The muscles of the shoulder

Name of muscle

Position

Attachments

Action/s

zee-us)

Large triangular-shaped muscle in upper back Its fibres are arranged in three groups - upper, middle and lower

Extends horizontally from the base of the skull (occipital bone) and cervical/thoracic vertebrae to scapula Its fibres are arranged in three groups - upper, middle and lower

The upper fibres raise the shoulder girdle, the middle fibres pull the scapula towards the vertebral column and the lower fibres draw the scapula and shoulder downwards

One of the most commonly found muscles to hold upper body tension, causing discomfort and restrictions in the neck and shoulder

Levator scapula (le-vay-tor skap-you-lee)

Strap-like muscle that runs almost vertically through the neck

Cervical vertebrae to the scapula

Elevates and adducts the scapula

Due to its attachments, tension in the levator scapula can affect mobility of both the neck and the shoulder

Rhomboids

(rom-boyds)

Fibres of these muscles lie between the scapulae

They attach to the upper thoracic vertebrae at one end and the medial border of the scapula at the other end

Adduct the scapula

Also known as the 'Christmas tree' muscles, due to arrangment of fibres Tension in these muscles often results in aching and soreness in between the scapulae

The muscles of the shoulder 125

Name of muscle

Position

Attachments

Action/s

Key facts

Supraspinatus

nay-tus)

Located in the depression above the spine of the scapula

Attached to the spine of the scapula at one end and the humerus at the other

Abducts humerus, assisting the deltoid

Is the only muscle of the rotator cuff that does not rotate the humerus

Infraspinatus

nay-tus)

Deep muscle covering the lower part of the scapula

Attaches to the middle two-thirds of the scapula below the spine of the scapula at one end and the top of the humerus at the other

Rotates humerus laterally (outwards)

One of the four rotator cuff muscles

Tension in this muscle can affect the range of mobility in the arm and the shoulder

Teres major

(te-reez may-jor)

Deep, small muscle located between lower border of scapula and humerus

Attaches to the bottom lateral edge of the scapula at one end and the back of the humerus at the other

Adducts and medially (inwardly) rotates humerus

Sometimes referred to as the 'little helper' of the latissimus dorsi muscle because they run together between the scapula and the humerus

Teres minor

(te-reez my-nor)

Deep, small muscle located above teres major

Attaches to the lateral edge of the scapula at one end and into the top of the posterior of the humerus at the other

Rotates humerus laterally (outwards)

One of the four rotator cuff muscles

Although the teres major and minor may appear similar by name, they wrap around the humerus in opposite directions and therefore have opposite rotary actions

Subscapularis

(sub-skap-

u-la-ris)

Large muscle located beneath the scapula

Attaches to the inside surface of the scapula to the anterior of the top of the humerus

Rotates the humerus medially, draws the humerus forwards and down when the arm is raised

One of the four rotator cuff muscles Often implicated in the case of a frozen shoulder

Deltoid

(del-toid)

Thick triangular muscle that caps the top of the humerus and shoulder

Attaches to the clavicle and the spine of the scapula at one end and to the side of the humerus at the other

Abducts arm, draws the arm backwards and forwards

The deltoid has anterior, lateral and posterior fibres and these give the shoulder its characteristic shape

Fig 4.7 The muscles of the shoulder
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