intrinsic muscles of the shoulder

Intrinsic Muscles of the Shoulder

If you'd like to support us, check out our awesome products:


The intrinsic muscles of the shoulder form the scapulohumeral group, mainly originating from the scapula and inserting onto the humerus.1

The intrinsic muscles can be further divided into the deltoid muscle, teres major and the rotator cuff muscles; supraspinatus, infraspinatus, subscapularis and teres minor.2

This article will primarily highlight theΒ origin,Β insertion,Β innervation and function of the intrinsic muscles of the shoulder.

Want discounted access to all Geeky Medics products, including our anatomy flashcard collection? Check out our bundles to save money and supercharge your learning πŸ”₯


The deltoid forms the rounded contour of the shoulder and is comprised anterior, intermediate and posterior fibres.1

Origin and insertion

The anterior (or clavicular) fibres originate from the lateral third of the clavicle. The intermediate (or acromial) fibres originate from the acromion process of the scapula. The posterior (or spinal) fibres originate from the spine of the scapula.

All fibres converge toward their insertion on theΒ deltoid tuberosityΒ on the middle of the shaft of theΒ humerus.


The deltoid is innervated by the axillary nerve (C5-6).


The functions of the deltoid muscle can be categorised based on the groups of fibres involved:

  • Anterior fibres: shoulder flexion and internal rotation.
  • Intermediate fibres: abduction of the shoulder (these fibres take over from supraspinatus which initiates shoulder abduction).
  • Posterior fibres: shoulder extension and external rotation.


Deltoid muscle
Figure 1. Deltoid muscle.3

Teres major

Teres major is a thick muscle which is positioned superiorly to latissimus dorsi.4

Origin and insertion

Teres major originates from the posterior aspect of the inferior angle of the scapula and inserts onto the medial lip of the bicipital grooveΒ (intertubercular sulcus) of the humerus.4


The majority of teres major is innervated by the lower subscapular nerve and a small portion is innervated by the thoracodorsal nerve (C5-8).4


Teres major acts to adduct the humerus as well as assisting in extension and internal rotation of the shoulder.4

Teres major
Figure 2. Teres major.4

Rotator cuff muscles

All four rotator cuff muscles originate from areas of the scapula and insert onto the humeral head.2

The glenohumeral (GH) joint is highly mobile, allowing a large range of movement, but this comes at the cost of stability. The resting tension of the rotator cuff muscles provides the primary stabilizing force on the GH joint.1,2


Supraspinatus arises from the scapula and runs beneath the cover of the acromion.5

Origin and insertion

Supraspinatus originates from the supraspinous fossa and the muscle’s tendon inserts onto the superior facet of the greater tubercleΒ of the humerus.5


Supraspinatus is innervated by the suprascapular nerve (C5).5


Supraspinatus acts to initiate abduction of the arm (especially between the first 15 degrees of movement) and then acts to assist the deltoid muscle (15-90 degrees of movement).5

Clinical relevance: impingement syndrome

Impingement syndrome is caused by rotator cuff tendonitis as the tendons pass beneath the acromion. The supraspinatus muscle’s tendon is most commonly affected.

Impingement syndrome typically presents with pain, weakness and restricted shoulder movement. Patients with impingement syndrome often complain of pain when their arms are raised (this is particularly common in mechanics and manual labourers who work with their arms overhead). When the arm is raised, the subacromial space narrows, which can result in impingement of the supraspinatus muscle tendon leading to an inflammatory response.

Clinical examination

Typical findings on clinical examination in supraspinatus impingement syndrome include:

  • Pain experienced between 60-120Β° of shoulder abduction (known as a ‘painful arc’).
  • Weakness and pain experienced when the supraspinatus muscle is isolated using the ‘Empty can/Jobe’s test

For more information, see the Geeky Medics shoulder examination guide.

Figure 3. Supraspinatus.5


Infraspinatus is a thick triangular muscle. The spine of the scapula acts to separate the origin of the supraspinatus muscle from the infraspinatus muscle.6

Origin and insertion

The infraspinatus muscle originates from the infraspinous fossa of the scapula, passing over the lateral border of the spine of the scapula before inserting onto the middle facet of the greater tuberosity on the humerus.6


Infraspinatus has the same innervation as supraspinatus – the suprascapular nerve (C5).6


Infraspinatus acts to externally rotate the arm.6

Figure 4. Infraspinatus.6


Subscapularis is another large triangular-shaped muscle.7

Origin and insertion

It originates from the subscapular fossa (ventral surface) and inserts onto the lesser tuberosity of the humerus (this is the only rotator cuff muscle which doesn’t attach to the greater tuberosity).7


Subscapularis is innervated by the upper and lower subscapular nerves (C5-6).7


Subscapularis acts to internally rotate and adduct the arm.7

Figure 5. Subscapularis.7

Teres minor

Teres minor is a narrow elongated muscle which is superior to teres major.8

Origin and insertion

Teres minor originates from the lateral border of the scapula, before inserting onto the inferior facet of the greater tubercle on the humerus.8


Teres minor is innervated by the axillary nerve (C5-6).8


Teres minor acts to externally rotate the arm.8

Mnemonic: SIT

SIT is a mnemonic to remember the superior to inferior attachments of the rotator cuff muscles onto the greater tubercle of the humerus.5

  • Supraspinatus
  • Infraspinatus
  • Teres minor
Teres minor
Figure 6. Teres minor.8


Muscle Origin Insertion Innervation Action
Deltoid Lateral β…“ clavicle + acromion & the spine of the scapula Deltoid tuberosity Axillary nerve

Anterior fibres: Flexion & internal rotation

Intermediate fibres: major abductor, takes over from supraspinatus

Posterior fibres:
extension & external rotation

Teres major Inferior angle of the scapula Medial lip of bicipital groove Lower subscapular nerve

Adducts & extends at the shoulder

Internally rotates the arm

Rotator cuff muscles
Supraspinatus Supraspinous fossa


Greater tubercle


Suprascapular nerve

Initiates abduction

(0-15 degrees) & assists deltoid for 15-90 degrees

Infraspinatus Infraspinous fossa Externally rotates
Subscapularis Subscapular Fossa Lesser tubercle Upper and lower subscapular nerves


Internally rotates arm

Teres minor Lateral border of the scapula Greater tubercle Axillary nerve

Externally rotates



  1. Drake, R et al. (2010). Gray’s Anatomy for students. 2ndedition. Philadelphia, PA: Churchill Livingstone Elsevier
  2. Matava MJ, Purcell DB, Rudzki JR (2005). “Partial-thickness rotator cuff tears”.Β Am J Sports Med.Β 33 (9): 1405–17. Available from: [LINK].
  3. OpenStax College. Deltoid muscle. Licence: [CC BY]. Available from: [LINK].
  4. Mikael HΓ€ggstrΓΆm, used with permission. Teres Major. Available from: [LINK].
  5. Mikael HΓ€ggstrΓΆm, used with permission. Supraspinatus. Available from: [LINK].
  6. Mikael HΓ€ggstrΓΆm, used with permission. Infraspinatus. Available from: [LINK].
  7. Β Anatomography. Subscapularis muscle. License [CC BY-SA 2.1 JP]. Available from [LINK].
  8. Β Anatomography. Teres minor muscle. License [CC BY-SA 2.1 JP]. Available from [LINK].


Print Friendly, PDF & Email