Thoracic Muscles

3 peripheral attachments of the diaphragm

-Lumbar vertebrae & arcuate ligaments -Costal cartilages of ribs 7-12 -Xiphoid process of the sternum

External Intercostals

11 pairs, run inferoanteriorly from the rib above to the rib below, & are continuous with the external oblique of the abdomen

External Intercostals Action & NN

Action: Elevates the ribs, increasing the thoracic volume NN: Intercostal Nerves (T1-T11)

Subcostal Action & NN

Action: Share the action of the internal intercostals NN: Intercostal Nerves

Innermost Intercostals Action & NN

Action: The interosseous part reduces the thoracic volume by depressing the ribcage, &interchondral part elevates the ribs NN: Intercostal nerves (T1-T11)

Transversus Thoracis Action & NN

Action: Weakly depress the ribs. NN: Intercostal Nerves (T1-T11)

Internal Intercostals Action & NN

Action: interosseous part reduces the thoracic volume by depressing the ribcage, & interchondral part elevates the ribs NN: Intercostal nerves (T1-T11)

Innermost Intercostals

Are the deepest of the intercostal muscles, & similar in structure to the internal intercostals. Are separated from the internal intercostals by the intercostal neurovascular bundle & found in the most lateral portion of the intercostal spaces

Left Crus

Arises from L1-L2 & their IV discs

Right Crus

Arises from L1-L3 & their IV discs. Some fibres from the right crus surround the oesophageal opening, acting as a physiological sphincter to prevent reflux of gastric contents into the oesophagus (Right yellow outline)

Transversus Thoracis Attachments

Attachments: From the posterior surface of the inferior sternum to the internal surface of costal cartilages 2-6

External Intercostal Attachments

Attachments: Originate at the lower border of the rib, inserting into the superior border of the rib below

Innermost Intercostals Attachments

Attachments: Originate at the lower border of the rib, inserting into the superior border of the rib below

Internal Intercostals Attachments

Attachments: Originate at the lower border of the rib, inserting into the superior border of the rib below

Subcostal Attachments

Attachments: Originate from inferior surface of the lower ribs, near the angle of the rib then attach to the superior border of the rib 2 or 3 below

Pathways through the diaphragm

The diaphragm divides the thoracic & abdominal cavities. Thus, any vessels that pass between the 2 cavities will pierce the diaphragm. There are 3 openings that act as conduit for these structures

Inferior Thoracic Aperture

The diaphragm is located at the inferior-most aspect of the ribcage, filling the

Central Tendon

The muscle fibres of the diaphragm combine to form... This tendon ascends to fuse with the inferior surface of the fibrous pericardium. Either side of the pericardium, the diaphragm ascends to form left & right domes. At rest, the right dome lies slightly higher than the left - this is thought to be due to the presence of the liver

Transversus Thoracis

These muscles of the thoracic cage are continuous with transversus abdominis inferiorly

Aortic opening (T12 level)/hiatus

Transmits the aorta, thoracic duct (a large lymphatic vessel) & azygous vein

Caval opening (T8 level)/hiatus

Transmits the inferior vena cava

Oesophagal opening (T10 level)/hiatus

Transmits the oesophagus, vagus nerves, & oesophageal branches of the left gastric vessels

Diaphragm

acts as the floor of the thoracic cavity & the roof of the abdominal cavity (B)

Peripheral & Central Attachments of the diaphragm

attachments of diaphragm can be divided into peripheral & central attachments

NN of diaphragm

diaphragm receives motor nn from phrenic nerve. Left half of diaphragm (known as a hemidiaphragm) is nn by left phrenic nerve, & vice versa. Each phrenic nerve is formed in the neck within cervical plexus from spinal roots C3-C5

Diaphragm

double-domed sheet of skeletal muscle, located at the inferior-most aspect of the rib cage. It serves 2 main functions: 1. Separates the thoracic cavity from the abdominal cavity 2. Undergoes contraction & relaxation, altering the volume of the thoracic cavity & the lungs, producing inspiration & expiration

Internal Intercostals

flat muscles lie deep to the external intercostals. They run from the rib above to the one below, but inferoposteriorly. Are continuous with the internal oblique muscle of the abdominal wall

Subcostals

found in inferior portion of the thoracic wall. Thin slips of muscle, which run from the internal surface of one rib, to second & third ribs below. The direction of the fibres parallels that of the innermost intercostal

Intercostals

lie in the intercostal spaces between ribs. Organized into 3 layers

Arterial supply of the diaphragm

majority of arterial supply to diaphragm delivered via the inferior phrenic arteries, which arise directly from the abdominal aorta. The remaining supply is from the superior phrenic, pericardiacophrenic, & musculophrenic arteries. The draining veins follow the aforementioned arteries

Right & Left crura

parts of the diaphragm that arise from the vertebrae are tendinous in structure, & are known as the

Diaphragm Actions

primary muscle of respiration. During inspiration, it contracts & flattens, increasing the vertical diameter of the thoracic cavity. This produces lung expansion, & air is drawn in. During expiration, the diaphragm passively relaxes & returns to its original dome shape. This reduces the volume of the thoracic cavity

5 muscles that make up the thoracic cage

the intercostals (external, internal & innermost), subcostals, & transversus thoracis. These act to change the volume of the thoracic cavity during respiration.