Anterior Thoracic Wall

Question 1

Name the muscles of the thoracic wall that anchor to the thoracic cage to act as accessory mm. in respiration.

Answer 1

The serratus posterior superior, serratus posterior inferior and the levator costarum.

Question 2

What is the function of the serratus posterior superior?

Answer 2

Superior: elevates the upper 4 ribs to increase thoracic volume.

Question 3

What is the function of the serratus posterior inferior?

Answer 3

Inferior pulls down on the ribs preventing the diaphragm from pulling them up. This allows the diaphragm to effectively increase the thoracic volume as well.

Question 4

List the remaining mm. that are found within the intercostal space (from superficial to deep).

Answer 4

External intercostal, internal intercostal, and the 3rd layer composed of - from front to back: transversus thoracis, innermost intercostals, and subcostals.

Question 5

Be able to label a diagram of a cross section through the thorax showing you understand the arrangement of the 3 layers of intercostal muscles that form the thoracic wall.

Answer 5

The diagram on page 136 is critical to your understanding of the muscle layers and how they in turn become membranous, as well as the nerve and blood supply to the thoracic wall (intercostal space).

Question 6

In which direction do the fibers of each of the layers extend? (External intercostals, internal intercostals and innermost intercostals)

Answer 6

External intercostals are directed inferior and medially (hands-in-pockets); internal intercostals go upward and medially (opposite to the externals), and the innermost intercostals are oriented in a similar direction to the internals.

Question 7

Describe the direction of the fibers and where they fade into membranous attachments:
EXTERNAL INTERCOSTALS

Answer 7

External intercostals go inferiorly/medially and become membranous anteriorly

Question 8

Describe the direction of the fibers and where they fade into membranous attachments:
INTERNAL INTERCOSTALS

Answer 8

Internal intercostals go upward/medially and become membranous posteriorly

Question 9

Describe the direction of the fibers and where they fade into membranous attachments:
3rd LAYER

Answer 9

3rd layer (transversus thoracis, innermost intercostals, and subcostals) go upward/medially and are linked to one another by intervening membranes.

Question 10

Where does the intercostal neurovascular bundle run between?

Answer 10

Between the internal and innermost intercostal layers.

Question 11

Which muscles make up the 3rd layer of intercostals?

Answer 11

transversus thoracis, innermost intercostals and subcostals (superficial to deep)

Question 12

From what vessel do the posterior intercostal aa. arise?

Answer 12

the aorta

Question 13

From which vessel do the anterior intercostal aa. arise?

Answer 13

The internal thoracic (mammary) artery.

Question 14

What structure(s) innervate the intercostal mm.?

Answer 14

The ventral rami of the true spinal (intercostal) nn.

Question 15

In what order is each intercostal neurovascular bundle arranged?

Answer 15

From superior to inferior: interostal vein, intercostal artery and intercostal nerve (VAN).

Question 16

What portion of the rib is designed to protect the NV bundles?

Answer 16

the costal groove

Question 17

Which component of the NV bundle is least protected by the costal groove? What is the clinical implication of this?

Answer 17

The intercostal nerve.
Insertion of a needle for thoracocentresis (removal of fluid from the pleural cavity) should have the needle placed mid-way between ribs to ensure the intercostal nerve of the upper rib is not punctured, nor is its collateral branch that passes close to the upper border of the lower rib.

Question 18

Which theory of referred pain comes into play if an intercostal nerve is injured?

Answer 18

Proximal distal

Question 19

What is the fascial layer found between the intercostal mm. and the pleura?

Answer 19

Endothoracic fascia

Question 20

What is the function of the endothoracic fascial layer?

Answer 20

It adheres the pleura to the back side of the thoracic musculature (innermost intercostal m. layer).