrine, improve the brain's ability to inhibit pain. The use of antidepressants in the treatment of chronic pain has significantly increased and they are often used as a first-line medication for ongoing pain.


Exercise: Regular exercise appears to be beneficial in activating descending pain pathways. Aerobic exercise, strength training, mind-body exercises (such as yoga or tai chi), exercise programs that combine different types of physical activity and training that develops coordination and balance have all demonstrated effectiveness in activating descending pathways.


The exercise program should be tailored to individual preferences and abilities. The goal is to make exercise a long-term habit. It's important that the chosen form of exercise is enjoyable.


Manual therapy: Manual therapy has been shown to activate descending pain pathways. Soft tissue manipulation can improve circulation, relax muscles and help release endogenous opioids, thereby reducing pain intensity. Acupuncture, dry needling techniques, and joint mobilization and manipulation treatments have also demonstrated similar effects in pain relief. Read more about the effectiveness of manual therapy here.


Psychophysical physiotherapy: Cognitive-behavioral therapy (CBT) can help patients modify their thoughts and beliefs about pain, potentially reducing the distress associated with it. Mindfulness and relaxation techniques can also activate descending pain pathways by fostering a mental state that can diminish the transmission of pain signals.


Self-management and understanding pain: Understanding pain and its mechanisms empowers individuals to take a more active role in pain management and modulation. Awareness of the impact of emotional and psychological factors on pain provides an explanations for why the nature and intensity of pain may vary, even when there appears to be no external cause for the change. This understanding makes the nature of pain less mysterious, reducing the anxiety associated with it. Consequently, it becomes easier to cope with the pain and not feel distressed by the negative impact of discomfort.


Electrical treatments: TENS, or transcutaneous electrical nerve stimulation, is a form of nerve stimulation administered through the skin that can relax muscles and reduce pain. Pain relief occurs partly through the activation of descending pathways and partly according to the so-called gate control theory. TENS is often used in the management of chronic pain due to its safety and ease of use.

 

The complex interaction between the ascending and descending pain pathways dictates how we perceive and respond to incoming pain signals and how they affect us. We can influence the intensity of pain and the distress it brings by activating the body’s own pharmacy. This can be achieved through both our actions and the power of our thoughts by activating pain-relieving descending pain pathways.


The most effective pain relief is often achieved by combining different pain management methods. By carefully mapping out the underlying factors, we can recommend strategies and plans tailored specifically for you to alleviate pain.

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