What Are Nociceptors?

The Science Behind Pain.

Woman suffering from shoulder pain. Credit: BSIP/UIG / Getty Images

While nociceptors are sometimes called "pain receptors", that's not exactly an accurate term. However, they play a pivotal role in how you feel and react to pain. Understanding the difference between nociceptors and pain is important in understanding how the brain works in processing sensations. 

There are thousands of ways you can experience pain. From stubbing your toe to cutting yourself while slicing vegetables, various degrees of pain are part of the human experience.

No matter how the pain is caused, they all share similar mechanisms in how the sensation is detected and transmitted. 

Nociceptors: Pain Transmission

If you bang your knee on a table or burn yourself, the pain is usually instantaneous. These cases are known as "acute", or new, pain. Acute pain starts from nociception, the nervous system's method of detecting damage to the body. Nociceptors are nerve endings, or sensory receptors, located all over the body. They are responsible for assessing damage to the body while you experience pain.

If you stub your toe, the nociceptors are activated right away.They send a signal to the brain, traveling through the peripheral nerves to the spinal cord. During transmission, the nociceptors' signals are processed constantly, with the brain having the largest impact on how you experience the pain.   

Nociceptors serve as alarms for the body, alerting you that something has happened you need to react to and only activated when they've been triggered by an event.

 

Nociceptors are divided into three categories:

  • Chemical: Chemicals activate nociceptors, such as when a cut becomes infected. To fight the infection, the area will become inflamed; your body is bringing more blood and chemicals to the area to help repair the damage.The chemicals activate nociceptors and produce pain. This is why after you have an injury or wound, even gentle touches or small movements can really hurt. 
  • Temperature:Temperature are common triggers of nociceptors. If you touch a hot stove, nociceptors signaling pain are activated right away, sometimes before you're even aware of what you've done. 
  • Mechanical: Mechanical pressure refers to anything that hinders or stretches movement, such as when you pull a hamstring or strain a tendon. The ligaments are stretched beyond their ability, stimulating nociceptors and sending pain signals to the brain. 

Nociceptor pain is a normal function and behaves in a generally predictable way. You can identify the cause of the pain, such as a hurt foot after stepping on something, and the category it falls into. However, not all pain falls into a nociceptor category. Injuries without a direct cause, such as the result of an internal disease, do no usually stimulate nociceptors. 

Nociceptors function to alert you of potential harm; in some cases, it's inaccurate. While a stubbed toe may hurt badly at the moment, it likely didn't cause lasting damage. But in the case of a burn, nociceptors work to alert you of damage to the nerves.

 

Many pain medications, like opioids, work by blocking chemicals that reduce your pain threshold. This is how the response to pain is controlled and why they only work in some cases; pain can be signaled by other receptors, not just nociceptors, so you can feel pain without activating nociceptors. 

Sources:

Dubin, A., Patapoutian, A. "Nociceptors: the Sensors of the Pain Pathway". Journal of Clinical Investigation, 3760-3772, 2010. 

 Fein, A. "Nociceptors and the Perception of Pain". University of Connecticut Health Center, 2012. 

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