Intrinsic Muscles of the shoulder

Muscles involved are:

Deltoid, Teres Major, and Rotator Cuff Muscles (Tendinous Muscles)

The main function of these muscles is to attach the pectoral girdle to the humerus

Deltoid:

Action: Flex, extend, abduct arm at shoulder, also provide a little bit of medial and lateral rotation but not much

Innervation: is provided by the axillary nerve (originating from c5 c6 spinal nerves and forming the terminal branch of the posterior cord of the brachial plexus)

Rotator (Tendinous) Cuff Muscles:

Supraspinatus Muscle: initiates abduction, provides no rotation and is innervated by the suprascapular nerve (coming from the superior trunk of the brachial plexus)

Infraspinatus Muscle: provides lateral rotation of humerus, and is innervated by suprascapular nerve

Teres Minor: also provides lateral rotation of humerus, and is innervated by the axillary nerve which is orginating from c5 c6 spinal roots and forms the terminal branch of the posterior cord of the brachial plexus

Subscapularis Muscle: provides medial rotation of the humerus and is innervated by the lower (comes from the posterior cord of the brachial plexus) and upper subscapular nerves

Teres Major Muscle:

Action: is to extend, adduct, medially rotate arm at shoulder

Innervation: by the lower subscapular nerve (coming from the posterior cord of the brachial plexus)

This muscle forms a small quadrangular space, where the axillary nerve and the posterior circumflex humoral artery flows through.

Note: To remember the actions of latissimus dorsi and teres major (these two muscles have the same actions except for depression of scapula is an extra action provided by the lat dorsi muscle).

Category: Anatomy Notes