Intercostal Muscles

The intercostal muscles sit in the gaps between neighboring ribs, called the intercostal spaces. An anatomy review on the NIH's NCBI Bookshelf describes eleven pairs of intercostal muscles that occupy these spaces and are arranged from superficial to deep. The muscles of the chest wall are supplied by the intercostal nerves, which arise mainly from the spinal nerves T1 through T11.

The external intercostal muscle is the most superficial layer. It starts on the lower border of the rib above and attaches to the upper border of the rib below. The internal intercostal muscles form the intermediate layer. The innermost intercostal muscles form the deepest layer of the chest wall.

The diaphragm is the main muscle used for breathing, and the intercostal muscles work with it. According to the National Heart, Lung, and Blood Institute (NHLBI), the muscles between the ribs contract to pull the rib cage both upward and outward during inhalation, which helps enlarge the chest cavity. During exhalation, the diaphragm and rib muscles relax, reducing the space in the chest cavity. NHLBI adds that the intercostal muscles play a role in breathing during physical activity.

The layers do different jobs. During inspiration, the external intercostal muscles contract and lift the sides of the ribs. The internal intercostal muscles lower the ribs and reduce the volume of the chest during forced expiration. When the muscles between the ribs pull inward with each breath, the sign is called intercostal retractions; MedlinePlus explains that it is due to reduced air pressure inside the chest, calls intercostal retractions a medical emergency, and says to seek medical help right away if they occur.

MedlinePlus lists strain of the muscles and tendons between the ribs among the possible causes of chest pain. Intercostal neuralgia is a different problem: it involves the intercostal nerves, not the muscles. It is described as nerve pain felt along the ribs, chest, or abdomen that is commonly sharp, aching, radiating, burning, or stabbing. The two most documented causes are probably tissue and nerve damage from chest surgery (thoracotomy) and herpes zoster (shingles) infection.

Chest pain has many possible causes, and a language reference cannot tell which one applies to a particular person.

Músculo is a masculine noun, and the adjective follows it and agrees in number: el músculo intercostal, los músculos intercostales. The Real Academia Española dictionary marks intercostal as an anatomy adjective meaning "que está entre las costillas," so the English and Spanish words are true cognates, not false friends.

Patient materials often prefer the plain description: MedlinePlus en español explains the term as los músculos entre las costillas. It calls intercostal retractions tiraje intercostal and describes a strain as distensión de los músculos y tendones entre las costillas.