The human rib cage forms a protective structure for the chest cavity. Within this framework are distinct anatomical regions known as intercostal spaces, precisely located between adjacent ribs, extending around the circumference of the chest. They play a role in the overall mechanics of the torso.
Understanding Intercostal Spaces
Intercostal spaces are the anatomical areas situated between one rib and the rib directly below it. Each space contains several types of tissues and structures, including three layers of intercostal muscles: the external, internal, and innermost intercostals. These muscle layers contribute to the integrity of the thoracic cage. Along with muscles, these spaces also house a neurovascular bundle, which includes intercostal nerves, arteries, and veins. This bundle is typically positioned between the internal and innermost intercostal muscles.
The intercostal muscles are important for breathing. The external intercostal muscles are primarily involved in inhalation, assisting in the elevation of the ribs and expansion of the rib cage. Conversely, the internal and innermost intercostal muscles contribute to exhalation, particularly forced exhalation, by aiding in the depression of the ribs. These coordinated muscle actions allow for changes in the size of the chest cavity, facilitating air movement into and out of the lungs.
Counting the Spaces
There are typically 11 intercostal spaces on each side of the human body. This number arises from the fact that humans generally have 12 pairs of ribs. Since the spaces are found between the ribs, there is one fewer space than the number of ribs. For numbering purposes, each intercostal space is identified by the rib that forms its superior (upper) border. For instance, the first intercostal space lies between the first and second ribs.
Significance of Intercostal Spaces
These spaces also hold clinical relevance for various medical procedures. Healthcare professionals often use intercostal spaces as access points for procedures such as listening to lung sounds, which helps in diagnosing respiratory conditions, and for thoracentesis, a procedure to remove fluid or air from the pleural space. When performing such procedures, the needle or catheter is typically inserted just above the superior border of a rib to avoid damaging the neurovascular bundle, which runs along the lower edge of each rib. Chest tubes, used for draining larger amounts of fluid or air, are also inserted through these spaces, commonly in the fourth or fifth intercostal space along the mid-axillary line. The spaces also offer a degree of protection for internal organs while allowing for the necessary flexibility and movement of the chest wall.