Pain 101 — The Basics: How Can We Make Sense of Pain?

Joseph R. Anticaglia MD
Medical Advisory Board

Pain tells us that there’s something’s wrong in the body. It has a peculiar way of speaking to us. Whether we complain about a mild headache or the intense, agonizing pain of a fractured thigh bone, it seems to say: “Listen up. It’s for your own good. There may be something terribly wrong going on in the body and you better act quickly to correct the problem.”

Pain is an “unpleasant sensory and emotional experience associated with actual or potential tissue damage” says the International Association for the Study of Pain


Pain appears in different ways. The pain intensity of a throbbing, migraine headache might prevent us from going to a PTA meeting, whereas the aching, modest neck discomfort won’t keep us from showing up for work. Pain can appear suddenly as in a heart attack or be chronic as low back pain.

Pain may be sharp and localized to a specific area of the body; for instance, after a cut finger or be widespread as in fibromyalgia. Pain can wear us down both physically and emotionally. Acute pain lasts less than six weeks. When pain lasts longer than three months, is called chronic or persistent pain, as in arthritis.

Pain 101

Pain receptors, called nociceptors, send nerve signals to the spinal cord. From there, the signals are passed along nerve pathways upward to the brain. The brain interprets the severity and location of the pain. It then sends back instructions to the body to act in a certain way. If you put your hand on a hot stove, in a blink of an eye you’ll remove your hand from the stove. How come?

Source: Wikibooks
  1. If you cut your finger with a knife or burn your hand, you have caused tissue damage. This activates pain receptors in the skin (nociceptors). The pain receptor fibers gather themselves together to form afferent nerve fibers or the 1st order neurons (see diagram).
  2. The afferent nerve fibers send electrical messages specifically to the dorsal horn of the gray matter in the spinal cord.
  3. From the dorsal horn, the nerve elements within the gray matter of the spinal cord cross over to the other side of the spinal cord. Next, the pain information is transmitted upwards to the thalamus in the brain (2nd order neurons). Therefore, pain in the right hand is interpreted by the left side of the brain and vice versa.
  4. The thalamus is a distribution center. The signals are relayed from the thalamus to the brain by way of the 3rd order neurons. The nerve signals go to the
    • Region of the brain in charge of physical sensation, for example, cut finger (somatosensory cortex)
    • Area of the brain responsible for thinking (frontal cortex)
    • Part of the brain connected to emotions (limbic system)

Once again, pain receptors from the skin travel to the spinal cord, cross over to the opposite side and then go upwards to the brain. The brain interprets the information. This happens in a fraction of a second so that you can identify sharp pain and localized

it to the cut finger or a sprained ankle. Also, you might feel annoyed and angry with yourself at being careless.

Understanding the physiology of pain is of great interest to scientists. How to relieve distressing pain without causing addiction is an ongoing challenge.


  1. Rolf-Detlef Treede; The International Association for the Study of Pain definition of pain: as valid in 2018 as in 1979, but in need of regularly updated footnotes; Pain Rep. 2018 Mar;
  2. K. Hanoch Kumar, P. Elavarasi; Definition of pain and classification of pain disorders; Journal of Advanced Clinical & Research Insights; May-June, 2016
  3. NIH; Pain Conditions Resources


Types of Sensory Nerve Fibers

Different nerve fibers transmit different nerve sensations to the spinal cord. Two such afferent nerve fibers are fast and slow fibers:

  • Fast Fibers

Sharp, pricking pain is relayed to the nervous system by fast fibers (A- delta fibers). They are larger compared to other fibers and are coated in myelin, which acts as an electrical insulator; both enhancing their ability to carry nerve impulses quickly.

  • Slow Fibers

Dull, achy pain is relayed to the nervous system by slow fibers (C fibers). These fibers are smaller, unmyelinated and carry sensory nerve impulses more slowly.

This article is intended solely as a learning experience. Please consult your physician for diagnostic and treatment options.