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Questions and Answers
What is the primary action of the subscapularis muscle?
What is the primary action of the subscapularis muscle?
Which nerve is responsible for innervating both the biceps brachii and coracobrachialis muscles?
Which nerve is responsible for innervating both the biceps brachii and coracobrachialis muscles?
Which muscle primarily contributes to shoulder flexion and horizontal adduction?
Which muscle primarily contributes to shoulder flexion and horizontal adduction?
What action does the serratus anterior partake in with the help of the subcostal nerve?
What action does the serratus anterior partake in with the help of the subcostal nerve?
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Which of the following muscles is primarily involved in shoulder adduction?
Which of the following muscles is primarily involved in shoulder adduction?
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What is the primary action of the trapezius muscle?
What is the primary action of the trapezius muscle?
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Which muscle is primarily responsible for the external rotation of the humerus?
Which muscle is primarily responsible for the external rotation of the humerus?
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What role do the rhomboid muscles play in shoulder movement?
What role do the rhomboid muscles play in shoulder movement?
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Which nerve innervates the trapezius muscle?
Which nerve innervates the trapezius muscle?
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What is the primary action of the latissimus dorsi muscle?
What is the primary action of the latissimus dorsi muscle?
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How does the levator scapulae muscle primarily function?
How does the levator scapulae muscle primarily function?
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What is the consequence of injury to the dorsal scapular nerve?
What is the consequence of injury to the dorsal scapular nerve?
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Which action is primarily associated with the posterior deltoid muscle?
Which action is primarily associated with the posterior deltoid muscle?
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Study Notes
Posterior Shoulder Muscles
- Trapezius: A large, superficial muscle spanning the upper back, neck, and shoulders; actions include scapular elevation, depression, retraction, and rotation; crucial for posture and shoulder girdle movement.
- Rhomboids: Composed of major and minor rhomboids, located deep to the trapezius; primarily retract the scapula; vital for scapular stability during movement.
- Latissimus Dorsi: A broad, large muscle originating from the lower back and inserting on the humerus; functions in shoulder extension, adduction, and internal rotation; contributes to pulling the arm downwards and backwards.
- Infraspinatus: A rotator cuff muscle beneath the scapula; chief role is external rotation of the humerus; essential for glenohumeral joint stability during movement.
- Teres Minor: A small, narrow muscle adjacent to the infraspinatus; function as an external rotator of the humerus; assists in stabilizing the glenohumeral joint.
- Deltoid (posterior): A component of the deltoid muscle; aids in shoulder abduction (initially) and external rotation; posterior fibers most prominent in lifting the arm posteriorly.
- Levator Scapulae: Located on the upper back; elevates the scapula; involved in shoulder shrugging and some downward scapular rotation.
Posterior Shoulder Nerves
- Spinal Accessory Nerve (CN XI): Innervates trapezius and sternocleidomastoid muscles; damage leads to weakness or paralysis; crucial for upper body range of motion.
- Dorsal Scapular Nerve: Innervates rhomboid muscles; injury decreases scapular retraction and affects posture.
- Suprascapular Nerve: Innervates supraspinatus and infraspinatus muscles; damage weakens abduction and external rotation of the shoulder.
Anterior Shoulder Muscles
- Pectoralis Major: A large, fan-shaped muscle on the anterior chest; actions include flexion, adduction, and internal rotation of the humerus; involved in horizontal adduction.
- Pectoralis Minor: A smaller muscle beneath the pectoralis major; actions include scapular protraction, downward rotation, and elevation.
- Biceps Brachii: A shoulder and elbow flexor; contributes to shoulder flexion and internal rotation, though its contribution is limited.
- Coracobrachialis: Responsible for shoulder flexion and adduction.
- Anterior Deltoid: The anterior fibers of the deltoid muscle; principally involved in shoulder flexion and horizontal adduction..
- Subscapularis: A rotator cuff muscle on the anterior scapula; function is internal rotation of the humerus.
Anterior Shoulder Nerves
- Musculocutaneous Nerve: Innervates biceps brachii, coracobrachialis, and some brachialis; provides sensation to parts of the forearm; involved in elbow and shoulder flexion, and forearm sensation.
- Lateral Pectoral Nerve: Innervates the clavicular portion of the pectoralis major.
- Medial Pectoral Nerve: Innervates the sternal portion of pectoralis major and pectoralis minor.
- Subcostal Nerve: Contributes to serratus anterior action; not directly associated with anterior shoulder joint movement but innervates related structures.
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Description
Test your knowledge on the posterior shoulder muscles, including the trapezius, rhomboids, latissimus dorsi, and infraspinatus. Understand their functions, locations, and importance in shoulder movement and stability. This quiz is perfect for anatomy and physiology students.
