This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Physiology
Which of the following is true upper esophageal sphincter? 
Select and explain. 
A. Its physiological not anatomical, B. It has pressure of 10 to 20 mmHg, C. It is under hormonal control, D. It is formed by striated muscles
A: Its physiological not anatomical
Answer: A: Its physiological not anatomical 
Explanation: Upper oesophageal sphincter(UES) is a true sphincter. It has pressure of 35-200mmHg. It is formed by cricopharyngeal muscle which is a striated muscle. It is under Neurochemical control.The only neurotransmitter of UES opening or closing muscles found to mediate contraction is acetylcholine acting through nicotinic cholinergic receptors. Ref: Medical Physiology, Indu Khurana