Final answer:
Hemorrhoids cause pain because they are located in a highly sensitive area innervated by somatic sensory fibers known as the area below the pectinate line.
Step-by-step explanation:
External piles, also known as hemorrhoids, cause pain because they are located below the pectinate line, which is a sensitive area innervated by somatic sensory fibers. In contrast, the area above the pectinate line is innervated by visceral sensory fibers and is relatively insensitive.
Referred pain occurs when visceral sensations are perceived in areas different from the source, commonly due to both sets of sensory fibers entering the spinal cord at the same level. In the case of hemorrhoids, the pain is felt because that's the direct location of the inflamed tissue.