A 52-year-old man comes to his primary care physician because of pain with defecation. The symptoms began 2 weeks ago. The pain is worse with straining, and the patient has occasionally noticed streaks of fresh blood on his stools. He works as a construction worker, and his diet consists mostly of fast food. His temperature is 37.3°C (99.1°F), blood pressure
is 142/85 mmHg, and pulse
is 73/min. Physical exam shows multiple purplish-blue sacs in the anal canal
. Which of the following structures is most likely responsible for providing sensory innervation to the lesion site?