Thoracic Wall Anatomy Quiz

Study Notes

The thoracic wall is bordered by 12 vertebrae, 12 pairs of ribs with their costal cartilages, the sternum, suprapleural membrane, and the diaphragm.
True ribs (1-7) attach directly to the sternum.
False ribs (8-10) attach indirectly to the sternum via the cartilage of the rib above.
Floating ribs (11-12) are free and do not attach to the sternum.
Costosternal joints are cartilaginous in the first rib and synovial in ribs 2-7.
Ribs 1, 11, and 12 articulate with their corresponding vertebrae.
Ribs 2-10 articulate with their own and the vertebra above.

A typical rib has a head with two articular facets, a neck, a tubercle (articulates with the transverse process and the lateral costotransverse ligament), an angle (point where the shaft bends forward), a shaft with a costal groove, and a sharp lower border lodging the neurovascular bundle.
The first rib is atypical, being the shortest, flattest, broadest, and most curved. It has one articular facet, a groove for the subclavian artery and vein, and little movement during respiration. It connects to the manubrium via a cartilaginous joint.

The sternum is composed of the manubrium, body, and xiphoid process.
Like the ribs, it's made of cancellous bone with hematopoietic tissue.
The manubrium has a jugular notch, a concavity for the sterno-clavicular joints (synovial), the first costal cartilages at its lateral border, and sternohyoid and sternothyroid attachments posteriorly.
The sternum body has articular facets along its lateral border for costal cartilages 2-7, which are synovial joints.
The xiphisternum projects downward to attach to the linea alba and typically ossifies in middle age.

The upper seven costal cartilages connect to the sternum at the sternocostal joints (true ribs).
Ribs 8-10 articulate via interchondral joints.
Ribs 11 and 12 are floating ribs, meaning their costal cartilages do not attach to the sternum.

Pectoralis major covers the chest wall, forming the anterior wall of the axilla. Its origin is from the clavicle, sternum, and ribs 1-6. The tendon inserts into the humerus.
Pectoralis minor lies beneath the pectoralis major, taking its origin from ribs 3-5. It inserts to the coracoid process of the scapula.
Both are accessory muscles of respiration.

The diaphragm is a dome-shaped, fibro-muscular sheet separating the thorax from the abdomen.
It is primarily responsible for inspiration through contraction.
Its anterior attachments are at the level of the xiphoid process, with posterior attachments below the 12th thoracic vertebra.
Its profile is inverted J-shaped, with crura posteriorly and xiphisternal attachment anteriorly. It has two domes, with the right higher than the left.

The diaphragm is innervated by the left and right phrenic nerves (C3, C4, C5). Patients with damage above C3 require mechanical respiration.

Thoracic vertebrae possess a body, superior and inferior demifacets, pedicle, superior and inferior articular processes, transverse process, lamina, spinous process, superior and inferior notches, vertebral canal.

Neurovascular bundles travel in the costal groove of the ribs between the internal and innermost intercostals, superior to the ribs.

External intercostal muscles: fibers directed superior-lateral to inferior-medial. Anteriorly they become a transparent membrane.
Internal intercostal muscles: fibers perpendicular to the external intercostals. Posteriorly they become the internal intercostal membrane from the rib angles.
Innermost intercostal muscles: are the deepest and thinnest.
All three intercostal muscles are accessory muscles of respiration.