The diaphragm is classified as a skeletal muscle. Most of the time it is under involuntary control but we can move it voluntarily at will. It is shaped like a dome and is the anatomical partition that separates the thoracic and abdominal cavities. It has a convexity that is upward. During inhalation it contracts and flattens downward (the opposite of what you would think), which allows the lungs to expand. When it relaxes it assists with exhalation, it rises to compress the lungs. It originates from the xiphoid process, the lumbar vertebrae, and the lower fifth or sixth costal cartilages.
It is immediately superior to the spleen on the left, the stomach, and the liver on the right. The adrenal glands are very close inferiorly. In most people the right side is ever so slightly higher than the left. It receives innervation from the Vagus.
The diaphragm separates the chest cavity from the abdomen and it is considered to be a skeletal muscle. Skeletal muscles contract because of nerve impulses. Smooth muscles also contract because of nerves but the contractions are much less forceful. The diaphragm is the primary muscle used when we inhale. When the diaphragm contracts, the lungs expand so that we may breathe in air. When someone has damage to the diaphragm, there can be a great deal of difficulty when breathing. The phrenic nerve is the nerve that controls the diaphragm and it is located at C3 - C5.