Trapezius

Naming: -

/tra-PEE-zee-us/

From the name we get the shape of the muscle is like a trapezoid.

General: -

It is a flat, large superficial muscle located on the upper most part of the back and the lower neck, from the skull and the spine and surrounding the pectoral girdle. It is an irregular box hence the name trapezius. It is a three-fiber muscle so it has three different movement.

Supply: -

-Blood supply of the trapezius comes from The Transverse Cervical Artery (a branch of the Thyrocervical Trunk) and the Dorsal Scapular Artery (a branch of the Subclavian Artery).

-Nerve supply is from Spinal Accessory Nerve (CN XI) and C3, C4.

Origin & Insertion: -

-Origin: The attachment runs from the medial 1/3 of the superior nuchal line and goes to occipital protuberance of the occipital bone, the ligamentum nuchae, the spinous processes of C7 to T12 each and the intervening supraspinous ligament. The majority of this attachment is by direct muscular slips; however, a triangular aponeurosis is in the trapezius between C6 and T3 which makes to a hollow aspect on the average person.

-Insertion: a continuous line of attachment to the clavicle and scapula; the upper fibers run inferiorly and laterally, the middle fibers pretty much horizontally, and the lower fibers goes superiorly and laterally. The upper fibers go down to the posterior border of the lateral 1/3 of the clavicle, while the middle fibers go to the medial border of the acromion and upper border of the crest of the spine of the scapula, being off from the smooth area on the medial part of the spine by a tiny bursa. The lowermost fibers changes to a tendon which hang to the tubercle on the lower edge at the medial end of the spine of the scapula.

Motion & Action: -

( Elevates the scapula at the scapulocostal joint, Retracts the scapula at the scapulocostal joint, Upwardly rotates the scapula at the scapulocostal joint, Retracts the scapula at the scapulocostal joint Depresses the scapula at the scapulocostal joint )

The fibers of the trapezius are divided into three parts, which have different actions at the physiological scapulothoracic joint between the scapula and thoracic wall, Descending (superior) fibers elevate the scapula (e.g., when squaring the shoulders).
Middle fibers retract the scapula (i.e., pull it posteriorly). Ascending (inferior) fibers depress the scapula and lower the shoulder. Descending and ascending trapezius fibers act together in rotating the scapula on the thoracic wall in different directions, twisting it like a wing nut.
The trapezius also braces the shoulders by pulling the scapulae posteriorly and superiorly, fixing them in position on the thoracic wall with tonic contraction; consequently, weakness of the trapezius causes drooping of the shoulders

In The Field Notes: -

Testing the trapezius: the shoulder is shrugged against resistance (the person attempts to raise the shoulders as the examiner presses down on them). If the muscle is acting normally, the superior border of the muscle can be easily seen and palpated.

Clinical Note: -

Paralysis of trapezius: particularly its upper part, results in the scapula moving forwards around the chest wall with the inferior angle moving medially. The usually smooth curve of its upper border between the occiput and the acromion may become markedly angulated.

Trapezius hypertonicity and spasm is a common cause of tension headaches among the general population. Due to the path of the accessory nerve and occipital nerve, they can become entrapped, causing the classic ram's horn distribution of a tension headache. This headache is bilateral, throbbing, traveling from the occipital region, and wrapping around to the top of the head and forehead region.
Stress, posture, and inadequate stretching before activity can exacerbate these symptoms. There are no prodromal or sensorineural exacerbations related to light or sound. Tension headaches are often treated with a suboccipital release, stretching, stress/anxiety relief, and NSAIDs.

Relations: -

The entire trapezius is superficial in the neck and the back (except for the most anterior portion, which is deep to the platysma).
Directly deep to the trapezius in the neck are the semispinalis capitis, the splenius capitis, and the levator scapulae. Directly deep to the trapezius in the trunk are the supraspinatus, the rhomboids, and the most superior part of the latissimus dorsi.
Directly anterior to the anterior border of the trapezius
are the splenius capitis, the levator scapulae, and the scalene (in the posterior triangle of the neck).
The trapezius is located within the superficial back arm line myofascial meridian.

Sources: -

- Moore - Clinically Oriented Anatomy 7th Edition (701).
- Joseph E Muscolino - The Muscular System Manual: The Skeletal Muscles of the Human Body
Book 4t edition (96-100).
-Nigel Palastanga & Roger Soames Anatomy and Human Movement Structure and Function 6th edition (53-54).
- Anatomy, Back, Trapezius Jared Ourieff; Brent Scheckel; Amit Agarwal – NLH