Muscles of Respiration
Muscles that act on skeletal structures, changing intrathoracic pressures.
Anterior scalene
- Originates on the transverse processes of C3-C7
- Inserts on the superior surface of the first rib.
- Elevates the first rib during forced inhalation, or, when the rib is fixed, flexes the neck (moves the head closer to the chest or shoulder).
Middle scalene
- Originates on the transverse processes of C2-C7.
- Inserts with the anterior scalene on the first rib.
- Elevates the first rib and flexes the neck.
Posterior scalene
- Originates on the transverse processes of C4-C6.
- Inserts on the second rib.
- Elevates rib 2; when this rib is fixed, it flexes the neck.
- Originates on the inferior internal surface of the sternum, costal cartilages of ribs 6-12, and the lumbar vertebrae L1-L3.
- Inserts into the central tendon.
- Expands the thoracic cavity to decrease intrapulmonary pressure and induce inspiration (inhalation).
Three layers of intercostal muscles:
External intercostals
- Originate on the inferior border of the ribs.
- Insert into the superior border of the ribs below.
- Elevate the ribs during inhalation.
Internal and innermost intercostals
- Originate on the superior border of the ribs.
- Insert into the inferior border of the ribs above.
- Depress ribs during forced exhalation (normal exhalation requires no active effort).
Transversus thoracis
- Originates on the posterior surface of the sternum (body and xiphoid process).
- Inserts into the internal surfaces of ribs 2-6.
- Depresses ribs during exhalation.