As ventilatory muscles, the sternocleidomastoids do which of the ...

[Ebrown]

As ventilatory muscles, the sternocleidomastoid s do which of the following?
 
  a. They elevate the upper chest, increasing chest anteroposterior diameter.
  b. They elevate the ribs and decrease chest anteroposterior diameter.
  c. They increase lateral chest movement dur-ing inspiration.
  d. They lower the sternum, thus increasing chest anteroposterior diameter.

Question 2

Which accessory muscles of ventilation work to pull the ribs closer together?
 
  a. External intercostals
  b. Internal intercostals
  c. Scalenes
  d. Sternocleidomastoid s

[ApricotDream]

Answer to Question 1

ANS: A
The sternocleidomastoid muscles can function to lift the upper chest. They receive nerve impulses from branches of the accessory nerves (cranial nerve XI) and cervical nerves C1 and C2. These muscles are active during forceful inspiration and become visible as thick bands on either side of the neck during the inspiratory phase in an individual who is in respiratory distress. This motion increases the anteroposterior diameter of the chest.

Answer to Question 2

ANS: B
The internal intercostal muscles (Figure 9-22) lie between the ribs and just behind the external intercostal muscles. They originate along the inferior border of the upper ribs and insert into the superior border of the lower ribs. The muscle fibers of the internal intercostal muscles run down-ward and less obliquely than the external intercostal muscle fibers. This orientation causes these muscles to pull the ribs together, which results in compression of the thoracic cavity.

[Ebrown]

TYSM

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