Human Anatomy - Kotsan I. Y. 2009

Respiratory muscles and types of breathing
Muscles of inspiration

The inspiratory Muscles, in turn, are divided into three subgroups: primary inspiratory muscles, accessory inspiratory muscles, and muscles of secondary (indirect) action.

Primary inspiratory muscles are those that are constantly involved in respiratory movements. They include the following muscles:

1) Diaphragm;

2) external intercostals;

3) internal intercostals;

4) levatores costarum;

5) serratus posterior superior;

6) serratus posterior inferior;

7) quadratus lumborum;

8) iliocostalis;

Accessory inspiratory muscles are those that participate in respiratory movements only when their fixed and movable attachment points functionally switch places (for example, the pectoralis minor acts as a respiratory Muscle only when its insertion on the scapula becomes the fixed point, and its origin on The thoracic cage becomes the movable point). Accessory inspiratory muscles include:

1) pectoralis major;

2) pectoralis minor;

3) serratus anterior;

4) subclavius;

5) scalene muscles;

6) sternocleidomastoid (its sternal HEAD);

7) anterior Neck Muscles: sternohyoid, sternothyroid, etc. (with a fixed Hyoid bone);

8) erector spinae (upon spinal extension, it helps increase the vertical dimension of the thoracic cage).

The muscles of secondary (indirect) action involved in inspiration are those that increase the volume of the thoracic cage not directly, but through an intermediate osteomuscular complex (for example, the levator scapulae contracts and moves the scapula upward, which in turn pulls on the pectoralis minor attached to the coracoid process, which subsequently elevates the Ribs from which it originates). These secondary inspiratory muscles include:

1) upper portion of the trapezius;

2) rhomboids;

3) levator scapulae;

4) sternocleidomastoid (its clavicular head).

The intermediate osteomuscular complex comprises the scapula along with the pectoralis minor and serratus anterior muscles, as well as the clavicle with the subclavius muscle.

The diaphragm, or thoracoabdominal partition (diaphragma (thoracoabdominale, m. phrenicus)), is an unpaired, broad muscle located between the thoracic and abdominal cavities (Figs. 105, 106). In shape, the diaphragm resembles a dome with its convexity directed toward the thoracic cavity. It consists of a central tendon situated in the middle part and a peripheral muscular part.

The muscle fibers of the diaphragm originate along the entire inner margin of the inferior thoracic aperture, ascend, and transition into tendinous fibers that intertwine to form the central tendon. According to the Water/144.html">Origin of the muscle fibers, the sternal, costal, and lumbar PARTS OF THE diaphragm are distinguished.

The sternal part of the diaphragm (pars sternalis diaphragmatis) originates from the posterior surface of the xiphoid process of the Sternum.

The costal part of the diaphragm (pars costalis diaphragmatis) constitutes the largest portion of the diaphragm and arises from the internal surface of the lower six ribs.

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Fig. 105. Diaphragm (anterior view). Original by M. F. Ivanytskyi

The lumbar part of the diaphragm (pars lumbalis diaphragmatis) consists of two crura: right and left (crus dextrum et crus sinistrum). Each crus originates from the anterolateral surface of the bodies of lumbar vertebrae I–III (right I–IV) and from the so-called arcuate ligaments: medial and lateral. The medial arcuate ligament arches over the psoas major muscle from the body of the first lumbar vertebra to its transverse process. The lateral arcuate ligament arches over the quadratus lumborum muscle from the transverse process of the first lumbar vertebra to the free tip of the XII rib.

The medial fascicles of the right and left diaphragmatic crura ascend, converge, and form the aortic hiatus (hiatus aorticus), through which the aorta passes from the thoracic cavity into the Abdominal cavity, and the Thoracic duct passes from the abdominal cavity into the thoracic. Slightly higher, the medial fascicles of both crura diverge and bound the esophageal hiatus (hiatus oesophageus), through which the Esophagus passes together with the vagus nerves.

In addition, slit-like intermuscular spaces are present within the crura of the lumbar part, through which pass the Sympathetic trunk, greater and lesser splanchnic nerves, and the azygos and hemiazygos Veins.

Between the origin sites of the sternal, costal, and lumbar muscular parts of the diaphragm lie paired, slit-like, triangular spaces: the sternocostal and lumbocostal triangles. In these triangles, the thoracic cavity is separated from the abdominal cavity only by the serous and fascial layers that cover the diaphragm superiorly and inferiorly. These triangles can be sites for The formation of diaphragmatic hernias, through which parts of abdominal Organs protrude into the thoracic cavity.

Fig. 106. Diaphragm and Muscles of the posterior abdominal wall (internal view).

On the right, the quadratus lumborum muscle and parts of the psoas Major and minor muscles have been removed

1 — sternocostal triangle, 2 — costal part of the diaphragm, 3 — vena cava opening, 4 — esophageal hiatus, 5 — aortic hiatus, 6 — left crus of the diaphragm, 7 — quadratus lumborum muscle, 8 — psoas minor muscle, 9 — psoas major muscle, 10 — iliacus muscle, 11 — iliac fascia, 12 — saphenous opening, 13 — fascia lata, 14 — obturator externus muscle, 15 — iliopsoas muscle, 16 — psoas major muscle (partially cut), 17 — iliacus muscle, 18 — thoracolumbar fascia (deep layer), 19 — right crus of the diaphragm, 20 — lateral arcuate ligament, 21 — medial arcuate ligament, 22 — lumbar part of the diaphragm, 23 — central tendon, 24 — sternal part of the diaphragm

The central tendon (centrum tendineum) occupies the central region of the diaphragm and is triangular in shape, with its sharpest apex directed anteriorly. In the posterior part of the central tendon lies the caval opening (foramen venae cavae), through which the INFERIOR VENA CAVA passes.

The Movements of the diaphragm occur due to the contraction of its muscular part, whereas the central tendon, composed of Cytology/practical/45.html">Dense Connective Tissue, passively follows these movements. During muscle fiber contraction, the central tendon descends and the dome of the diaphragm flattens, whereas during relaxation, conversely, the central tendon and the dome ascend.

It should be noted that the convexity of the diaphragm is uneven. For instance, the middle part of the central tendon lies lower than its lateral portions, which are more convex and are therefore designated as the right and left domes (the convexity of the diaphragm is explained by the fact that intra-abdominal pressure exceeds intrathoracic pressure). Normally, the right dome is higher than the left and reaches the fourth intercostal space; the left dome reaches only the fifth intercostal space, which is significant for determining the normal boundaries of Internal Organs.

In newborns and children, due to the more horizontal orientation of the ribs, the diaphragm is positioned higher than in adults. The diaphragmatic dome is more convex, and the central tendon is relatively small. As a person ages, the convexity of the diaphragm decreases. In elderly and senile individuals, the diaphragm is markedly flattened, and its central tendon enlarges due to some degree of atrophy of its muscle fibers.

The thoracic and abdominal surfaces of the diaphragm are covered with fasciae. Superiorly, the diaphragm is covered by the endothoracic fascia, which is continuous with the diaphragm from the inner surface of the chest wall. Inferiorly, the diaphragm is covered by an extension of the endoabdominal fascia. The Lungs and Heart lie adjacent to the thoracic surface of the diaphragm, while the Liver, Stomach, and Spleen are adjacent to its abdominal surface; the Pancreas, duodenum, Kidneys, and Adrenal Glands adjoin those areas of the diaphragm not covered by the parietal Peritoneum.

Function: The diaphragm is the primary respiratory muscle. During contraction, it descends, its dome flattens, and the volume of the thoracic cavity increases (inspiration); upon relaxation, the diaphragm ascends, the dome becomes more pronounced, and the volume of the thoracic cavity decreases, resulting in expiration. Furthermore, working in synergy with the Abdominal muscles, the diaphragm assists the abdominal press, thereby influencing several abdominal organs (enhancing their peristalsis, stimulating the secretion of digestive juices from Major Digestive Glands, facilitating the evacuation of hollow organs, etc.).

Innervation: Phrenic nerve.

All other muscles involved in the act of inspiration are described in the previous topic, "Muscles of the Trunk," and in the subsequent topics, "Muscles of the Head" and "Muscles of the Neck."