Ascending part of trapezius muscle

At a glance

English

Ascending part of trapezius muscle

Latin (TA2)

Pars ascendens musculi trapezii

System

Muscle

Region

Neck

Side

Paired, left and right

About the ascending part of trapezius muscle

Trapezius is the large, flat, diamond-shaped muscle of the upper back and neck. It has three functional parts named by fibre direction: a descending upper part, a transverse middle part and an ascending lower part. The ascending part is the triangular lower region, whose fibres rise from the middle of the back towards the shoulder blade. It lies just under the skin and covers the lower rhomboid and part of latissimus dorsi.

These fibres arise from the tips of the spinous processes of roughly the fourth to the twelfth thoracic vertebrae and from the supraspinous ligament between them. They pass upwards and outwards, converge, and end in a flat aponeurosis. This glides over the smooth triangular area at the inner end of the scapular spine, a small bursa often lying between them, and attaches to a tubercle at the outer tip of that area.

Acting on the scapula, the ascending fibres pull its medial end downwards and so depress and retract the shoulder blade. Their most important role is in upward rotation: working as a couple with the descending part and serratus anterior, they swing the glenoid cavity upwards, which is needed to raise the arm above shoulder height. They also hold the scapula steady against the chest wall in throwing and overhead pressing. Motor supply comes from the accessory nerve; fibres from the third and fourth cervical ventral rami carry pain and position sense.

Weak lower trapezius lets the scapula ride up and tilt, giving altered scapular movement and sometimes a winged appearance, often with pain about the shoulder. Damage to the accessory nerve during neck surgery or lymph node biopsy weakens the whole muscle, with a drooping shoulder and difficulty lifting the arm overhead. In facioscapulohumeral muscular dystrophy the lower and middle fibres tend to weaken first. Drawing the shoulder blades down with straight arms trains this part.

Attachments, action and supply

Origin

Spinous processes of about T4 to T12 and the intervening supraspinous ligament.

Insertion

Tubercle at the medial end of the scapular spine, via an aponeurosis gliding over the smooth triangular area.

Action

Depresses and retracts the scapula and, with the upper fibres and serratus anterior, rotates it upwards.

Nerve supply

Accessory nerve (CN XI) for movement; C3 and C4 ventral rami for sensation and proprioception.

Blood supply

Transverse cervical artery, with contributions from the dorsal scapular and posterior intercostal arteries.