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Shoulder Muscles: Anatomy, Support & Movement

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  • 0:05 Shoulder Muscles
  • 0:34 Stabilizers
  • 2:29 Arm-Movers
  • 5:12 Lesson Summary
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

The shoulder contains muscles that not only stabilize the shoulder but also move the arm. This lesson identifies and describes the muscles responsible for shoulder positioning, adduction, abduction, flexion, extension and shoulder rotation.

Shoulder Muscles

The shoulder muscles are appendicular muscles that attach to the appendicular skeleton. That is the bones of the arm and leg. The shoulder muscles serve to stabilize our pectoral girdle and move our arms. This lesson will identify and describe the main muscles associated with the shoulder. We will divide these muscles into two convenient groups: those that stabilize the pectoral girdle and those that move the arm.

Stabilizers

Location of the trapezius muscles
Trapezius Muscle

The trapezius - or traps, as commonly referred to - are large, paired muscles on the dorsal side of the body (that's the back side). The traps have multiple origins, including the skull and the vertebral column. They insert on the clavicle and scapula of the pectoral girdle. Contraction of the trapezius muscles results in elevation and retraction of the shoulders, as well as extension of the neck. All of these things help to hold the shoulder in position or stabilize the shoulder.

If we remove the trapezius, we can see the deeper levator scapulae, which, as its name suggests, elevates and stabilizes the scapula. Now, this muscle originates on the cervical vertebrae and inserts on the scapulae - that's plural for scapula. Inferior to the levator scapulae are the rhomboids, which originate on the thoracic vertebrae and insert on the scapula. They retract and adduct and stabilize the shoulders.

We can see two major shoulder stabilizers on the ventral, or front side, of the body. Let's take a look. The pectoralis minor originates on the superior ribs and inserts on the scapula. Therefore, it depresses and protracts, or abducts the shoulder. The serratus anterior originates on the ribs, courses around the thoracic cavity and inserts on the scapula, thus helping with stabilization and protraction of the shoulder. Let me make a side note. The serratus anterior is named, in part, because of its appearance. Like a serrated knife, this muscle has a serrated appearance on the front surface of the body as you see it moving in towards the ribs.

Arm-Movers

Now that we have identified the major shoulder stabilizers, let's take a look at the muscles that move the arm. These muscles are easiest to remember when grouped by the action they perform; that is, abduction, medial and lateral rotation of the arm, all at the shoulder.

The deltoids are arm abductor muscles.
Deltoid Muscle Location

The deltoid is the major arm abductor, as it originates on the clavicle and scapula and it inserts on the humerus. The supraspinatus originates on the scapula and inserts on the humerus as well, thus assisting with abduction of the arm. The supraspinatus is named for its position above the spine of the scapula, not the vertebral column spine.

The pectoralis major originates on the ribs and sternum and it inserts on the humerus, thus causing flexion and adduction of the arm. Now, this movement is demonstrated when a person does a pushup. The coracobrachialis originates from the scapula and inserts on the humerus, thus assisting with adduction and flexion of the arm.

The latissimus dorsi, also known as the lats, are paired muscles that originate on the vertebral column and insert on the humerus. Now, contraction of the lats results in adduction of the arm. The attachment of the lats can also cause extension of the arm, as demonstrated when we raise our elbows behind us.

The subscapularis is named for its position relative to the scapula. It originates on the deep, or ventral, surface of the scapula and inserts on the ventral aspect of the humerus. Because of these attachments, it causes medial rotation of the shoulder. The teres major muscle has similar attachments, and thus helps with medial rotation of the shoulder as well.

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