Trapezius muscle

Trapezius
trapezius
muscles connecting the upper extremity to the vertebral column; trapezius is labeled at upper left.
Latin	musculus trapezius
Gray's	subject #121 432
Origin	external occipital protuberance, nuchal ligament, medial superior nuchal line, spinous processes of vertebrae C7-T12
Insertion	posterior border of the lateral third of the clavicle, acromion process, and spine of scapula
Artery	transverse cervical artery [1]
Nerve	accessory nerve (motor) cervical spinal nerves C3 and C4 (motor and sensation)
Actions	rotation, retraction, elevation, and depression of scapula
Antagonist	serratus anterior muscle, Latissimus dorsi

In human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula (shoulder blade). Its functions are to move the scapulae and support the arm.

The trapezius has three functional regions: the superior region (descending part), which supports the weight of the arm; the intermediate region (transverse part), which retracts the scapulae; and the inferior region (ascending part), which medially rotates and depresses the scapulae.

Terminology

The two trapezius muscles together resemble a trapezoid (trapezium in British English), or diamond-shaped quadrilateral. The word "spinotrapezius" refers to the human trapezius. The trapezium group is also referred to as the tri-axle back plate, although this is not commonly used in modern texts. In other mammals, it refers to a portion of the analogous muscle.

Anatomy

The Trapezoic arises from the external occipital protuberance and the medial third of the superior nuchal line of the occipital bone (both in the back of the head), from the ligamentum nuchae, the spinous process of the seventh cervical (both in the back of the neck), and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament (both in the upper back).

From this origin:

• the superior fibers proceed downward and laterally. They are inserted into the posterior border of the lateral third of the clavicle.
• the inferior fibers proceed upward and laterally. They 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.
• the middle fibers proceed horizontally. They are inserted into the medial margin of the acromion, and into the superior lip of the posterior border of the spine of the scapula.

At its occipital origin, the trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. The superficial and deep epimysia are continuous with an investing deep fascia that encircles the neck and also contains both sternocleidomastoid muscles.

At the middle, the muscle 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.

Innervation

Motor functions are supplied by the accessory nerve (CN XI) and the ventral rami of the third (C3) and fourth (C4) cervical nerves. Sensation, including pain and proprioception, travel via the C3 and C4 ventral rami. Since it is a muscle of the upper limb, the trapezius is not innervated by dorsal rami despite being placed superficially in the back.

It is possible to feel the muscles of the superior trapezius become active by holding a weight in one hand in front of the body and, with the other hand, touching the area between the shoulder and the neck.

Exercise

The upper portion of the trapezius can be developed by elevating the shoulders. Common exercises for this movement are shoulder shrugs and upright rows. Middle fibers are developed by pulling shoulder blades together. The lower part can be developed by drawing the shoulder blades downward while keeping the arms almost straight and stiff. It is mainly used in throwing, with the muscles called deltoids.

Muscle imbalances, which can heavily affect posture and compromise shoulder health, can result if all three sections of the trapezius are not developed equally.^[2]

References

External links

Superficial Back Dissection Video showing trapezius

• LUC trapezius
• Trapezius (anatomy) at GPnotebook
• Muscles/TrapeziusUpper at exrx.net

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.