Axial Muscles- Muscles of Respiration

Question 1

What are the muscles of respiration?

Answer 1

• Involved in the process of inhalation and exhalation
• When inhaling, several muscles contract to increase the thoracic cavity dimensions, allowing the lungs to fill with air
• When exhaling, some respiratory muscles contract and others relax, collectively decreasing the dimensions of the thoracic cavity and forcing air out of the lungs
• Muscles of respiration are found on the anterior and posterior surfaces of the thorax
• Are covered by more superficial muscles (such as the pectoral muscles, trapezius and latissimus dorsi) that can move the upper limbs
• The posterior thorax muscles assist with respiration as well
• Superficial to erector spinae muscles

Question 2

What are the serratus posterior superior muscles?

Answer 2

• Attached to ribs 2-5
• Elevates these ribs during forced inhalation
• Increases the lateral dimensions of the thoracic cavity

Question 3

What are the serratus posterior muscles?

Answer 3

• Attached to ribs 8-12
• Depresses these ribs during forced exhalation
• Decreases the lateral dimensions of the thoracic cavity

Question 4

What are the external intercostals?

Answer 4

• Extend inferomedially from the superior rib to the adjacent inferior rib
• Assist in expanding the thoracic cavity by elevating the ribs during inhalation
• Contraction of the external intercostals increases the transverse dimensions of the thoracic cavity

Question 5

What are internal intercostals?

Answer 5

• Lie deep to the external intercostals
• Muscle fibers are at right angles to the external intercostals
• Depress the ribs, but only during forced exhalation
  (normal exhalation takes no active muscular effort)

Question 6

What is the transversus thoracis?

Answer 6

• Extends across the inner surface of the thoracic cage
• Attaches to ribs 2-6
• Helps depress ribs

Question 7

What is the diaphragm?

Answer 7

• An internally placed, dome-shaped muscle that forms a partition between the thoracic and abdominopelvic cavities
• The most important muscle associated with respiration
• Diaphragm movements are also important in helping return venous blood to the heart from the inferior half of the body

Question 8

What is the central tendon of the diaphragm?

Answer 8

• Muscle fibers of the diaphragm converge from its margins towards a fibrous central tendon
• When the diaphragm contracts, the central tendon is pulled inferiorly toward the abdominopelvic cavity
• Increases the vertical dimensions of the thoracic cavity during contraction
• When the diaphragm compresses the abdominopelvic cavity, it also increases intra-abdominal pressure (needed for urination, defecation and childbirth)