biology

Trapezius

Trapezius is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Trapezius rather than just read about it. In short: The trapezius, historically known as cucullaris, is a large paired trapezium-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It moves the scapula and supports the arm.

Key takeaways

Trapezius belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Trapezius to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Trapezius from memory before moving on to harder problems.

Reference excerpt

The trapezius, historically known as cucullaris, is a large paired trapezium-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It moves the scapula and supports the arm. The trapezius has three functional parts:

an upper (descending) part, which supports the weight of the arm; a middle region (transverse), which retracts the scapula; and a lower (ascending) part, which medially rotates and depresses the scapula.

Name and history The trapezius muscle resembles a trapezium in North American English, also known as a trapezoid in British and other forms of English, meaning an irregular quadrilateral. The word "spinotrapezius" refers to the human trapezius, although it is not commonly used in modern texts. In other mammals, it refers to a portion of the analogous muscle.

Structure

The superior or upper (or descending) fibers of the trapezius originate from the spinous process of C7, the external occipital protuberance, the medial third of the superior nuchal line of the occipital bone (both in the back of the head), and the nuchal ligament. From this origin, they proceed downward and laterally to be inserted into the posterior border of the lateral third of the clavicle. The middle fibers, or transverse of the trapezius arise from the spinous process of the seventh cervical (both in the back of the neck), and the spinous processes of the first, second, and third thoracic vertebrae. 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. The inferior or lower (or ascending) fibers of the trapezius arise from the spinous processes of the remaining thoracic vertebrae (T4–T12). From this origin, they proceed upward and laterally to 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. 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 well-marked tendinous ellipse (the so-called oval aponeurosis). The rest of the muscle arises by numerous short tendinous fibers. It is possible to feel the muscles of the superior trapezius as they 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.

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

Function Contraction of the trapezius muscle can have two effects: movement of the scapulae when the spinal origins are stable, and movement of the spine when the scapulae are stable. Its main function is to stabilize and move the scapula.

Scapular movements The upper fibers elevate the scapulae, the middle fibers retract the scapulae, and the lower fibers depress the scapulae. In addition to scapular translation, the trapezius induces scapular rotation. The upper and lower fibers tend to rotate the scapula around the sternoclavicular articulation so that the acromion and inferior angles move up and the medial border moves down (upward rotation). The upper and lower fibers work in tandem with serratus anterior to upwardly rotate the scapulae, and work in opposition to the levator scapulae and the rhomboids, which effect downward rotation. An example of trapezius function is an overhead press. When activating together, the upper and lower fibers also assist the middle fibers (along with other muscles such as the rhomboids) with scapular retraction/adduction. The trapezius also assists in abduction of the shoulder above 90 degrees by rotating the glenoid upward. Injury to cranial nerve XI will cause weakness in abducting the shoulder above 90 degrees.

Spinal movements When the scapulae are stable, a co-contraction of both sides can extend the neck.

Clinical significance Dysfunction of the trapezius can result in winged scapula, sometimes further specified as "lateral winging" and in an abnormal mobility or function of the scapula (scapular dyskinesia). There are multiple causes of trapezius dysfunction.

Palsy Trapezius palsy, due to damage of the spinal accessory nerve, is characterized by difficulty with arm adduction and abduction, and associated with a drooping shoulder, and shoulder and neck pain. Intractable trapezius palsy can be surgically managed with an Eden–Lange procedure.

Facioscapulohumeral muscular dystrophy The trapezius muscle is one of the commonly affected muscles in facioscapulohumeral muscular dystrophy (FSHD). The lower and middle fibers are affected initially, and the upper fibers are commonly spared until late in the disease.

Underdevelopment Although rare, underdevelopment or absence of the trapezius has been reported to correlate to neck pain and poor scapular control that are not responsive to physical therapy. Absence of the trapezius has been reported in association with Poland syndrome.

Society and culture

Exercises The upper portion of the trapezius can be developed by elevating the shoulders. Common exercises for this movement are any version of the clean, particularly the hang clean, and the shoulder shrug. The uppermost area can be trained through neck extension. Middle fibers are developed by pulling shoulder blades together. This adduction also uses the upper/lower fibers. 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 deltoid muscle and rotator cuff.

References

External links

Superficial Back Dissection Video showing trapezius

This article incorporates text in the public domain from page 432 of the 20th edition of Gray's Anatomy (1918)

Illustrations

Trapezius: Position of trapezius and its parts:.mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{} Superior fibers of the trapezius Middle fibers of the trapezius Inferior fibers of the trapezius — Position of trapezius and its parts:.mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{} Superior fibers of the trapezius Middle fibers of the trapezius Inferior fibers of the trapezius

Worked examples

Example 1 — a first encounter with Trapezius

Start with the simplest possible case. Write down what Trapezius claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Trapezius before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Trapezius ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Trapezius

In research: Trapezius appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Trapezius in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Trapezius is common in secondary-school and first-year university syllabi. It links to neighbouring topics Back anatomy, Muscles of the upper limb, so understanding it makes those chapters shorter.
In everyday life: Look for Trapezius outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Trapezius in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Trapezius means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Trapezius out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trapezius in simple terms?

Why does Trapezius matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Trapezius?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Trapezius.