Muscle and Tendon Physiology — MCQs

10 questions

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

Sequence the events in neuromuscular action potential conduction: 1. Sodium channels open in the end plate 2. Calcium enters at the nerve terminal 3. Release of acetylcholine

Tetanic contraction is due to accumulation of?

The protein responsible for elasticity of the muscle is:

Granulation tissue is replaced by connective tissue in what stage of wound healing?

Golgi tendon organs are innervated by which type of nerve fibre?

Third extensor compartment of wrist contains tendon of?

The image below shows a pressure sore. Which stage does this belong to?

Inverse stretch reflex is mediated :

Q10

Which muscle tendon is stretched in patellar tendon reflex?

Muscle and Tendon Physiology Indian Medical PG Practice Questions and MCQs

Question 1: 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 2: Sequence the events in neuromuscular action potential conduction: 1. Sodium channels open in the end plate 2. Calcium enters at the nerve terminal 3. Release of acetylcholine

A. $1 \rightarrow 2 \rightarrow 3$
B. $1 \rightarrow 3 \rightarrow 2$
C. $3 \rightarrow 2 \rightarrow 1$
D. $2 \rightarrow 3 \rightarrow 1$ (Correct Answer)

Explanation: ***Correct: $2 \rightarrow 3 \rightarrow 1$*** - **Calcium entry at the nerve terminal** is the initial trigger - when an action potential reaches the presynaptic nerve terminal, voltage-gated calcium channels open, allowing Ca²⁺ influx - **Acetylcholine release** follows - the increased intracellular calcium causes synaptic vesicles containing acetylcholine to fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft - **Sodium channels open in the end plate** last - acetylcholine binds to nicotinic receptors on the motor end plate, opening ligand-gated sodium channels, which depolarizes the muscle membrane and triggers muscle contraction *Incorrect: $1 \rightarrow 2 \rightarrow 3$* - Places sodium channel opening first, which is physiologically impossible - Sodium channels at the motor end plate only open in response to acetylcholine binding - Cannot occur before acetylcholine is released from the nerve terminal *Incorrect: $1 \rightarrow 3 \rightarrow 2$* - Incorrectly sequences sodium channel opening before calcium entry - Violates the fundamental principle that calcium influx is required for neurotransmitter release - Acetylcholine cannot be released without prior calcium entry *Incorrect: $3 \rightarrow 2 \rightarrow 1$* - Places acetylcholine release before calcium entry, which is impossible - Calcium-triggered exocytosis is an absolute requirement for neurotransmitter release - Without calcium influx, vesicles cannot fuse with the presynaptic membrane

Question 3: Tetanic contraction is due to accumulation of?

A. Na+
B. K+
C. Ca2+ (Correct Answer)
D. Cl-

Explanation: ***Ca2+*** - **Tetanic contraction** results from a rapid succession of muscle stimulations, leading to the sustained elevation of **intracellular calcium (Ca2+)** levels. - This persistent high Ca2+ concentration in the sarcoplasm allows for continuous binding to **troponin**, maintaining the activation of cross-bridge cycling. *Na+* - **Sodium (Na+)** influx is primarily responsible for the **depolarization** of the muscle cell membrane, leading to an **action potential**. - While essential for initiating the contraction, Na+ accumulation itself does not directly cause the sustained high Ca2+ levels characteristic of tetany. *K+* - **Potassium (K+)** efflux is crucial for the **repolarization** of the muscle cell membrane after an action potential. - Accumulation of K+ in the extracellular space can contribute to muscle fatigue and reduce excitability, but it does not directly lead to tetanic contraction. *Cl-* - **Chloride (Cl-)** ions play a significant role in stabilizing the resting membrane potential and contributing to muscle **repolarization**, particularly in skeletal muscle. - While important for muscle function, changes in Cl- concentration do not directly cause the sustained Ca2+ release required for tetanic contraction.

Question 4: The protein responsible for elasticity of the muscle is:

A. Myosin
B. Titin (Correct Answer)
C. Actin
D. Tropomyosin

Explanation: ***Titin*** - **Titin** is a giant protein that functions as a molecular spring within the sarcomere, providing **passive elasticity** to muscle. - It helps anchor **myosin filaments** and contributes to the muscle's ability to **stretch and recoil**. *Myosin* - **Myosin** is primarily responsible for generating force and muscle contraction through its interaction with **actin**, not for elasticity. - It forms the thick filaments and uses **ATP hydrolysis** to power the cross-bridge cycle. *Actin* - **Actin** forms the thin filaments and serves as the binding site for myosin heads during muscle contraction. - While essential for contraction, it does not provide the primary elastic properties of muscle. *Tropomyosin* - **Tropomyosin** is a regulatory protein that wraps around actin filaments and blocks myosin-binding sites in the relaxed state. - It plays a role in **muscle contraction regulation**, not in providing elasticity.

Question 5: Granulation tissue is replaced by connective tissue in what stage of wound healing?

A. 7 days (Correct Answer)
B. 14 days
C. 21 days
D. 1 month

Explanation: ***21 days*** - Granulation tissue formation is prominent until about **21 days**, after which it starts to reorganize into fibrous connective tissue [1][2]. - In this stage, collagen deposition increases, contributing to **wound strength** and integrity [2]. *1 month* - By this time, connective tissue maturation continues but the primary transition from granulation tissue typically completes by **21 days** [2]. - It may lead to overestimation of healing progression as remodeling may still be ongoing. *14 days* - At **14 days**, granulation tissue is still present and not yet fully replaced by connective tissue [1]. - This stage primarily involves **vascularization** and **inflammatory responses**, not complete fibrous change [1]. *7 days* - This early phase is characterized by **hemostasis** and **inflammation**, with granulation tissue just beginning to form [1]. - Significant connective tissue replacement has not yet occurred, as the wound healing process is still at the initial stages. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 117-119. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 119-121.

Question 6: Golgi tendon organs are innervated by which type of nerve fibre?

A. Ia
B. Ib (Correct Answer)
C. II
D. III

Explanation: ***Ib*** - **Golgi tendon organs (GTOs)** are encapsulated sensory receptors located in the musculoskeletal junction that monitor **muscle tension**. - They are innervated by **Ib afferent nerve fibers**, which are large diameter, myelinated nerve fibers with a high conduction velocity that transmit information to the central nervous system. *Ia* - **Ia afferent nerve fibers** innervate **muscle spindles**, which detect changes in **muscle length** and the rate of change of muscle length. - While both Ib and Ia fibers are involved in proprioception, their specific sensory receptors and functions differ. *II* - **Type II afferent nerve fibers** also innervate **muscle spindles**, primarily sensing sustained changes in **muscle length** (static stretch). - They do not innervate Golgi tendon organs; their role is distinct in providing information about muscle position. *III* - **Type III afferent nerve fibers** are smaller, thinly myelinated fibers that respond mainly to **nociceptive (pain)** and **temperature stimuli** in muscles and joints. - They are not involved in sensing muscle tension or length and do not innervate Golgi tendon organs.

Question 7: Third extensor compartment of wrist contains tendon of?

A. ECRL
B. ECRB
C. EPL (Correct Answer)
D. EPB

Explanation: EPL - The **extensor pollicis longus (EPL)** tendon passes through the **third dorsal extensor compartment** of the wrist [1]. - This compartment is located between Lister's tubercle and the ulnar side of the dorsal tubercle [1]. ECRL - The **extensor carpi radialis longus (ECRL)** tendon is found in the **second dorsal extensor compartment** of the wrist [1]. - It shares this compartment with the extensor carpi radialis brevis [1]. ECRB - The **extensor carpi radialis brevis (ECRB)** tendon is located in the **second dorsal extensor compartment**, alongside the ECRL [1]. - Its primary function is wrist extension and radial deviation. EPB - The **extensor pollicis brevis (EPB)** tendon is part of the **first dorsal extensor compartment** of the wrist [1]. - This compartment also contains the abductor pollicis longus (APL) tendon [1].

Question 8: The image below shows a pressure sore. Which stage does this belong to?

A. Stage 1
B. Stage 2
C. Stage 3
D. Stage 4 (Correct Answer)

Explanation: ***Stage 4*** - The image clearly shows **extensive tissue loss**, including exposed bone and muscle, indicating a **deep tissue injury**. - The presence of large areas of **dead tissue (eschar)**, undermining, and tunneling are characteristic features of a stage 4 pressure sore. *Stage 1* - This stage involves **intact skin** with non-blanchable redness, indicating only superficial damage. - There is no **break in the skin** or tissue loss in Stage 1 pressure sores. *Stage 2* - Characterized by **partial-thickness skin loss**, presenting as an open blister or shallow ulcer. - **No visible deeper tissue** such as fat, muscle, or bone is exposed in this stage. *Stage 3* - Involves **full-thickness skin loss** with visible subcutaneous fat, but bone, tendon, or muscle are not exposed. - While there may be **undermining or tunneling**, the deep structures are not yet visible as seen in the image.

Question 9: Inverse stretch reflex is mediated :

A. Unmyelinated C fibres
B. Dorsal Column
C. Muscle spindle
D. Golgi tendon organ (Correct Answer)

Explanation: ***Golgi tendon*** - The **Golgi tendon organ (GTO)** is a **proprioceptor** located at the junction of muscle fibers and tendons, sensitive to changes in muscle tension. - When muscle tension becomes excessive, the GTO is activated, inhibiting the alpha motor neurons innervating that muscle, leading to muscle relaxation, which is the **inverse stretch reflex**. *Unmyelinated C fibres* - These fibers are primarily involved in transmitting **slow, dull pain** and **temperature sensations**, but not proprioceptive reflexes. - Their conduction velocity is much slower than that required for rapid protective reflexes. *Dorsal Column* - The dorsal column-medial lemniscus pathway is responsible for transmitting **fine touch, vibration, and proprioception** to the brain, but it is an ascending sensory pathway and does not directly mediate spinal reflexes. - This pathway is involved in conscious perception, not the direct arc of a reflex. *Muscle spindle* - The **muscle spindle** is responsible for the **stretch reflex** (myotatic reflex), which causes muscle contraction in response to stretch. - It detects changes in **muscle length and rate of change of length**, which is distinct from the inverse stretch reflex mediated by the GTO.

Question 10: Which muscle tendon is stretched in patellar tendon reflex?

A. Biceps femoris
B. Semitendinosus
C. Quadriceps femoris (Correct Answer)
D. Adductor magnus

Explanation: ***Quadriceps femoris*** - The patellar tendon reflex is an example of a **stretch reflex**, where striking the patellar tendon directly stretches the quadriceps femoris muscle. - This stretch activates **muscle spindles** within the quadriceps, leading to its contraction and subsequent leg extension. *Biceps femoris* - The biceps femoris is part of the **hamstring muscle group**, located on the posterior aspect of the thigh. - Its primary action is **knee flexion** and hip extension, and it is not directly stretched during the patellar tendon reflex. *Semitendinosus* - The semitendinosus is also a **hamstring muscle** and functions in knee flexion and hip extension. - It is located medially on the posterior thigh and is not involved in the patellar tendon reflex arc. *Adductor magnus* - The adductor magnus is a large muscle on the **medial side of the thigh**, primarily responsible for **hip adduction**. - It is not directly stretched by tapping the patellar tendon and does not participate in the patellar reflex.

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