Muscular system · Upper limb

Upper trapezius !

The upper trapezius runs from the neck to the top of the shoulder; it shrugs the shoulder and helps rotate the shoulder blade upward.

Official name: Trapezius, upper (descending) part

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What it is

The upper part of the large diamond-shaped muscle of the upper back and neck.

What it does

Shrugs the shoulder and helps rotate the shoulder blade upward.

Key facts

Origin

External occipital protuberance, superior nuchal line, nuchal ligament

Insertion

Lateral third of the clavicle

Action

Elevates and upwardly rotates the scapula; extends and side-bends the neck

Nerve

Accessory nerve (CN XI); C3–C4 (proprioception)

Blood supply

Transverse cervical artery, occipital artery

Relations

Superficial

Skin of the nape and top of the shoulder; the investing layer of deep cervical fascia splits to enclose it

Deep

Splenius capitis, semispinalis capitis and levator scapulae; the accessory nerve and the superficial branch of the transverse cervical artery run on its deep surface

In front

The posterior triangle of the neck, with the sternocleidomastoid as its front border; the triangle holds CN XI, the trunks of the brachial plexus and the lymph nodes of the posterior neck

Below

The lateral third of the clavicle, where it inserts opposite the origin of the front deltoid; below the C7 level it continues as the middle trapezius

How to find it

With the person seated and the examiner behind, a shrug against downward pressure on both shoulders makes it stand out as the sloping ridge from the base of the skull to the outer end of the clavicle. Comparing both sides shows a droop or loss of bulk.

Examination

• Resisted shrug: weakness or a lower, flatter shoulder on one side points to an accessory nerve (CN XI) lesion; normal head turning with a weak shrug places the lesion below the branch to the sternocleidomastoid, as in the posterior triangle

On imaging

Ultrasound and MRI show it as a thin sheet over the back of the neck and shoulder. After accessory nerve injury, often from surgery or a biopsy in the posterior triangle, CT or MRI shows the muscle thin and fatty compared with the other side. Ultrasound can follow the nerve in the posterior triangle; electromyography confirms denervation.

Clinical notes

• The accessory nerve can be cut during a lymph node biopsy or a neck dissection in the posterior triangle: the shoulder droops and aches, the arm cannot be raised fully to the side and the scapula wings laterally
• Neck dissections that spare CN XI were developed to avoid this painful 'shoulder syndrome'
• Scapular dyskinesis often shows an overactive upper trapezius (the shoulder hikes up as the arm rises) with weak lower trapezius and serratus anterior

Anatomical variants

• Rare: absence or underdevelopment of part of the muscle, and accessory slips

Development

The trapezius and sternocleidomastoid grow from one premuscle mass in the occipital region, just behind the last pharyngeal arch; the accessory nerve enters it early and is carried down as the mass spreads to the shoulder girdle and spine.

Related conditions

• Tension-type headache
• Acromioclavicular joint separation
• Winged scapula

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2)

pars descendens musculi trapezii TA2 2227

Official Spanish (DeCS)

Porción descendente del músculo trapecio

English (TA2)

Trapezius, upper (descending) part

Related

• Clavicle

Sources: Terminologia Anatomica (TA2); Anatomy, Back, Trapezius; Anatomy of the Human Body (20th ed.): Development of the Muscles (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.