<prompt> Which of the following is true upper esophageal sphincter?Its physiological not anatomicalIt has pressure of 10 to 20 mmHgIt is under hormonal controlIt is formed by striated muscles  <response>: Upper oesophageal sphincterUES 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 