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AN9.1-3 | Pectoral region — Gate Quiz
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Pectoralis major performs all of the following movements EXCEPT:
Correct! Pectoralis major does NOT perform abduction. Its actions are: adduction, medial rotation, and flexion (clavicular head) of the humerus. Abduction is performed by the deltoid and supraspinatus.
Pectoralis major actions: (1) Adduction, (2) Medial rotation, (3) Flexion (clavicular head). The sternal head can extend the flexed arm. It does NOT abduct. When paralysed, the anterior axillary fold disappears.
Incorrect. Pectoralis major adducts, medially rotates, and flexes the arm (clavicular head). It does NOT abduct — that is the function of deltoid and supraspinatus.
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Which nerves supply pectoralis major?
Correct! Pectoralis major has dual innervation: the lateral pectoral nerve (C5, C6, C7) supplies mainly the clavicular head, while the medial pectoral nerve (C8, T1) supplies mainly the sternocostal head. Both nerves arise from the brachial plexus.
Lateral pectoral nerve: primarily clavicular head of pec major. Medial pectoral nerve: primarily sternocostal head of pec major (and pectoralis minor). Long thoracic nerve: serratus anterior (winging of scapula when injured).
Incorrect. Pectoralis major receives dual supply: both the lateral and medial pectoral nerves. The long thoracic nerve supplies serratus anterior.
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Pectoralis minor attaches to which structure on the scapula?
Correct! Pectoralis minor originates from the 3rd, 4th, and 5th ribs (near their costal cartilages) and inserts into the coracoid process of the scapula. It protracts and depresses the scapula and assists in forced inspiration.
Pectoralis minor: Origin — 3rd–5th ribs. Insertion — coracoid process of scapula. Nerve — medial pectoral nerve. Actions — protracts and depresses the scapula; elevates ribs in forced inspiration. Key landmark for axillary vessels.
Incorrect. Pectoralis minor inserts into the coracoid process of the scapula (not the acromion, spine, or glenoid).
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During a modified radical mastectomy at a hospital in Chennai, the surgeon identifies pectoralis minor as a key landmark. The axillary vessels and brachial plexus lie in which relationship to pectoralis minor?
Correct! The axillary vessels and the cords of the brachial plexus lie posterior (deep) to pectoralis minor. This is why pectoralis minor serves as the key landmark for identifying axillary contents during mastectomy and lymph node dissection.
Pectoralis minor divides axillary lymph nodes into 3 levels: Level I (lateral/inferior to pec minor) → Level II (posterior to pec minor) → Level III (medial/superior to pec minor). The cords of brachial plexus are named by their relationship to the axillary artery, which lies deep to pec minor.
Incorrect. The axillary vessels and brachial plexus cords lie posterior (behind/deep to) pectoralis minor. Pectoralis minor divides the axilla into three levels for lymph node staging.
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Serratus anterior is innervated by which nerve, whose injury causes winging of the scapula?
Correct! Serratus anterior is innervated by the long thoracic nerve (C5, C6, C7 — 'C5, C6, C7 — Bell's palsy of the thorax'). Injury causes winging of the scapula because the medial border of the scapula lifts away from the thoracic wall.
Long thoracic nerve (C5, C6, C7) → Serratus anterior → Medial winging (medial border of scapula lifts). Dorsal scapular nerve → Rhomboids → Lateral winging. Serratus anterior protracts and rotates the scapula (essential for arm elevation above 90°).
Incorrect. The long thoracic nerve supplies serratus anterior. Its injury = medial winging of the scapula. Dorsal scapular nerve supplies rhomboids (rhomboid winging = lateral winging).
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The subclavius muscle is important clinically because it protects which structure in clavicle fractures?
Correct! The subclavius muscle lies between the clavicle and the subclavian vessels. In clavicle fractures, the subclavius acts as a buffer, protecting the subclavian artery and vein from direct injury by the fractured bone fragments.
Subclavius: Origin — 1st rib. Insertion — inferior surface of clavicle. Action — depresses and steadies clavicle. Nerve — nerve to subclavius (C5, C6). Clinical: acts as buffer protecting subclavian vessels in clavicle fractures.
Incorrect. Subclavius protects the subclavian vessels (artery and vein) from injury during clavicle fractures by acting as a cushion between the bone and the neurovascular structures.
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The anterior axillary fold, visible on clinical inspection, is formed by which muscle?
Correct! The anterior axillary fold is formed by the lower border of pectoralis major as it crosses from the chest to insert into the lateral lip of the intertubercular groove of the humerus.
Axillary folds: Anterior = pectoralis major. Posterior = teres major + latissimus dorsi. Clinical: Loss of the anterior axillary fold occurs with pectoralis major injury (avulsion, rupture). The posterior axillary fold is important in identifying the posterior boundary of the axilla.
Incorrect. The anterior axillary fold is pectoralis major. The posterior axillary fold is formed by teres major and latissimus dorsi.
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A patient is unable to raise the arm above 90°. On examination, when pushing against a wall, the medial border of the scapula becomes prominent ('wings out'). The cause is injury to which nerve?
Correct! Injury to the long thoracic nerve paralyses serratus anterior, causing winging of the scapula (medial border lifts away from thorax). Serratus anterior is essential for rotating the glenoid upward to allow arm elevation above 90°.
Serratus anterior (long thoracic nerve, C5-7): protracts and upwardly rotates the scapula. Without it, the arm cannot be raised above 90°. Classic cause: injury during first rib resection, radical mastectomy, or carrying heavy bags on the shoulder.
Incorrect. Medial winging of the scapula (medial border prominent) is caused by serratus anterior paralysis due to long thoracic nerve injury.
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Pectoralis major originates from all of the following EXCEPT:
Correct! Pectoralis major does NOT originate from the coracoid process. Its three heads originate from: (1) Clavicular head — medial half of clavicle; (2) Sternocostal head — sternum + costal cartilages of ribs 1–6; (3) Abdominal head — aponeurosis of external oblique.
Pectoralis major origin: (1) Clavicular head — medial clavicle. (2) Sternocostal head — sternum + costal cartilages 1–6. (3) Abdominal head — anterior rectus sheath. Coracoid process is the insertion of pectoralis minor.
Incorrect. Pectoralis major does NOT arise from the coracoid process (that is pectoralis minor's insertion). Its origins are clavicle, sternum, and upper costal cartilages.
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The cephalic vein runs in the deltopectoral groove and drains into which vessel?
Correct! The cephalic vein runs in the deltopectoral groove (between deltoid and pectoralis major), then passes through the deltopectoral triangle (clavipectoral fascia) to drain into the axillary vein just below the clavicle.
Cephalic vein: Lateral forearm → lateral arm → deltopectoral groove → deltopectoral triangle → axillary vein. Clinical use: IV access site, used for subclavian vein catheterization (cephalic cutdown), PICC line access.
Incorrect. The cephalic vein drains into the axillary vein after passing through the clavipectoral fascia in the deltopectoral triangle.
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