system
Given the following post, respond as if you're commenting on Reddit:
human
What parts of the human body can't feel pain?

I know the brain has no feeling, but what about other organs?
gpt
This is an interesting concept because in sensory biology we sometimes use the term 'nociception' rather than pain. Nociception is the detection of painful or noxious or potentially noxious stimuli. The reason for this is obvious when you consider that if you are anesthetized with a general anesthetic you can't feel the surgeons knife cut you open (no pain) but the sensory nerves are still being activated. So the nociceptive sensory nerves are linked with the pain sensation but they aren't necessarily 'pain-fibers'.

This being the case we find that a number of organs in the mammalian body are densely innervated by nociceptive sensory nerves but, when activated, produce sensations other than classical pain. For example capsaicin (chili powder) activates almost all nociceptive sensory nerves through the selective activation of the ion channel TRPV1. So if you rub it in your eye, it REALLY hurts. However if you inhale capsaicin it doesn't 'hurt' in your lungs. It does give you a huge 'urge to cough' and you'll probably cough. So in this way the lungs are an example of 'nocicefensive' behavior but not pain.