Extrinsic Shoulder Muscles

Question 1

Coracobrachialis -anterior compartment

• Origin and insertion?
• Action?
• Innervation?

Answer 1

• Origin: coracoid process of scapula
• Insertion: passes through axilla to insert onto medial shaft of humerus
• Action: Flexion of arm at shoulder, weak adduction
• Innervation: musculocutaneous nerve (C5-7)

Question 2

Biceps brachii -anterior compartment

• Origin and insertion?
• Action?
• Innervation?

Answer 2

• Origin: long head supraglenoid tubercle of scapula, short head coracoid process of scapula
• Insertion: radial tuberosity and bicipital aponeurosis
• Innervation: musculocutaneous nerve (C5-7)

Question 3

Brachialis -anterior compartment

• Origin and insertion?
• Actions?
• Innervation?

Answer 3

• Origin: medial & lateral surfaces of humeral shaft
• Insertion: ulna tuberosity (just distal to elbow joint)
• Actions: elbow flexion
• Innervation: musculocutaneous nerve and a bit of radial nerve

Question 4

Triceps brachii -posterior compartment of arm

• Origin and insertion?
• Action?
• Innervation?

Answer 4

Triceps brachii has three heads
- Origin:
Long head - infraglenoid tubercle on scapula
Lateral head - humerus, superior to radial groove
Medial head - humerus, inferior to radial groove
- Insertion: heads converge to form one tendon and insert onto olecranon of ulna
- Actions: elbow extension
- Innervation: radial nerve

Question 5

Trapezius -superficial extrinsic shoulder muscle

• Origin and insertion?
• Action?
• Innervation?

Answer 5

• Origin: skull, nuchal ligament, spinous processes C7-T12
• Insertion: clavicle, acromion of scapula and scapula spine
• Actions: upper fibres elevate and rotate scapula, middle fibres retract scapula, lower fibres pull scapula inferiorly
• Innervation: accessory nerve

Question 6

Latissimus dorsi -superficial extrinsic shoulder muscle

• Origin and insertion?
• Actions?
• Innervation?

Answer 6

• Origin: spinous processes T6-T12, iliac crest, thoracolumbar fascia
• Insertion: intertubercular sulcus of humerus
• Actions: extension, adduction and medial rotation of upper limb
• Innervation: thoracodorsal nerve

Question 7

Lavatory scapulae -extrinsic deep shoulder muscle

• Origin and insertion?
• Actions?
• Innervation?

Answer 7

• Origin: transverse process C1-C4
• Insertion: medial border of scapula
• Action: elevates scapula
• Innervation: dorsal scapula nerve

Question 8

Rhomboid major -extrinsic deep shoulder muscle

• Origin and insertion?
• Actions?
• Innervation?

Answer 8

• Origin: spinous processes T2-T5 (the inferior of the two rhomboids)
• Insertion: medial border of scapula
• Actions: retracts and rotates scapula
• Innervation: dorsal scapula nerve

Question 9

Rhomboid minor -extrinsic deep shoulder muscle group

• Origin and insertion?
• Actions?
• Innervation?

Answer 9

• Origin: spinous processes C7-T1
• Insertion: medial border of scapula at level of scapula spine, superior to rhomboid major
• Actions: retracts and rotates scapula
• Innervation: dorsal scapula nerve

Question 10

Pectoralis major

• Origin and insertion?
• Innervation?
• Actions?

Answer 10

• Origin: 2 heads; clavicular and anterior sternum
• Insertion: shaft of humerus
• Innervation: lateral and medial pectoral nerves
• Actions: adducts and medially rotates humerus, scapula anterior-inferior movement

Question 11

Pectoralis minor

• Origin and insertion?
• Innervation?
• actions?

Answer 11

• Origin: 3rd-5th ribs
• Insertion: coracoid process
• Actions: stabilises scapula by pulling inferiorly and anteriorly
• Innervation: medial pectoral nerve