Thoracic Wall: Muscles & Vessels

Thoracic Wall (Muscles & Vessels)

• The thoracic cavity and its wall are cone-shaped, narrow above and wide below.
• The diaphragm, the floor of the thoracic cavity, is pushed upward by the abdominal organs.
• The thorax contains the primary organs of the respiratory and cardiovascular systems.
• The thoracic wall is composed of bones, forming the thoracic cage, with a thoracic inlet superiorly and an outlet inferiorly.
• Eleven intercostal spaces lie between the ribs.
• These spaces contain intercostal muscles in layers, intercostal nerves, arteries, and veins.

Intended Learning Outcomes (ILOs)

• Identify the components of the thoracic wall.
• Name the boundaries and structures passing through the thoracic inlet.
• Name the boundaries and structures passing through the thoracic outlet.
• Recognize the origin, insertion, nerve supply, extent, direction of fibers, and action of intercostal muscles.
• Mention the mechanism of respiration.
• Identify the origin, features, and branches of intercostal nerves.
• Recognize the origin, branches, and termination of intercostal arteries.
• Recognize the origin, tributaries, and termination of intercostal veins.

Agenda

• What are the components of the Thoracic Wall?
• What are the boundaries and structures passing through the thoracic inlet?
• What are the boundaries and structures passing through the thoracic outlet?
• What is the origin, insertion, nerve supply, extent, direction of fibers, and action of intercostal muscles?
• What is the mechanism of respiration?
• What is the origin, features, and branches of intercostal nerves?
• What is the origin, branches, and termination of intercostal arteries?
• What is the origin, tributaries, and termination of intercostal veins?

Thoracic Inlet (Superior Thoracic Aperture)

• Boundaries:
  • Anteriorly: suprasternal notch.
  • Posteriorly: first thoracic vertebra.
  • Laterally: inner border of the first rib and its costal cartilage.
• Structures passing:
  • Tubes: trachea and esophagus.
  • Arteries: common carotid, subclavian, internal thoracic, and superior intercostal.
  • Veins: right and left brachiocephalic, vertebral, and inferior thyroid.
  • Nerves: phrenic, vagus, sympathetic chain, and left recurrent laryngeal.
  • Lymphatics: thoracic duct.

Thoracic Outlet

• Boundaries:
  • Anteriorly: xiphoid process.
  • Posteriorly: last thoracic vertebra and last two ribs.
  • Laterally: costal margin (7th-10th costal cartilages).
• Structures Passing: Structures piercing the diaphragm.
• Structures Crossed: Structures that pass by the diaphragm.

Intercostal Spaces

• Definition: Spaces between adjacent ribs.
• Number: 11 spaces.
• Contents:
  • Intercostal muscles (3 layers).
  • Intercostal nerves.
  • Intercostal arteries.
  • Intercostal veins.
  • Lymphatics.

Intercostal Muscles

• External Intercostal Muscles:

  • Origin: Lower border of rib above.
  • Insertion: Upper border of rib below.
  • Direction of fibers: Downward and forward.
  • Action: Elevation of ribs (inspiration).

• Internal Intercostal Muscles:

  • Origin: Costal groove of rib above.
  • Insertion: Upper border of rib below.
  • Direction of fibers: Downward and backward.
  • Action: Depression of ribs (expiration).

• Innermost Intercostal Muscles:

  • Origin: Middle of intercostal space.
  • Insertion: Middle of intercostal space.
  • Direction of fibers: Downward and backward.
  • Action: Depression of ribs (expiration).

• Subcostal Muscles:

  • Origin: Costal groove near posterior angle.
  • Insertion: Inner surface of ribs below.
  • Direction of fibers: Downward and backward.
  • Action: Depresses ribs (forced exhalation).

• Sternocostalis Muscles:

  • Origin: Body and xiphoid process of sternum.
  • Insertion: Costal cartilages of ribs 2-6 .
  • Direction of fibers: Upward and laterally.
  • Action: Forced inspiration.

Intercostal Arteries

• Anterior Intercostal Arteries:

  • Number: 2 in each of the upper 9 spaces.
  • Origin: Upper 6 from internal thoracic artery, lower 3 (7th, 8th, and 9th) from musculophrenic.
  • Termination: Anastomose with posterior intercostal artery and its collateral branch.

• Posterior Intercostal Arteries:

  • Number: 1 in each of the 11 spaces.
  • Origin: First two from costo-cervical trunk, others from descending aorta.
  • Termination: Anastomosis with anterior intercostal artery and its collateral branch.

Intercostal Veins

• Anterior Intercostal veins:
  • Number: 2 in each of the upper 9 spaces.
  • Course: Pass with the corresponding arteries.
  • Termination:
    • 1st, 2nd, and 3rd: Internal thoracic vein.
    • 4th, 5th, and 6th: Vena comitantes of the internal thoracic artery.
    • 7th, 8th, and 9th: Vena comitantes of the musculophrenic artery.
• Posterior Intercostal Veins:
  • Number: 1 in each of the 11 spaces.
  • Course: Pass with the corresponding arteries.
  • Termination: Tributaries to azygos and hemiazygos veins.

Internal Thoracic Artery

• Origin: First part of the subclavian artery.
• Course: Descend behind the clavicle, medial ends of the upper 6th costal cartilages, 1.5 cm lateral to the sternal margin.
• Termination: In the 6th intercostal space, by dividing into superior epigastric and musculophrenic arteries.
• Branches: Anterior intercostal arteries, pericardiophrenic artery, perforating arteries, musculophrenic artery, and superior epigastric artery.