The vagus nerve provides parasympathetic innervation to the viscera above the diaphragm. It causes decreased heart rate and contractility, increases bronchial gland secretion and increased contraction of bronchiolar smooth muscle.
The proximal portion of the gastrointestinal tract receives parasympathetic innervation from the vagus nerve. This includes the distal esophagus, stomach, liver, gallbladder, pancreas, spleen and small intestine. Parasympathetic tone in these organs causes increased motility, increased secretions and relaxation of sphincters.
The ascending and transverse colon both receive parasympathetic innervation from the vagus nerve. Parasympathetic input causes increased contractions, secretions and motility as well as relaxation of various sphincters.
The descending and sigmoid colon as well as the rectum are the only parts of the gastrointestinal system that receive parasympathetic innervation from the pelvic splanchnic nerves. Input from these nerves is similar to input from the vagus nerve in that it causes increased contractions, secretions and motility as well as relaxation of various sphincters.
The pelvic splanchnic nerves provide innervation to the lower urinary tract. Parasympathetic input causes contraction of the detrusor muscle and relaxation of the internal sphincter, resulting in bladder emptying. Parasympathetic input to the ureter may increase contractility.
The reproductive organs receive parasympathetic innervation from the pelvic splanchnic nerves. Parasympathetic input is responsible for production of erection in penile tissue.
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