The word dystonia describes abnormal involuntary sustained muscle contractions and spasms. Pitocin is commonly used to induce uterine contractions. Tonic seizures produce constant contractions of the muscles. Pain can come from possible lacerations, incisions, uterine contractions and sore nipples. Bisacodyl works by stimulating enteric nerves to cause peristalsis, i.e., colonic contractions. This prevents nerve impulses from triggering muscle contractions. They produce toxins that interfere with normal muscle contractions. It does this through regular contractions called peristalsis. The sympathetic stimulation also increases the rate of heart contractions and cardiac output. Berger showed that these potentials were not due to scalp muscle contractions. The food bolus is moved along the gut by waves of muscular contractions (peristalsis). Clonus is a series of involuntary, rhythmic, muscular contractions and relaxations. The strength of heart muscle contractions controls the stroke volume. Negatively inotropic agents weaken the force of muscular contractions. People may report pain, aching, and itching with the contractions.