Final answer:
Referred pain is when pain from internal organs is felt elsewhere due to sensory fibers entering the spinal cord at the same level. Nociceptors detect pain signals, but conscious perception requires brain processing. Reflex arcs allow for quick reactions to pain without brain input.
Step-by-step explanation:
The phenomenon of referred pain occurs when pain arising from internal organs is felt in different, often distant, areas of the body. This is due to the fact that visceral sensory fibers and somatosensory fibers from the internal organs and the referred location enter the spinal cord at the same level. The brain thus confuses the origin of the sensory input, leading to the perception of pain in an area different from the actual source.
Nociceptors are the sensory receptors that detect signals that we perceive as pain. The conscious perception of pain only occurs after these signals reach the brain, specifically the primary somatosensory cortex after being processed through various nociceptive pathways, including one to the thalamus, and sometimes directly to the hypothalamus for an autonomic response.
In some cases involving reflex responses, the spinal cord can respond to pain without input from the brain, allowing for quicker reactions through a reflex arc. For example, pulling your hand back from a hot surface occurs almost instantaneously, demonstrating this reflex action.