Human Anatomy (with Fundamentals of Dynamic and Sports Morphology) - Ivanitsky M. F. 2008

Myology
Respiratory Muscles

During contraction, the respiratory Muscles cause the chest to enlarge or reduce in size, which alters the volume of the thoracic cavity and the Lungs contained within it.

When the chest enlarges, the volume of the thoracic cavity and lungs increases, the air pressure in the lungs drops, and atmospheric pressure forces air into the lungs, resulting in inhalation.

Exhalation occurs when the muscles that expand the chest relax, while the tone of the muscles that facilitate its collapse—thereby reducing the volume of the thoracic cavity—increases.

The chest typically expands simultaneously in three mutually perpendicular directions: vertical, transverse, and anteroposterior.

Expansion of the chest in the vertical direction occurs primarily due to the descent of the Diaphragm, whereas the increase in its anteroposterior and transverse dimensions results from the simultaneous movement of the Ribs outward, upward, and forward.

During chest expansion, the muscles must overcome gravity and the elastic resistance of the chest itself and its attached structures. In contrast, during descent, these two factors not only pose no obstacle but actually assist the movement. Chest descent can occur solely by virtue of its weight and elasticity; however, any forced or semi-forced exhalation requires muscular effort.

During Respiration, the movement of each rib occurs simultaneously in two joints: the joint between the rib HEAD and the bodies of two adjacent vertebrae (with the exception of the two lowest ribs) and the joint between the rib tubercle and the transverse process of the underlying vertebra. The axes of rotation of these joints are oriented such that, when extended posteriorly, they intersect at a more obtuse angle in the upper ribs than in the lower ribs. As a result, the upper ribs move forward to a greater extent than the lower ones, while the lower ribs move predominantly sideways.

All muscles involved in the Mechanics of Breathing are generally divided into two groups: inspiratory muscles (those that produce inhalation) and expiratory muscles (those that produce exhalation).

In turn, each of these groups can be subdivided into three categories:

a) primary respiratory muscles, which invariably participate in respiratory movements upon contraction (e.g., the intercostal muscles);

b) accessory muscles, which participate in respiratory movements only when the fixed and mobile attachment points of the Muscle functionally exchange roles (e.g., the pectoralis minor Functions as a respiratory muscle only when its attachment point on the scapula becomes the fixed point, while its origin on the chest acts as the mobile point);

c) muscles that exert an indirect effect on the chest via an intermediate musculoskeletal complex (e.g., contraction of the levator scapulae muscle slightly elevates its coracoid process, to which the pectoralis minor is attached, thereby enhancing the function of the latter as an accessory respiratory muscle).

The primary Muscles of inspiration are:

1) the diaphragm, whose contraction flattens its dome and thereby increases the volume of the thoracic cavity in the vertical direction;

2) the external and internal intercostal muscles; the former possess a greater moment arm and greater torque during inspiration, whereas the latter do so during expiration;

3) the levatores costarum muscles (see p. 202);

4) the serratus posterior superior muscle (see p. 199);

5) the serratus posterior inferior muscle (during diaphragmatic and full breathing) (see p. 199);

6) the quadratus lumborum muscle (under the same condition) (see p. 212);

7) the iliocostalis muscle (under the same condition) (see p. 200).

The accessory muscles of inspiration are:

1) the scalene muscles—anterior, middle, and posterior (when the cervical spine is fixed) (see p. 206);

2) the sternocleidomastoid muscle (when the head is fixed) (see p. 151);

3) the pectoralis minor muscle (when the Pectoral Girdle is fixed) (see p. 147);

4) the subclavius muscle (under the same condition) (see p. 152);

5) the lower portion of the pectoralis major (with a fixed humerus) (see p. 146);

6) the lower fascicles of the serratus anterior (with a fixed scapula) (see p. 147);

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

In addition, the vertical dimension of the thoracic cavity is increased by the extension of THE Vertebral Column, primarily in its thoracic region. Therefore, the accessory muscles can also include:

8) the muscles that extend the vertebral column in its thoracic region, among which the erector spinae is of the greatest importance (see p. 200).

The indirect expansion of the chest involves:

1) the upper part of the trapezius, which facilitates the elevation of the lateral angle of the scapula and, at the same time, pulls the attachment site of the pectoralis minor upward (see p. 147);

2) the rhomboid muscles, which, by elevating the scapula, promote the elevation of the ribs through it and through the pectoralis minor, and partly through the serratus anterior (see p. 148);

3) the levator scapulae (see p. 151);

4) the clavicular head of the sternocleidomastoid muscle (see p. 151);

This list demonstrates that a significant number of muscles participate in the breathing mechanism during forced inspiration.

The diaphragm (Fig. 66) is a thin muscle composed of Striated Muscle tissue. In shape, this muscle resembles an irregular dome with its apex directed upward toward the thoracic cavity. The muscle features a central tendinous part and a peripheral muscular part. The mediastinal Organs and The Heart lie superiorly against the tendinous center. The diaphragm is located between the thoracic and abdominal cavities. It comprises three parts: the sternal, costal, and lumbar parts. The sternal part (the weakest) originates from the xiphoid process of the Sternum; the costal part arises from the inner surface of the cartilages of the lower six ribs; and the lumbar part originates from the Vertebral Column and arcuate ligaments. This part consists of two crura — right and left.

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Fig. 66. Diaphragm (inferior view):

1 — xiphoid process of the sternum; 2 — sternal part; 3 — esophageal hiatus; 4 — costal part; 5 — aortic hiatus; 6 — lumbocostal triangle; 7 — quadratus lumborum m.; 8 — psoas minor m.; 9 — psoas major m.; 10 — lateral arcuate ligament; 11 — medial arcuate ligament; 12, 13 — right crus of the lumbar part; 14 — lumbar part; 15 — caval opening; 16 — tendinous center (after G. F. Ivanov)

The arcuate ligaments enclose the upper section of the muscles: the medial ligament encloses the psoas major muscle (part of the iliopsoas muscle), and the lateral ligament encloses the quadratus lumborum muscle.

The diaphragm contains several openings through which vital structures pass. Between the medial fascicles of the crura of the lumbar part of the diaphragm lies the aortic hiatus, 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 cavity.

The medial fascicles of the diaphragmatic crura diverge anteriorly and superiorly to the aortic hiatus, forming the esophageal hiatus, through which the Esophagus passes along with its accompanying vagus nerves, right and left. In the tendinous center, within its right half, is a large opening for the INFERIOR VENA CAVA.

The diaphragm responds very well to training. In individuals with good physical development, the muscular part of the diaphragm is significantly better developed and considerably larger in size than in those with weaker overall physical development. The mobility of the diaphragm during respiration is greater in athletes than in non-athletes (6–8 cm instead of 3–4 cm).

The primary function of the diaphragm is its Participation in the act of breathing. Its movements occur due to the contraction of the muscular part, while the tendinous center, composed of tendinous and elastic fibers, passively follows these movements. When the muscle fibers contract, the diaphragm descends, and upon relaxation, it ascends. Furthermore, the descent occurs actively, whereas the upward movement — i.e., stretching and elevation — occurs passively due to the difference between intra-abdominal and intrathoracic pressure. As the diaphragm contracts and descends, the vertical dimension of the thoracic cavity increases, enhancing the flow of air into the lungs, as well as the flow of Blood AND Lymph toward the heart.

Thus, the diaphragm functions as a respiratory muscle that works during inspiration, as well as a muscle that facilitates the propulsion of blood toward the heart. This latter function of the diaphragm is partly related to the fact that upon contraction, it exerts pressure on the Liver located directly beneath it, resulting in a partial expulsion of blood from the liver through the hepatic Veins into the inferior vena cava in the immediate vicinity of its entry into the heart.

In addition, the diaphragm exerts pressure on several other abdominal organs, helping to enhance their peristalsis, stimulate the secretion of digestive juices from the large glands (The Liver and Pancreas), and empty hollow organs. In relation to the Abdominal muscles, the diaphragm can act either as a synergist or an antagonist. It acts as their synergist when an increase in intra-abdominal pressure is required; however, during normal respiratory excursions, it acts as their antagonist. The descent of the diaphragm is possible only under the condition that the abdominal muscles are fully or at least partially relaxed. Indeed, the abdominal organs, which contain a large amount of Water, are practically incompressible, and the downward Displacement of the diaphragm is possible only with the simultaneous downward and anterior displacement of these organs. The latter can occur only with the complete or partial relaxation of the abdominal muscles. Observing respiratory movements in a living human, it is easy to verify that every inspiration produced by the contraction of the diaphragm is accompanied by a slight protrusion of the anterior abdominal wall. In cases where inspiration is produced primarily by the elevation of the ribs, such a protrusion may not occur.

THE POSITION OF the diaphragm may vary depending on age, respiratory excursions, and body position. In children, the diaphragm is located higher than in adults. In the supine position, it shifts upward much more than in the standing position. At the same time, the shape of the abdomen also differs between standing and lying down; in the standing position, when the abdominal organs shift downward due to gravity, a slight protrusion of the anterior abdominal wall occurs. These displacements are more pronounced in elderly individuals, which is associated with the general descent (ptosis) of the abdominal organs. If the trunk flexes and the chest and pelvis move closer together, the vertical dimension of the abdominal cavity also decreases, resulting in an increased anterior protrusion of the abdominal wall and a displacement of the organs in the same direction. Conversely, during strong extension of the vertebral column (e.g., in the "bridge" position), the vertical dimension of the abdominal cavity increases, the tone of the abdominal wall muscles rises, and a retraction of the wall is observed. In this case, the diaphragm is positioned higher.

Being a striated muscle, the diaphragm can operate beyond our conscious control and without voluntary impulses, as, for example, during Sleep.

The intercostal muscles fill the intercostal spaces, forming two layers: the external and internal intercostal muscles.

The external intercostal muscles (see Fig. 64) are located superficially, extending from the tubercles of the ribs anteriorly to the junctions of the osseous and cartilaginous PARTS OF THE ribs. Their fibers run obliquely from the lower border of each superior rib to the upper border of the inferior rib, passing downward and forward from behind and above.

The internal intercostal muscles (see Fig. 64) originate from the upper border of the inferior ribs, run upward and forward, and insert into the lower border of the superior ribs. Posteriorly, they reach the angles of the ribs, and anteriorly, they extend to the sternum.

The function of all these muscles is to counteract intra-thoracic pressure during expiration and atmospheric pressure during inspiration, thereby facilitating rib movement during respiration. The external intercostals have a greater leverage (moment of force) during inspiration, whereas the internal intercostals are more effective during expiration; however, both groups participate in both phases of breathing.

The muscles involved in expiration are:

1) the abdominal muscles, which are direct antagonists of the diaphragm;

2) the internal and external intercostals (see p. 221);

3) the subcostals;

4) the transversus thoracis;

5) the serratus posterior inferior (see p. 199);

6) the quadratus lumborum (see p. 212);

7) the iliocostalis (see p. 200).

The subcostal muscles are flat, thin, triangular

muscles located on the inner surface of the lower ribs near their angles. They originate from the inner surfaces of the ribs and insert into the ribs above. The fiber direction of these muscles coincides with that of the internal intercostals. The subcostals assist in expiration.

The transversus thoracis muscle lies on the posterior surface of the costal cartilages. It originates from the xiphoid process and the lower surface of the body of the sternum, inserting into ribs II–VI approximately at the junction of their osseous and cartilaginous parts.

The transversus thoracis acts as a synergist to the internal intercostal muscles, primarily aiding in the depression of the ribs.

Rib depression during costal expiration is also assisted by the serratus posterior inferior, quadratus lumborum, and iliocostalis muscles. Although the diaphragm and abdominal muscles have opposing functions during respiration, they can act not only as antagonists but also as synergists (during straining).

During certain athletic movements, the abdominal press muscles contract whenever trunk stabilization is required (for example, when performing a wrestler's bridge, lifting heavy weights, and during other exercises).

It is customary to distinguish between abdominal (or diaphragmatic) breathing and thoracic (or costal) breathing, the latter being subdivided into upper costal and lower costal breathing. Mixed (complete) breathing refers to a pattern where abdominal and thoracic breathing are combined.

The common belief that men and women exhibit different breathing patterns is disputed by many authors who argue that there are no innate sex-related respiratory differences. The only variation in rib movement between men and women lies in the amplitude of the movement arc.

However, certain extrinsic factors can alter the breathing pattern: gastrointestinal distension, various abdominal pathologies, Pregnancy in its final months, or compression of the costal margin by a tight belt—in short, anything that hinders the descent of the diaphragm promotes the predominance of thoracic breathing.

During any Physical Exercise involving the exertion of certain respiratory muscles, breathing movements can be maintained through the isolated contraction of other muscles. It is recommended to keep breathing regardless of muscular tension. Nevertheless, following this rule can sometimes be extremely difficult (e.g., when the trunk is stabilized and all its muscles are tense, such as in a wrestling or gymnastic bridge).

The diaphragm plays a critically important role in abdominal-type breathing. During inspiration, it descends primarily due to the contraction of its lumbar and costal parts. Conversely, during thoracic breathing, the diaphragm may actually elevate slightly during inspiration, following the movement of the ribs. In mixed breathing, the diaphragm descends while the ribs elevate simultaneously.

Diaphragmatic breathing is subject to finer regulation than costal breathing. The efficiency of the respiratory mechanism depends not only on an individual's innate chest Structure, but also on training, through which a narrow chest with proper breathing technique can function significantly better than a wide chest with poor breathing technique.

The mechanics of respiration can vary considerably depending on body position. For example, elevating the arms and the pectoral girdle increases the tone of the accessory muscles that assist inspiration (pectoralis minor, subclavius, pectoralis major). The "hands on hips" position also creates more favorable conditions for utilizing these accessory muscles.

Diaphragmatic function becomes more challenging during a hang with bent legs or on tiptoes, as well as in a handstand and an arched hang, because in all these positions the contracting diaphragm must lift the abdominal viscera (M. A. Jafarov).