Spasms of the internal urethral sphincter are associated with penile erection. The internal urethral sphincter provides involuntary control of urination. Voiding urine begins with voluntary relaxation of the external urethral sphincter. The upper esophageal sphincter surrounds the upper part of the esophagus. Opening of the upper esophageal sphincter is triggered by the swallowing reflex. The external urethral sphincter provides voluntary control of urination. The result is a hypertensive nonrelaxed esophageal sphincter. Metoclopramide also increases the tone of the lower esophageal sphincter. This is due to congenital hypertrophy of the pyloric sphincter. Near the cardia is the lower oesophageal sphincter. Medications that reduce the lower esophageal sphincter (LES) pressure should be avoided. The pelvic muscle near the vagina, the anal sphincter, and the uterus contract. This is due to neuropathy of the bladder sphincter. Internal ophthalmoplegia means involvement limited to the pupillary sphincter and ciliary muscle. Also, parasympathetic stimulation of the internal anal sphincter will relax this muscle to allow defecation.