Diaphragm

The diaphragm is a dome-shaped musculotendinous partition that separates the thoracic cavity from the abdominal cavity in mammals. It is the primary muscle of respiration, enabling the expansion of the thoracic cavity during inhalation and aiding exhalation through its relaxation.

Anatomy and innervation: The diaphragm consists of a central tendinous sheet and peripheral muscular parts that attach to the ribs, sternum, and lumbar spine. It is innervated mainly by the phrenic nerves, originating from spinal cord segments C3–C5. Blood supply comes primarily from the inferior phrenic arteries, with contributions from the pericardiophrenic and superior phrenic arteries; venous drainage mirrors these pathways.

Function and physiology: During inspiration, the diaphragmatic muscles contract, flattening the dome and moving the central tendon downward. This expands the volume of the thoracic cavity and decreases intrathoracic pressure, drawing air into the lungs. Exhalation is usually a passive process driven by elastic recoil, with the diaphragm returning to its dome shape. The diaphragm works in concert with intercostal and accessory muscles, especially during vigorous breathing or exercise.

Clinical significance: Diaphragmatic dysfunction can arise from phrenic nerve injury, resulting in diaphragmatic paralysis, or from structural defects such as diaphragmatic hernias and eventration. Congenital diaphragmatic hernias can cause severe respiratory problems in newborns due to impaired lung development. Diaphragmatic weakness or paralysis may contribute to dyspnea and reduced exercise tolerance in other conditions.

Other uses: The term diaphragm also refers to a contraceptive device, a flexible latex or silicone cup placed over the cervix with spermicide to prevent pregnancy. In equipment such as cameras and microphones, a diaphragm is a thin, flexible membrane that acts as a sound or light barrier or sensor component.