Thoracic diaphragm


 * For other types of diaphragm, see Diaphragm.

In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. The diaphragm separates the thoracic cavity (with lung and heart) from the abdominal cavity (with digestive system and urogenital system). In its relaxed state, the diaphragm is shaped like a dome. It is controlled by the phrenic nerve.

In order to avoid confusion with other types of diaphragm, it is sometimes referred to as the thoracic diaphragm. Any reference to the diaphragm is understood to refer to this structure.

Function
It is crucial in respiration: in order to draw air into the lungs, the diaphragm contracts, thus enlarging the thoracic cavity and reducing intra-thoracic pressure (the external intercostals muscles also participate in this enlargement). When the diaphragm relaxes, air is exhaled by elastic recoil of the lung and the tissues lining the thoracic cavity in conjunction with the abdominal muscle which act as the antagonist pair to diaphragm's contraction Antagonist (muscle). The diaphragm is also found in other vertebrates such as reptiles.

It is responsible for all the breathing related to voice.

The diaphragm also helps to expel vomit, feces, and urine from the body by increasing intra-abdominal pressure.

Pathology
A hiatal hernia can result from a tear or weakness in the diaphragm near the gastroesophageal junction.

If the diaphragm is struck, or otherwise spasms, breathing will become difficult. This is called having the wind knocked out of you.

A hiccup occurs when the diaphragm contracts periodically without voluntary control.

Diaphragmatic injuries result from either blunt or penetrating trauma.

Anatomy
The Diaphragm is a dome-shaped musculofibrous septum which separates the thoracic from the abdominal cavity, its convex upper surface forming the floor of the former, and its concave under surface the roof of the latter. Its peripheral part consists of muscular fibers which take origin from the circumference of the thoracic outlet and converge to be inserted into a central tendon.

The muscular fibers may be grouped according to their origins into three parts:

There are two lumbocostal arches, a medial and a lateral, on either side.

Crura and central tendon
At their origins the crura are tendinous in structure, and blend with the anterior longitudinal ligament of the vertebral column.

The central tendon of the diaphragm is a thin but strong aponeurosis situated near the center of the vault formed by the muscle, but somewhat closer to the front than to the back of the thorax, so that the posterior muscular fibers are the longer.

Openings in the Diaphragm
The diaphragm is pierced by a series of apertures to permit of the passage of structures between the thorax and abdomen. Three large openings—the aortic, the esophageal, and the vena cava—and a series of smaller ones are described.

Variations
The sternal portion of the muscle is sometimes wanting and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers.