Like most systems in the body, the muscular system does not work in isolation. The most obvious systems that interact with muscular system are the skeletal system, the nervous system and the circulatory system. Muscles are also involved in the digestive system, the respiratory system and the immune system.
The Skeletal System
Most of the muscular system exists for the exclusive purpose of interacting with the skeletal system. Muscles move bones in relationship to each other whenever you move your legs or arms. Smaller muscles move your jaws and fingers.
The Nervous System
The nervous system can be viewed as complex information-possessing systems whose input is the senses and whose output is the muscles. Sometimes the muscles act as input to the nervous system in sensors such as the golgi sensors, which tell us when muscles are overextended.
The Circulatory System
The circulatory system brings nutrients to the muscles and takes away wastes. The circulatory system also carries hormones that regulate muscular activity. The pump for the circulatory system is the heart--a muscle.
The Digestive System
The muscular system interacts with the digestive system in several places. The muscles of the jaw masticate food, and then muscles along the esophagus move food from the mouth to the stomach. Muscles along the intestines move digesting food along, and muscles control sphincters that isolate the sections of the digestive system.
The Respiratory System
The main interaction between the muscular system and the respiratory system is the diaphragm: a large, flat muscle that separates the lungs from the intestines. It is the movement of the diaphragm that causes the lungs to inflate and deflate.
The Immune System
The muscular system interacts with the immune system via the lymph system. The lymph vessels run through the muscles, and the regular action of the muscles pumps lymph through the lymph vessels. The lymph system does not have a pump like the circulatory system does.