The Nerves and Blood Vessels in the Thoracic Region
The thoracic region of the body showcases the remarkable complexity of human physiology. Nerves, blood vessels, and arteries in this critical region enable sensation and allow blood to flow throughout the entire body. The rib cage is innervated 12 pairs of spinal nerves. Each spinal nerve leaves the vertebral canal via intervertebral foramina and then branches into an anterior and posterior ramus. The anterior ramus runs along the inferior border of the rib in the intercostal space, becoming the intercostal nerve. The 12th anterior ramus is called the subcostal nerve.
The intercostal nerves have many branches:
Rami communicantes: These branches connect the intercostal nerves to ganglia of the sympathetic trunk, the string of interconnected sympathetic ganglia along each side of the vertebral column.
Collateral branches: These branches run just below the main nerve, on the rib below.
Lateral cutaneous branches: These nerve branches innervate the skin of the side of the chest.
Anterior cutaneous branches: These branches are the terminal portions of the anterior rami that innervate the skin of the anterior thorax.
Muscular branches: These branches innervate the intercostal muscles.
Pleural sensory branches: These branches innervate the parietal pleura.
Peritoneal sensory branches: These branches run to the parietal peritoneum (thin serous membrane lining the abdominal wall) on the 7th through 11th intercostal nerves.
The diaphragm gets its motor-nerve supply from the phrenic nerve. (Remember, C3, 4, 5 keep the diaphragm alive.) The sensory nerve supply comes from the phrenic nerve and the lower six intercostal nerves.
The thoracic wall is served by a bunch of arteries and veins.
Anterior intercostal arteries: The first six anterior intercostal arteries stem directly from the internal thoracic artery. The rest of them branch off the musculophrenic artery.
Posterior intercostal arteries: Two of these arteries branch off the superior intercostal artery in the first two intercostal spaces, and the remaining posterior intercostal arteries are branches of the descending thoracic aorta.
Anterior intercostal veins: These veins return blood to the internal thoracic and musculophrenic veins.
Posterior intercostal veins: Most of these veins return blood to the azygos and hemiazygos veins.