A 3-day-old full-term male infant presents with abdominal distention and failure to pass meconium. Contrast enema shows a transition zone between a dilated proximal segment and a narrow distal bowel. Rectal suction biopsy 2 cm above the dentate line reveals absence of ganglion cells in both the myenteric and submucosal plexuses. The narrow contracted distal segment marked **C** in the diagram is aganglionic. Which of the following best explains the pathophysiology of functional obstruction in the segment marked **C**?