Muscular Tissue — MCQs
Intermediate filaments in connective tissue are which type of structural component?
An electron microscopy of muscle biopsy shows 'parking lot' appearance. Which additional finding would confirm myotonic dystrophy?
Which of the following statements is NOT true regarding red muscle fibers?
What is the role of gap junctions in cardiac muscle function?
Which of the following is NOT a hybrid muscle?
In the context of muscle physiology, which structure is described as a threadlike component that extends along the length of a muscle fiber?
Intercalated disc is present in:
The connective tissue layer around each muscle fascicle is called:
The most distinguishing feature between skeletal and smooth muscle is the absence of ------ in smooth muscle.
Identify the type of connective tissue present in the image.
Muscular Tissue Indian Medical PG Practice Questions and MCQs
Question 1: Intermediate filaments in connective tissue are which type of structural component?
- A. Keratin
- B. Vimentin (Correct Answer)
- C. Lamin
- D. Desmin
Explanation: ***Vimentin*** - **Vimentin** is the most common intermediate filament found in cells of **mesenchymal origin**, including those in connective tissue (e.g., fibroblasts) [1]. - It plays a crucial role in maintaining **cell shape**, integrity, and in processes like cell migration and adhesion within connective tissue [1]. *Keratin* - **Keratins** (also known as cytokeratins) are the primary intermediate filaments found in **epithelial cells**, providing structural integrity to tissues like skin, hair, and nails [1]. - They are not typically found in connective tissue cells, which have different structural requirements. *Desmin* - **Desmin** is an intermediate filament predominantly found in **muscle cells** (skeletal, cardiac, and smooth muscle). - It helps in maintaining the structural and mechanical integrity of the **sarcomere** and muscle fibers. *Lamin* - **Lamins** are unique intermediate filaments that form the **nuclear lamina**, a fibrous network underlying the inner nuclear membrane found in almost all nucleated cells. - They provide structural support to the nucleus and are involved in chromatin organization and gene regulation.
Question 2: An electron microscopy of muscle biopsy shows 'parking lot' appearance. Which additional finding would confirm myotonic dystrophy?
- A. Ragged red fibers
- B. Ring fibers (Correct Answer)
- C. Central cores
- D. Nemaline rods
Explanation: ***Ring fibers*** - **Ring fibers** are a classic histopathological feature seen in **myotonic dystrophy**, characterized by peripheral myofibrils arranged circularly around a central core [1]. - The "parking lot" appearance on electron microscopy refers to collections of **sarcoplasmic reticulum** and **T-tubules**, which can be seen in various myopathies but are often prominent in myotonic dystrophy, complementing the presence of ring fibers [1]. *Ragged red fibers* - **Ragged red fibers** are characteristic of **mitochondrial myopathies**, indicating abnormal proliferation of mitochondria beneath the sarcolemma. - They are typically identified with **Gomori trichrome stain** and are not a feature of myotonic dystrophy. *Central cores* - **Central cores** are a hallmark of **central core disease**, a congenital myopathy, and are regions within muscle fibers where oxidative enzyme activity is absent. - These are not typically associated with myotonic dystrophy; rather, they suggest a different underlying genetic defect affecting muscle structure. *Nemaline rods* - **Nemaline rods** are rod-like inclusions observed in muscle fibers in **nemaline myopathy**, an inherited disorder often associated with mutations in genes encoding components of the thin filament. - They are distinct from the pathological findings in myotonic dystrophy and point to a specific type of congenital myopathy. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 732-733.
Question 3: Which of the following statements is NOT true regarding red muscle fibers?
- A. Decreased glycolytic enzymes
- B. Used for aerobic activity
- C. Increased blood flow
- D. Increased muscle fiber length (Correct Answer)
Explanation: ***Increased muscle fiber length*** - The length of muscle fibers is generally determined by the muscle's anatomical structure and function, not by whether they are red or white fibers. - While red muscle fibers (slow-twitch) are optimized for **endurance** and **sustained contractions**, this optimization does not involve an inherent increase in the length of individual muscle fibers. *Decreased glycolytic enzymes* - Red muscle fibers, also known as slow-oxidative fibers, primarily rely on **aerobic metabolism** for ATP production. - They have a lower content of glycolytic enzymes compared to white muscle fibers, which are specialized for **anaerobic glycolysis**. *Increased blood flow* - Red muscle fibers have a rich capillary supply, leading to **increased blood flow**, which is essential for delivering oxygen and nutrients for sustained aerobic activity. - This extensive vascularization contributes to their characteristic red appearance and their ability to resist fatigue. *Used for aerobic activity* - Red muscle fibers are well-suited for prolonged, low-intensity activities due to their high concentration of **mitochondria**, myoglobin, and oxidative enzymes. - They are primarily responsible for maintaining posture and performing **endurance activities** such as long-distance running.
Question 4: What is the role of gap junctions in cardiac muscle function?
- A. Are not found in cardiac muscles
- B. Are not found in smooth muscles
- C. Have no significant role in cardiac muscle function
- D. Facilitate impulse transmission between cardiac myocytes (Correct Answer)
Explanation: ***Facilitate impulse transmission between cardiac myocytes*** - **Gap junctions** are specialized channels between adjacent cells that allow for direct communication and rapid movement of **ions** and small molecules. - In cardiac muscle, they form an essential part of **intercalated discs**, enabling the heart to function as a **syncytium** by allowing electrical impulses to spread quickly from one myocyte to another. *Are not found in cardiac muscles* - This statement is incorrect; **gap junctions** are a defining feature of **cardiac muscle** and are crucial for its coordinated contraction. - They are located within the **intercalated discs** that connect individual cardiac muscle cells. *Are not found in smooth muscles* - This statement is incorrect; **gap junctions** are indeed found in **smooth muscle**, particularly in single-unit smooth muscle, where they contribute to synchronized contractions, such as in the **gastrointestinal tract**. - They allow for the rapid propagation of electrical signals, leading to coordinated muscle activity. *Have no significant role in cardiac muscle function* - This statement is incorrect; **gap junctions** play a critically significant role in cardiac muscle function by ensuring the **rapid and synchronized spread of electrical impulses**. - Without functional gap junctions, the heart would not be able to contract efficiently or effectively as a pump.
Question 5: Which of the following is NOT a hybrid muscle?
- A. Sternocleidomastoid
- B. Flexor pollicis brevis
- C. Brachialis
- D. Adductor pollicis (Correct Answer)
Explanation: ***Adductor pollicis*** - The adductor pollicis is solely innervated by the **deep branch of the ulnar nerve (C8, T1)**, making it a non-hybrid muscle. - Its primary actions are **adduction, opposition, and flexion of the thumb**. *Sternocleidomastoid* - This muscle is considered hybrid because it is innervated by two different nerves: the **spinal accessory nerve (CN XI)** and branches from the **cervical plexus (C2-C3)**. - The spinal accessory nerve innervates primarily the motor function, while the cervical plexus provides proprioceptive fibers. *Flexor pollicis brevis* - This muscle often has a dual innervation, with its superficial head supplied by the **median nerve** and its deep head by the **ulnar nerve** [1]. - This dual innervation pattern qualifies it as a hybrid muscle [1]. *Brachialis* - The brachialis muscle is typically innervated by the **musculocutaneous nerve (C5, C6)**, but it also receives a small contribution from the **radial nerve (C7)**. - This additional supply from the radial nerve makes it a hybrid muscle.
Question 6: In the context of muscle physiology, which structure is described as a threadlike component that extends along the length of a muscle fiber?
- A. Sarcomere
- B. Sarcolemma
- C. Myofibril (Correct Answer)
- D. Myofilament
Explanation: ***Myofibril*** - A **myofibril** is a cylindrical organelle that runs longitudinally inside a muscle fiber and contains **contractile proteins**. - Myofibrils are composed of repeating units called **sarcomeres**, which are the fundamental units of muscle contraction. *Sarcomere* - A **sarcomere** is the basic contractile unit of a muscle fiber, extending from one Z-disc to the next. - While it is a key component for muscle contraction, it is a **segment within a myofibril**, not the threadlike component that extends the entire length of the fiber. *Sarcolemma* - The **sarcolemma** is the cell membrane of a muscle fiber, responsible for transmitting nerve impulses to the muscle cell. - It encloses the muscle fiber but is not an internal, threadlike contractile component. *Myofilament* - **Myofilaments** are the individual protein filaments (actin and myosin) that make up a sarcomere within a myofibril. - They are the **smallest contractile elements**, but they are not the threadlike structure that extends along the entire muscle fiber.
Question 7: Intercalated disc is present in:
- A. Cardiac muscle (Correct Answer)
- B. Smooth muscle
- C. Skeletal muscle
- D. All of the options
Explanation: ***Cardiac muscle*** - **Intercalated discs** are unique structures found only in cardiac muscle, forming specialized cell-cell junctions [1]. - These discs contain **gap junctions** for electrical coupling and **desmosomes** for strong adhesion, allowing the heart muscle to contract in a coordinated fashion. *Smooth muscle* - **Smooth muscle cells** are spindle-shaped and lack striations and organized sarcomeres. - They do not possess intercalated discs; instead, communication and coordination are often mediated by **gap junctions** scattered along the cell membranes [2]. *Skeletal muscle* - **Skeletal muscle cells** are long, multinucleated, and highly organized with prominent striations [3]. - They do not have intercalated discs as individual muscle fibers are innervated separately and generally do not directly communicate via specialized junctions for coordinated contraction. *All of the options* - As **intercalated discs** are characteristic features *only* of **cardiac muscle**, this option is incorrect. - Their presence in all three muscle types would contradict the specific cellular organization of smooth and skeletal muscle.
Question 8: The connective tissue layer around each muscle fascicle is called:
- A. Epimysium
- B. Perimysium (Correct Answer)
- C. Sarcolemma
- D. Endomysium
Explanation: ***Perimysium*** - This **connective tissue sheath** surrounds a bundle of muscle fibers, known as a **fascicle**. - It contains **blood vessels** and **nerves** that supply the muscle fibers within the fascicle. *Epimysium* - This is the **outermost layer of connective tissue** that surrounds the entire skeletal muscle. - It blends with the **deep fascia** and helps to separate individual muscles from surrounding tissues. *Sarcolemma* - This refers to the **plasma membrane** of a muscle fiber (muscle cell). - It plays a crucial role in transmitting the **electrical impulses** that initiate muscle contraction. *Endomysium* - This delicate layer of connective tissue surrounds and **insulates each individual muscle fiber**. - It contains **capillaries** and **nerve fibers** that supply the individual muscle cells.
Question 9: The most distinguishing feature between skeletal and smooth muscle is the absence of ------ in smooth muscle.
- A. Actin
- B. Troponin (Correct Answer)
- C. Tropomyosin
- D. Myosin
Explanation: ***Troponin*** - **Smooth muscle** lacks the **troponin complex** (troponin I, C, and T) that is essential for initiating contraction in skeletal and cardiac muscle. - Instead of troponin, smooth muscle uses **calmodulin** to bind calcium, which then activates **myosin light chain kinase** to regulate contraction. *Tropomyosin* - **Tropomyosin** is present in both **skeletal** and **smooth muscle**, though it plays a different regulatory role in smooth muscle. - In smooth muscle, tropomyosin does not block myosin binding sites, but rather modulates the interaction between actin and myosin. *Myosin* - **Myosin** is a fundamental motor protein found in all types of muscle, including both **skeletal** and **smooth muscle**. - It forms thick filaments and interacts with actin to generate force and muscle contraction. *Actin* - **Actin** is a primary component of thin filaments and is universally present in all muscle types, including **skeletal** and **smooth muscle**. - It provides the framework along which myosin heads slide to produce muscle shortening.
Question 10: Identify the type of connective tissue present in the image.
- A. Loose and irregular
- B. Specialized
- C. Dense irregular (Correct Answer)
- D. Dense regular
Explanation: ***Dense irregular*** - The image shows **densely packed collagen fibers** arranged in an **irregular, haphazard fashion**, characteristic of dense irregular connective tissue. - This type of tissue provides **strength** and resistance to stress from multiple directions, found in the **dermis of the skin** and organ capsules. *Loose and irregular* - **Loose connective tissue** would show more ground substance and fewer, loosely arranged fibers, whereas this image displays high fiber density. - While it is "irregular" in fiber arrangement, the density of fibers rules out the "loose" classification. *Specialized* - **Specialized connective tissues** include cartilage, bone, blood, and adipose tissue, which have distinct cellular and extracellular matrix components not seen here. - This tissue lacks the specific cellular and matrix characteristics that would classify it as specialized (e.g., chondrocytes in lacunae, osteocytes, blood cells). *Dense regular* - **Dense regular connective tissue** features collagen fibers arranged in parallel bundles, providing strength in one direction. - Examples include **tendons and ligaments**, which are structurally organized in an orderly, aligned manner, unlike the displayed irregular arrangement.
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