Muscle Review – Trapezius, Levator scapula, Latissimus Dorsi, Teres major

MBLEx Prep Course MBLEx Prep Course – Lesson 1 Muscle Review – Trapezius, Levator scapula, Latissimus Dorsi, Teres major

MBLEx Muscle Review

Introduction

The kinesiology section of each lesson in this MBLEx Prep Course is followed by a Muscle Review. A total of 114 muscles are covered in this course. Each review includes the muscle’s Origin, Insertion, Actions, and Nerve (OINA). Additional notes and study tips are included to help reinforce your understanding, boost retention, and improve your ability to apply this knowledge in clinical settings.

Study Tip:

When reviewing each muscle, try to visualize not only the muscle itself but also the surrounding structures. Consider:

Which muscles lie deep to it? Which ones are superficial?
What muscles are medial, lateral, proximal, or distal to the illustrated muscle?
Is the muscle part of a functional group? (e.g., semitendinosus is part of the hamstrings)
What are its synergists and antagonists?
How does it contribute to movement?

A study method that many students find useful is to create your own flashcards using blank index cards. Writing the information in your own words and sketching simple illustrations engages active learning. Doing this as you work your way through the MBLEx Prep Course will significantly improve retention.

While it is unlikely that you will see more than one or two questions on muscle innervation, learning them can still be valuable. Understanding muscle innervations will help when learning dermatomes and myotomes.

👉 Tip: Get familiar with the major peripheral nerves of the body, such as the radial, median, ulnar, axillary, sciatic, femoral, tibial, and fibular nerves.

Trapezius

Origin: External occipital protuberance, medial third of the superior nuchal line, ligamentum nuchae, spinous processes of C7-T12

Insertion: Lateral third of the clavicle, acromion process, and upper crest of the scapular spine

Action:

Upper fibers: Elevate scapula, assist in cervical extension
Middle fibers: Retract scapula (adduction)
Lower fibers: Depress and upwardly rotate scapula

Innervation: Accessory nerve (CN XI), cervical nerves (C3, C4)

Notes & Tips

Palpate the upper trapezius by placing your fingers just superior to the clavicle and lateral to the cervical spine, near the posterior aspect of the shoulder. The middle and lower fibers are thinner and harder to isolate. When studying, visualize how fiber direction affects function—upper fibers pull up, middle retract, and lower depress. The trapezius is sometimes confused with the levator scapulae, which also elevates the scapula but does not retract it. Its innervation (CN XI, 11th cranial nerve) is unique compared to most back muscles, which are usually innervated by spinal nerves.

Levator Scapulae

Origin: Transverse processes of C1-C4

Insertion: Medial (vertebral) border of the scapula, between the superior angle and the scapular spine

Action: Elevation and downward rotation of the scapula

Innervation: Dorsal scapular nerve (C5), cervical nerves (C3, C4)

Notes & Tips

The levator scapulae is named after its function—it elevates the scapula. It runs diagonally along the side of the neck, making it easy to palpate near the superior angle of the scapula.

This muscle often becomes tight due to forward-head posture, which can contribute to neck pain and stiffness. Stretching and myofascial release techniques can help alleviate tension.

Latissimus Dorsi

Origin: Spinous processes of T7-L5, sacrum, thoracolumbar fascia, posterior iliac crest, lower 3 or 4 ribs

Insertion: Intertubercular (bicipital) groove of the humerus

Action: Extension, adduction, and medial (internal) rotation of the humerus at the glenohumeral joint

Innervation: Thoracodorsal nerve (C6, C7, C8)

Notes & Tips

The latissimus dorsi is one of the largest muscles in the upper body and plays a key role in pulling movements such as pull-ups, swimming strokes, and rowing motions. It is sometimes referred to as the “swimmer’s muscle” due to its importance in arm extension and adduction. It can be palpated along the posterior and lateral thoracic region, extending toward its insertion on the proximal humerus.

👉 Tip: The latissimus dorsi works synergistically with the teres major to perform similar functions—both extend, adduct, and medially rotate the humerus.

Teres Major

Origin: Inferior angle of the scapula (dorsal surface)

Insertion: Medial lip of the intertubercular (bicipital) groove of the humerus

Action: Extension, medial (internal) rotation, and adduction of the humerus

Innervation: Lower subscapular nerve (C5, C6)

Notes & Tips

The teres major is sometimes called the “lat’s little helper” because it functions almost identically to the latissimus dorsi. It shares an insertion site with the latissimus dorsi and assists in the same motions.
Palpation Tip: The teres major is located just inferior to the teres minor and can be palpated along the posterior axillary border, especially when the arm is actively resisted into internal rotation.

The levator scapulae primarily elevates the scapula. It also contributes to downward rotation, meaning the medial border of the scapula moves upward while the glenoid fossa tilts downward. Additionally, when acting unilaterally, it can assist in ipsilateral neck lateral flexion and rotation.

The latissimus dorsi inserts on the anterior side of the humerus in the intertubercular groove. Because of this insertion, when the muscle contracts, it pulls the humerus inward, creating medial (internal) rotation. This is similar to how pulling on a rope from one side determines its direction—since the muscle wraps around to the front, it rotates the humerus inward.

The trapezius is primarily innervated by the accessory nerve (CN XI), which controls motor function. However, C3 and C4 spinal nerves provide sensory and proprioceptive input. This is unique because most back muscles are innervated entirely by spinal nerves, whereas the trapezius receives its motor supply from a cranial nerve. The combination of cranial and cervical nerve input reflects the muscle’s role in both neck and shoulder movement.

Weakness in the lower trapezius can lead to poor scapular stability and control, making overhead movements difficult. Without adequate activation of the lower trapezius, the upper trapezius and levator scapulae may compensate, causing excessive scapular elevation and reducing proper upward rotation, which can contribute to impingement issues and postural dysfunction.

The teres major performs similar actions to the latissimus dorsi—extension, adduction, and medial rotation of the humerus. Both muscles insert on the medial lip of the intertubercular groove, allowing them to work together in pulling the humerus backward and inward. However, unlike the latissimus dorsi, the teres major does not contribute significantly to trunk movements.

The levator scapulae can be palpated by locating the superior angle of the scapula and following the muscle upward along the posterolateral neck, where it attaches to the transverse processes of C1-C4. It is often tender due to tension from poor posture.

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