Shoulder and Arm Muscles

Trapezius (Traps)

  • Large, paired muscles on the dorsal (back) side of the body.
  • Origins:
    • Skull
    • Vertebral column
  • Insertion:
    • Clavicle
    • Scapula of the pectoral girdle
  • Contraction results in:
    • Elevation of shoulders
    • Retraction of shoulders
    • Extension of the neck
    • Stabilization of the shoulder

Levator Scapulae

  • Deeper muscle (visible when trapezius is removed).
  • Action: elevates and stabilizes the scapula.
  • Origin: Cervical vertebrae
  • Insertion: Scapula

Rhomboids

  • Location: Inferior to the levator scapulae
  • Origin: Thoracic vertebrae
  • Insertion: Scapula
  • Actions:
    • Retract the shoulders
    • Adducts the shoulders
    • Stabilizes the shoulders

Pectoralis Minor

  • Location: Ventral (front) side of the body
  • Origin: Superior ribs
  • Insertion: Scapula
  • Actions:
    • Depresses the shoulder
    • Protracts (abducts) the shoulder

Serratus Anterior

  • Location: Ventral (front) side of the body
  • Origin: Ribs
  • Courses around the thoracic cavity
  • Insertion: Scapula
  • Actions:
    • Stabilizes the shoulder
    • Protracts the shoulder
  • Named for its serrated (like a serrated knife) appearance on the front of the body.

Muscles That Move the Arm (grouped by action)

Abduction

Deltoid
  • Major arm abductor
  • Origin: Clavicle and scapula
  • Insertion: Humerus
Supraspinatus
  • Assists with abduction of the arm
  • Origin: Scapula
  • Insertion: Humerus
  • Named for its position above the spine of the scapula (not the vertebral column spine).

Adduction

Pectoralis Major
  • Origin: Ribs and sternum
  • Insertion: Humerus
  • Also causes flexion of the arm. The movement is demonstrated during a push-up.
Coracobrachialis
  • Origin: Scapula
  • Insertion: Humerus
  • Assists with adduction and flexion of the arm.
Latissimus Dorsi (Lats)
  • Paired muscles
  • Origin: Vertebral column
  • Insertion: Humerus
  • Actions:
    • Adduction of the arm
    • Extension of the arm (demonstrated when raising elbows behind the back)

Medial Rotation

Subscapularis
  • Named for its position relative to the scapula
  • Origin: Deep (ventral) surface of the scapula
  • Insertion: Ventral aspect of the humerus
  • Action: Medial rotation of the shoulder
Teres Major
  • Similar attachments to the subscapularis
  • Action: Medial rotation of the shoulder

Lateral Rotation

Infraspinatus
  • Insertion: Dorsal (back) surface of the humerus.
  • Action: Lateral rotation of the shoulder.
Teres Minor
  • Insertion: Dorsal (back) surface of the humerus
  • Action: Lateral rotation of the shoulder.

Rotator Cuff

  • Composed of four muscles:
    • Supraspinatus
    • Infraspinatus
    • Subscapularis
    • Teres Minor
  • Collectively responsible for rotation of the shoulder.
  • Throwing sports (e.g., baseball) put a lot of strain on the rotator cuff muscles and can frequently cause injury.

Summary of Shoulder Muscles and Actions

Shoulder Stabilizers

  • Trapezius
  • Rhomboids
  • Levator Scapulae
  • Serratus Anterior
  • Pectoralis Minor

Arm Abduction

  • Deltoid
  • Supraspinatus

Arm Adduction

  • Pectoralis Major
  • Latissimus Dorsi
  • Coracobrachialis

Arm Flexion

  • Pectoralis Major
  • Coracobrachialis

Arm Extension

  • Latissimus Dorsi

Rotator Cuff Muscles and Actions

  • Subscapularis: Medial rotation
  • Supraspinatus: Abduction
  • Infraspinatus: Lateral rotation
  • Teres Minor: Lateral rotation