Intercostal muscle

Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing. These muscles help expand and shrink the size of the chest cavity to facilitate breathing.

Anatomy

There are three layers of intercostal muscles which are named from their relative position, and they are the external intercostal muscles, the internal intercostal muscles, and the innermost intercostal muscles.

External intercostal muscles

The external intercostal muscles, the most superficial, aid in quiet and forced inhalation. They originate on ribs one through 11, with insertion on ribs two through 12. The external intercostals are responsible for the elevation of the ribs, and expanding the thoracic cavity volume. These muscles help in inhalation by increasing the lateral and anteroposterior diameter of the thoracic cavity.

Internal intercostal muscles

The internal intercostal muscles lie just below the external intercostal muscles, and are oriented in just the opposite direction. The internal intercostal muscles depress the ribs and decrease the thoracic cavity volume, aiding in forced exhalation.

Innermost intercostal muscles

The innermost intercostal muscles, the deepest layer, aid in forced exhalation, and are the most powerful of the intercostal muscles. They also depress the ribs and decrease thoracic cavity volume.

Function

The intercostal muscles' main role is to assist in breathing. When the diaphragm contracts, it reduces the pressure in the thoracic cavity, allowing the lungs to expand and fill with air. The intercostal muscles aid in this process by elevating the ribs, further increasing the volume of the thoracic cavity.

Clinical significance

Damage or injury to the intercostal muscles can cause pain and difficulty in breathing. Conditions such as intercostal neuralgia, which is inflammation of the nerve that runs along the rib, and costochondritis, inflammation of the chest wall, can cause severe pain in the intercostal muscles.

See also

• Respiratory system
• Thoracic diaphragm
• Human rib cage

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