Thorax

• Intercostal nerve

• Lateral cutaneous branch
• Anterior cutaneous branch

• Thoracic spinal nerve

• External intercostal muscle
• Internal intercostal muscle

• Innermost intercostal muscles

Several groups of muscles are found in the chest wall. Some of these muscles attach ribs to other ribs, while others join ribs and sternum or vertebrae.
muscles

The function common to all of these muscles is that they can move the ribs, in addition to whatever other movements they produce. Movement of the ribs is the fundamental action producing respiration, as detailed following.

The space between adjacent ribs is filled with a set of intercostal muscles, of which there are three layers-the external, internal, and innermost intercostal muscles.

These muscle groups differ from each other in the direction in which their muscle fibres are arranged and the degree to which they are present at all points around the full curvature of the chest wall, from the vertebral column posteriorly to the costal cartilages anteriorly.

At points where an intercostal muscle itself is not present, it is represented by a membrane (e.g., the external intercostal muscle is not continuous all the way anterior to the costal cartilages, and, anteriorly, the anterior intercostal membrane is found in its place).

Also a separate and distinct muscle may be found in the plane of the innermost intercostal muscles and may be thought of as a continuation of that layer of intercostal musculature called intercostalis intemus (e.g., the transversus thoracis and subcostal muscles).

Apart from the intercostal muscles, the chest wall is an attachment for many important muscles of the upper limb abdomen and neck. Movement of the ribs is an essential part of changing the shape and volume of the chest and is essential for respiration.

There is no agreement about the activity of specific intercostal muscles in the various phases of respiration. Most agree that the external intercostals are elevators of the ribs (and therefore active in inspiration), but the role of the internal and the innermost intercostals is unclear.

Eleven pairs of intercostal veins exist. On both the right and left sides , the first intercostal vein drains superiorly and directly into the brachiocephalic vein. On the right, intercostal veins 2 to 4 collect into a common trunk, the right superior intercostal vein, which drains into the azygos vein (an important vein, which is a major tributary of the superior vena cava).
V e I n s

The remaining intercostal veins on the right (for interspaces 5 to 11) drain directly into the azygos vein, as it courses superior and just anterior to the vertebral column. On the left side, intercostal veins 2 and 3 form a left superior intercostal vein, which crosses the left side of the aortic arch to drain into the left brachiocephalic vein.


Intercostal veins 4 to 11 remain separate and drain independently into the accessory hemiazygos vein (for left intercostal veins 4 to 8), or the hemiazygos vein (for left intercostal veins 9 to 11). In midthorax, the accessory hemiazygos vein crosses the midline to drain into the azygos vein.

The hemiazygos vein also crosses the midline to drain into the azygos vein or may instead first join the accessory vein. hemiazygos vein. In this fashion, most of the venous drainage of both sides of the chest wall ultimately empties into the azygos vein.

arterial supply

The arterial supply to the chest wall arises in two main sources: the intercostal vessels and the various branches of the subclavian and axillary arteries that reach the chest. Each intercostal artery runs a roughly semicircular course, arising posteriorly (from different sources) and coursing around the chest wall to unite with the internal thoracic artery anteriorly.

The component originating from the aorta (or other posterior source) is called the posterior intercostal artery and the component branching from the internal thoracic artery is known as the anterior intercostal artery, although in fact they form one single continuous vessel. Along its course each artery gives off several branches, supplying nearby muscles, connective tissues, bones, and skin.

The collateral supply between intercostal spaces is so extensive that to produce ischaemic injury to just one intercostal space if they ocluded . The origins of the 12 intercostal arteries are subject to considerable variation. The upper two intercostal arteries, on both sides, usually arise from the left and right superior or suprime intercostal arteries, themselves branches of the costocervical trunk of the subclavian artery.

These upper intercostal arteries arch posteriorly, drape over the apex of each lung, and then turn inferiorly to lie just anterior to the necks of ribs 1 and 2. Here vessels assume a position just inferior to the rib and course anteriorly around the chest wall as the first and second intercostal arteries. The second intercostal artery forms collateral connections with the third intercostal artery.

Segmental arteries for the next nine intercostal spaces (i.e., intercostal arteries 3 to 11) arise from the thoracic (descending) aorta in pairs (one each for left and right side of the chest wall). The 12th intercostal artery lying inferior to the 12th rib, also arises from the aorta and is known as the subcostal artery.

Because the aorta lies on the left side of the posterior thoracic wall, the lower nine right intercostal arteries are longer than the lower nine intercostal arteries on the left. As they move toward the right side, the right side intercostal arteries 3 to 12 pass anterior to the vertebrae but posterior to the oesophagus, thoracic duct, and azygos veins.


The lower nine left intercostal arteries, originating from the aorta, simply move laterally into the intercostal space, lying posterior to the hemiazygos and azygos veins. On both the left and right sides, the sympathetic trunks lie anterior to the intercostal arteries at all levels.
Moving from anterior to posterior, a series of separate arteries helps supply the chest wall. Each also forms anastomoses with intercostal arteries in the area of the chest supplied..

The internal thoracic artery arises from the inferior surface of the first part of the subclavian artery and travels inferiorly down the inner surface of the chest wall, just deep to the costal cartilages. It lies about 1 cm lateral to the margin of the sternum. At the level of the sixth rib, it divides into its terminal musculophrenic and superior epigastric branches.

The superior thoracic artery is a small branch of the first part of the axillary artery.

It passes medial to the pectoralis minor and anastomoses with the upper two to three intercostal arteries. The lateral thoracic artery is another branch of the axillary artery, from its second part. It descends along the lateral border of the pectoralis minor and supplies many muscles on the anterolateral chest wall.

The lateral thoracic artery anastomoses with the internal thoracic, subscapular, and intercostal arteries. In the female it has an especially large branch supplying the breast. The subscapular artery, arising from the third part of the axillary artery, descends along the posterior axillary wall parallel to the inferior border of the latissimus dorsi. It anastomoses with many other arteries around the scapula and with the lateral thoracic and intercostal vessels as well. The dorsal scapular artery arises from the subclavian artery, passes to the posterior side of the trunk, and descends along the medial border of the scapula, deep to the rhomboid muscles. It anastomoses with the upper posterior intercostal arteries.

• Aorta

• Posterior intercostal artery
• Lateral cutaneous branch
• Internal thoracic artery
• Anterior intercostal branch



Eleven pairs of intercostal nerves course between adjacent ribs, and the subcostal nerves course below each 12th rib. These nerves are the continuation of the ventral primary rami of thoracic segments of the spinal cord. The intercostal nerves travel just inferior to the inferior margin of the rib, in the costal groove.
Nerves

• Each intercostal nerve contains somatic sensory and motor axons as well as sympathetic axons that innervate sweat glands, arrector pili muscles (for the elevation of hairs), and vascular smooth muscle. Each intercostal nerve innervates deep structures, such as the intercostal muscles, the lateral rim of the diaphragm, and the parietal pleura, and has cutaneous branches innervating the skin and superficial fasciae. Intercostal nerves 7 to 12 continue inferomedially to innervate the abdominal wall.

Intercostal Nerve Block

• Costal angle (mostly)
• Posterior axillary line
• Anterior axillary line
• Fracture site
• Parasternal line
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Intercostal Nerve Block