Muscles of Respiration

Brief Definition

In the process of ventilation, muscles move the lung and chest wall for inspiration and forced (non-passive) expiration.

The Long Description

The Muscles of respiration can be divided into those used during inspiration and expiration.

Inspiration

• Diaphragm - Thin, dome-shaped sheet of muscle inserted at the lower ribs. Contraction of the diaphragm moves the abdomen downward and forward increasing the vertical dimensions of the chest cavity. The ribs are also lifted outward increasing the diameter of the thorax. In normal tidal breathing, the diaphragm moves about 1cm (may move up to 10cm during forced expiration. Paralysis of the diaphragm causes paradoxical movement in which it moves up rather than down with inspiration. This occurs when a person sniffs.
• External Intercostal Muscles - Connect adjacent ribs and under contraction, the ribs move upward and forward. Paralysis of the intercostal muscles does not seriously affect breathing because the diahragm is so effective.
• Accessory Muscles of Inspiration
  • scalen muscles - Elevate the first two ribs
  • sternomastoids - Raise the sternum (may contract vigorously during exercise)
  • alae nasi - Flare the nostrils
  • Other small muscles in the neck and head

Expiration (Non-Passive Only)

• Muscles in the Abdominal Wall - Contract forcefully during coughing, vomiting, and defecation.
  • rectus abdominus
  • internal and external obliques
  • transversus abdominus
• Internal Intercostal Muscles - Pull ribs downward and inward (opposite to external intercostal muscles)

It is crucially important that these muscles work together in a coordination. Some newborn children. particularly premature infants, have uncoordinated respiratory muscle activity, especially during sleep (e.g. the thoracic muscles try inspire while the abdominal muscles expire). This may be a factor in "sudden infant death syndrome." ( West, p. 120).

Sample problems:

Fill in the Blank.

You are hit by a poison dart that causes muscle paralysis. Now when you breath, your diaphragm moves up upon inspiration. This is called __________ ___________.

True or False

_______ Essentially no muscles are used during passive expiration.

_______ External intercostal muscles are critical for proper inspiration.

_______ The respiratory muscles of the abdominal wall are used during defecation.

_______ Malfuntcion of the diaphragm may mean a risk of pregnancy.

Answers:

Paradoxical Movement, T,F,T,F

For more information on this topic, please refer to West , page .

Also, check out the following links that may be helpful:

• Johns Hopkins School of Medicine Interactive Respiratory Physiology
• University of Arkansas
• VR QuickTime of Model Gross Anatomy
• And, as always, if you have questions, or if you can suggest a helpful link, please e-mail me.

No!
Please don't make me go to any of those pages!
I want to go somewhere completely different!

This page was written by Brian Welch , a student in this course.

BME 403 Pages maintained by the T.A., Douglas Miles.