Muscles in the Thoracic Region that Help You Breathe
Clinical anatomy identifies several muscles of the shoulder attached to the thoracic cage. The scalene muscles elevate the 1st and 2nd ribs and bend the neck to the side. So what’s left? The muscles of the thoracic cage that help you breathe — namely, the diaphragm and respiratory muscles:
The thoracic cage is made up of bones and cartilage along with joints and an assortment of muscles and other soft tissues. The part that opens into the neck is called the superior thoracic aperture, and the bottom of the thoracic cage (the inferior thoracic aperture) is closed by a muscle called the diaphragm. Its main function is to protect your heart, lungs, and major blood vessels located inside.
The diaphragm: The main respiratory muscle found in the thorax is called the diaphragm. It’s a thin muscle that curves up into two dome shapes called cupulae. The diaphragm separates the thoracic cavity from the abdominal cavity and has openings that allow structures to pass from one cavity to the other. The diaphragm can be divided into three parts:
Sternal: Originates (attaches) at the xiphoid.
Costal: Originates from the lower six ribs and their cartilages.
The diaphragm is secured to the thoracic cage by the following ligaments and tendons:
Right crus: Attached to the sides of the first three lumbar vertebrae and discs. Some of its fibers form a loop around the esophageal orifice.
Left crus: Attached to the first two lumbar vertebrae and the disc between them.
Median arcuate ligament: Connects the two crura.
Medial arcuate ligament: Attaches to part of the diaphragm as it extends from the 2nd lumbar vertebra to the transverse process of the 1st lumbar vertebra. It passes over the psoas muscles.
Lateral arcuate ligament: Attaches to part of the diaphragm as it runs from the transverse process of the 1st lumbar vertebra to the 12th rib. It lies over the quadratus lumborum muscle.
Central tendon: Inserts into this tendon, which is partially fused with the pericardium.
The diaphragm has three openings that allow passage of various structures:
Aortic opening: Anterior to the 12th thoracic vertebra and allows room for the aorta, thoracic duct, and azygos vein.
Esophageal opening: At the level of the 10th thoracic vertebra and transmits the esophagus, vagal nerves, esophageal branches of the gastric vessels, and some lymphatic vessels.
Caval opening: At the level of the 8th thoracic vertebra, this opening leaves room for the inferior vena cava and terminal branches of the right phrenic nerve.
The intercostal muscles: Three muscles that help your diaphragm during breathing are located in the intercostal spaces between each of the ribs: the external intercostal, the internal intercostal, and the innermost intercostal muscles. The innermost intercostals are lined by the endothoracic fascia (a sheet of fibrous tissue), which in turn is lined by the parietal pleura (thin serous membrane). When the intercostal muscles contract, they bring the ribs closer together.
Five additional muscle groups are found on each side of the thoracic cage:
Transversus thoracis muscles: Run from the posterior part of the sternum to the internal portion of the 2nd through 6th costal cartilages.
Subcostal muscles: Attach to the internal surface of the lower ribs and travel inferiorly to attach to the superior border of the second or third rib below.
Levatores costarum muscles: Start at the transverse processes of the 7th through 11th thoracic vertebrae and insert into the next rib below.
Serratus posterior superior muscles: Run from the spinous processes of the last cervical vertebrae and the first three thoracic vertebrae to the superior borders of the 2nd through 4th ribs.
Serratus posterior inferior muscles: Start at the spinous processes of the last two thoracic vertebrae and the first two lumbar vertebrae and attach to the inferior borders of the 8th through 12th ribs.