Muscles and Their Actions — MCQs
Which of the following is true about nerve injuries?
All of the following muscles have dual nerve supply, EXCEPT?
Which muscle is not part of the superficial anterior compartment of the forearm?
Winging of scapula is due to paralysis of
A young boy presents with multiple humerus fractures, resulting in loss of sensation over the lateral side of the forearm, along with difficulty in elbow flexion and forearm supination. What is the most likely nerve injury responsible for these symptoms?
Damage to median nerve produces:
Which muscle paralysis can cause winging of the scapula?
What is the nerve supply of the structure marked in the image?
The lateral boundary of the cubital fossa is formed by
The image shows a highlighted region on the dorsal aspect of the hand (anatomical snuffbox). Which of the following anatomical structures form the boundaries or floor of this region?
Muscles and Their Actions Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is true about nerve injuries?
- A. Froment sign seen in median nerve palsy is due to Flexor pollicis longus action
- B. All lumbricals are supplied by median nerve
- C. Waenburg sign is seen in median nerve palsy
- D. Median nerve is also named as labourer's nerve (Correct Answer)
Explanation: ***Median nerve is also named as labourer's nerve*** - The median nerve is sometimes called the "laborer's nerve" because it innervates many of the muscles essential for **fine motor control** and **dexterous hand movements** predominantly used in manual labor. [1] - It supplies most of the **flexors in the forearm** and several intrinsic hand muscles, making it crucial for a strong grip and coordinated hand actions. [1] *Froment sign seen in median nerve palsy is due to Flexor pollicis longus action* - **Froment's sign** is observed in **ulnar nerve palsy**, not median nerve palsy. - It occurs when the adductor pollicis is weak, and the **flexor pollicis longus** (median nerve-innervated) compensates by hyperflexing the interphalangeal joint of the thumb to grasp an object. *All lumbricals are supplied by median nerve* - The **first two lumbricals** (from the radial side) are typically supplied by the **median nerve**. [1] - The **third and fourth lumbricals** (from the ulnar side) are supplied by the **ulnar nerve**. [1] *Waenburg sign is seen in median nerve palsy* - There is no widely recognized clinical sign called "Waenburg sign" associated with median nerve palsy. - Common signs of **median nerve palsy** include **ape hand deformity**, **hand of benediction**, and sensory loss in the radial three and a half digits. [1]
Question 2: All of the following muscles have dual nerve supply, EXCEPT?
- A. Flexor digitorum profundus
- B. Pectineus
- C. Brachialis
- D. Flexor digitorum superficialis (Correct Answer)
Explanation: No changes were made to the original explanation because none of the provided references met the relevance criteria for the specific muscles and nerves discussed. ***Flexor digitorum superficialis*** - This muscle is solely innervated by the **median nerve**. - It works to **flex the middle phalanges** of the medial four digits. *Flexor digitorum profundus* - The medial half of the muscle, which supplies the ring and little fingers, is innervated by the **ulnar nerve**. - The lateral half, which supplies the index and middle fingers, is innervated by the **anterior interosseous nerve** (a branch of the median nerve). *Pectineus* - This muscle typically receives innervation from both the **femoral nerve** and the **obturator nerve**. - Its primary action is **adduction and flexion of the hip**. *Brachialis* - While primarily innervated by the **musculocutaneous nerve**, a small component also receives innervation from the **radial nerve**. - It is a powerful **flexor of the elbow joint**.
Question 3: Which muscle is not part of the superficial anterior compartment of the forearm?
- A. FDS
- B. FCR
- C. Palmaris longus
- D. Flexor pollicis longus (FPL) (Correct Answer)
Explanation: **Flexor pollicis longus (FPL)** - The **FPL** is located in the **deep anterior compartment** of the forearm, differentiating it from the superficial muscles [1]. - Its primary function is **flexion of the thumb's interphalangeal joint**, requiring a deeper anatomical position for mechanical advantage [1]. *FDS* - The **Flexor digitorum superficialis (FDS)** is a key muscle of the superficial anterior compartment, visible just beneath the skin and fascia. - It is responsible for **flexing the middle phalanges** of the medial four digits. *FCR* - The **Flexor carpi radialis (FCR)** is situated in the superficial anterior compartment, running obliquely across the forearm. - It functions in **flexion and abduction of the wrist**. *Palmaris longus* - The **Palmaris longus** is a superficial anterior compartment muscle, though it is absent in a significant portion of the population. - When present, its main action is **flexion of the wrist** and tightening of the palmar aponeurosis.
Question 4: Winging of scapula is due to paralysis of
- A. Serratus anterior (Correct Answer)
- B. Rhomboid major
- C. Trapezius
- D. Levator scapulae
Explanation: ***Serratus anterior*** - The **serratus anterior muscle** is responsible for **protraction and rotation of the scapula**, holding it close to the thoracic wall. - Paralysis of this muscle, often due to injury to the **long thoracic nerve**, causes the **medial border of the scapula** to protrude posteriorly, a condition known as **medial scapular winging**. - This is the **classic and most common cause** of scapular winging. *Rhomboid major* - The rhomboid major muscle primarily performs **retraction and downward rotation of the scapula**. - Paralysis of this muscle would lead to the scapula being displaced laterally and superiorly, not winging. *Trapezius* - The trapezius muscle has multiple actions, including **elevating, depressing, retracting, and rotating the scapula**. - Paralysis of the trapezius (e.g., due to **accessory nerve damage**) can cause **lateral scapular winging** where the inferior angle protrudes, along with shoulder drooping and difficulty shrugging. - However, **serratus anterior paralysis** is the classic answer for scapular winging in exam contexts. *Levator scapulae* - The levator scapulae muscle is primarily involved in **elevating and downwardly rotating the scapula**. - Dysfunction of this muscle would impair shoulder elevation but would not be the direct cause of scapular winging.
Question 5: A young boy presents with multiple humerus fractures, resulting in loss of sensation over the lateral side of the forearm, along with difficulty in elbow flexion and forearm supination. What is the most likely nerve injury responsible for these symptoms?
- A. Median nerve
- B. Axillary
- C. Radial nerve
- D. Musculocutaneous nerve (Correct Answer)
- E. Ulnar nerve
Explanation: ***Musculocutaneous nerve*** - The **musculocutaneous nerve** innervates the biceps brachii and brachialis muscles, responsible for **elbow flexion** and **forearm supination**, and provides sensation to the **lateral forearm** via the lateral cutaneous nerve of the forearm. - A fracture of the humerus can damage this nerve, leading to the observed **motor and sensory deficits**. *Median nerve* - The median nerve primarily controls **flexion of the wrist and fingers**, and **pronation of the forearm**, as well as sensation to the palmar aspect of the thumb, index, middle, and radial half of the ring finger. - Its injury would not typically cause difficulty with **elbow flexion** or sensory loss over the **lateral forearm**. *Axillary* - The axillary nerve primarily innervates the **deltoid** and **teres minor muscles**, important for shoulder abduction and external rotation. - An injury would lead to **weakness in shoulder abduction** and sensory loss over the lateral shoulder (regimental badge area), not the lateral forearm. *Radial nerve* - The radial nerve controls **extension of the wrist and fingers** and sensation over the posterior arm, forearm, and hand. - Injury typically results in **wrist drop** and difficulty extending the arm, not primarily elbow flexion or lateral forearm sensation. *Ulnar nerve* - The ulnar nerve innervates intrinsic hand muscles and flexor carpi ulnaris, controlling **finger abduction/adduction** and **ulnar wrist flexion**. - Sensory distribution includes the medial hand and medial 1.5 fingers, not the **lateral forearm**. - Injury causes **claw hand deformity** and sensory loss in the medial hand, not the symptoms described.
Question 6: Damage to median nerve produces:
- A. Ape thumb (Correct Answer)
- B. Winging of scapula
- C. Claw hand
- D. Wrist drop
Explanation: Ape thumb - Damage to the median nerve specifically affects the thenar muscles (via the recurrent branch): abductor pollicis brevis, opponens pollicis, and the superficial head of flexor pollicis brevis [1]. - Loss of these muscles results in the characteristic "ape thumb" deformity, where the thumb lies in the same plane as the palm and cannot be opposed [1]. - The patient loses the ability to perform thumb opposition, which is essential for precision grip and many hand functions [1]. Winging of scapula - Winging of the scapula is caused by damage to the long thoracic nerve, which innervates the serratus anterior muscle. - This condition is not associated with median nerve injury. Claw hand - A claw hand deformity is typically caused by damage to the ulnar nerve, affecting the lumbricals and interossei muscles. - It results in hyperextension of the metacarpophalangeal joints and flexion of the interphalangeal joints, particularly of the 4th and 5th digits. - This is distinct from median nerve pathology. Wrist drop - Wrist drop is a classic sign of radial nerve damage, affecting the extensor muscles of the wrist and fingers. - It results in the inability to extend the wrist and digits, which is not a feature of median nerve injury.
Question 7: Which muscle paralysis can cause winging of the scapula?
- A. Teres minor
- B. Deltoid
- C. Serratus anterior (Correct Answer)
- D. Supraspinatus
Explanation: ***Serratus anterior*** - Paralysis or weakness of the **serratus anterior muscle**, innervated by the **long thoracic nerve**, causes winging of the scapula. - This muscle is responsible for **protraction and upward rotation of the scapula**, keeping it flat against the chest wall; without its function, the medial border of the scapula protrudes posteriorly. *Teres minor* - The **teres minor** is part of the rotator cuff and is involved in **external rotation** and **adduction of the arm**. - Its paralysis would primarily affect shoulder movement and stability, but not directly lead to **scapular winging**. *Deltoid* - The **deltoid muscle** is the primary muscle for **abduction of the arm** beyond the first 15 degrees. - Paralysis of the deltoid would result in significant difficulty lifting the arm, but it does not cause the **scapula to wing**. *Supraspinatus* - The **supraspinatus muscle** initiates **abduction of the arm** (first 15 degrees) and helps stabilize the shoulder joint. - Its paralysis would impair arm elevation but does not directly result in **scapular winging**.
Question 8: What is the nerve supply of the structure marked in the image?
- A. Anterior interosseous nerve
- B. Posterior interosseous nerve
- C. Ulnar nerve
- D. Median nerve (Correct Answer)
Explanation: ***Median nerve*** - The image points to the **lateral two lumbricals**. The **median nerve** innervates the first and second (lateral two) lumbrical muscles. - These muscles contribute to **flexion of the metacarpophalangeal joints** and **extension of the interphalangeal joints** of the index and middle fingers. *Anterior interosseous nerve* - The anterior interosseous nerve is a branch of the **median nerve** and primarily supplies deep muscles of the forearm, such as the **flexor pollicis longus**, **flexor digitorum profundus (lateral half),** and **pronator quadratus**. - It does not directly innervate the lumbricals in the hand. *Posterior interosseous nerve* - The posterior interosseous nerve is a branch of the **radial nerve**. - It primarily innervates the **extensor muscles of the forearm** and wrist, not the lumbrical muscles. *Ulnar nerve* - The **ulnar nerve** innervates the **medial two lumbricals** (third and fourth), as well as most of the other intrinsic hand muscles, including the interossei. - The nerve supply of the lumbricals is split between the median and ulnar nerves, with the lateral two supplied by the median nerve.
Question 9: The lateral boundary of the cubital fossa is formed by
- A. Biceps
- B. Brachialis
- C. Brachioradialis (Correct Answer)
- D. Pronator teres
Explanation: ***Brachioradialis*** - The **brachioradialis muscle** forms the **lateral boundary** of the cubital fossa. - It originates from the lateral supracondylar ridge of the humerus and inserts on the distal radius. - This muscle is a **flexor of the elbow** and assists in bringing the forearm to a neutral position from pronation or supination. *Pronator teres* - The **pronator teres muscle** forms the **medial boundary** of the cubital fossa. - It originates from the medial epicondyle of the humerus and coronoid process of the ulna, inserting on the lateral surface of the radius. - This muscle is primarily responsible for **pronation of the forearm** and assists in elbow flexion. *Brachialis* - The **brachialis muscle** forms part of the **floor of the cubital fossa** (along with the supinator muscle). - It lies deep to the biceps brachii and inserts on the coronoid process and ulnar tuberosity. - It is a powerful **elbow flexor**, acting directly on the ulna. *Biceps* - The **biceps brachii** does not form a boundary of the cubital fossa. - Its **tendon passes through the fossa** as content, while the **bicipital aponeurosis** contributes to the roof. - The biceps is a major flexor and supinator of the forearm.
Question 10: The image shows a highlighted region on the dorsal aspect of the hand (anatomical snuffbox). Which of the following anatomical structures form the boundaries or floor of this region?
- A. Abductor pollicis longus muscle.
- B. Styloid process of the radius.
- C. Extensor pollicis longus muscle.
- D. All of the above anatomical structures. (Correct Answer)
Explanation: ***All of the above anatomical structures.*** - The image highlights the **anatomical snuffbox**, a triangular depression on the radial dorsal aspect of the hand. Its boundaries are formed by the tendons of the **extensor pollicis longus muscle** (ulnar side), and the **abductor pollicis longus** and **extensor pollicis brevis muscles** (radial side). - The **styloid process of the radius** forms the floor of the anatomical snuffbox along with the scaphoid and trapezium bones. All the options listed are key anatomical features associated with this region. *Extensor pollicis longus muscle.* - This muscle forms the **ulnar (medial) border** of the anatomical snuffbox. - Its tendon can be palpated during **thumb extension** and contributes to the overall structure of the highlighted area. *Abductor pollicis longus muscle.* - This muscle, along with the extensor pollicis brevis, forms the **radial (lateral) border** of the anatomical snuffbox. - Its tendon is visible and palpable on the radial side of the highlighted region when the thumb is abducted. *Styloid process of the radius.* - This bony prominence is located at the **distal end of the radius** on the radial side of the wrist. - It forms part of the **proximal floor** of the anatomical snuffbox, contributing to its definition.
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