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TRAPEZIUS
- This article is about the human skeletal muscle. For the trapezius muscles found in cats, see trapezius muscles (cat).
In human anatomy, the trapezius is a large superficial muscle on a person's back.
Trapezius gets its name from its trapezium-like shape; the corners being the neck, the two shoulders, and the thoracic vertebra, T12.
A person can feel trapezius on themselves by holding a weight in front of them in one hand, and with the other, touching between the shoulder and the neck. They should feel a sheet of muscle become active.
Its muscle fibers at the neck run downward and laterally towards the arm. The fibers from the vertebrae run upward, also towards the shoulder.
Because the fibers run in different directions, it has a variety of actions. It elevates, retracts, adducts and rotates the scapula. The superior fibers elevate the scapula, the middle fibers retract it, and the inferior fibers depress it. When the superior and inferior fibers act together they superiorly rotate the scapula.
The functions of the Trapezius muscle include scapular elevation (shrugging up), scapular adduction (drawing the shoulder blades together) and scapular depression (pulling the shoulder blades down).
The word "Spinotrapezius", when applied to humans, refers to the trapezius, although it not commonly used in modern texts. In other mammals, it refers to a portion of the analogous muscle. See trapezius muscles (cat) for more details.
The trapezius can be developed using shoulder shrugs.
Anatomical details
The Trapezius (Fig. 409) is a flat, triangular muscle, covering the upper and back part of the neck and shoulders. It arises from the external occipital protuberance and the medial third of the superior nuchal line of the occipital bone, from the ligamentum nuchæ, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebræ, and from the corresponding portion of the supraspinal ligament. From this origin, the superior fibers proceed downward and lateralward, the inferior upward and lateralward, and the middle horizontally; the superior fibers are inserted into the posterior border of the lateral third of the clavicle; the middle fibers into the medial margin of the acromion, and into the superior lip of the posterior border of the spine of the scapula; the inferior fibers converge near the scapula, and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. At its occipital origin, the Trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. At the middle it is connected to the spinous processes by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebræ, and forms, with that of the opposite muscle, a tendinous ellipse. The rest of the muscle arises by numerous short tendinous fibers. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corresponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra.
Variations.—The attachments to the dorsal vertebræ are often reduced and the lower ones are often wanting; the occipital attachment is often wanting; separation between cervical and dorsal portions is frequent. Extensive deficiencies and complete absence occur.
The clavicular insertion of this muscle varies in extent; it sometimes reaches as far as the middle of the clavicle, and occasionally may blend with the posterior edge of the Sternocleidomastoideus, or overlap it.
External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.
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