Muscular System — MCQs
Golgi tendon organ function is?
A 25 year old female presents with generalized restriction of eye movement in all direction, intermittent ptosis, proximal muscle weakness and fatigability.Which is the MOST useful test in making the diagnosis?
Arrange the following parts of sarcomere from periphery to center. 1. Z line 2. M line 3. A band 4. H zone
The most distinguishing feature between skeletal and smooth muscle is the absence of ------ in smooth muscle.
Which of the following is true regarding Lambert-Eaton myasthenic syndrome?
During a 100 m sprint which of the following is used by the muscle for meeting energy demands?
What is a key difference between smooth muscle and skeletal muscle physiology?
Postmortem caloricity may be seen in all the following causes of death, except:
Which of the following is the constituent of the marked area in the given electron microscope picture of the muscle?
The coracoid process is a type of epiphysis that is:
Muscular System Indian Medical PG Practice Questions and MCQs
Question 1: Golgi tendon organ function is?
- A. Detects the dynamic change in muscle length
- B. Detects the muscle stretch
- C. Detects the muscle strength
- D. Detects the muscle tension (Correct Answer)
Explanation: ***Detects the muscle tension*** - The **Golgi tendon organ (GTO)** is a proprioceptor located at the musculotendinous junction, specifically designed to monitor and respond to changes in **muscle tension** or force. - When muscle tension increases, such as during a strong contraction, the GTO sends inhibitory signals to the motor neurons of the same muscle, leading to muscle relaxation and preventing injury (autogenic inhibition). *Detects the dynamic change in muscle length* - This function is primarily attributed to **muscle spindles**, which are specialized sensory receptors that detect changes in the **length** and rate of change of length of a muscle. - Muscle spindles are responsible for the **stretch reflex**, initiating a contraction when a muscle is stretched too quickly. *Detects the muscle stretch* - While GTOs are involved in reflex responses that can follow muscle stretch, their primary role is not to detect the stretching itself, but rather the **tension** that results from that stretch. - **Muscle spindles** are the primary mechanoreceptors responsible for detecting the stretch of a muscle. *Detects the muscle strength* - "Muscle strength" is a broader term referring to the force a muscle can exert, which is controlled by a combination of neural input and muscle fiber characteristics. - While GTOs contribute to the overall proprioceptive feedback regulating muscle force, they specifically detect **tension** rather than directly measuring "strength" as a global concept.
Question 2: A 25 year old female presents with generalized restriction of eye movement in all direction, intermittent ptosis, proximal muscle weakness and fatigability.Which is the MOST useful test in making the diagnosis?
- A. CPK
- B. Edrophonium test (Correct Answer)
- C. EMG
- D. Muscle biopsy
Explanation: ***Edrophonium test*** - The **Edrophonium test** (Tensilon test) is highly useful for diagnosing **myasthenia gravis** due to its rapid onset and short duration of action. - In a patient with suspected myasthenia gravis, such as this one presenting with **generalized restriction of eye movement**, **intermittent ptosis**, and **fatigable proximal muscle weakness**, the administration of edrophonium will lead to a temporary but significant improvement in muscle strength. It works by inhibiting the breakdown of acetylcholine, thereby increasing its availability at the neuromuscular junction [1]. *CPK* - **Creatine phosphokinase (CPK)** levels are typically normal in myasthenia gravis, as it is a disorder of the **neuromuscular junction**, not a primary muscle disease. - Elevated CPK levels usually indicate muscle damage, seen in conditions like **myositis** or **muscular dystrophies**, which are not suggested by the patient's symptoms. *EMG* - **Electromyography (EMG)**, specifically **repetitive nerve stimulation (RNS)** or **single-fiber EMG (SFEMG)**, can show characteristic decremental responses or increased jitter/blocking in myasthenia gravis [2], but it is less direct and often more invasive than the Edrophonium test for initial diagnostic confirmation. - While supportive, it is generally considered a secondary diagnostic tool after a strong clinical suspicion and is not the *most useful* initial test compared to the rapid symptomatic improvement seen with edrophonium. *Muscle biopsy* - A **muscle biopsy** is generally not useful in diagnosing myasthenia gravis as the muscle tissue itself is structurally normal. - This diagnostic tool is reserved for primary **muscle disorders** like muscular dystrophies or inflammatory myopathies, which would show characteristic histological changes.
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: 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 5: Which of the following is true regarding Lambert-Eaton myasthenic syndrome?
- A. Deep tendon reflexes are preserved
- B. Pyridostigmine can be used as treatment
- C. Associated with autoantibodies against P/Q-type calcium channels (Correct Answer)
- D. It is a presynaptic disorder of the neuromuscular junction that can cause weakness
Explanation: ***Associated with autoantibodies against P/Q-type calcium channels*** - **Lambert-Eaton Myasthenic Syndrome (LEMS)** is an **autoimmune disorder** where antibodies attack **presynaptic P/Q-type voltage-gated calcium channels** at the neuromuscular junction [1]. - This attack impairs the release of **acetylcholine**, leading to **muscle weakness**, particularly in the proximal limbs [2]. *Deep tendon reflexes are preserved* - In LEMS, **deep tendon reflexes are typically diminished or absent** at rest due to insufficient neurotransmitter release [2]. - Reflexes may transiently improve with **post-tetanic potentiation** after sustained muscle contraction [2]. *Pyridostigmine can be used as treatment* - **Pyridostigmine**, an **acetylcholinesterase inhibitor**, has limited efficacy in LEMS because the primary defect is in **acetylcholine release**, not its breakdown [1]. - While it may provide some mild benefit, it is **less effective** compared to its use in **myasthenia gravis** [1]. *It is a presynaptic disorder of the neuromuscular junction that can cause weakness* - While LEMS is indeed a **presynaptic disorder of the neuromuscular junction** that causes weakness, this statement is **less specific** than the correct option. - The most defining characteristic, which is specific to its pathophysiology, is the presence of **autoantibodies against P/Q-type calcium channels** [2].
Question 6: During a 100 m sprint which of the following is used by the muscle for meeting energy demands?
- A. Phosphofructokinase
- B. Phosphocreatine (Correct Answer)
- C. Glucose 1 - phosphate
- D. Creatine phosphokinase
Explanation: ***Phosphocreatine*** - **Phosphocreatine (PCr)** is the primary energy source for a **100m sprint** (lasting 10-20 seconds). - The **ATP-PC (phosphagen) system** provides **immediate energy** by rapidly regenerating **ATP** from ADP through the transfer of a high-energy phosphate group. - This system is crucial for **short bursts of maximal intensity exercise** where energy demand exceeds the capacity of glycolysis and oxidative phosphorylation to respond quickly enough. - Phosphocreatine stores can fuel maximum effort for approximately **10-15 seconds**, making it ideal for sprint activities. *Phosphofructokinase* - **Phosphofructokinase (PFK)** is a key regulatory enzyme in **glycolysis**, not an energy substrate. - While PFK-catalyzed glycolysis contributes ATP during intense exercise, it cannot provide energy as rapidly as the phosphocreatine system. - Glycolysis becomes more prominent after the first 10-15 seconds of maximal effort. *Glucose 1-phosphate* - **Glucose 1-phosphate** is an intermediate in **glycogenolysis** (breakdown of glycogen to glucose-6-phosphate). - It is part of the pathway leading to glucose availability for glycolysis, but is not a **direct, immediate energy source** for muscle contraction. - Unlike phosphocreatine, it cannot directly regenerate ATP. *Creatine phosphokinase* - **Creatine phosphokinase (CPK)**, also known as **creatine kinase (CK)**, is the **enzyme** that catalyzes the reversible transfer of phosphate from phosphocreatine to ADP. - It facilitates the energy transfer reaction but is **not an energy substrate** itself. - The enzyme enables the phosphocreatine system to function, but the actual energy comes from phosphocreatine.
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: Postmortem caloricity may be seen in all the following causes of death, except:
- A. Barbiturates poisoning (Correct Answer)
- B. Septicemia
- C. Strychnine poisoning
- D. Tetanus
Explanation: ***Barbiturates poisoning*** - **Barbiturate poisoning** is a **CNS depressant** that typically leads to **hypothermia**, not postmortem caloricity, due to central nervous system depression and reduced metabolic rate. - The body's temperature tends to fall faster than normal after death in such cases. - Barbiturates suppress the thermoregulatory center and decrease metabolic activity. *Septicemia* - **Septicemia** often causes **hyperpyrexia** (high fever) ante-mortem due to systemic inflammation and infection. - This elevated core temperature can persist for a short period after death, resulting in **postmortem caloricity**. - The inflammatory response generates significant heat that remains temporarily post-death. *Strychnine poisoning* - **Strychnine poisoning** leads to severe **convulsions** and muscle rigidity due to inhibition of inhibitory neurotransmitters. - Sustained periods of intense muscle activity generate excessive **heat** ante-mortem, which is retained postmortem, causing caloricity. - The violent convulsions and opisthotonus posture produce marked heat generation. *Tetanus* - **Tetanus** is characterized by muscle spasms and rigidity caused by the **tetanospasmin toxin** blocking inhibitory signals. - The prolonged and intense **muscle contractions** before death generate a large amount of heat, contributing to postmortem caloricity. - Similar mechanism to strychnine but caused by bacterial toxin rather than plant alkaloid.
Question 9: Which of the following is the constituent of the marked area in the given electron microscope picture of the muscle?
- A. $\alpha$-actinin (Correct Answer)
- B. Nebulin
- C. Titin
- D. Tropomodulin
Explanation: ***$\alpha$-actinin*** - The image highlights the **Z-disc**, which is primarily composed of **$\alpha$-actinin**. - **$\alpha$-actinin** anchors the **thin filaments (actin)** at the Z-disc and helps maintain the structural integrity of the sarcomere. *Nebulin* - **Nebulin** is a large protein associated with thin filaments, regulating their **length** and contributing to their **stability**, but it is not the main constituent of the Z-disc. - It extends along the entire length of the thin filament, rather than forming the Z-disc itself. *Titin* - **Titin** is the largest known protein, responsible for the **elasticity** of muscle and connecting the Z-disc to the M-line. - While it associates with the Z-disc, it does not constitute the primary structural component of the Z-disc itself. *Tropomodulin* - **Tropomodulin** caps the **pointed (minus) end** of the **actin filaments**, regulating their length and ensuring stability in the sarcomere. - It is located at the ends of the thin filaments, away from the Z-disc.
Question 10: The coracoid process is a type of epiphysis that is:
- A. Atavistic (Correct Answer)
- B. Pressure
- C. Traction
- D. Aberrant
Explanation: ### Explanation The **coracoid process** of the scapula is a classic example of an **atavistic epiphysis**. In human anatomy, epiphyses are classified based on their functional and evolutionary characteristics. **1. Why "Atavistic" is Correct:** An atavistic epiphysis represents a bone that was once an independent element in lower vertebrates (phylogenetically) but has become fused to another bone in humans. In birds and reptiles, the coracoid is a separate, major bone of the pectoral girdle. In humans, it has lost its independence and exists merely as a process that fuses with the scapula. **2. Analysis of Incorrect Options:** * **Pressure Epiphysis:** These are found at the ends of long bones and are weight-bearing or transmit pressure across a joint (e.g., Head of the femur, Lower end of the radius). * **Traction Epiphysis:** These develop due to the "tug" or pull of tendons or muscles. They do not take part in joint formation (e.g., Greater and lesser trochanters of the femur, Tubercles of the humerus). * **Aberrant Epiphysis:** These are deviations from the norm and are not always present (e.g., Epiphysis at the head of the first metacarpal or the base of other metacarpals). **3. NEET-PG High-Yield Pearls:** * **OS Coxae:** The **os acetabuli** (the bone that forms the floor of the acetabulum) is another example of an atavistic epiphysis. * **Coracoid Ossification:** It develops from two primary centers and one secondary center. Most bones in the fetus are modeled in cartilage before enchondral ossification [1]. * **Clinical Significance:** The coracoid process serves as the origin for the short head of the biceps brachii and coracobrachialis, and the insertion for the pectoralis minor. It is often referred to as the "Surgeon's Lighthouse" because it serves as a landmark for avoiding the brachial plexus during shoulder surgery.
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