Anatomical Aspects of Exercise Physiology — MCQs

10 questions

Golgi tendon organ function is?

Arrange the following parts of sarcomere from periphery to center. 1. Z line 2. M line 3. A band 4. H zone

During heavy exercise the cardiac output (CO) increases up to five fold while pulmonary arterial pressure rises very little. This physiological ability of the pulmonary circulation is best explained by

During exercise in physiological limits, what is the effect on end systolic volume?

During exercise increase in O2 delivery to muscles is because of all except:

Least useful for a 800-m run in a competitive event would be

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?

Which of the following is the constituent of the marked area in the given electron microscope picture of the muscle?

Q10Easy

What is the fastest acting receptor/transduction mechanism?

Anatomical Aspects of Exercise Physiology 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: 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 3: During heavy exercise the cardiac output (CO) increases up to five fold while pulmonary arterial pressure rises very little. This physiological ability of the pulmonary circulation is best explained by

A. Large amount of smooth muscle in pulmonary arterioles
B. Increase in the number of open capillaries (Correct Answer)
C. Sympathetically mediated greater distensibility of pulmonary vessels
D. Smaller surface area of pulmonary circulation

Explanation: ***Increase in the number of open capillaries*** - During heavy exercise, the significant increase in cardiac output is accommodated by the **recruitment of previously closed pulmonary capillaries**. - This recruitment, along with **distension of existing capillaries**, reduces overall pulmonary vascular resistance, allowing blood flow to increase without a substantial rise in pulmonary arterial pressure. *Large amount of smooth muscle in pulmonary arterioles* - While pulmonary arterioles do contain smooth muscle, their primary role is in **regulating regional blood flow** and response to hypoxia, not facilitating large increases in overall blood flow during exercise. - The pulmonary circulation is characterized by **low resistance** and high capacitance compared to the systemic circulation, meaning it has less smooth muscle tone at baseline. *Sympathetically mediated greater distensibility of pulmonary vessels* - The pulmonary vasculature has **limited sympathetic innervation** compared to systemic vessels, and sympathetic activity plays a minor role in its distensibility during exercise. - Changes in pulmonary vascular resistance during exercise are primarily due to **mechanical factors** (recruitment and distension) rather than neurogenic control. *Smaller surface area of pulmonary circulation* - The pulmonary circulation actually has a **vast capillary surface area** crucial for efficient gas exchange. - A smaller surface area would lead to **higher resistance** and a greater pressure increase for a given flow, which contradicts the observation during exercise.

Question 4: During exercise in physiological limits, what is the effect on end systolic volume?

A. ESV decreases (Correct Answer)
B. ESV increases
C. ESV first decreases and then increases
D. ESV remains unchanged

Explanation: ***ESV decreases*** - During exercise, **sympathetic nervous system activity** increases, leading to enhanced cardiac contractility. - Improved contractility allows the heart to eject a greater percentage of its end-diastolic volume, resulting in a smaller **residual volume** in the ventricle after systole. *ESV increase* - An increase in ESV would indicate a **reduced ejection fraction** and poorer cardiac efficiency, which is contrary to the physiological adaptations during exercise. - This typically occurs in conditions of **heart failure** or myocardial dysfunction, not healthy exercise. *ESV first decrease and then increases* - While there are complex physiological responses during exercise, the primary and sustained effect on ESV within physiological limits is a **net decrease** due to increased contractility. - A subsequent increase would suggest a decline in cardiac function or the onset of fatigue beyond physiological limits. *ESV remain unchanged* - An unchanged ESV would imply no significant alteration in **cardiac contractility** or **ejection efficiency**, which is inconsistent with the cardiovascular demands and adaptations during exercise. - The body actively works to optimize cardiac output by increasing stroke volume, partly by reducing ESV during exercise.

Question 5: During exercise increase in O2 delivery to muscles is because of all except:

A. Oxygen dissociation curve shifts to left (Correct Answer)
B. Increased extraction of oxygen from the blood
C. Increased stroke volume
D. Increased blood flow to muscles

Explanation: ***Oxygen dissociation curve shifts to left*** - A **left shift** in the oxygen-hemoglobin dissociation curve means hemoglobin has a **higher affinity for oxygen**, making it *less likely to release* oxygen to the tissues. - During exercise, the body requires *more oxygen delivery* to muscles, thus a *right shift* (facilitating oxygen release) would be beneficial, not a left shift. *Increased extraction of oxygen from the blood* - Exercising muscles increase their **oxygen consumption**, leading to a *greater arteriovenous oxygen difference* as more oxygen is extracted from the blood flowing through them. - This is a key mechanism for increasing oxygen supply without necessarily increasing blood flow proportionally. *Increased stroke volume* - During exercise, **stroke volume increases** to pump *more blood per beat*, directly contributing to a higher cardiac output. - A higher cardiac output ensures that a *larger volume of oxygenated blood* reaches the exercising muscles. *Increased blood flow to muscles* - **Vasodilation** in the active muscles combined with **vasoconstriction** in inactive tissues redirects blood flow, prioritizing oxygen delivery to the working muscles. - This *enhances the supply of oxygen-rich blood* where it is most needed during physical exertion.

Question 6: Least useful for a 800-m run in a competitive event would be

A. Lohmann reaction (Correct Answer)
B. Pale muscle fibres
C. Muscle glycogen
D. Oxidative phosphorylation

Explanation: ***Lohmann reaction*** - The **Lohmann reaction** (creatine kinase reaction) is primarily involved in rapid, **short-burst energy production** for activities lasting a few seconds (e.g., sprints). - An 800-meter run is a middle-distance event requiring sustained energy from both anaerobic and aerobic pathways, where the immediate **phosphocreatine** system (Lohmann reaction) is quickly depleted and less useful for the majority of the race. *Pale muscle fibres* - **Pale muscle fibers** (Type II or fast-twitch fibers) are characterized by a high capacity for **anaerobic metabolism** and rapid, powerful contractions. - While they are crucial for the initial burst and speed in an 800-m run, their high glycolytic capacity makes them essential for the sustained high-intensity effort required, even as the race progresses beyond pure sprint. *Muscle glycogen* - **Muscle glycogen** is the primary stored carbohydrate fuel for **anaerobic glycolysis**, which is a significant energy pathway during the high-intensity portions of an 800-m run. - Its breakdown provides quick ATP generation without oxygen, supporting the rapid pace required throughout much of the race. *Oxidative phosphorylation* - **Oxidative phosphorylation** (aerobic respiration) becomes increasingly important as an 800-m race progresses, contributing a substantial portion of the ATP required for sustained muscle contraction. - It allows for the efficient production of large amounts of ATP when oxygen is available, crucial for maintaining pace and minimizing fatigue over the middle distance.

Question 7: 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 8: 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 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: What is the fastest acting receptor/transduction mechanism?

A. Adenylyl cyclase-cyclic AMP pathway
B. Phospholipase C-IP3:DAG pathway
C. Intrinsic ion channel operation (Correct Answer)
D. Nuclear receptor

Explanation: **Explanation:** The speed of a receptor's response is determined by the number of biochemical steps involved between ligand binding and the final physiological effect. **Why Option C is Correct:** **Intrinsic ion channel operation** (also known as **Ionotropic receptors**) represents the fastest transduction mechanism. In these receptors (e.g., Nicotinic ACh receptors, GABA-A receptors), the receptor itself is an ion channel. Upon ligand binding, the channel undergoes an immediate conformational change to allow ion flow [1]. This process occurs within **milliseconds**, making it ideal for rapid neurotransmission and muscle contraction. **Why the other options are incorrect:** * **Options A & B (G-Protein Coupled Receptors - GPCRs):** These utilize the Adenylyl cyclase and Phospholipase C pathways. They are slower because they require a "middleman" (G-proteins) and the generation of second messengers (cAMP, IP3, DAG). Their response time is typically in **seconds**. * **Option D (Nuclear Receptors):** These are the slowest. They involve ligand transport into the nucleus, binding to DNA, and subsequent gene transcription and protein synthesis. This process takes **hours to days**. **NEET-PG High-Yield Pearls:** * **Fastest to Slowest Sequence:** Ionotropic (ms) > Metabotropic/GPCR (seconds) > Enzyme-linked (minutes) > Nuclear receptors (hours/days). * **Classic Example:** The **Nicotinic ACh receptor** at the neuromuscular junction is the prototype for rapid ionotropic signaling. * **Clinical Correlation:** Rapid-acting drugs often target ion channels (e.g., local anesthetics blocking Na+ channels), whereas drugs with delayed onset (e.g., Steroids, Thyroxine) act via nuclear receptors.

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