What are intercoastal muscles?

The intercostal muscles are located between the ribs. There are three layers: the external, internal and innermost. The external intercostal muscles are responsible for raising the ribcage, while the internal intercostal muscles lower it. The innermost intercostal muscles help with fine-tuning the movements of the ribcage.

External Intercostal Muscles:

- These are the thickest and most superficial layer of intercostal muscles.

- They are located between the ribs, running obliquely from the rib above to the rib below.

- The fibers of these muscles are oriented outwardly from vertebrae to the sternum, giving them a fan-shaped appearance.

- The external intercostal muscles are innervated by the intercostal nerves from the thoracic spinal cord.

Function:

- Primary function: The main role of the external intercostal muscles is to elevate (pull upwards) the ribcage during inhalation.

- Accessory function: When the diaphragm is fully contracted and the ribcage cannot expand any further, the contraction of these muscles helps elevate the sternum slightly, increasing lung volume.

Internal Intercostal Muscles:

- These are thin, flat muscles that lie deep to the external intercostal muscles.

- They are located between the ribs, also running obliquely from the rib above to the rib below, but in the opposite direction to the external muscles.

- The internal intercostal muscles are innervated by the intercostal nerves.

Function:

- Primary function: The internal intercostal muscles lower (depress) the ribcage during exhalation.

- During forced expiration, such as coughing or deep breathing, the internal intercostal muscles work synergistically with the abdominal muscles to expel air from the lungs effectively.

Innermost Intercostal Muscles:

- Also called the transverse thoracic muscles or transversus thoracis muscles.

- These muscles are the deepest and most delicate of the intercostal muscles.

- They consist of short and scattered bundles of muscle fibers that run horizontally (transversely) between the ribs.

- The innermost intercostal muscles are innervated by the intercostal nerves.

Function:

- Support and stabilization: These muscles play a role in maintaining the stability and shape of the thoracic cavity.

- Accessory role: They can assist the internal and external intercostal muscles in lowering and raising the ribcage, respectively.

In summary, the intercostal muscles contribute significantly to the process of breathing by elevating (external intercostal muscles) and lowering (internal intercostal muscles) the ribcage. The innermost intercostal muscles assist with providing stability and fine-tuning movements.