Interkostalen

Interkostalen refers to the muscles located between the ribs. These muscles play a crucial role in respiration, acting as accessory muscles of breathing. There are three main layers of intercostal muscles: the external intercostals, the internal intercostals, and the innermost intercostals.

The external intercostal muscles are the outermost layer. Their fibers run downwards and forwards from the lower border of one rib to the upper border of the rib below. During inhalation, these muscles contract, pulling the ribs upwards and outwards, thereby increasing the volume of the thoracic cavity and drawing air into the lungs.

Beneath the external intercostals lie the internal intercostal muscles. Their fibers run downwards and backwards, perpendicular to those of the external intercostals. The internal intercostals primarily function during forced exhalation, contracting to pull the ribs downwards and inwards, reducing the volume of the thoracic cavity and expelling air from the lungs.

The innermost intercostal muscles are the deepest layer, lying just inside the internal intercostals. They are thinner and their actions are similar to those of the internal intercostals, assisting in forced exhalation. The intercostal muscles are innervated by the intercostal nerves, which are branches of the thoracic spinal nerves.