This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
Which of the following is the origin of electrical slow wave activity in gastrointestinal tract smooth muscle? 
Select and explain. 
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
A: The interstitial cells of Cajal
Answer: A: The interstitial cells of Cajal 
Explanation: Ans. A. The interstitial cells of Cajala. Electrical slow wave activity in the gastrointestinal tract appears to originate from specialized pacemaker cells (interstitial cells of Cajal) located between the longitudinal and circular muscle layers and within the submucosal and myenteric plexuses.b. These pacemaker cells input directly onto the smooth muscle and receive input from enteric nerves.c. Rhythmic, phasic contractions are characteristic of the gastric antrum and the small and large intestines.