Muscles of the Shoulder Quiz

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Which nerve pair provides the motor innervation of the large fan-shaped muscle of the upper chest?

A Suprascapular and axillary nerves
B Spinal accessory and dorsal scapular nerves
C Medial and lateral pectoral nerves ✓
D Long thoracic and thoracodorsal nerves
E Upper and lower subscapular nerves

The answer is C: Medial and lateral pectoral nerves

Explanation

Why C is correct

See Anterior or Pectoral Region. Option C is correct. Pectoralis major is the large, fan-shaped muscle of the upper chest. It has a clavicular head, from the medial clavicle (collarbone), and a sternocostal head, from the sternum (breastbone) and upper costal cartilages (the cartilage that joins the ribs to the sternum), and both heads attach to the intertubercular sulcus, the groove at the top of the humerus. It adducts and medially rotates the arm, meaning that it pulls the arm in towards the body and turns it inwards, and the clavicular head also flexes the arm. Its motor supply comes from the lateral and medial pectoral nerves, which are branches of the brachial plexus, the network of nerves that supplies the arm. The muscle therefore has a dual nerve supply; the smaller pectoralis minor beneath it is supplied by the medial pectoral nerve. Because several different nerves supply the muscles around the shoulder, it is safest to learn each nerve together with its muscle. A memory aid: the pectoral muscles are supplied by the pectoral nerves.

Muscle: pectoralis major is the large, fan-shaped muscle of the upper chest.
Action: adducts and medially rotates the arm.
Nerve supply: the lateral and medial pectoral nerves, branches of the brachial plexus.

Why the other options are incorrect

A. Suprascapular and axillary nerves: The suprascapular nerve supplies supraspinatus and infraspinatus, and the axillary nerve supplies deltoid and teres minor. These nerves supply muscles around the shoulder joint rather than the muscle asked about in the stem.
B. Spinal accessory and dorsal scapular nerves: The spinal accessory nerve supplies trapezius and the dorsal scapular nerve supplies the rhomboids and levator scapulae. These are back muscles rather than the large fan-shaped muscle of the upper chest, so the pair is off-target.
D. Long thoracic and thoracodorsal nerves: The long thoracic nerve supplies serratus anterior and the thoracodorsal nerve supplies latissimus dorsi. Neither nerve supplies the large fan-shaped muscle of the upper chest, so this pair is not the motor innervation asked for.
E. Upper and lower subscapular nerves: The upper and lower subscapular nerves supply subscapularis, one of the rotator cuff muscles on the costal surface of the scapula. They do not supply the large fan-shaped muscle of the upper chest, so this pair is wrong for the stem.

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More questions from this set. Start the quiz to answer them and see each explanation.

1
Which muscle primarily protracts the scapula when a person pushes their hand against a wall?
2
Which action is most directly produced by contraction of the pectoralis minor muscle?

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