Microscopic Anatomy of Muscle Tissues — MCQs
All of the following are true about skeletal muscle except?
What is the anatomical arrangement of fibers in the masseter muscle that contributes to its strength?
Arrange the following parts of sarcomere from periphery to center. 1. Z line 2. M line 3. A band 4. H zone
A 4-year-old boy is brought to the physician by his parents due to frequent falls, inability to jump, and easy fatigue. Physical examination reveals weakness in the pelvic and shoulder girdles, as well as enlargement of the child's calf muscles. The serum level of creatine kinase is elevated. A biopsy of calf muscle reveals marked variation in size and shape of muscle fibers, with foci of muscle fiber necrosis, myophagocytosis, regenerating fibers, and fibrosis. Molecular diagnostic assays performed on muscle biopsy from the patient would show alterations in the length of the primary transcript for which muscle-associated protein?
Single-unit smooth muscles are seen in which of the following?
Which of the following are supportive proteins?
What is a key difference between smooth muscle and skeletal muscle physiology?
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?
Identify the type of muscle shown in the image.
The lateral boundary of the cubital fossa is formed by
Microscopic Anatomy of Muscle Tissues Indian Medical PG Practice Questions and MCQs
Question 1: All of the following are true about skeletal muscle except?
- A. Have multiple nuclei
- B. Have transverse striations
- C. The nuclei are central (Correct Answer)
- D. They are cylindrical in shape
Explanation: The nuclei are central - Skeletal muscle fibers are **multinucleated**, but their nuclei are typically located **peripherally** (just beneath the sarcolemma), not centrally. - This peripheral placement allows the contractile proteins to occupy the majority of the cell's volume. *Have multiple nuclei* - Skeletal muscle cells develop from the fusion of multiple myoblasts, resulting in **syncytia** with numerous nuclei. - This high number of nuclei supports the large volume and metabolic demands of these long, contractile cells. *Have transverse striations* - The organized arrangement of **actin and myosin filaments** into sarcomeres creates a characteristic pattern of light (I bands) and dark (A bands) bands [2]. - These regularly repeating bands are visible as **transverse striations** under a light microscope [1]. *They are cylindrical in shape* - Individual skeletal muscle fibers are typically long and **cylindrical**, maintaining a relatively uniform diameter along their length. - This shape is well-suited for their primary function of generating force and shortening.
Question 2: What is the anatomical arrangement of fibers in the masseter muscle that contributes to its strength?
- A. Bipennate arrangement of fibers
- B. Parallel arrangement with oblique fibers (Correct Answer)
- C. Random arrangement of fibers
- D. Circumpennate arrangement of fibers
Explanation: The original text cannot be accurately cited with the provided references because they do not contain specific information regarding the masseter muscle's anatomical fiber arrangement. ***Parallel arrangement with oblique fibers*** - The **masseter muscle** has a complex arrangement with **parallel fibers running in oblique directions**, which is the key to its strength and power. - The **superficial part** has fibers running **obliquely downward and backward**, while the **deep part** has fibers running more **vertically**. - This arrangement allows the muscle to generate **powerful biting force** by combining multiple fiber orientations, maximizing cross-sectional area and force production. - The masseter is sometimes classified as **multipennate** due to this complex architecture, but the fundamental arrangement is **parallel fibers with oblique orientation**. *Bipennate arrangement of fibers* - A **bipennate arrangement** (like the rectus femoris) has fibers approaching a central tendon from two sides like a feather. - While the masseter is powerful, its fiber arrangement is better described as **oblique parallel** or **multipennate** rather than strictly bipennate. - The masseter's two heads (superficial and deep) have different fiber orientations, which is not characteristic of a simple bipennate muscle. *Random arrangement of fibers* - Skeletal muscles require an **organized fiber arrangement** for effective force transmission. - A **random arrangement** would result in inefficient force generation and poor coordination of muscle contraction. *Circumpennate arrangement of fibers* - **Circumpennate** (or multipennate) arrangement has fibers converging from multiple directions to central tendons, as seen in the **deltoid muscle**. - While some sources describe the masseter as multipennate due to its complex architecture, the more precise anatomical description emphasizes its **parallel fibers with oblique orientation** in distinct superficial and deep parts.
Question 3: Arrange the following parts of sarcomere from periphery to center. 1. Z line 2. M line 3. A band 4. H zone
- A. 2,3,4,1
- B. 4,2,3,1
- C. 3,1,4,2
- D. 1,3,4,2 (Correct Answer)
Explanation: ***1,3,4,2*** - The **Z line** is found at the **periphery** of the sarcomere, defining its boundaries and anchoring the **actin filaments**. - Moving inwards, the **A band** is next, representing the entire length of the **myosin filament**, which may also overlap with actin. - The **H zone** is located within the A band, comprising only **myosin filaments** without actin overlap. - Finally, the **M line** is at the **center** of the sarcomere, bisecting the H zone and anchoring the myosin filaments. *2,3,4,1* - This sequence is incorrect because the **M line** is at the **center** and the **Z line** is at the **periphery**, which is the reverse of the expected order for from periphery to center. - Such an arrangement would place the innermost structure first and outermost last, not reflecting the correct spatial organisation. *4,2,3,1* - This order is incorrect as the **H zone** and **M line** are more central, while the **Z line** is peripheral. - Placing structures like the H zone and M line at the beginning does not align with arrangement from periphery to center. *3,1,4,2* - This option is incorrect because the **A band** includes both actin and myosin filaments, while the **Z line** is at the periphery of the sarcomere. - The given order does not represent a progression from the periphery to the center of the sarcomere.
Question 4: A 4-year-old boy is brought to the physician by his parents due to frequent falls, inability to jump, and easy fatigue. Physical examination reveals weakness in the pelvic and shoulder girdles, as well as enlargement of the child's calf muscles. The serum level of creatine kinase is elevated. A biopsy of calf muscle reveals marked variation in size and shape of muscle fibers, with foci of muscle fiber necrosis, myophagocytosis, regenerating fibers, and fibrosis. Molecular diagnostic assays performed on muscle biopsy from the patient would show alterations in the length of the primary transcript for which muscle-associated protein?
- A. Creatine kinase
- B. Desmin
- C. Dystrophin (Correct Answer)
- D. Glycogen phosphorylase
Explanation: ***Dystrophin*** - The clinical features, including muscle weakness, calf muscle hypertrophy, and elevated **creatine kinase**, indicate a muscular dystrophy, most characteristically associated with **dystrophin** deficiency [1]. - **Muscle biopsy results** showing variation in muscle fiber size and necrosis further support the diagnosis of **Duchenne muscular dystrophy**, where dystrophin mutations are commonly identified [1]. *Desmin* - Although desmin is a muscle protein, it is primarily involved in **muscle fiber structure** and not directly associated with the symptoms or findings noted in this case. - Conditions linked to desmin abnormalities usually involve **myofibrillar myopathies**, which present differently than the scenario described here. *Glycogen phosphorylase* - Glycogen phosphorylase is crucial in **glycogen metabolism**, and its deficiency typically leads to metabolic myopathies presenting with **exercise intolerance** rather than the distinct symptoms of muscle necrosis seen here. - The muscle pathology observed (necrosis and regeneration) does not correlate with typical presentations seen in glycogen storage diseases. *Creatine kinase* - While creatine kinase levels are elevated in many muscle disorders, including dystrophies, it is not a structural protein and thus does not fit the question's focus on **primary transcript alterations** [2]. - Measuring creatine kinase assists in diagnosing muscle damage but does not indicate a molecular defect like **dystrophin**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1244-1245. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1245-1246.
Question 5: Single-unit smooth muscles are seen in which of the following?
- A. Iris
- B. Ductus deferens
- C. Trachea
- D. Ureter (Correct Answer)
Explanation: ***Ureter*** - The ureter contains **single-unit smooth muscle** which exhibits spontaneous electrical activity and contraction, allowing for peristaltic movement of urine. - In single-unit smooth muscle, cells are connected by **gap junctions**, enabling them to contract as a coordinated unit. *Iris* - The iris contains **multi-unit smooth muscle**, which allows for fine, independent control of each muscle cell for precise pupil dilation and constriction. - Multi-unit smooth muscle cells are not connected by gap junctions and require individual neural stimulation. *Ductus deferens* - The ductus deferens primarily consists of **multi-unit smooth muscle**, which is necessary for the strong, rapid contractions required for sperm expulsion during ejaculation. - This type of muscle allows for graded contractions depending on the intensity of nervous stimulation. *Trachea* - The smooth muscle in the trachea (trachealis muscle) is primarily **multi-unit smooth muscle**, facilitating independent regulation of airway diameter. - Contraction of the trachealis muscle can reduce the tracheal lumen, aiding in coughing or regulating airflow.
Question 6: Which of the following are supportive proteins?
- A. Titin
- B. Dystropin
- C. All of the options (Correct Answer)
- D. Desmin
Explanation: ***Correct: All of the options*** - **Titin**, **Dystrophin**, and **Desmin** are all well-known supportive proteins within muscle tissue, playing crucial roles in maintaining structural integrity and function. - These proteins contribute to the elasticity, stability, and transmission of force within muscle fibers. **Titin** - A giant sarcomeric protein responsible for muscle elasticity and maintaining the structural integrity of myofibrils. - Acts as a molecular spring, anchoring myosin thick filaments to the Z-disk and contributing to passive muscle force. **Dystrophin** - Provides a critical link between the muscle cytoskeleton and the extracellular matrix. - Its absence or malfunction leads to muscle degeneration, as seen in **Duchenne muscular dystrophy**. **Desmin** - An intermediate filament protein that forms a scaffold around sarcomeres. - Connects sarcomeres to each other, to the sarcolemma, and to organelles like mitochondria. - Essential for maintaining alignment and mechanical integration of myofibrils within muscle cells.
Question 7: What is a key difference between smooth muscle and skeletal muscle physiology?
- A. Calcium is required for contraction.
- B. Troponin is absent in smooth muscle. (Correct Answer)
- C. Myosin is essential for contraction.
- D. Potassium is required for contraction.
Explanation: ***Troponin is absent in smooth muscle.*** * Smooth muscle contraction is regulated by **calcium-calmodulin complex** and subsequent activation of **myosin light chain kinase (MLCK)**, in contrast to skeletal muscle's reliance on the troponin-tropomyosin system. * **Troponin** is a calcium-binding protein found in skeletal and cardiac muscle, which plays a critical role in regulating muscle contraction by initiating the movement of tropomyosin, thereby exposing myosin-binding sites on actin. *Calcium is required for contraction.* * While calcium is indeed required for contraction in both smooth and skeletal muscle, the **mechanism of its action** differs, making this statement insufficiently discriminative as a *key difference*. * In both muscle types, an increase in intracellular **calcium** initiates the contractile process, but the downstream signaling pathways diverge significantly. *Myosin is essential for contraction.* * **Myosin** is a fundamental motor protein essential for contraction in *all* muscle types, including skeletal, cardiac, and smooth muscle. * This statement highlights a similarity, not a key difference, as **actin-myosin cross-bridge cycling** is the basis of force generation in all muscle tissues. *Potassium is required for contraction.* * **Potassium ions** are crucial for maintaining the resting membrane potential and for repolarization following an action potential, which is necessary for muscle excitability, but they do not directly trigger muscle contraction. * The influx of calcium (or release from intracellular stores) is the direct trigger for contraction, not potassium.
Question 8: 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.
Question 9: Identify the type of muscle shown in the image.
- A. Cruciate muscle
- B. Multipennate muscle (Correct Answer)
- C. Parallel muscle
- D. Unipennate muscle
Explanation: ***Multipennate muscle*** - The image displays the deltoid muscle, which is a classic example of a **multipennate muscle** - In **multipennate muscles**, muscle fibers are organized in multiple fascicles that attach obliquely to a central tendon, allowing for great strength and a broad range of motion - The muscle shown demonstrates fibers converging at multiple angles to central tendons, characteristic of this muscle type *Cruciate muscle* - **Cruciate muscles** have fibers that cross each other in an 'X' pattern, which is not characteristic of the muscle shown - An example is the masseter muscle where fibers cross each other - This crossing pattern is not seen in the deltoid muscle *Parallel muscle* - **Parallel muscles** have fibers that run parallel to the long axis of the muscle, such as the rectus abdominis or sartorius - The muscle in the image clearly shows fibers converging at oblique angles rather than running in parallel - This arrangement is distinctly different from the pennate pattern shown *Unipennate muscle* - **Unipennate muscles** have fibers that attach obliquely to only one side of a central tendon - Examples include the extensor digitorum longus and flexor pollicis longus - The muscle shown has fibers attaching to multiple sides of central tendons, making it multipennate rather than unipennate
Question 10: 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.
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