Anatomy of the Thoracic Cavity

Intercostal Arteries and Veins

• Each intercostal space contains a single posterior intercostal artery and two anterior intercostal arteries.
• The first two posterior intercostal arteries branch from the superior intercostal artery, a branch of the costocervical trunk of the subclavian artery.
• The posterior intercostal arteries of the lower nine spaces are branches of the descending thoracic aorta.
• The anterior intercostal arteries of the first six spaces branch from the internal thoracic artery.
• The anterior intercostal arteries of the lower spaces branch from the musculophrenic artery, a terminal branch of the internal thoracic artery.
• Each intercostal artery branches to muscles, skin, and parietal pleura.
• Posterior intercostal veins drain backward into the azygos or hemiazygos veins.
• Anterior intercostal veins drain forward into the internal thoracic and musculophrenic veins.

Intercostal Nerves

• The intercostal nerves are the anterior rami of the first 11 thoracic spinal nerves; the 12th is the subcostal nerve.
• Each nerve enters an intercostal space between the parietal pleura and the posterior intercostal membrane.
• It runs forward inferiorly to the intercostal vessels in the subcostal groove of the corresponding rib.
• The first six nerves are distributed within their intercostal spaces.
• The 7th–9th nerves exit their spaces, passing deep to the costal cartilages, and enter the anterior abdominal wall.
• The 10th and 11th nerves pass directly into the abdominal wall since their corresponding ribs are floating.
• Rami communicantes connect the intercostal nerves to the sympathetic trunk.
• Collateral branches run forward inferiorly to the main nerve.
• Lateral cutaneous branches reach the skin of the side of the chest, dividing into anterior and posterior branches.
• Anterior cutaneous branches run near the midline; they divide into medial and lateral branches.
• Muscular branches are numerous.
• Pleural sensory branches extend to the parietal pleura.
• Peritoneal sensory branches (7th–11th intercostal nerves only) extend to the parietal peritoneum.
• The first intercostal nerve joins the brachial plexus via a large branch equivalent to the lateral cutaneous branch of typical intercostal nerves.
• The second intercostal nerve connects to the medial cutaneous nerve of the arm via an intercostobrachial nerve, which is equivalent to the lateral cutaneous branch of other nerves. The 2nd nerve therefore innervates the skin of the axilla and the upper medial side of the arm.
• Except for the first two nerves, the intercostal nerves innervate the skin and parietal pleura of the intercostal spaces.
• Intercostal nerves innervate the intercostal muscles, levatores costarum, and serratus posterior muscles.
• The 7th–11th intercostal nerves innervate the skin and parietal peritoneum of the abdominal wall.
• They also innervate external, internal oblique, transversus abdominis, and rectus abdominis muscles.

Suprapleural Membrane

• The suprapleural membrane is a dense fibrous sheet that seals the thoracic outlet.
• It is attached laterally to the first rib and costal cartilage.
• It attaches medially to the apex of the 7th cervical vertebra's transverse process.
• It protects the underlying pleura and resists changes in intrathoracic pressure.

Diaphragm

• The diaphragm is the primary muscle of respiration.
• It has three parts: sternal, costal, and vertebral.
• The sternal part arises from the xiphoid process.
• The costal part arises from the lower six ribs and their costal cartilages.
• The vertebral part arises from the lumbar vertebrae via crura. The right crus is thicker and longer.
• It has three major openings: aortic, esophageal, and caval.
• The diaphragm inserts into a central tendon.
• The central tendon is fused with the inferior surface of the fibrous pericardium.
• Some of the right crus's muscle fibers pass to the left, encircling the esophageal orifice.
• These fibers might act as a sphincter.
• The diaphragm has a dome shape, with the right dome higher than the left.
• The level of the diaphragm varies with respiratory phase, posture, and abdominal distention.
• The diaphragm is lower when sitting or standing and higher when supine or after a meal.
• The diaphragm is shaped like an inverted J when viewed from the side.
• Other openings: greater, lesser, and lowest splanchnic nerves pierce the crura.
• sympathetic trunks pass posterior to the medial arcuate ligament.
• superior epigastric vessels are between sternal and costal origins.
• Left phrenic Nerve pierces the dome to innervate peritoneum on its undersurface.
• The bundles of 7th–11th intercostal spaces pass into the anterior abdominal wall between the muscular slips of the diaphragm's costal origin.

Intercostal Neuralgia

• Intercostal neuralgia is pain in the intercostal nerves.

Test your knowledge on the anatomy of the thoracic cavity with this quiz. From the intercostal neurovascular bundle to the diaphragm's function, explore essential structures and their roles. Ideal for students of anatomy or medical professionals.