Muscles - Thoracic Cage

Question 1

What are the five muscles of the thoracic cage?

Answer 1

1) External intercostals
2) Internal intercostals
3) Innermost intercostals
4) Transversus thoracis
5) Subcostals

These muscles are important for changing the volume of the thoracic cavity during respiration.

Question 2

External intercostals?

Answer 2

There are 11 pairs of external intercostal muscles. They runs inferoanteriorly from the rib above to the rib below, and are continuous with the external oblique of the abdomen.

Attachments - originate at the lower border of the rib, inserting into the superior border of the rib below.

Actions - elevates the ribs, increasing the thoracic volume during inhalation.

Innervation - Intercostal nerves (T1-T11)

Question 3

Internal intercostals?

Answer 3

These flat muscles lie deep to the external intercostals. Like the external intercostals, they run from the rib above to the one below, but in an opposite direction (inferoposteriorly). They are continuous with the internal oblique muscle of the abominal wall.

Attachments - originates from the lateral edge of the costal groove and inserts into the superior surface of the rib below.

Actions - the interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the rib.

Innervation - intercostal nerves (T1-T11)

Question 4

Innermost intercostals?

Answer 4

These muscles are the deepest of the intercostal muscles, and are similar in structure to the internal intercostal muscles.

They are separated from the internal intercostals by the intercostal neurovascular bundle and are found in the most lateral port of the intercostal spaces.

Attachments - Originates from the medial edge of the costal groove and inserts into the superior surface of the rib below.

Actions - the interosseous part reduces the thoracic volum by depressing the ribcage, and the interchondral part elevates the ribs.

Innervation - intercostal nerves (T1-T11)

Question 5

Transversus thoracis?

Answer 5

These muscles of the thoracic cage are continuous with transversus abdominis inferiorly.

Origin - posterior surface of the inferior sternum

Insertion - internal surface of costal cartilages 2-6

Actions - weakly depresses the ribs

Innervation - intercostal nerves (T2-T6)

Question 7

Subcostals?

Answer 7

The subcostals are found in the inferior portion of the thoracic wall. They comprise of thin slips of muscle, which run from the internal surface of one rib, to the second and third ribs below. The direction of the fibres parallels that of the innermost intercostals.

Origin - inferior surface of the lower ribs, near the angle of the rib.

Insertion - superior border of the rib 2 or 3 below it.

Actions - shares the action of the internal intercostals.

Innervation - intercostal nerves.