Physiology Which of the following is the origin of electrical slow wave activity in gastrointestinal tract smooth muscle? A The interstitial cells of Cajal B The smooth muscle of the circular muscle layer C The smooth muscle of the longitudinal muscle layer D The smooth muscle of the muscularis mucosa 💡 Explanation Which of the following is the origin of electrical slow wave activity in gastrointestinal tract smooth muscle? ✓ Correct Answer: A. The interstitial cells of Cajal