Thoracic diaphragm

The thoracic diaphragm is a dome-shaped skeletal muscle separating the thoracic and abdominal cavities. Its contraction flattens the dome, enlarging the chest cavity and helping draw air into the lungs.

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Inhalation: The movement of air into the lungs as the thoracic cavity expands and lung pressure falls. Diaphragm contraction is the main muscular action that initiates quiet inhalation.
Diaphragmatic crura: Tendinous and muscular pillars anchoring the diaphragm to the upper lumbar vertebrae. These posterior attachments help form the muscle's central support and major passageways.
Diaphragmatic paralysis: Loss of effective contraction in one or both sides of the diaphragm, often from nerve injury. It directly demonstrates the respiratory consequences of impaired diaphragm movement.
Internal intercostal muscles: Muscles between the ribs that mainly assist forced expiration by depressing the rib cage. Their principal respiratory action opposes the diaphragm's inspiratory action.
Pleural cavity: The thin fluid-filled space between the lung surface and the chest wall lining. Pressure changes transmitted through this space let diaphragm-driven chest expansion enlarge the lungs.
Central tendon of diaphragm: A strong, aponeurotic sheet at the center of the diaphragm into which its muscle fibers converge. The converging fibers pull this tendon downward as the diaphragm contracts.
Eventration of the diaphragm: Abnormal elevation of an intact diaphragm caused by thinning or underdevelopment of its muscle. It changes diaphragm position without creating the defect found in a hernia.
Valsalva maneuver: Forceful attempted exhalation against a closed airway that raises pressure in the chest and abdomen. It recruits the diaphragm and abdominal muscles for bracing rather than ordinary airflow.
Intra-abdominal pressure: The pressure within the abdominal cavity, influenced by abdominal contents and surrounding muscles. When the diaphragm descends, it compresses abdominal contents and raises this pressure.
Phrenic nerve: A nerve arising mainly from spinal nerve roots C3–C5 that supplies the diaphragm's motor control. Its signals trigger diaphragm contraction; injury can impair breathing.