UNDERSTANDING PAIN: WHAT IS IT? AND WHY DOES IT HAPPEN?

Pain is perceived when a message travels from the pain receptors (nociceptors) to the brain. It can be short-lasting (acute) or long-lasting (chronic), and people can describe it in various ways. It can affect different parts of your nervous system causing neuropathic, central, and even phantom pain. It is a global health concern that impacts all, irrespective of age, gender, ethnicity, economic status, or geography. Worldwide, an estimated  1 in 5 adults suffer from pain, with another 1 in 10 adults diagnosed with chronic pain yearly.

Pain is complex, and people experience it differently. How you experience pain depends on the communication between your brain and nociceptors and how the brain interprets the pain signals it receives.

Continue reading to learn more about the causes of pain, the different kinds of pain, how the body responds to pain, and why we feel pain differently.

What Causes Pain?

Pain is an unpleasant sensation your body usually feels in response to tissue damage following an injury or a medical condition.  

We feel pain when specific nerve receptors, called nociceptors, detect this tissue damage and transmit the information along the spinal cord to the brain. Feeling pain helps your body avoid potentially dangerous situations and limits further injury to the body.

For example, when you touch something hot, a pain message reaches your brain. In response, your brain orders your muscles to contract so that you pull your hand away immediately and prevent further harm.        

Similarly, when you twist your ankle, the more you walk on it, the more it hurts. Consequently, you start walking less for a while to allow your ankle to heal from the injury. 

What Are The Types Of Pain?

Pain is very diverse. Different types of pain have different durations, locations, and severity.

Acute pain

Intense pain that lasts less than three months is usually known as acute pain. It makes your body aware of localized tissue damage or an injury and triggers your body’s fight-or-flight response.

Experiencing acute pain prompts your body to take the right actions that can help your healing.

Different types of acute pain usually go away after your body heals from the injury or damage, such as:

• Somatic pain: This is the localized pain you feel on your skin or in the tissue under your skin, including the muscles, joints, skeleton, and connective tissues. Headaches, pain from a paper cut, and pain in the pelvis are all examples of somatic pain. Somatic pain can be described in different ways, such as sharp, aching, cramping, or gnawing.
• Visceral pain: People experience visceral pain when internal organs and tissues are injured or damaged. Visceral pain is vague, not localized, and can occur in the chest, abdomen, intestines, and pelvis.
• Referred pain: Referred pain occurs when you experience pain at a location in your body different from the source of injury or tissue damage. For example, a heart attack can cause jaw pain, and an injured pancreas can trigger back pain. 

Chronic pain

Chronic pain is pain that persists for more than three months despite treatment or medication. 

Although feeling pain can be useful in helping your body heal, sometimes the pain does not resolve for a long time, even after the injury has healed. In other cases, chronic pain can persist without an underlying cause.

Common types of chronic pain include:

• Arthritis, or joint pain
• Migraines or headaches
• Neck or lower back pain
• Fibromyalgia (non-specific pain in the muscles)
• Persistent pain in scar tissue
• Orchialgia (testicular pain)

Patients often describe their chronic pain as: 

• Aching
• Shooting
• Burning
• Squeezing
• Throbbing
• Stinging
• Stiffness

More specific types of pain include neuropathic, central, and phantom pain.

Neuropathic pain

This pain occurs following damage to the nervous system. You may feel neuropathic pain in any part of your nervous system – peripheral nerves, spinal cord, and brain.

When the nerve fibers are damaged, they send faulty signals to the pain centers causing feelings of tenderness, numbness, tingling, burning, or electric shock-like pain.

Neuropathic pain can be caused by:

• Diabetes
• Alcoholism
• Chemotherapy
• Radiation therapy
• Nerve damage from trauma or surgery

Central pain

Central pain can occur following damage to the central nervous system – the spinal cord, brain, and brainstem. It can cause feelings of aching, burning, and pressing sensations.

This type of pain can be caused by:

• A stroke
• Tumors
• Epilepsy
• Trauma to the brain or spinal cord
• Parkinson’s disease

Phantom pain

Phantom pain, or phantom limb pain, is a painful sensation that feels like it is coming from a missing limb or an amputated body part.

It is still not clear what exactly causes phantom pain. Nonetheless, people affected often describe the pain as:

• Burning
• Shooting
• Stabbing
• Crushing
• Cramping
• Throbbing
• Pins and needles

How Pain Works

Different parts of your nervous system are involved in sensing pain, including your brain, spinal cord, and nerves. 

There are generally three main steps involved in pain perception:

• Pain is detected by nociceptors
• Pain signals are transmitted to the spinal cord by the peripheral nervous system
• Pain signals are transmitted to the brain by the central nervous system

Pain messages can travel in two main routes; ascending (upwards towards the brain) and descending (downward from the brain).

In the ascending route, sensory information is carried from the body to the brain via the spinal cord. The brain then analyzes and understands the messages and produces a pain sensation if it perceives a threat. 

In response, the brain sends a signal downward via your spinal cord to your reflex organs and orders them to react to the pain stimulus.

Your pain experience depends on how the sensory information reaches your brain and how the brain processes this information. Furthermore, research shows that many of the chemicals involved in pain sensation are also involved in feelings of anxiousness, depression, worry, and stress. 

Therefore, the perception of pain is a highly personalized experience that affects different people differently.  

Why Do We Experience Pain Differently?

Different chemical or physical changes in your pain system (brain, spinal cord, and nerves) can make it more or less sensitive to sensory information.

As a result, you may have tissue damage without feeling hurt, and you may also feel pain without injury or tissue damage. Moreover, the amount of tissue damage does not always match the level of pain experienced. 

The changes that can alter your sensitivity to pain include:

• The pain nerves can become extremely sensitive and deliver pain messages to your brain and spinal cord even when there isn’t much injury or damage. Consequently, your body becomes highly sensitive to pain. 
• The pain nerves can start firing off pain signals randomly without any stimulation. Accordingly, you may start feeling pain without even moving or touching anything.
• Nerves that do not usually transmit pain messages may start to do so, causing you to feel that the pain is spreading.
• Feelings of stress, anxiety, worry, or depression can create a sense of danger in the brain, causing it to process more feelings of pain.  
• In some extremely rare cases, people are born with a genetic disorder known as congenital insensitivity to pain with anhidrosis (CIPA), which prevents them from feeling pain. The pain-sensing neurons (nociceptors) of people with CIPA cannot deliver signals to the brain, leading to the inability to feel pain.  

Just because you don’t have underlying physiological damage or injury does not make your pain imaginary or any less painful. All these alterations in your pain system can change how much pain you feel and when you feel it.  

If you have been experiencing ongoing pain for over 12 weeks, contact your healthcare provider for an assessment and diagnosis. 

Living with chronic pain can be very challenging. Nevertheless, several lifestyle changes and pain management modalities can help relieve your pain and improve the quality of your life.

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Sources:

• The difference between acute and chronic pain
• Not All Pain is Created Equal: Basic Definitions and Diagnostic Work-Up - PMC
• General Pathways of Pain Sensation and the Major Neurotransmitters Involved in Pain Regulation - PMC
• Congenital Insensitivity to Pain and Anhydrosis (CIPA) Syndrome; A Report of 4 Cases - PMC    

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