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Diaphragm Muscle: Definition, Anatomy & Function

Instructor: Charity Hacker

I am a nursing instructor with over 20 years of nursing experience and a Masters Degree in Nursing Education.

Breathing is essential to life and depends almost completely on the function of the diaphragm. In this lesson, you will learn what the diaphragm is, what it's made of, and how it functions.

All About the Diaphragm

So, you want to learn more about the diaphragm? Let's imagine the diaphragm as an orchestra conductor. Each little movement that it makes creates a different effect. The orchestra conductor doesn't just direct the creation of music, but it keeps time and rhythm so the musicians don't have to. The conductor also reads the sheet music and conveys this information to the orchestra. Read on to see how the diaphragm does each of these things.

What Is a Diaphragm?

The diaphragm, also known as the thoracic diaphragm, is a large structure located at the bottom of the thoracic cavity that facilitates the breathing process. The thoracic cavity is your chest area where your heart and lungs are held. The diaphragm also serves as a divider between the thoracic and the abdominal cavities. The abdominal cavity is below the thoracic cavity.

The diaphragm as the floor of the thoracic cavity
Picture of the respiratory system with diaphragm.

The Anatomy of the Diaphragm

What Does It Look Like?

The diaphragm is located at the bottom of the thoracic cavity. In the relaxed position, it is shaped like a dome, actually two domes. There is a left sided dome under the left lung and a right sided dome under the right lung. Why are there two domes instead of one? Because the left lung is smaller than the right. If it were one continuous dome, either the left side would be too big or the right side would be too small. The domes are convex, meaning they bow upwards. When the diaphragm is contracted it looks like a flat sheet.

The diaphragm has a few openings, or holes in it, to facilitate passage of major arteries, veins, and nerves. In the picture, you can see four of these openings. The esophageal, aortic, and caval are the largest openings. The aortic opening carries the aorta (a major artery), the thoracic duct (a lymph vessel), and the azygos vein (an important vein connecting the upper and lower venous systems). The esophagus passes through the esophageal opening, along with the vagus nerves and some other blood and lymph vessels. The caval opening allows the inferior vena cava to pass through the right side of the phrenic nerve. The inferior vena cava is the primary vein of the lower half of the body. The phrenic nerve is the main nerve that drives the breathing process. There are other small openings, for example, the opening for the Lesser Splanchnic Nerve as seen in the picture.

The musclulature and openings of the diaphragm
Picture of the diaphragm showing openings and musculature.

What Is It Made Of?

The diaphragm is a musculotendinous structure, meaning it is made of muscles and tendons. Muscles have points of origin where they begin and points of insertion where they end, called attachments. The diaphragm originates from several locations. Primarily it is attached to the sternum at the xyphoid process, the lower six ribs and the spaces in between, and the lower part of the spine. Specifically, the diaphragm is attached to the spine by the processes that protrude laterally from the vertebrae, called crura, and their matching ligaments. The spinal attachment is in the upper lumbar section.

The diaphragm's insertion point is called the central tendon. It is clover shaped with three leaflets called the right, middle, and left leaflets. These can be seen in the picture of the diaphragm musculature. The central tendon is described as aponeurotic. Aponeurosis is the term for a flat tendon that forms the origin or insertion point of a flat muscle. The central tendon causes the diaphragm to contract, or flatten, causing inspiration.

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