Muscles of Respiration

The breathing pump muscles are a complex arrangement that form a semirigid bellows around the lungs. Essentially, all muscles that attach to the rib cage have the potential to generate a breathing action. Muscles that expand the thoracic cavity are inspiratory muscles and induce inhalation, while those that compress the thoracic cavity are expiratory and induce exhalation. These muscles possess exactly the same basic structure as all other skeletal muscles, and they work in concert to expand or compress the thoracic cavity.

  

Primary Muscles

 The primary inspiratory muscles are the external intercostals and the diaphragm.muscles of expiration depress them.The muscles of inspiration elevate the ribs and sternum, and the muscles of expiration depress them..

The primary expiratory muscles are the internal intercostals, intercostalis intimi and subcostals.

Accessory Muscles

The accessory inspiratory muscles are the sternomastoid, the scalenus anterior, medius and posterior, the pectoralis major and minor, the inferior fibres of serratus anterior and latissimus dorsi, the serratus posterior anterior may help in inspiration also the iliocostalis cervicis.

The accessory expiratory muscles are the abdominal muscles: rectus, abdominis, external oblique, internal oblique and transversus abdominis. And in the thoracolumbar region the lowest fibres of iliocostalis and longissimus, the serratus posterior inferior and quadratus lumborum.