The scalenus anterior muscle together with a total of three paired scalene muscles belongs to the deep neck muscles. It arises from the cervical vertebrae 3 to 6 (C3-C6) and slopes diagonally to the 1st rib. The scalenus anterior muscle performs three main mechanical tasks, it is involved in lateral flexion and rotation of the neck, and in its function as a respiratory aid muscle in the elevation of the first rib.

What is scalenus anterior muscle?

The scalenus anterior muscle, like the other two scalenus muscles, is paired and belongs to the deep neck muscles. The German term "anterior rib support muscle" indicates its function as a respiratory aid muscle.

The muscle originates from the cervical vertebrae C3 to C6 and pulls obliquely sideways to the first rib, so that when bilateral contraction and fixation of the cervical spine a pull on the first rib is exerted, so that the rib and thus the thorax lift. This means that the process of inhalation is supported. Between the scalenus anterior muscle and the scalenus medius muscle, ie, between the anterior and the medial rib support muscles, there is a triangular gap, the scalenus gap, through which nerves and blood vessels run. Among other things runs through the Skalenusl├╝cke the Arteria subclavia.

It is an important, paired body artery, of which the left branch originates directly from the aortic arch and the right branch originates from the trunk with the right cervical artery (brachiocephalic trunk). branches. The two arteries supply the head, neck, shoulders and arms with oxygen-rich blood. The nerves that run through the scalenus gap originate from the brachial plexus, whose branches innervate the arms, shoulders and chest.

Anatomy & Construction

The musculus scalenus anterior, the anterior rib-retaining muscle, corresponds in anatomical structure to the skeletal musculature. Its muscle tissue consists mainly of striated, red muscle, which has a high content of myoglobin, because the muscle is often exposed to continuous loads.

The skeletal musculature is characterized by the fact that the force required for the contraction of the muscle fibers can be infinitely dosed by appropriate nerve impulses. Another characteristic feature is that the tension of the skeletal muscles is largely subject to volitional control. The scalenus anterior requires a good abutment to perform its primary function of elevating the first rib or the entire thorax. It therefore fans out at the upper end, so that on contraction, the unilateral tensile load is distributed among the four cervical vertebrae C3 to C6 and the problem of herniated disc in the cervical region is minimized.

At the lower end, the two rib support muscles have grown on specially designed small tuberosities (tubercles) on the first costal arch (tuberculum musculus scalenus anterior). The sensory and motor innervation occurs through spinal nerve branches, which emerge from the spinal canal between the cervical vertebrae C5 to C7.

Function & Tasks

One of the main tasks of the two scaleni anterior muscles is the active support of breathing. Simultaneous contraction of the two anterior rib support muscles pulls the ribs upwards. As a result, the chest area expands, so that the inhalation is supported. In other functions, the two muscles significantly support a lateral neck flexion and a lateral rotation in the horizontal plane.

Cervical dislocations to the right or left and head turns to the right or left can be achieved by a one-sided contraction of the right or left scalenus anterior muscle. In addition to the motor tasks, the two anterior rib support muscles take on a protective function. Due to its oblique course from the first costal arch to the cervical vertebrae, a triangular space is created between the scalenus medius and the scalenus gap. It is used to conduct and protect important blood and nerve vessels that supply the head, shoulders and arms with oxygen-rich blood or innervate them sensory and motor.

Diseases

Chronic stress or other causes of hardening of the anterior or medial ribs of the spine may result in narrowing of the esophageal scab, putting pressure on the subclavian artery or on the nerve fibers of the plexus brachial plexus (nerve compression).

The narrowing of the gap between the scalenes leads to the so-called scalene syndrome, which can be manifested by pain in the forearm or paresthesia on the hand. Symptoms such as tingling, numbness and cold feeling are also typical companions of a scalene syndrome. If the subclavian artery is also compressed, it will result in poor blood supply and, in many cases, even fall in blood pressure. Similar symptoms are caused by thoracic outlet syndrome, also known as shoulder girdle compression syndrome, in which nerve fibers, the main artery and the major vein (subclavian vein) are equally affected by compression.

As a trigger for the bottlenecks, inter alia, an enlargement (hypertrophy) of the scalenus anterior muscle in question. Excessive contraction of the anterior rib retaining muscle can cause a hyperadductive syndrome, manifesting in a strong elevation of the uppermost rib to which the muscle has grown. In the course of this, too, there is a compression of the nerves with comparable symptoms as described above. The complaints usually occur at night, with women being affected more frequently than men.

The fact that nerve compression in the neck area leads to paresthesia and paralysis on the arms and shoulders makes use of modern anesthesia in surgical procedures in the shoulder area and on the arms. In a regional anesthetic procedure, the brachial plexus is anesthetized in the scalenus gap. The need for general anesthesia is eliminated.

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