QS Study

The Diaphragm

It is a dome-shaped muscle forming the partition between the thoracic and abdominal cavities. It is the primary muscle used in respiration, which is the process of breathing. This dome-shaped muscle is located just below the lungs and heart.

Fig – The diaphragm as seen from below


It attaches to the xiphoid process, the inner surface of the lower six costal cartilages and to the L1 through the L3 lumbar vertebrae. The muscle fibers may be grouped into three parts:

(A) The sternal part – Arises by two fleshy slips from the back of the xiphoid process. It consists of small left and right strips that arise from the posterior surface of the xiphoid process.

(B) The costal part – Arises from the inner surfaces of the cartilages and the adjacent parts of the lower six ribs on each side, inter-digitating with the transversus abdominis. It consists of six slips that arise from the lower six ribs (rib 7 to rib 12) and their costal cartilages.

(C) The lumber part – Arises from the medial and lateral lumbocostal arches and from the lumbar vertebrae by right and left crura. It arises by means of vertical columns, also known as crura, and from the arcuate ligaments.

Nerve supply

(A) Motor – The phrenic nerves are the sole motor nerves to the diaphragm.

(B) Sensory

(i) The phrenic nerves are sensory to the central part.

(ii) The lower six thoracic nerves are sensory to the peripheral part of the diaphragm.


(i) The diaphragm is the principal muscle of inspiration and holds the most important value for the overall process of exchange of gases.

(ii) It acts in all expulsive acts to give additional power to each effort.

(iii) The right crus of the diaphragm may have a sphincter action on the lower end of the oesophagus.

(iv) The diaphragm increases abdominal pressure to help the body get rid of vomit, urine, and feces.