Final answer:
The innervation above the pectinate line is provided by visceral sensory fibers, making it fairly insensitive, while below the line, somatic sensory fibers are responsible for high sensitivity to pain.
Step-by-step explanation:
The pectinate line, located in the canal, serves as a significant anatomical landmark that separates two different types of innervation. Above the pectinate line, the area is innervated by visceral sensory fibers. This part of the canal is relatively insensitive to pain because visceral fibers are less able to convey pain, temperature, and touch sensations.
Below the pectinate line, the region is innervated by somatic sensory fibers, particularly from the inferior rectal nerves, which are branches of the pudendal nerve. The presence of somatic fibers means that this area is very sensitive to these sensations, including pain.
Understanding the differences in innervation above and below the pectinate line is clinically significant, especially when considering procedures like hemorrhoidectomy or interpreting symptoms related to pathology. This knowledge also relates to the embryological development as the innervation correlates with the origins of the hindgut (above the line) and the proctodeum (below the line).
In summary, the mucosa above the pectinate line has a higher pain threshold and is innervated by visceral fibers, while the area below has a lower pain threshold and is innervated by somatic fibers, which is why it's much more sensitive to pain and other sensations.