Human Anatomy (with the fundamentals of dynamic and sports morphology) - Ivanitsky M. F. 2008

Myology
Muscles of the Trunk and Neck

The Muscles of the Trunk and neck are conventionally subdivided according to topographical and anatomical criteria into the muscles of the back and nuchal region, the muscles of the anterior neck, the chest muscles, and the Abdominal muscles.

The Functions of the muscles of the trunk and neck are diverse:

1. Ensuring the vertical posture of The Human Body.

2. Maintaining equilibrium and executing movements of THE Vertebral Column and HEAD.

3. Participating in The formation of the walls of the thoracic and abdominal cavities.

4. Supporting THE POSITION OF the abdominal viscera and regulating intra-abdominal pressure.

5. Executing respiratory movements.

Muscles producing movements of the Vertebral Column

The vertebral column, and along with it the entire trunk, neck, and head, can perform the following movements.

1) extension and flexion (backward and forward trunk bending);

2) lateral movements (right and left tilting);

3) rotation around the vertical axis;

4) circumduction.

To accomplish these movements, six functional Muscle groups are required.

Extension of the Vertebral Column

The muscles that extend the vertebral column include those that cross the transverse axis of rotation and are located posterior to it on the back surface of the trunk and neck:

1) trapezius (see p. 150);

2) posterior serratus muscles, superior and inferior;

3) splenius capitis and cervicis muscles;

4) erector spinae muscle;

5) transversospinales muscle;

6) short back muscles.

The back muscles are arranged in several layers. The superficial ones are the trapezius and latissimus dorsi (see p. 150); beneath them lie the levator scapulae (see p. 151) and rhomboid muscles (see p. 149); and located even deeper are the posterior serratus muscles.

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Fig. 61. Muscles of the back:

1 — splenius capitis m.; 2 — levator scapulae m.; 3 — minor rhomboid m.; 4 — major rhomboid m.; 5 — latissimus dorsi m.; 6 — external oblique m. of the abdomen; 7 — thoracolumbar fascia; 8 — erector spinae m.; 9 — inferior posterior serratus m.; 10 — spinal m.; 11 — longissimus m.; 12 — superior serratus m.

The serratus posterior superior muscle (Fig. 61) originates from the spinous processes of the two lower cervical and two upper thoracic vertebrae, and inserts into the posterior surface of Ribs II–V. When the vertebral column is fixed, this muscle elevates the ribs; conversely, when the ribs serve as a fixed base and the muscle contracts unilaterally, it AIDS in lateral flexion of the vertebral column. If the serratus muscles of the right and left sides act simultaneously with fixed ribs, they contribute to a certain degree to the extension of the vertebral column.

The serratus posterior inferior muscle (see Fig. 61) originates from the thoracolumbar fascia in the region of the spinous processes of the two lower thoracic and two upper lumbar vertebrae, inserting into the posterior surface of the four lower ribs. The direction of the fibers of this muscle is opposite to that of the preceding muscle, which accounts for their differing functions regarding the ribs: the first elevates the ribs, while the second depresses and spreads them.

Working simultaneously, these muscles can expand the thoracic cavity in a vertical direction, thereby facilitating inspiration.

In individuals with well-trained Respiratory Muscles, one can sometimes observe a bellows-like expansion of the chest, caused by the elevation of the upper ribs and the simultaneous depression of the lower ones. There is reason to believe that this latter function is performed by the serratus posterior inferior muscle. In cases where the pull of this muscle is insufficient, the lower ribs move upward despite its contraction. By helping to pull the lower ribs downward, the serratus posterior inferior muscle acts as a synergist to the Diaphragm. When the ribs are fixed, this muscle assists in extending the vertebral column.

The splenius capitis and cervicis muscle (see Fig. 61) originates from the nuchal ligament, and through it from the spinous processes of cervical vertebrae III–VII and the upper six thoracic vertebrae, inserting into the lateral part of the superior nuchal line, the mastoid process of the Temporal bone, and the transverse processes of cervical vertebrae II and III.

This muscle assists in the movement of the head and the cervical region of the vertebral column. Contracting on one side, it bends the head laterally and slightly backward; contracting simultaneously on both the right and left sides, it contributes to the extension of the head and the upper portion of the vertebral column.

The contours of this muscle can be observed in the upper region of the neck, situated between the anterior border of the trapezius and the posterior border of the sternocleidomastoid muscle.

The erector spinae muscle (see Fig. 61) extends along the entire length of the vertebral column, from the sacrum to the Skull, filling the groove between the spinous and transverse processes. This muscle is the most powerful extensor of the vertebral column. The right and left muscles form two prominent columns running parallel to the spinous processes on either side.

Originating from the posterior surface of the sacrum, the spinous processes of the lumbar vertebrae, and partially from the iliac crest and thoracolumbar fascia, this muscle ascends and divides into three main parts: the medial part — the spinal muscle, which lies directly adjacent to the spinous processes; the intermediate part — the longissimus muscle, which rests upon the transverse processes of the vertebrae; and the lateral part — the iliocostalis muscle, the bundles of which attach to the ilium, sacrum, and ribs.

The spinal muscle terminates on the spinous processes of the thoracic vertebrae (its inconstant parts may reach the spinous processes of the cervical vertebrae and the Occipital bone), the longissimus on the mastoid process of the temporal bone, and the iliocostalis in the region of the rib angles.

The function of the erector spinae muscle is to extend the vertebral column. In addition, the longissimus muscle, reaching up to the skull, assists in the flexion and extension of the head, whereas the iliocostalis depresses the ribs. Acting unilaterally, the muscle participates in lateral flexion of the vertebral column to the same side, provided this contraction occurs simultaneously with the contraction of the lateral flexors on that same side.

The transversospinales muscle group is located beneath the longissimus and spinal muscles. It extends from the sacrum to the occipital bone and consists of individual muscles passing from the transverse processes of some vertebrae to the spinous processes of others. In turn, this muscle group is divided into three layers: the superficial layer formed by the semispinalis muscle, the middle layer by the multifidus, and the deep layer by the rotators.

The semispinalis muscle (Fig. 62) runs from the transverse processes of inferior vertebrae to the spinous processes of superior vertebrae, lying directly beneath the spinal muscle.

The multifidus muscle (see Fig. 62) lies beneath the semispinalis and partially (in its lower section) beneath the longissimus muscles. It originates from the sacrum and extends up to the spinous process of cervical vertebra II, attaching to the spinous processes of the vertebrae. This muscle extends the vertebral column.

The rotators run from the transverse processes of the vertebrae to the Base of the spinous processes. These muscles form the deepest muscular layer of the back and are best developed in the thoracic region of the vertebral column. Because the fibers of these muscles run obliquely, their primary function is not so much the extension of the vertebral column as its rotation around a vertical axis.

The short muscles of the back include the intertransversarii, interspinales, levatores costarum, and a group of muscles situated between the occipital bone, the atlas, and the axis.

Fig. 62. Muscles of the neck and head (posterior view):

1 — temporal m.; 2 — epicranius m. (occipital belly); 3 — posterior auricular m.; 4 — semispinalis m.; 5 — interspinal m.; 6 — multifidus m.; 7 — omohyoid m.; 8 — inferior oblique capitis m.; 9 — superior oblique capitis m.; 10 — rectus capitis posterior major m.; 11 — rectus capitis posterior minor m.

The intertransverse and interspinal muscles are located in the spaces between the spinous and transverse processes. These muscles are present in the cervical and lumbar Regions of the vertebral column (less frequently in the thoracic region). The interspinal muscles participate in the extension of the vertebral column, whereas the intertransverse muscles aid in its lateral flexion.

The levatores costarum muscles are present only in the thoracic region of the vertebral column. They run downward from the transverse processes of the thoracic vertebrae to the adjacent rib. The function of these muscles is to elevate the ribs and cause lateral movement of the vertebral column accompanied by its extension.

A group of suboccipital muscles is situated between the occipital bone, the atlas, and the axis. Two of these run downward from the occipital bone to the posterior tubercle of the atlas and the spinous process of the axis. These are the rectus capitis posterior Major and minor muscles (see Fig. 62).

The suboccipital group also includes the superior and inferior oblique capitis muscles (see Fig. 62). The first runs from the occipital bone to the transverse process of the atlas, while the second extends from this transverse process to the spinous process of the axis. The function of these muscles consists in extension of the head, its rotation, and lateral flexion.

The Fasciae of the back are particularly well developed in its lower region, whereas in the upper region the fascial layer is very thin.

The thoracolumbar fascia is located on the back, representing one of the strongest fascial structures in the human body. It consists of two layers, superficial and deep, which enclose the erector spinae muscle posteriorly and anteriorly. They converge along the lateral border of the muscle, forming a thickening at this site.

A number of muscles originate from the Fascia of the back, notably the serratus posterior inferior, latissimus dorsi, as well as the internal oblique and transverse abdominal muscles.

Flexion of the Vertebral Column

The Muscles responsible for the flexion of the trunk, neck, and head are those whose resultant vectors lie anterior to the transverse axes passing through the centers of the intervertebral discs and anterior to the transverse axis of the atlanto-occipital joint. These include the muscles of the anterior neck (both superficial and deep), the abdominal muscles, and the iliopsoas muscle. The most important of these are as follows:

1) sternocleidomastoid (see p. 151);

2) scalene muscles (see p. 206);

3) longus capitis and longus colli (see p. 207);

4) rectus abdominis (see p. 209);

5) oblique abdominal muscles (see p. 210);

6) iliopsoas (see p. 174);

The first three muscles belong to the neck musculature and participate in the flexion of the cervical spine and forward tilting of the head; the next two are part of the abdominal press and take part in the flexion of the lumbar spine. The last muscle was already discussed (see p. 150); it participates in vertebral flexion only when the lower extremities are fixed.

Muscles of the Neck

All Neck Muscles can be divided into three groups.

1. Superficial neck muscles: the platysma and the prominently protruding sternocleidomastoid located beneath it.

2. Muscles Attached to the Hyoid bone.

3. Deeply situated muscles attached directly to the Vertebral Column and running from the vertebral column to the ribs.

Superficial Neck Muscles

The platysma (Fig. 63) is located immediately beneath the Skin and appears as a broad muscular sheet covering almost the entire anterior region of the neck. Inferiorly, it extends over the clavicle, while superiorly it reaches the parotid fascia and the angle of the Mouth. Its fibers run upward and slightly medially toward the median plane of the body. The sites of origin and insertion of the platysma are the fascial layers of the regions to which its fibers extend.

The function of the muscle is that, upon contraction, it tightens the skin of the neck and helps pull it forward, facilitating the dilation of Blood Vessels—primarily Veins—whenever accelerated and enhanced venous return from the head is required. During intense physical exertion, contraction of the platysma can frequently be observed.

Reaching the angle of the mouth, this muscle helps pull it downward and backward.

Muscles Attached to the Hyoid Bone

These muscles can be divided into two groups: 1) those lying inferior to the hyoid bone—the infrahyoid muscles, and 2) those lying superior to this bone—the Suprahyoid muscles. The former pull the hyoid bone and Larynx downward, while the latter pull them upward. All these muscles indirectly participate in the flexion of the vertebral column and the depression of the Mandible.

Four muscles are located inferior to the hyoid bone: the omohyoid, sternohyoid, sternothyroid, and thyrohyoid.

The omohyoid muscle (see Fig. 63) originates from the upper border of the scapula, runs medially and upward, passes posterior to the sternocleidomastoid muscle, and attaches to the hyoid bone. The omohyoid has two bellies—superior and inferior—positioned at an angle to each other. An intermediate tendon lies between them.

The omohyoid muscle depresses the hyoid bone and also pulls the sternocleidomastoid slightly forward, thereby reducing its pressure on the underlying blood Vessels and nerves. The elevating and adducting effects of this muscle on the scapula are negligible due to its low lifting capacity.

The sternohyoid muscle (see Fig. 63) originates from the posterior surface of the manubrium of the Sternum and the clavicle, inserting into the inferior border of the body of the hyoid bone. When contracted, this muscle pulls the hyoid bone, and through it the larynx, downward.

The sternothyroid muscle originates from the posterior surface of the manubrium of the sternum and the Cartilage of the first rib, inserting into the thyroid cartilage of the larynx. This muscle is almost entirely covered by the omohyoid and sternohyoid muscles. It pulls the thyroid cartilage downward.

The thyrohyoid muscle originates from the thyroid cartilage and inserts into the hyoid bone. The thyrohyoid and sternothyroid muscles act together to depress the hyoid bone. Regarding the upward and downward Movements of the thyroid cartilage, these muscles are antagonists.

Four muscles are also located above the hyoid bone: the digastric, stylohyoid, mylohyoid, and geniohyoid.

The digastric muscle (see Fig. 63) originates from the mastoid notch of the temporal bone and inserts into the digastric fossa of the mandible. The muscle has two bellies (anterior and posterior), between which lies a well-defined tendon,

passing superior to the hyoid bone and attaching to it via a ligament that forms a pulley. The posterior belly is covered by the sternocleidomastoid muscle.

The function of the digastric muscle is to depress the mandible, open the mouth, and elevate the hyoid bone along with the larynx.

The stylohyoid muscle (see Fig. 63) originates from the styloid process of the temporal bone, runs downward and anteriorly, and inserts into the hyoid bone.

The function of the muscle is to pull the hyoid bone posteriorly and superiorly. This muscle largely acts as a synergist to the posterior belly of the digastric muscle. If the hyoid bone is fixed by the muscles located inferior to it, the stylohyoid muscle takes some part in flexing the head forward.

The mylohyoid muscle (see Fig. 63), together with its contralateral counterpart, forms a thin muscular plate (the floor of the Oral Cavity) that closes the entire space between the mandible and the hyoid bone.

Fig. 63. Muscles of the neck:

1, 3 — digastric m. (anterior belly); 2 — mylohyoid m.; 4 — body of hyoid bone; 5 — thyrohyoid m.; 6 — thyroid cartilage; 7 — omohyoid m. (superior belly); 8 — sternohyoid m.; 9 — cricothyroid m.; 10 — Thyroid Gland; 11–13 — sternocleidomastoid m.; 14 — clavicle; 15 — pectoralis major m.; 16 — deltoid m.; 17 — trapezius m.; 18 — anterior scalene m.; 19 — middle scalene m.; 20 — omohyoid m. (inferior belly); 21 — posterior scalene m.; 22 — levator scapulae m.; 23 — pharyngeal Constrictor muscles; 24 — splenius capitis m.; 25 — semispinalis m.; 26 — nuchal fascia; 27 — longus capitis m.; 28 — occipitalis m. (occipital belly); 29 — auricularis posterior m.; 30 — digastric m. (posterior belly); 31 — styloid process; 32 — stylohyoid m.; 33 — hyoglossus m. (after G.F. Ivanov)

The muscle originates on the internal surface of the body of the mandible. Its fibers run posteriorly, inferiorly, and medially. Where they meet along the midline, a raphe is formed. This muscle inserts into the hyoid bone.

When the mandible is fixed, the mylohyoid muscle participates in elevating and pulling the hyoid bone forward. Conversely, if the hyoid bone is fixed, the muscle can assist in depressing the mandible. When both the hyoid bone and the mandible are fixed, this muscle, working with other muscles of the anterior neck, helps flex the head forward.

The geniohyoid muscle lies directly above the mylohyoid muscle and runs in an anteroposterior direction close to the median plane of the body. It originates from the mental spine and inserts into the body of the hyoid bone. The muscle pulls the hyoid bone forward and upward, depresses the mandible, and reinforces the floor of the oral cavity.

Deep Muscles of the Neck

The group of deep neck muscles lies directly adjacent to the vertebral column and participates in its movement. These muscles can be divided into two groups: lateral and medial.

The lateral group consists of three scalene muscles: anterior, middle, and posterior.

The anterior scalene muscle (see Fig. 63) originates from the transverse processes of the III–VI cervical vertebrae and inserts into the scalene tubercle of the first rib.

The middle scalene muscle (see Fig. 63) originates from the transverse processes of all cervical vertebrae and inserts into the superior surface of the first rib, slightly posterior to the attachment site of the previous muscle.

The posterior scalene muscle (see Fig. 63) originates from the transverse processes of the V and VI cervical vertebrae and inserts into the second rib.

When the Thorax is fixed, the scalene muscles laterally flex and bend the cervical spine. In addition, they can assist in rotating the cervical spine around its vertical axis (torsion). If the vertebral column is fixed, the scalene muscles elevate the First and Second ribs and aid in inspiration.

The Medial Group of deep neck muscles includes four muscles running along the anterior surface of the vertebrae from the third thoracic vertebra to the external base of the skull. These muscles include: the longus colli, longus capitis, rectus capitis anterior, and rectus capitis lateralis.

The longus colli muscle originates from the anterior surface of the bodies of the II–III thoracic and V–VII cervical vertebrae, inserting into the II–VI cervical vertebrae and the transverse processes of the lower three cervical vertebrae. The function of the muscle is to flex the cervical spine.

The longus capitis muscle originates from the transverse processes of the third to sixth cervical vertebrae and inserts into the external base of the skull. It flexes the head forward and laterally, and also rotates it slightly.

The rectus capitis anterior and lateralis muscles originate from the transverse process of the atlas, course superiorly and medially, and insert into the basilar part of the occipital bone. These muscles flex the head forward and to the side.

Cervical fascia

The cervical fascia has a highly complex Structure. It is subdivided into three layers: superficial, pretracheal, and prevertebral.

The Superficial layer of the cervical fascia is very weakly developed.

The pretracheal layer encloses all the cervical muscles and Organs located anterior to the deep neck muscles and the vertebral column. It gives rise to numerous extensions that sheathe the cervical muscles both anteriorly and posteriorly.

This layer attaches to the hyoid bone and is conventionally divided into two parts: suprahyoid and infrahyoid. The suprahyoid part envelops the digastric muscle and the submandibular gland, featuring superficial and deep leaves. The former attaches to the inferior border of the mandible and covers the submandibular gland externally, whereas the latter encases the mylohyoid muscle from below. On the face, the superficial leaf covers the parotid gland, while the deep leaf transitions into the fascia enveloping the Pharynx. The infrahyoid part of the pretracheal cervical fascia encloses all the muscles attached to the hyoid bone.

Located directly anterior to the Trachea within the pretracheal space—situated between the fascial layers—are small blood vessels (inferior thyroid veins), the thyroid isthmus, and partially the Thymus. Extending inferiorly, the pretracheal space continues into the anterior Mediastinum of the thoracic cavity.

The prevertebral layer of the cervical fascia covers the deep neck muscles and the vertebral column anteriorly. Superiorly, it reaches the external base of the skull, and inferiorly, it continues into the fascia lining the internal walls of the thoracic cavity.

The anterior region of the neck serves as a pathway for major blood vessels and nerves (including the carotid Arteries, jugular veins, and Vagus nerve) as well as Internal Organs (the larynx, trachea, pharynx, Esophagus, and thyroid gland).

The anterior region of the neck is traditionally divided into three areas: anterior, sternocleidomastoid, and lateral. The first is unpaired, while the latter two are paired. When a median plane is established, the anterior cervical region is subdivided into two anterior Triangles of the neck, each bounded superiorly by the lower margin of the mandible and posteriorly by the sternocleidomastoid muscle. The anterior cervical triangle is further divided by the digastric and omohyoid muscles into three smaller triangles: the submandibular, carotid, and muscular (omotracheal) triangles. The lateral region, or lateral cervical triangle, is bounded by the posterior margin of the sternocleidomastoid muscle, the anterior margin of the trapezius muscle, and the clavicle. The depression corresponding to this triangle is referred to as the greater supraclavicular fossa.

Muscles of the abdomen

The BOUNDARIES OF THE abdomen are generally defined as follows: superiorly by the inferior margin of the rib cage, and inferiorly by the inguinal ligaments (right and left), the superior margin of the Pubic Symphysis, and the iliac crests. However, these boundaries are conventional; they correspond neither to the boundaries of the Abdominal cavity nor to the arrangement of the abdominal wall muscles. The abdominal cavity is considerably larger, as its superior limit is determined by the position of the diaphragm—whose dome reaches the level of the 4th intercostal space on the right and the 6th intercostal space on the left—while its inferior limit is defined by the pelvic floor.

A distinction is made between the muscles that primarily form the anterior and lateral walls of the abdomen and those that contribute to the posterior wall. The former include the rectus abdominis, pyramidalis, external oblique, internal oblique, and transversus abdominis muscles; the latter include the quadratus lumborum and the psoas muscles (major and minor).

Rectus abdominis muscle

(Fig. 64) is located anteriorly, immediately to the right and left of the abdominal midline. This muscle originates from the external surfaces of the V, VI, and VII costal cartilages and from the xiphoid process. It courses inferiorly to insert onto the superior margin of the pubic bone. Along its course, it features three or four transverse tendinous intersections (inscriptiones tendineae), with two located above the umbilicus, one at the umbilical level, and one below it. These represent remnants of the segmented body structure that is prominently expressed in the thoracic region.

The functions of the rectus abdominis are diverse. It restrains intra-abdominal pressure, assists in forming the abdominal press, acts as a flexor of the vertebral column during overcoming (concentric) work, pulls The thoracic cage downward, lowers the ribs, and thus aids in expiration.

This muscle possesses a considerable cross-sectional area, a high lifting capacity, and a large leverage relative to the transverse axes of Rotation of the vertebral column, making it the primary flexor of the spine.

Fig. 64. Muscles of the abdomen (deep layer):

1 — tendinous intersection of rectus abdominis m.; 2 — rectus abdominis m.; 3 — umbilicus; 4 — internal oblique abdominis m.; 5 — pyramidalis m.; 6, 15 — anterior lamina of rectus sheath; 7 — femoral m.; 8 — posterior wall of Inguinal Canal; 9 — sartorius m.; 10 — Spermatic Cord (cut); 11 — inguinal ligament; 12 — fascia lata; 13 — anterior superior iliac spine; 14 — transversalis fascia; 16 — arcuate line; 17 — aponeurosis of transversus abdominis m.; 18 — site of division of internal oblique aponeurosis into anterior and posterior laminae; 19 — transversus abdominis m.; 20 — posterior lamina of rectus sheath; 21 — external intercostal mm.; 22 — internal intercostal mm.; 23 — serratus anterior m.; 24 — rectus abdominis m. (cut) (after G. F. Ivanov)

When the upper torso is fixed, contraction of the rectus abdominis results in elevation of the pelvis, which is particularly evident during the execution of the L-sit exercise.

Since this Muscle consists of several segments with independent innervation, it does not necessarily contract as a whole; rather, its upper, middle, or lower portions can contract in isolation. However, achieving such isolated contraction requires systematic training.

The rectus abdominis is clearly visible and readily palpable beneath the skin. During isolated contraction of this muscle—especially when the remaining abdominal wall muscles are relaxed and drawn in—it stands out very sharply subcutaneously.

The rectus abdominis is enclosed within a sheath formed by the aponeuroses of the oblique and transverse abdominal muscles. The sheath comprises two laminae: anterior and posterior. In the upper two-thirds, the anterior lamina is formed exclusively by the aponeurosis of the external oblique and the anterior leaf of the internal oblique aponeurosis, whereas the posterior lamina is formed by the aponeurosis of the transversus abdominis and the posterior leaf of the internal oblique aponeurosis.

In the lower third of the rectus abdominis muscle, the aponeuroses of the oblique and transverse abdominal muscles pass to its anterior surface, forming the anterior wall of the rectus sheath. Consequently, in its lower third, the rectus abdominis lacks a posterior sheath wall, with its posterior surface covered solely by the transversalis fascia. The function of the rectus sheath is to stabilize the muscle, enabling its maximum participation in trunk movements, particularly flexion and lateral bending. Furthermore, the rectus sheath helps reinforce the anterior abdominal wall, which is formed by all the abdominal muscles.

The pyramidalis muscle (see Fig. 64) is triangular in shape. It lies adjacent to the midline, extending from the anterior surface of the superior ramus of the pubis to the linea alba. It acts to tense the linea alba. The pyramidalis is inconstant and may be absent.

The external oblique muscle (see Fig. 37) is a thin, broad, flat muscle. It originates via individual slips from the eight lower ribs and the iliac crest. Its five upper slips interdigitate with those of the serratus anterior, while its three lower slips interdigitate with the latissimus dorsi. The fibers of the external oblique run anteroinferiorly. Most of the muscle fibers continue into an aponeurosis that contributes to the Formation of the anterior wall of the rectus sheath, the linea alba, the anterior wall of the inguinal canal, and the inguinal ligament. Via the linea alba, it connects with the contralateral external oblique aponeurosis.

The inferior margin of the aponeurosis is thickened to form the inguinal ligament, which extends from the anterior superior iliac spine to the pubic bone.

The functions of the muscle include pulling the rib cage downward, assisting in the flexion of the vertebral column and its rotation in the opposite direction. When the rib cage is fixed, this muscle draws the pelvis toward it by flexing the vertebral column, as, for example, during the L-sit exercise.

In certain areas, the fiber orientation of the muscles corresponds to that of the contralateral muscles.

The internal oblique muscle (see Fig. 64) is a broad, flat, and thin muscle located almost entirely beneath the external oblique. It originates from the thoracolumbar fascia, the iliac crest, and partially from the inguinal ligament. Its fiber direction varies: the posterior fibers run superiorly, the middle fibers run anteriorly, and the inferior fibers run anteroinferiorly. The middle and lower muscle fascicles transition into an aponeurosis that helps form the rectus sheath and the linea alba. The posterior fascicles attach to the lower three ribs.

The function of the muscle is to flex the vertebral column, pull the rib cage downward, and rotate the trunk toward the side of the contracting muscle. When the upper half of the trunk is fixed, the muscle elevates the pelvis, flexing the vertebral column.

The transversus abdominis muscle (see Fig. 64) is broad, thin, and flat. Superficially, it is covered by the internal and external oblique muscles, while in its anterior region, it is partially covered by the rectus abdominis.

The transversus abdominis originates from the inner surface of the cartilages of the lower six ribs, the thoracolumbar fascia, the iliac crest, and the inguinal ligament. Its muscular portion transitions into a tendinous one.

The aponeurosis of the muscle passes posterior to the rectus abdominis in its upper two-thirds, and anterior to it in the lower third. Like the preceding two muscles, it participates in forming the rectus sheath and the linea alba.

The inferior fibers of the muscle run not only transversely but also descend inferiorly, attaching to the pubic bone.

The function of the upper part of the muscle, which runs transversely between the costal cartilages of the lower ribs on the right and left sides, is to approximate these ribs, thereby assisting in expiration. The muscle as a whole restrains intra-abdominal pressure, acting like an elastic corset. The middle portion encircles the central abdominal region, largely determining its shape.

The lower fascicles of the internal oblique and transversus abdominis detach to form the small cremaster muscle, which travels within the spermatic cord into the Scrotum.

The quadratus lumborum lies lateral to the bodies of the lumbar vertebrae and anterior to the thoracolumbar fascia. The muscle has the shape of an irregular, vertically elongated quadrilateral. It originates from the ilium and the transverse

processes of the lower lumbar vertebrae, and inserts into the XII rib and the transverse processes of the upper lumbar vertebrae. The muscle depresses this rib and laterally flexes the vertebral column.

The abdominal press. The abdominal press comprises the muscles that bound the abdominal cavity: the muscles of the anterolateral abdominal wall (rectus abdominis, external and internal obliques, transversus abdominis), quadratus lumborum, diaphragm, and pelvic floor muscles.

The function of the abdominal muscles is diverse and complex. Excluding the quadratus lumborum, all of them act as flexors of the vertebral column, antagonizing the muscles located on its posterior surface. When the abdominal muscles contract simultaneously with the back muscles on one side of the body, lateral flexion of the trunk occurs. Because the oblique fibers run diagonally, these muscles also participate in twisting the vertebral column and the entire trunk around its vertical axis.

Fig. 65. Diagram of the coordinated contraction of individual fascicles of the right external oblique and left internal oblique abdominal muscles. Acting in synergy, these muscle fascicles facilitate the rotation of the trunk to the left around its vertical axis

During this movement, the external oblique works in concert with the contralateral internal oblique (Fig. 65).

When the upper part of the trunk is fixed, the abdominal muscles flex the pelvis or laterally tilt it (for example, during many gymnastic exercises on the high bar, parallel bars, pommel horse, as well as in pole vaulting, etc.).

By pulling the rib cage downward, the abdominal muscles facilitate its depression and, consequently, expiration. Furthermore, by contracting together with all the muscles that enclose the abdominal cavity—particularly the diaphragm—they increase intra-abdominal pressure, which is observed during straining. They stabilize the position of the abdominal viscera and the trunk, which is essential during Physical Exercise, aid in the evacuation of internal hollow organs (Urinary Bladder, rectum), and additionally play a vital role in childbirth in women.

Connective Tissue structures of the abdominal muscles

In the abdominal region, the superficial fascia is well-developed, covering the exterior of the abdominal muscles. In the inferior region, it divides into two layers—superficial and deep—between which the subcutaneous vessels pass.

The proper fascia of the abdomen is divided into several layers corresponding to the muscles that form the abdominal wall. In the area of the superficial ring of the inguinal canal, it continues onto the cremaster muscle. Inferiorly, this fascia attaches to the inguinal ligament and the iliac crest.

The deep lamina of the proper fascia of the abdomen lines the inner surface of the transversus abdominis muscle and is termed the transversalis fascia. This fascia forms part of the internal abdominal fascia, which lines the entire abdominal cavity from within and is known as the endoabdominal fascia.

Areas of least resistance in the abdominal wall. The fibers of the abdominal muscles run in vertical (rectus abdominis), oblique (oblique muscles), and transverse (transversalis muscle) directions. Although the abdominal wall is relatively thin, muscle fiber Separation is generally absent, except in those regions of the abdominal wall that offer the least resistance to intra-abdominal pressure. These areas include the linea alba, the umbilical ring, the inguinal and femoral canals, the floor of the lesser pelvis, and, in some cases, the diaphragm. The first three structures are of the greatest practical significance.

The linea alba is a connective tissue structure extending from the tip of the xiphoid process to the pubic symphysis. It is formed by the convergence and interweaving of the aponeurotic fibers of all abdominal muscles. The linea alba reinforces the position of the abdominal muscles, serves as the attachment site for the pull of the transversus abdominis and partially the oblique muscles, and integrates the muscles of the right and left sides of the abdomen into a single functional unit.

The umbilical ring, located along the linea alba, is the site where the umbilical cord passes through the abdominal wall in the fetus. Some separation of the connective tissue fibers may occur here. Occasionally, this separation is so pronounced that an opening forms in the linea alba through which the Peritoneum and intestinal loops can protrude beneath the skin (umbilical hernia).

The inguinal canal (see Fig. 64) is a slit-like passage between the abdominal muscles in the lower abdomen. In males, the canal transmits the spermatic cord, while in females, it transmits the round ligament of the Uterus.

The inguinal canal has four walls and two openings. The anterior wall is formed by the aponeurosis of the external oblique muscle of the abdomen, the inferior wall by the inguinal ligament, the superior wall by the lower edge of the internal oblique and transversus abdominis muscles, and finally, the posterior wall by the transversalis fascia.

The superficial opening of the inguinal canal, or the superficial inguinal ring, is formed by the division of the aponeurosis of the external oblique abdominal muscle into two crura: a medial crus attached to the pubic symphysis, and a lateral crus attached to the pubic tubercle. The deep opening of the inguinal canal, or the deep inguinal ring, has indistinct margins. It is a depression in the transversalis fascia of the abdomen and is sharply demarcated only on its medial side.

The femoral canal is the space bounded by the inguinal ligament, the pubic bone, and the femoral vein, which is normally filled with loose connective tissue. Under pathological conditions, internal organs (greater omentum, loops of the Small Intestine) may pass through it onto the thigh.

Protrusions through the abdominal wall above the inguinal ligament are called inguinal hernias, whereas those below the inguinal ligament are called femoral hernias. The appearance of inguinal hernias is typically preceded by the enlargement of the superficial inguinal ring. Such protrusions occur due to a combination of internal and external factors (insufficient tone and elasticity of the connective tissue structures along the inguinal canal, and excessive strains causing a sharp increase in intra-abdominal pressure). With good abdominal wall tone, even very strong muscular exertion (such as lifting heavy loads) does not lead to hernia formation. Conversely, in individuals with poor tissue tone, particularly in the elderly, separation of the abdominal wall layers and the formation of protrusions occur in the absence of any significant physical strain. Physical exercises enhance the Elastic properties of the inguinal canal walls, thereby increasing their resistance to intra-abdominal pressure and preventing The Development of hernias.

Lateral flexion of the vertebral column

Lateral bending of the vertebral column occurs According to the parallelogram of forces rule during the simultaneous contraction of the flexors and extensors on that side. They are assisted by the unilateral action of:

1) the levator scapulae muscle (with a fixed scapula) (see p. 150);

2) the quadratus lumborum muscle (see p. 210);

3) the intercostal muscles (see p. 221);

4) the intertransversarii muscles (see p. 202).

Rotation of the vertebral column

Rotation of the vertebral column around its longitudinal axis, or twisting, is primarily performed by the following muscles when acting unilaterally:

1) the sternocleidomastoid muscle, which rotates and elevates the head to the opposite side (see p. 150); it is assisted, when the hyoid bone is fixed, by the stylohyoid muscle (see p. 205);

2) the upper part of the trapezius muscle, which has a slight rotational component directed to the opposite side (see p. 148);

3) the scalene muscles (see p. 206) together with the contralateral levator scapulae muscle (see p. 152), which form a force couple that rotates the Head and Neck;

4) the external oblique abdominal muscle acting in concert with the contralateral internal oblique muscle (see p. 210);

5) the rotatores muscles (see p. 201) located between the spinous and transverse processes, assisted by other deep back muscles;

6) the iliopsoas muscle (with a fixed Femur) (see p. 174).

It should be noted that during the rotation of the vertebral column, and consequently the entire trunk, simultaneous contraction may occur between the ipsilateral extensors and contralateral flexors, whose vector components form a force couple.

Circular motion of the vertebral column

Circular movement of the vertebral column (circumduction) occurs through the sequential engagement of all muscle groups of the torso that perform extension, flexion, lateral bending, and rotation. This movement can be performed by the upper spine while standing, with the lower spine, pelvis, and lower limbs fixed, or by the lower spine—for example, while hanging by the hands—with the upper spine fixed.