Smooth muscle in the gastrointestinal tract

In the gastrointestinal (GI) tract, the smooth muscle contractions are classified as either tonic (e.g. continuous) or phasic (e.g. rhythmic). Both are important for the maintenance of a proper GI function. Tonic contractions push against the luminal contents and maintain tension in the gut. Phasic contractions rhythmically occur throughout the GI tract to propel the bolus and increase surface area. Phasic contractions occur continuously within the GI tract. Unlike skeletal contractions that require a direct motor neuron to occur, phasic smooth muscle contractions can occur without a direct neural stimulus, due to the action of the myenteric plexus.