USMLE Step 1 Respiratory Physiology Review 60 05 Muscles of Inspiration

USMLE Step 1 Respiratory Physiology Review 60 05 Muscles of Inspiration

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Play USMLE Audio MP3 60 05 Muscles of Inspiration Below

Begin 60 05 Muscles of Inspiration Transcription

Moving now to the muscles of inspiration.  Inhalation or inspiration is an active process. Inhalation occurs when the inspiratory muscles of the body contract. The major muscle of inspiration is a sheet of muscle located between the thoracic and abdominal cavities.  What is this muscle called?

  • The major muscle of inspiration is the diaphragm.

What shape does the diaphragm have when it is relaxed?

  •  When relaxed, the diaphragm is dome shaped. When the diaphragm contracts, its dome descends.

What effect does contraction of the diaphragm have on the thoracic cavity?

  •  The thoracic cavity expands vertically when the diaphragm contracts.

Besides the diaphragm, there are muscles attached to the ribs that contract during inspiration. What are these muscles called?

  • External intercostal muscles.

What happens to the thorax when the external intercostal muscles contract?

  •  When the external intercostal muscles contract, the thorax expands laterally and interiorly. In cases of forced or deep inspiration, the thorax must expand beyond what is necessary for normal inspiration. The muscles that facilitate this are called accessory respiratory muscles.

Which accessory muscles lift the first two ribs? They start with the letter S.

  • The scalene muscles.

Which accessory muscles lift the sternum?This answer also starts with an S.

  •  The sternomastoids.

Student doctor, please pause the tape and summarize what we have discussed about the muscles of inspiration. Inspiration occurs when the inspiratory muscles contract.

  • The major muscle of inspiration is the diaphragm, which is a sheet of muscle located between the thoracic and abdominal cavities. When relaxed, the diaphragm is dome shaped. When the diaphragm contracts, its dome descends and the thoracic cavity expands vertically. The external intercostal muscles are muscles attached to the ribs and are also inspiratory muscles. When they contract, the thorax expands laterally and interiorly. Accessory respiratory muscles expand the thorax beyond what is necessary for normal inspiration. The scalene muscles are accessory muscles that lift the first two ribs. The sternomastoids are accessory muscles that lift the sternum.

 

****END OF TRANSCRIPTION****

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