Why Do Paper Cuts Hurt So Much?

We've all had them and wondered, "how the heck can this stupid thing hurt so darn much?" While you probably already know that most paper cuts occur on your finger tips and that they have more nerves than most other areas of your body, you've probably still wondered why a knife cut in the same spot seems to hurt less. Well, Mental Floss can help fill you in:

Well, the blade of even a fairly dull knife tends to be more straight and sharp than the dull and flexible edge of a piece of paper. When a knife cuts your skin, it leaves a relatively clean cut compared to paper, which will flex a little and do more microscopic damage to the skin.

There's more to the story, of course, but you'll have to visit the link to read about all of that.

Link

There is probably a difference in the neurological response to the stimuli as well. "periaqueductal gray matter of the midbrain activates enkephalin-releasing neurons that project to the raphe nuclei in the brainstem. 5-HT (serotonin) released from the raphe nuclei descends to the dorsal horn of the spinal cord where it forms excitatory connections with the "inhibitory interneurons" located in Laminae II (aka the substantia gelatinosa). When activated, these interneurons release either enkephalin or dynorphin (endogenous opioid neurotransmitters), which bind to mu opioid receptors on the axons of incoming C and A-delta fibers carrying pain signals from nociceptors activated in the periphery." (See: Gate control theory of pain)

I remember something about this and papercuts in my book "Neuroanatomy Through Clinical Cases" by Hal Blumenfeld.

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