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  • Writer's pictureNazan Garcia

Pain is a complex phenomenon

Pain is a complex phenomenon and cannot always be explained by our current anatomical and physiological understanding of the body.

chronic pain

Pain is the most common ailment for which acupuncture is used

What is this thing called pain?

Through the ages, philosophers and scientist have been contemplating and examining the definition of pain. Its meaning has changed over the recorded history and reflects the contemporary spirit and understanding of the time (Gebhart, 2018).

According to Gebhart (2018) physicians treat patients, not according to the patient's presentation but according the philosophical background they hold. Physicians with a mechanistic view of pain will look for the anatomical cause of pain, whereas physicians with more holistic views will focus on issues of stress, emotions and lifestyle that will assist in the adaptive responses to pain.

Still, from a mechanistic standpoint, pain terminology has been revised to reflect patient experiences and advances in pain research.

Originally, in 1994, pain was thought to be caused by lesions or dysfunction of the nervous system: neuropathic pain.

It wasn't until 2005 that the International Association for the Study of Pain (IASP) added the stimulation of nociceptors as a cause of pain: nociceptive pain.

Nociplastic pain is a third mechanistic descriptor of pain that has recently been proposed in the presence of conditions that have challenged the dualistic classification of pain, such as fibromyalgia or irritable bowel syndrome (Kosek et al. 2016). Furthermore, the literature is full of reports where the presence of tissue injury does not elicit pain, and where pain can be felt even when there is no tissue injury (Fisher, Hassan, and Connor, 1995; Bedson and Croft, 2008; Schiphof, et al. 2013)

The definition of pain is still being debated. The IASP proposed the first definition in 1979, and it has been revised several times since then (Raja et al. 2020).

Pain is a complex phenomenon and cannot always be explained by our current anatomical and physiological understanding of the body.

The latest (2017) definition from the IASP states that pain is “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”. The definition comes accompanied with notes with further clarifications. Overall, the definition recognises the complexity of pain, which is a very personal experience with physical, psychological, and social components, and thus fits into the biopsychosocial model (Van Griensven, Strong, and Unruh, 2013).

Sensory receptors - interaction with the environment

Sensory receptors, also known as afferent neurons, are specialised nerve cells that allow humans to interact with their surroundings. We have special sensory receptors in the eyes, ears, tongue, nose, and skin. These receptors transmit information about the environment to the brain, where it is processed and interpreted. For example, we have specialised sensory receptors in the eyes that capture light but the brain interprets as colours. Sensory receptors in the ear detect vibration, which the brain interprets as sounds.

In the skin we have various somatosensory receptors that pick up:




-proprioception: the ability to sense our body's position and movement.

-nociception: the detection of potentially damaging stimuli (stimuli is the plural of stimulus)

Same receptors can also be found in muscles, ligaments, tendons, bones, joint capsules, and the walls of visceral organs (Betts et. al, 2018).

Pain is a complex phenomenon

When we touch something that is too hot or too cold, or when we come into contact with a toxic chemical, or when our angry mother picks us up by the ears, we are activating nociceptor sensory receptors and those signals are called noxious stimuli. Nociceptors detect signals that cause or threaten to cause damage to normal tissue and warn the body of potential dangers (IASP, 2017).

That noxious stimulus is transmitted to the brain via the spinal cord and involves three neurons known as first-order, second-order, and third-order neurons (Picture 1).

The interesting thing is that by the time the original stimulus reaches the brain, you may or may not feel pain. This is because there is a complex modulation process in the brain and spinal cord that is influenced by cognitive, emotional, spiritual, and environmental factors (Arntz and Claassens, 2004; Moseley and Arntz, 2007; Dubin and Patapoutian, 2010; Woo, 2010; Kirkpatrick et al. 2015; Siddall, Lovell, and MacLeod, 2015; McCance and Huether, 2019)

All of these variables can influence the interpretation and intensity of the noxious stimulus, which means that the same stimulus is perceived differently (more or less painful) depending on whether you are in a happy or sad mood. Some evidence suggests, for example, that lower back pain worsens when there is psychological distress or a depressive mood (Pincus et al., 2002).

Acupuncture and the modulation of pain

Acupuncture is thought to interact with the modulation process of the brain and spinal cord by deactivating 'pain' centres in the brain (Zhang, Wang, and McAlonan, 2012; Longhurst, Chee-Yee, and Li, 2017), activating and improving opioid sensitivity (Harris et al, 2009), and regulating biochemicals involved in pain relief (Zhao, 2008).


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-Arntz, A. and Claassens, L., 2004. The meaning of pain influences its experienced intensity. Pain, 109(1-2), pp.20-25.

-Bedson, J. and Croft, P.R., 2008. The discordance between clinical and radiographic knee osteoarthritis: a systematic search and summary of the literature. BMC Musculoskeletal Disorders, 9(1), pp.1-11.

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