Scalene Muscles

The scalene muscles (Fig. 8.7) normally consist of three muscles: the scalenus anterior, scalenus medius, and scalenus posterior. Sometimes, a fourth muscle is present, the scalenus minimus. In most cases, though, it does not exist but is replaced by vertebropleural ligaments.

The scalenus anterior originates at the transverse processes of C3-C6 and attaches to the first rib, at the scalene tubercle.

Temporal bone

Occiput

Sternocleidomastoid Muscle Attaches

Clavicles Sternum

Fig. 8.6 Sternocleidomastoid muscle.

Clavicles Sternum

Temporal bone

Occiput

Fig. 8.6 Sternocleidomastoid muscle.

Muscle Attachment First Rib
Fig. 8.7 Scalene muscles.

The scalenus medius originates at the transverse processes of C2-C7, to attach caudally at the first rib.

Between these two scalene muscles, we find the scalene hiatus or the "thoracic inlet," through which the subclavian artery and the brachial plexus pass. A spasm of the scalene muscles can irritate these structures.

The scalenus posterior attaches at the posterior tubercles of the transverse processes of C4-C6 and extends to the second rib.

The scalenus minimus, lastly, originates cranially at the anterior tubercles of the last two cervical vertebrae and runs to the pleural dome. The scalene muscles tend to spasms, but can also be affected by shortening and fibrosis. This depends on function. Trigger points can imitate the symptoms of neuralgia of the median nerve. The scalene muscles do for the CSC what the iliopsoas does for the LSC. They are primarily for bending the CSC, but can also assist in forming lordosis, if necessary. This ambivalent function perhaps explains their susceptibility to spasms.

Together with the longus capitis and longus colli, the scalene muscles belong to the prevertebral muscles. They are enclosed by the deep neck fascia and part of the Sibson's fascia that forms the upper thoracic diaphragm. As such, they have a connection to the central tendon and the visceral compartment.

Functions

Bilateral

• The frontal scalene muscles can flex the CSC.

• Together, they stabilize the CSC in the frontal plane.

• They are important muscles for inhalation. Electromyographic studies have shown that they become active together with the diaphragm. By pulling the upper thoracic aperture and therefore the pleural dome upward, they prevent the diaphragm from pulling the lungs caudally during inhalation. They are responsible for high thoracic respiration.

Unilateral

• Ipsilaterally, the scalene muscles are sidebenders of the CSC.

Innervation

Still said something like this about the diaphragm (Fig. 8.8): "Through you, we live, and through you, we die" (Still's biography140). This is all the more true because the diaphragm in fact influences all vital functions:

• The gas exchange in the lungs is regulated by changes in pressure during inhalation and exhalation.

Cellular metabolism is also activated by the pressure changes that induce respiration. During inhalation, a centrifugal pressure is created that is counteracted by the peripheral muscles. This produces rhythmic pressure changes that influence diffusion and osmosis. Inhalation sucks the blood towards the thorax. The abdominal organs are compressed; the venous sinuses of the skull and the neck veins are widened.

• The upward and downward movement of the diaphragm mobilizes all the organs in a rhythmic fashion, around their physiological movement axes.

• If necessary, the diaphragm assists in matters of posture. Changes in pressure conditions in the abdomen and chest can modulate the posture of the spinal column. Thereby, it can provide stability for the trunk and at the same time facilitate the movements of the extremities.

• Also of importance are the vascular and neural structures that pass through the diaphragm.

Because of its numerous functions, the diaphragm is in a dysfunctional state in every patient. The diaphragm separates the thoracic from the abdominal cavity and consists of two parts:

Muscle Scal
Fig. 8.8a, b Diaphragm.

• A fibrous part, the central tendon, to which organs attach

• A peripheral muscular part, which is responsible for its movements

The muscular part has attachments on the five last ribs and first three lumbar vertebrae. Nerves, vessels, and organs pass through openings of the diaphragm. The muscle fibers roughly run a course from cranial medial to caudal lateral, from the central tendon to the periphery.

Innervation

• Sensory: the central tendon is supplied by the two phrenic nerves, just like the dorsal part of the muscular part.

• The lateral muscle part is supplied sensorily from the segments T7 toTlO.

Respiratory Movement and its Influence on the Locomotor System

The following muscles participate in respiration: Inhalation

• Primary inhalatory muscles:

- diaphragm

- scalene muscles

In rest position, only these two muscles are normally active.

• Accessory respiratory muscles:

- trapezius

- pectoralis major

— pectoralis minor

— quadratus lumborum

— serratus anterior

— long back stretchers

— intercostal muscles

The recruitment of these muscles depends on the depth of inhalation. First to be recruited are the intercostal muscles, from cranial to caudal.

During inhalation, the crus of the diaphragm pulls the central tendon down. This lowers the pressure in the chest, which leads to the inhalation of air. At the same time, pressure is increased in the abdomen and thereby also on the abdominal wall. These changes are proportional to the depth of inhalation.

The central tendon is moved downward until it is checked by pressure in the abdomen. After that, the costal fibers of the diaphragm pull the ribs upward. The thorax with sternum is raised. The diaphragm is supported in this process by the scalene muscles. The intercostal muscles stabilize the ribs against each other. In deeper inhalation, the other inhalatory muscles are also utilized.

The spinal column must be stabilized in order to lift the chest and widen the ribs. This is done by the iliopsoas and quadratus lumborum in the LSC and by the long back stretchers in the thoracic region.

The quadratus lumborum and the iliopsoas additionally stabilize the last two ribs and the upper LSC, by which the crus of the diaphragm gains a stable support.

Busquet Muscular Chains
Fig. 8.9a-c a, b Movements of the peripheral bones during inhalation, c Movements of the trunk skeleton during inhalation.

The shoulder blade fixators stabilize the scapula and give the serratus anterior and pectoral muscles the opportunity to raise the ribs.

The scalene muscles extend the cervical spinal column. At the end of a deep inhalation, the SCM is activated. It pulls the sternum up and prevents a flexion of the occiput, so that the gaze can continue to be directed straight ahead.

The abdominal muscles work eccentrically. They control the descent of the abdominal organs.

What happens to the pelvis, the cranium, and the extremities during inhalation? (See Fig. 8.9.)

The downward movement of the central tendon presses the abdominal organs downward and forward. This exerts pressure on the pelvic floor and abdominal muscles. The pressure on the pelvic floor pulls the pubic branches backward, the apex of the sacrum with the coccyx forward, and the ischiadic tubers medially. This pulls the iliac wings forward and outward. The pull of the pelvic floor on the coccyx mobilizes the basis of the sacrum dorsally into a contranu-tation. These movements are supported by the iliopsoas, which pulls the LSC into flexion and presses the pubic branches backward.

The pelvis also makes a movement, as we have described for the extension pattern. This conforms to the flexion movement of the craniosacral rhythm.

The lower extremities make a flexion-external rota-tion-abduction movement. The extension of the CSC and adduction of the shoulder blades rotate the shoulder joint outward. The flexion-abduction-exter-nal rotation of the shoulders is facilitated.

During inhalation, the upper thoracic aperture is raised. The cervical fascia is tightened like the roof of a tent. This pulls the temporal bones into external rotation. The SCM and trapezius muscles pull the occiput into extension, which corresponds to a craniosacral flexion.

The nuchal ligament supports these efforts passively. The extension of the CSC makes it taut. One way to avoid this pull is to pull the back of the head forward and downward, that is, into the cranial flexion.

The downward movement of the diaphragm and the resulting tension on the central tendon is neutralized by the elevation of the chest. This allows the SBS to move cranially.

Inhalation thus completely matches the flexion pattern of the PRM as described by Sutherland. The flexion stage is, like inhalation, an active stage. Exhalation is the opposite: a passive stage.

Exhalation

• The exhalation stage in rest is normally a passive process, in which the elasticity of the tissue returns the structures to their original position.

• In deep exhalation, it is mostly the abdominal muscles that are active. For some authors, the internal intercostal muscles are exhalatory muscles, as well as the transversus thoracis (Basmajian).

The diaphragm and the scalene muscles relax, just like the accessory respiratory musculature after having been activated in deep inhalation. In deep exhalation, the abdominal muscles become active. The content of the abdomen is compressed and pushed upward, while the chest is simultaneously pulled caudally.

In the ISJ, a posterior rotation of the ilium with an in-flare occurs. The extremities make an internal rotation. The exhalatory position of the chest, via the ribs, pulls the upper TSC into flexion and the CSC into lordosis. The skull bones return into their original position. Compared with the position during inhalation, this corresponds to an extension-internal rotation. The position of the occiput corresponds to that of the sacrum.

Note: It is noteworthy that the head remains horizontal in both inhalation and exhalation. In our opinion, this is due to the associated action of the SCM, trapezius, and suboccipital muscles.

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Responses

  • gilly
    Is scaleni important for the inhalation?
    4 years ago
  • connie
    Which muscle helps to stabilize the ribs against the pull of the diaphragm during the exhalation?
    3 years ago

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