Trapezius Lower (Ascending Part)
Back · Trunk
The ascending, or lower, part of the trapezius forms the lower triangle of the muscle over the mid and lower back. It arises from the spinous processes and supraspinous ligaments of T4 to T12 and its fibres run upward and laterally to converge on a tubercle at the medial end of the spine of the scapula. Because the fibres pull downward and inward on the scapular spine, they depress the scapula and, together with the upper fibres, rotate the glenoid cavity superiorly, forming a force couple that allows the arm to be raised fully overhead. Its motor supply is the accessory nerve (CN XI), with proprioception from the anterior rami of C3-C4.
Origin, Insertion, Action & Nerve
Origin
Spinous processes and supraspinous ligaments of T4–T12
Insertion
Tubercle at the medial end of the spine of the scapula
Action
Depresses the scapula and rotates the glenoid cavity superiorly
Nerve
Motor: accessory nerve (CN XI); proprioception: anterior rami of C3–C4
Attachments explained
The Trapezius Lower (Ascending Part) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Spinous processes and supraspinous ligaments of T4–T12
Insertion
Tubercle at the medial end of the spine of the scapula
Action & function
When the Trapezius Lower (Ascending Part) contracts, it produces the following movement: Depresses the scapula and rotates the glenoid cavity superiorly.
As part of the Back group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Trapezius Lower (Ascending Part) receives its nerve supply from the Motor: accessory nerve (CN XI); proprioception: anterior rami of C3–C4. This nerve carries fibres from spinal segment(s) C3, C4.
Because a muscle can only contract when its nerve is intact, injury to the Motor: accessory nerve or to its spinal roots (C3, C4) can weaken or paralyse the Trapezius Lower (Ascending Part), impairing the movements it normally produces (depresses the scapula and rotates the glenoid cavity superiorly). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Trapezius Lower (Ascending Part) (the OIANS method)
Learn the lower trapezius as the depressor and as the lower partner in scapular rotation: its fibres rise from the lower thoracic spines to the medial end of the scapular spine, so their downward pull lowers the shoulder girdle and, paired with the upper fibres, spins the glenoid up for overhead motion. Thinking of that upper-and-lower force couple explains why both parts are needed to lift the arm.
Remember it shares the accessory nerve (CN XI) and C3-C4 proprioception with the other two parts, so nerve recall is identical across the muscle. The distinguishing point to memorise is its role in the force couple: the upper and lower parts cooperate to upwardly rotate the scapula, and losing the lower part specifically undermines that overhead rotation.
Frequently asked questions
Where is the Trapezius Lower (Ascending Part) located?
The Trapezius Lower (Ascending Part) is a muscle of the Back group, located in the Trunk.
What is the origin of the Trapezius Lower (Ascending Part)?
Spinous processes and supraspinous ligaments of T4–T12
What is the insertion of the Trapezius Lower (Ascending Part)?
Tubercle at the medial end of the spine of the scapula
What movements does the Trapezius Lower (Ascending Part) produce?
Depresses the scapula and rotates the glenoid cavity superiorly
What nerve supplies the Trapezius Lower (Ascending Part)?
Motor: accessory nerve (CN XI); proprioception: anterior rami of C3–C4
Is the Trapezius Lower (Ascending Part) free to study in OIANS?
The Trapezius Lower (Ascending Part) is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
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