anatomy shoulder muscles

What four muscle groups?

Anterior shoulder girdle muscles, Serratus Anterior/Subclavius, Rotator Cuff muscles, and Scapulohumeral muscles

pectoralis major

orgin

inserion

innervation

action

orgin: clavicle (medial) , sternum(anterior), and first 7 costal cartilages.

inserion: Crest of the greater tubercle (lateral lip of the intertubercular sulcus)

innervation: Lateral pectoral nerve (C5-C7) and medial pectoral nerve (C8-T1)

action:

• clavicular: Flexes the humerus.

• sternocostal: Extends the humerus from a flexed position.

• both heads together: Adduction and medial rotation of the humerus.

What movement is pectoralis major especially known for?

Horizontal adduction ("pushing muscle")

Pectoralis Minor

orgin

inserion

innervation

action

small, traingular

deep to pectoralis major

orgin: Ribs 3-5.

inserion: Coracoid process of the scapula.

innervation: Medial pectoral nerve (C8-T1).

action: Depresses the scapular tip and protracts the scapula.

Tightness of pectoralis minor can contribute to what posture?

Rounded shoulder posture.

subclavis

orgin

inserion

innervation

action

deep to pec major, between clavicle and rib 1

origin: rib 1

inserion: clavicle ( middle, inferior surface)

innervation: subclavian nerve ( C5- C6)

action: Pulls clavicle medially, stabilizes the sternoclavicular joint, and depresses the shoulder tip.

Serratus anterior

orgin

inserion

innervation

action

between scapula and rib cage

orgin: Ribs 1-8 or 9, lateral

inserion: Medial border of the scapula

innervation: Long thoracic nerve (C5-C7)

action:

• protract scapula

• lift ribs with fixed scapula

• keep scapula ( costal surface) opposed to rib cage (thoracic wall)

What happens if the long thoracic nerve is injured?

Winged scapula

what are the rotator cuff muscles?

Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.

supraspinatus

orgin

inserion

innervation

action

orgin: supraspinous fossa (medial 2/3)

inserion: greater tubercle of humerus (upper facet)

innervation: Suprascapular nerve (C5-C6)

action:

• stabilize humerus head in gleniod cavity ( rotator cuff muscle)

• inities first 15 degrees of abduction

infraspinatus

orgin

inserion

innervation

action

orgin: infraspinous fossa (medial 2/3)

inserion: greater tubercle of humerus (middle facet)

innervation: Suprascapular nerve (C5-C6)

action:

• stabilize humerus head in gleniod cavity ( rotator cuff muscle)

• laterally rotate humerus

Teres Minor

orgin

inserion

innervation

action

orgin: lateral border of scapula ( upper 2/3, posterior surface)

inserion: greater tubercle of humerus ( inferior facet)

innervation: axillary nerve ( C5-C6)

action:

• stabilize humerus head in gleniod cavity ( rotator cuff muscle)

• laterally rotate humerus

Subscapularis

orgin

inserion

innervation

action

orgin: subscapular fossa of scapula( medial 2/3)

inserion: lesser tubercle of humerus

innervation: upper and lower subscapular nerve ( C5-C7

action:

• stabilize humerus head in gleniod cavity ( rotator cuff muscle)

• medially rotate humerus

Scapulohumeral muscles

Teres major

deltoid

Teres major

orgin

inserion

innervation

action

orgin: scapula ( inferior angle, posterior surface)

inserion: crest of lesser tubercle ( medial lip of intertubercular sulcus)

innervation: lower subscapular nerve (C5 -C7)

action: extend, addcuct, medially rotate humerus

Deltoid

orgin

inserion

innervation

action

3 parts of fibers (clavicular/anterior, acromial/middle, and spinal/posterior)

orgin:

• clavicle (lateral 1/3)

• acromion

• spine

inserion: deltoid tuberosity of humerus

innervation: Axillary nerve ( C5-C6)

action:

• Clavicular : flex and medially rotate humerus

• Acromial: abduct arm ( after initial 15 degrees from supraspinatus)

• Spinal: extends arm