Shoulder Girdle

Anatomy: Shoulder Girdle Muscles

Groups of Shoulder Muscles

There are three main groups of shoulder muscles:

  1. Superficial Extrinsic (Thoracoappendicular)

  2. Deep Extrinsic (Thoracoappendicular)

  3. Intrinsic (Scapulohumeral)

These groups consist of muscles that connect the upper extremity to the thorax and control the movement of the glenohumeral joint, which is vital for a wide range of arm movements. Proper functioning of these muscles is essential for activities such as lifting, throwing, and pushing.

Superficial Extrinsic Muscles

1. Trapezius Muscle

  • Action: Responsible for elevation and upward rotation of the scapula, which is crucial for shoulder abduction.

  • Origin: Superior nuchal line (occipital bone), and the spinal processes of cervical vertebrae C7 to T3.

  • Insertion: Spine of scapula and lateral portion of the clavicle.

  • Innervation: Accessory Nerve (CN XI), along with contributions from cervical spinal nerves (C3-C4).

2. Latissimus Dorsi Muscle

  • Action: Extension, internal rotation, and adduction of the shoulder joint, playing a big role in movements like pulling and swimming.

  • Origin: Spinous processes of T7-T12, thoracolumbar fascia, and iliac crest.

  • Insertion: Bicipital groove of the humerus.

  • Innervation: Thoracodorsal nerve (C6-8).

Deep Extrinsic Muscles

1. Levator Scapulae Muscle

  • Action: Elevation and downward rotation of the scapula, important for shrugging the shoulders.

  • Origin: Transverse processes of C1-C4.

  • Insertion: Superior angle of the scapula.

  • Innervation: Dorsal scapular nerve (C5) and cervical nerves (C3-C4).

2. Rhomboid Minor Muscle

  • Action: Retraction (drawing the scapula towards the spine) and downward rotation of the scapula.

  • Origin: Spinous processes of C7-T1.

  • Insertion: Medial border of the scapula at its upper portion.

  • Innervation: Dorsal scapular nerve (C5).

3. Rhomboid Major Muscle

  • Action: Similar to the rhomboid minor, it aids in retraction and downward rotation of the scapula.

  • Origin: Spinous processes of T2-T5.

  • Insertion: Medial border of the scapula.

  • Innervation: Dorsal scapular nerve (C5).

4. Serratus Anterior Muscle

  • Action: Protraction and upward rotation of the scapula, crucial for reaching forward and pushing movements.

  • Origin: Ribs 1-8.

  • Insertion: Anterior surface of the medial border of the scapula.

  • Innervation: Long thoracic nerve (C5-7).

Intrinsic Muscles (Rotator Cuff)

1. Supraspinatus Muscle

  • Origin: Supraspinous fossa of the scapula.

  • Insertion: Greater tubercle of the humerus.

  • Innervation: Suprascapular nerve (C5-6).

  • Action: Abduction of the shoulder, vital for the first 15 degrees of arm lift.

2. Infraspinatus Muscle

  • Origin: Infraspinous fossa of the scapula.

  • Insertion: Greater tubercle of the humerus.

  • Innervation: Suprascapular nerve (C5-6).

  • Action: External rotation of the shoulder, allowing for movements like throwing.

3. Teres Minor Muscle

  • Origin: Lateral border of the scapula.

  • Insertion: Greater tubercle of the humerus.

  • Innervation: Axillary nerve (C5-6).

  • Action: External rotation of the shoulder, working alongside the infraspinatus.

4. Subscapularis Muscle

  • Origin: Subscapular fossa (anterior surface of the scapula).

  • Insertion: Lesser tubercle of the humerus.

  • Innervation: Upper and lower subscapular nerves (C5-6).

  • Action: Internal rotation of the shoulder, critical for stabilizing the shoulder joint during various activities.

Pectoral Girdle Muscles

1. Pectoralis Major Muscle

  • Action: Adduction, flexion, and internal rotation of the shoulder; involved in actions such as pushing and lifting.

  • Origin: Lateral clavicle (clavicular head) and sternum (sternocostal head).

  • Insertion: Bicipital groove of the humerus.

  • Innervation: Medial and lateral pectoral nerves (C5-7, C8-T1).

2. Pectoralis Minor Muscle

  • Action: Protraction and depression of the scapula, helping stabilize the shoulder girdle.

  • Origin: Ribs 3-5.

  • Insertion: Coracoid process of the scapula.

  • Innervation: Medial pectoral nerve (C8-T1).

3. Subclavius Muscle

  • Action: Depression of the scapula and elevation of rib 1, playing a role in stabilizing the clavicle.

  • Origin: Rib 1.

  • Insertion: Subclavian groove of the clavicle.

  • Innervation: Subclavian nerve (C5-6).

References

  • Alsup, Kathleen & Fox, Glenn. BlueLink Images. Available from: University of Michigan Medical School. https://sites.google.com/a/umich.edu/bluelink/resources/bluelink, ©2014-2024.

  • Biel, Andrew. Trail Guide to the Body. Available from: Books of Discovery, (6th Edition). Milady, 2023.

  • Netter, Frank. Netter Atlas of Human Anatomy: Classic Regional Approach. Available from: Elsevier, (8th Edition). Elsevier Health Sciences (US), 2022.