The human rib cage protects vital organs like the heart and lungs. This bony structure dynamically changes shape during respiration. Understanding the components within the spaces between the ribs is important for comprehending breathing mechanics and how conditions can affect this region. These spaces contain a complex network of muscles, nerves, and protective membranes.
Intercostal Muscles
The spaces between the ribs, called intercostal spaces, house several layers of intercostal muscles. These muscles connect adjacent ribs and are fundamental to breathing mechanics. There are three main types: external, internal, and innermost intercostal muscles. These groups work in concert, allowing the rib cage to expand and contract.
The external intercostal muscles are the most superficial layer and primarily facilitate inhalation. When you breathe in, these muscles contract, pulling the ribs upward and outward, which increases the volume of the chest cavity. This expansion creates a pressure difference, drawing air into the lungs.
Conversely, the internal intercostal muscles, located beneath the external layer, are mainly active during forced exhalation. They contract to pull the ribs downward and inward, thereby decreasing the volume of the chest cavity and expelling air from the lungs. The innermost intercostal muscles support the internal intercostals, also aiding in forced exhalation and stabilizing the intercostal space.
Intercostal Nerves and Blood Vessels
Within each intercostal space, a neurovascular bundle runs along the underside of each rib. This bundle consists of an intercostal vein, artery, and nerve. The intercostal nerves originate from the anterior rami of the thoracic spinal nerves. These nerves are responsible for sensory feedback from the chest wall and motor control of the intercostal muscles.
The intercostal arteries supply the area and include both anterior and posterior branches. Posterior intercostal arteries typically arise from the thoracic aorta, while anterior intercostal arteries branch from the internal thoracic artery. These arteries supply the intercostal muscles, skin, and parietal pleura. Within the costal groove, the vein is positioned superiorly, the artery in the middle, and the nerve inferiorly. This arrangement is consistent across the intercostal spaces.
The Pleura
The pleura is a double-layered membrane that envelops the lungs and lines the inner chest cavity. The outer layer, known as the parietal pleura, attaches to the chest wall. The inner layer, called the visceral pleura, directly covers the surface of the lungs. Between these two layers lies a narrow space called the pleural cavity, which contains a small amount of lubricating pleural fluid.
This fluid allows the two pleural layers to glide smoothly past each other with minimal friction during lung expansion and contraction. This smooth movement is important for efficient lung function. The pleura also plays a role in lung expansion by creating a slight negative pressure that helps draw the lungs outward during inhalation.
Common Conditions Affecting the Rib Space
Several conditions can affect the structures within the rib space, causing pain. Intercostal muscle strains occur when the muscles between the ribs are overstretched or torn. This can result from vigorous activities like twisting, lifting, or repetitive movements, or from direct chest trauma. Symptoms include sharp pain that worsens with movement, deep breathing, coughing, or sneezing, along with tenderness in the affected area.
Intercostal neuralgia involves nerve pain along the intercostal nerves. This neuropathic pain can manifest as burning, sharp, or shooting sensations around the ribs, upper chest, or upper back. A common cause is the reactivation of the herpes zoster virus, leading to shingles, which can cause persistent pain even after the rash resolves. Other causes include chest trauma, nerve compression, or surgical injury.
Pleurisy, also known as pleuritis, is an inflammation of the pleura. When the pleural layers become inflamed, they can rub against each other, causing sharp, stabbing chest pain that intensifies with deep breaths, coughing, or sneezing. Common causes include viral or bacterial infections, such as pneumonia, and autoimmune diseases. In some cases, inflammation can lead to fluid accumulation in the pleural space, known as pleural effusion.