Thoracic diaphragm

The thoracic diaphragm is a skeletal muscle that forms the floor of the thoracic cavity and the roof of the abdominal cavity. It plays a crucial role in respiration by contracting and relaxing to facilitate the movement of air into and out of the lungs.

Anatomy

The thoracic diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. It is attached to the xiphoid process of the sternum, the lower six ribs, and the upper lumbar vertebrae. The diaphragm has three major openings: the aortic hiatus, the esophageal hiatus, and the caval opening.

Muscle Fibers

The muscle fibers of the diaphragm are divided into three parts:

• The sternal part, which attaches to the xiphoid process.
• The costal part, which attaches to the lower six ribs.
• The lumbar part, which attaches to the upper lumbar vertebrae.

Central Tendon

The central tendon is a strong, aponeurotic structure in the center of the diaphragm. It serves as the insertion point for the muscle fibers and is crucial for the diaphragm's function.

Function

The primary function of the thoracic diaphragm is to facilitate breathing. During inhalation, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity and allowing air to enter the lungs. During exhalation, the diaphragm relaxes and returns to its dome shape, decreasing the volume of the thoracic cavity and expelling air from the lungs.

Innervation

The diaphragm is innervated by the phrenic nerve, which originates from the cervical spinal cord segments C3, C4, and C5. The mnemonic "C3, 4, 5 keeps the diaphragm alive" is often used to remember the nerve roots that contribute to the phrenic nerve.

Blood Supply

The blood supply to the diaphragm comes from several sources:

• The pericardiacophrenic artery and the musculophrenic artery, branches of the internal thoracic artery.
• The superior phrenic arteries, branches of the thoracic aorta.
• The inferior phrenic arteries, branches of the abdominal aorta.

Clinical Significance

The diaphragm can be involved in various medical conditions, including:

• Diaphragmatic hernia, where abdominal organs protrude into the thoracic cavity.
• Diaphragmatic paralysis, which can result from damage to the phrenic nerve.
• Hiccups, which are involuntary contractions of the diaphragm.

See Also

• Respiratory system
• Abdominal cavity
• Thoracic cavity
• Phrenic nerve