Final answer:
Allodynia is the condition where a normally painless stimulus causes pain. It differs from hyperesthesia, hyperpathia, and hyperalgesia, which involve heightened sensitivity to stimuli, increased pain responses, and increased pain from usually painful stimuli, respectively.
Step-by-step explanation:
The sensory disorder when a normally painless stimulus causes pain is known as allodynia. Allodynia can be a result of various medical conditions and is not the same as hyperesthesia (increased sensitivity to stimuli), hyperpathia (increased reaction to painful stimuli), or hyperalgesia (increased pain from a stimulus that normally provokes pain).
In relation to nociception, or the neural process of encoding and processing noxious stimuli, nociceptors are the type of receptor cell responsible for transducing pain stimuli. Nociception responds to injured stimuli and is not typically activated by stimuli such as pleasant melodies or delicious apples. The nociceptive system does not necessarily require the same pathways as other sensory modalities, for example, nociceptive pathways do not pass through the ventral posterior thalamus for sensory modalities like audition (hearing).
Congenital insensitivity to pain is a rare genetic disorder where individuals are unable to experience pain. They can still detect differences in temperature and pressure but they do not respond to pain-inducing stimuli, leading to a higher risk of injuries and complications.