Muscles Used for Breathing

The main muscle of respiration is the diaphragm. Other muscles that aid in respiration include the external intercostals, scalenes, sternomastoids, abdominal muscles and internal intercostals.

Diaphragm

In quiet, gentle inhalation, the diaphragm contracts, lowering air pressure inside the lungs and drawing air in. When exhaling quietly, the diaphragm relaxes and the pressure reverses, expelling air.

External Intercostals

The external intercostals are between the ribs. During active inhalation, they expand the rib cage laterally, anteriorly and posteriorly.

Scalenes/Sternomastoids

These are the shrugging muscles. They serve to lift the sternum and the upper ribs during active inhalation.

Abdominal Wall

In active exhalation, the muscles of the abdominal wall--rectus abdominis, internal and external obliques and transverse abdominis--contract, raising abdominal pressure. This, in turn, raises the diaphragm, raising pressure in the lungs and expelling air.

Internal Intercostals

The internal intercostals are deep to the external intercostals. Like their counterparts, they draw the ribs in, expelling air during active exhalation.

Fun Fact

Hiccups are caused by an irritated diaphragm.

References

• Muscles of Respiration