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What is Which of the following is true upper esophageal sphincter? and explain in detail?
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