TBL9 - Thoracic Wall

Question 1

Where are the ribs and intercostal muscles derived from? Where are the sternum and costal cartilages derived from?

Answer 1

Like the vertebral column, the ribs and intercostal muscles are formed by somite-derived mesenchymal cells while the sternum and costal cartilages are derivates of mesenchymal cells in the parietal mesoderm

Question 2

What provides articulation surfaces for the clavicles? What do the lateral borders of the sternal manubrium, body, and xiphoid process provide?

Answer 2

1) The supero-lateral border of the manubrium provides articulation surfaces for the clavicles
2) The lateral borders of the sternal manubrium, body, and xiphoid process provide articular sites for the costal cartilages, the hyaline cartilaginous anterior ends of ribs 1-7

Question 3

What is a landmark for articulation of the 2nd ribs? What do the costal cartilages of ribs 8-10 attach to and what do they form?

Answer 3

1) The sternal angle is a landmark for articulation of the 2nd ribs
2) The costal cartilages of ribs 8-10 attach to the cartilage of the rib above to form the costal margin and the short 11th and 12th ribs, which lack costal cartilages, end posterior to the costal margin

Question 4

What part of the vertebrae also provides articular sites for the ribs? What are intercostal spaces covered by?

Answer 4

1) Costal facets on the thoracic vertebral bodies and transverse processes provide posterior articular sites for the ribs
2) The intercostal spaces (ICS) are covered by external and internal intercostal muscles

Question 5

Where is the subcostal space and which spinal nerve constitutes the subcostal nerve?

Answer 5

1) The space below the 12th rib does not lie between ribs and thus is referred to as the subcostal space
2) The anterior ramus (branch) of spinal nerve T12 is the subcostal nerve

Question 6

Why does rib counting during physical exams start at the second rib?

Answer 6

Because the 1st rib is not palpable, rib counting in physical examinations starts with the 2nd rib adjacent to the subcutaneous and easily palpated sternal angle

Question 7

Define the boundaries of the superior thoracic aperture and list the structures that pass through it

Answer 7

1) The superior thoracic aperture is bounded:
a) Posteriorly, by vertebra T1, the body of which protrudes anteriorly into the opening
b) Laterally, by the 1st pair of ribs and their costal cartilages
c) Anteriorly, by the superior border of the manubrium
2) Structures that pass between the thoracic cavity and the neck through the oblique, kidney-shaped superior thoracic aperture include the trachea, esophagus, nerves, and vessels that supply and drain the head, neck, and upper limbs

Question 8

Why do a diminished radial pulse, cutaneous pallor, and coldness of the upper limb indicate a supernumerary cervical rib?

Answer 8

1) People usually have 12 ribs on each side, but the number is increased by the presence of cervical and/or lumbar ribs
2) Supernumerary (extra) ribs also have clinical significance in that they may confuse the identification of vertebral levels in radio graphs and other diagnostic images
3) When clinicians refer to the superior thoracic aperture as the thoracic outlet, they are emphasizing the arteries and T1 spinal nerves that emerge from the thorax through this aperture to enter the lower neck and upper limbs. Hence, various types of thoracic outlet syndrome (TOS) exist in which emerging structures are affected by obstructions of the superior thoracic aperture

Question 9

Recognize the vertical positions designated by the midclavicular, midaxillary, and scapular lines on the thoracic wall. Using the anterior median (aka midsternal) line, extrapolate positions of the bilateral parasternal lines

Answer 9

1) The midclavicular line (MCL) passes through the midpoint of the clavicle, parallel to the AML
2) The midaxillary line (MAL) runs from the apex (deepest
part) of the axillary fossa (armpit), parallel to the AAL
3) The scapular lines (SLs) are parallel to the posterior
median line and intersect the inferior angles of the scapula
4) The anterior median (midsternal) line (AML) indicates the intersection of the median plane with the anterior thoracic wall. Additional lines are extrapolated along the borders of palpable bony sternum such as the parasternal lines

Question 10

What is the function of these lines? Where are nipples positioned?

Answer 10

1) The lines facilitate anatomical and clinical descriptions of the thoracic wall
2) The nipples in men and young nulliparous women are positioned adjacent to the midclavicular lines at the 4th ICS

Question 11

Where do abdominal organs push the diaphragm? What forms the superior projection of the abdominal cavity? How high can the liver reach in the abdominal cavity?

Answer 11

1) Abdominal organs push the diaphragm superiorly
2) The liver, stomach, and spleen create the superior projection
3) The superior surface of the liver can reach the 4th ICS

Question 12

What do the phrenic nerves do during normal inspiration? What does this do to the diaphragm? What happens to the diaphragm during normal expiration?

Answer 12

1) During normal inspiration, the phrenic nerves induce contraction of the diaphragm, which flattens its right and left domes (created by the abdominal organs) and draws air into the lungs
2) Relaxation of the diaphragm during normal expiration returns the domes to their resting positions and helps expel air from the lungs

Question 13

What do normal adult respiratory rates range from?

Answer 13

Normal adult respiratory rates range from 12-20 breaths/minute

Question 14

Why after ipsilateral paralysis of the diaphragm, does the paralyzed dome ascend during inspiration and descend during expiration?

Answer 14

1) Paralysis of half of the diaphragm (one dome or hemidiaphragm) because of injury to its motor supply from the phrenic nerve does not affect the other half because each dome has a separate nerve supply
2) Instead of descending as it normally does during inspiration owing to diaphragmatic contraction, the paralyzed dome ascends as it is pushed superiorly by the abdominal viscera that are being compressed by the active contralateral dome. Instead of ascending during expiration, the paralyzed dome descends in response to the positive pressure in the lungs

Question 15

What occurs during forced inspiration?

Answer 15

During forced inspiration, as when exercising, the external intercostal muscles contract to elevate the ribs and expand the anterior/posterior and transverse dimensions of the thoracic cavity

Question 16

What does concurrent contraction of the scalene muscles in the neck do?

Answer 16

Concurrent contraction of the scalene muscles in the neck fixes the first two ribs and thereby assists the elevation of the ribs below

Question 17

What do the internal intercostal muscles do during forced expiration?

Answer 17

During forced expiration, contraction of the internal intercostal muscles lowers the elevated ribs to their resting position

Question 18

Why do patients experiencing dyspnea lean on their knees to assist respiration?

Answer 18

1) When people with respiratory problems (e.g., asthma) or with heart failure have difficulty breathing (dypsnia), they use their accessory respiratory muscles to assist the expansion of their thoracic cavity
2) They lean on their knees or on the arms of a chair to fix their pectoral girdle, so these muscles are able to act on their rib attachments and expand the thorax

Question 19

What innervates the intercostal muscles? What provides sensory innervation to the anterolateral thoracic wall?

Answer 19

1) Anterior rami of the thoracic spinal nerves constitute the intercostal nerves that innervate the intercostal muscles
2) Lateral cutaneous branches of the anterior rami provide sensory innervation to the anterolateral thoracic wall

Question 20

Where do the lateral cutaneous branches of spinal nerve T2 extend into?

Answer 20

The lateral cutaneous branches of spinal nerve T2 (2nd intercostal nerve) extend into dermatomes of the medial sides of the arms

Question 21

What do the posterior rami of the intercostal nerves supply?

Answer 21

The posterior rami of the intercostal nerves supply the intrinsic muscles of the back and provide cutaneous branches to the posterior thoracic wall

Question 22

What is the function of white and gray communicating rami to and from paravertebral ganglia of sympathetic trunks?

Answer 22

White and gray communicating rami to and from paravertebral ganglia of the sympathetic trunks enable intercostal nerves to convey visceral motor fibers to smooth muscle and sweat glands in the body wall

Question 23

Where do posterior and anterior intercostal arteries anastomose? Where do the internal thoracic arteries arise from? Name the two terminal branches of the internal thoracic arteries

Answer 23

1) Posterior and anterior intercostal arteries, which arise from the thoracic aorta and internal thoracic arteries, respectively, anastomose in the ICS
2) The internal thoracic arteries arise from the subclavian arteries
3) The internal thoracic arteries terminate in the 6th intercostal space by dividing into the superior epigastric and the musculophrenic arteries