The stomach of the cat can be divided into distinct regions of motor activity. The proximal end of the stomach relaxes when food is digested. While food is being digested this portion of the stomach either has rapid stationary contractions or a sustained tonic contraction of muscle. These different actions result in either the food being moved around or the food moving towards the distal portion of the stomach. The distal portion of the stomach undergoes rhythmic cycles of partial depolarization. This depolarization sensitizes muscle cells so they are more likely to contract. The stomach is not only a muscular structure, it also serves a chemical function by releasing hydrochloric acid and other digestive enzymes to break down food.