Thoracic wall and diaphragm Flashcards
Outline the thoracic wall.
- The skeleton of the thoracic wall consists of the 12 thoracic vertebrae, the 12 pairs of ribs and costal cartilages and the sternum.
- The thoracic cavity is roofed in above the lung apices by the suprapleural membrane and is floored by the diaphragm. The floor is highly convex (domes of the diaphragm), so that when the diaphragm is relaxed in expiration, the volume of the thoracic cavity is much less than inspection of the bony cage would suggest.
- The liver and spleen and the upper parts of the stomach and both kidneys lie in the abdominal cavity wholly or partly covered by ribs.
- At the back, the ribs articulate with the vertebral column in 2 places - by their heads (joints of costal heads) and by their tubercles (costotransverse joints). Collectively, these form the costovertebral joints.
- At the front the ribs joint their costal cartilages (costochondral joints). The upper 7 costal cartilages articulate with the sternum at the sternocostal joints, the next 3 articulate with each other (interchondral joints) and the 8th articulates with the 7th costal cartilage to complete the costal margin. The last 2 costal cartilages have free ends.
- The manubriosternal joint is a symphysis between the manubrium and body of the sternum, and the xiphisternal joint is a symphysis between the body and the xiphoid process.
Describe the joints of the costal heads.
- The head of a typical rib possesses two articular facets that slope away from each other, separated by a ridge.
- Each facet makes a small synovial joint with a demifacet of a vertebral body; the lower rib facet with the upper costal facet of its own vertebra, and the upper facet with the lower costal facet of the vertebra above.
- The ridge between the two is attached to the intervertebral disc by the intra-articular ligament.
- The front of the joint capsule is reinforced by the radiate ligament which consists of three bands.
- The upper band passes to the body of the vertebra above, the lower band to the vertebra below, while the central band runs horizontally, deep to the anterior longitudinal ligament, and blends with the intervertebral disc.
- The first rib articulates with T1 vertebra only, never coming into contact with C7, and the last two ribs also articulate only with their own vertebrae.
Describe the costotranverse joints.
- The tubercle of a typical rib has two facets.
- The medial facet, covered with hyaline cartilage, articulates with a facet near the tip of the transverse process of its own vertebra at a small synovial joint.
*. The lateral facet (non-articular) gives attachment to the lateral costotransverse ligament which runs to the tip of the transverse process and is one of three ligaments helping to stabilize the joint. - The other two are the costotransverse ligament, which occupies the space between the back of the neck of the rib and the front of the transverse process, and the superior costotransverse ligament, which passes as two laminae from the crest of the neck of the rib to the undersurface of the transverse process of the vertebra above.
- The anterior lamina is continuous with the posterior intercostal membrane; the posterior is in the same plane as the external intercostal muscle. * The fibres of these two laminae are at right angles to each other, in a similar manner to the fibres of the intercostal muscles.
- The lower two ribs do not possess tubercles and make no synovial joints with transverse processes.
Describe the costochondral joints.
Every rib makes with its costal cartilage a primary cartilaginous joint. The costal cartilage represents no more than the unossified anterior part of a rib.
Describe the interchondral joints.
Adjacent surfaces of costal cartilages 6 and 7, 7 and 8, and 8 and 9 are joined to each other by small synovial joints; 9 and 10 are connected by ligamentous fibres.
Describe the sternocostal joints.
- The first costal cartilage articulates with the manubrium by a primary cartilaginous joint. Thus the manubrium and the first ribs are fixed to each other and move together as one.
- The next six costal cartilages each articulate with the sternum by a synovial joint - a single cavity except in the case of the second, which articulates with the manubrium and body.
Describe the manubriosternal joint.
- At this symphysis between the manubrium and body of the sternum, the surfaces are covered by hyaline cartilage and there is an intervening disc of fibrocartilage which may become ossified in the elderly.
- Sometimes (30%) cavitation appears in the disc so that the joint may appear to be synovial, but this is simply a degenerative change that does not alter the fact that the joint is a symphysis.
Describe the xiphisternal joint.
This is another symphysis, between the body of the sternum and the xiphoid process. Ossification from middle age onwards is common.
Outline the thoracic muscles.
- The muscles of the thoracic wall lie in the same three morphological layers as those of the abdominal wall, but in the thoracic region they have become divided up by the presence of ribs.
- They are innervated segmentally by anterior rami.
- In the outer thoracic layer the external intercostal muscles correspond to the external oblique in the abdomen and in the middle layer the internal intercostals correspond to the internal oblique.
- The inner layer is broken up into three muscles, the subcostals, innermost intercostals and the transversus thoracis.
- This incomplete layer corresponds to the transversus abdominis.
- Between it and the middle layer is the neurovascular plane, continuous with that of the abdominal wall; in it run intercostal vessels and nerves, with their collateral branches.
What are the 4 muscles of the external layer of thoracic muscles?
- Serratus posterior superior.
- Serratus posterior inferior.
- Levator costae.
- External intercostals.
Outline the serratus posterior muscles.
- Two small muscles of the external layer have migrated posteriorly, and lie on the surface of the erector spinae mass.
- They are the posterior serratus muscles and are supplied by anterior rami.
- Each arises from four spinous processes, two in the thorax and two beyond it, and each is inserted into four ribs.
- Serratus posterior superior arises from the spinous processes of the lowest two cervical and the upper two thoracic vertebrae and is inserted just lateral to the angles of ribs 2–5.
- Many tendinous fibres in the sheet of muscle give it a characteristic glistening appearance which provides a useful landmark in exposures of this region.
- The dorsal scapular nerve and vessels run down on the posterior surface of the muscle, between it and the rhomboids.
- Serratus posterior inferior arises from the lower two thoracic and the upper two lumbar spinous processes and is inserted just lateral to the angles of the lowest four ribs.
- The serratus posterior muscles are weak muscles of respiration.
- The superior muscle elevates the upper ribs (inspiration) while the inferior muscle depresses the lower ribs (expiration).
Outline levator costae muscles.
- Although morphologically associated with the muscles of the back, the levator costae muscles are functionally classified as thoracic muscles.
- Each one of each of the 12 pairs is fan-shaped, spreading down from the tip of a transverse process (from C7 to T11 vertebra) to be inserted into the upper border of the rib below, lateral to its tubercle, and presumably helps to elevate it.
- They are supplied by the posterior rami of spinal nerves (from C8 to T11).
Outline the external intercostals.
- The chief muscles of the outer layer are the external intercostals.
- The fibres of the external intercostal muscles pass obliquely downwards and forwards from the sharp lower border of the rib above to the smooth upper border of the rib below.
- Each muscle extends from the superior costotransverse ligament at the back of the intercostal space as far forwards as the costochondral junction; here it is replaced by the anterior intercostal membrane. This extends to the side of the sternum.
- Between the bony ribs is muscle; between the costal cartilages is membrane.
Outline the internal intercostals of the middle layer of thoracic muscles.
The internal intercostal muscle fibres run downwards and backwards, from the costal groove to the upper border of the rib below.
* Each muscle, unlike an external intercostal, extends as far forwards as the side of the sternum; it is replaced posteriorly by the posterior intercostal membrane, which extends from the angle of the rib to the superior costotransverse ligament at the posterior limit of the space.
What are the 3 muscles of the inner layer of thoracic muscles?
- Subcostal muscles.
- Innermost intercostal muscles.
- Transversus thoracis.
Of the three groups of muscles in this layer the innermost intercostals line the rib cage at the side, while the subcostals are at the back, and the transversus thoracis at the front. They cross more than one intercostal space.
Outline the subcostal muscles.
Lying in the paravertebral gutter are the subcostal muscles attached to the inner surfaces of ribs. They are separated from the posterior border of the innermost intercostals by a space across which the intercostal nerves and vessels are in contact with the parietal pleura.
Outline the innermost intercostal muscles.
The innermost intercostal muscles (intercostales intimi) are attached to the inner surfaces of ribs on the lateral part of the thoracic wall.
Outline the transversus thoracis muscle.
- Transversus thoracis arises from the posterior surface of the lower part of the sternum, whence digitations diverge on each side to the second to the sixth costal cartilages.
- This muscle was formerly called sternocostalis, which was a more exact name.
- The transversus thoracis group is the best inclusive name for all three muscles of the inner layer because it conforms with the transversus abdominis muscle.
Describe the intercostal space.
- The intercostal spaces (between the ribs) are filled in by the muscles of the three layers described above.
- Running in the plane between the intermediate and inner layers are the intercostal nerves and vessels.
- The vein, artery and nerve lie in that order from above downwards, under cover of the downward projection of the lower border of the rib. * Thus a needle or trocar for pleural drainage is inserted just above the rib that forms the lower boundary of the space, in order to avoid the main nerve and vessels that are at its upper boundary.
- The collateral branches of nerve and vessels that run along the upper border of a rib are small and can be ignored.
- A needle introduced to deliver an anaesthetic solution on an intercostal nerve is inserted just below the lower border of a rib.
