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Why are the ribs able to move during breathing?
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bone
A long bone of the human body, showing a magnified cross section of the interior.
The rib cage is able to move during breathing because it is a semirigid, expansile structure designed to increase in size. This mobility is facilitated by several anatomical features:12
- Joints: Small joints located between the ribs and the vertebral column allow for a gliding motion during respiration.1
- Muscular Action: The intercostal muscles play a critical role; when the external intercostals contract, they cause the ribs to rotate upward and laterally, which increases the circumference of the chest cavity.3
- Structural Configuration: The first seven ribs are attached to the sternum by pliable costal cartilages, while the lower five ribs have a configuration that provides additional freedom for the expansion of the lower rib cage and the movement of the diaphragm.12
These movements expand the chest, reducing pressure within the lungs to draw in air, while expiration occurs through the relaxation of these muscles and the elastic recoil of the thoracic structures.23