Nerve and Muscle Physiology Practice Questions

Q: Most common type of calcium channels of skeletal muscles is?

L-type. ***L type*** - **L-type calcium channels**, also known as **dihydropyridine receptors (DHPRs)**, are the predominant type of calcium channel found in skeletal muscle. - In skeletal muscle, they serve as voltage sensors that **mechanically link** to ryanodine receptors (RyRs) on the sarcoplasmic reticulum to trigger calcium release without significant calcium influx from the extracellular space. *N-type* - **N-type calcium channels** are primarily found in **neurons** and play a crucial role in neurotransmitter release at synapses. - They are not the primary calcium channels involved in skeletal muscle excitation-contraction coupling. *T-type* - **T-type calcium channels** are low-voltage activated channels found in various excitable cells, including cardiac muscle and neurons, where they contribute to **pacemaker activity** and repetitive firing. - They are not the main calcium channels responsible for excitation-contraction coupling in skeletal muscle. *R-type* - **R-type calcium channels** are found in various neural cells and are involved in diverse functions, including **synaptic transmission**, but their precise physiological role is less clearly defined compared to other types. - These channels are not the primary calcium entry pathways in skeletal muscle and do not play a significant role in its contraction.

Q: What is the primary action observed in the withdrawal reflex?

Flexion. ***Flexion*** - The **withdrawal reflex** is a protective reflex that causes the affected limb to **flex** and withdraw from a painful stimulus. - This **flexion** is mediated by the contraction of flexor muscles and relaxation of extensor muscles, moving the limb away from danger. *Extension* - **Extension** is the opposite of flexion and would move the limb closer to or maintain its position relative to the painful stimulus. - This action is typically observed in the **crossed extensor reflex**, where the contralateral limb extends to support the body, not in the direct withdrawal of the stimulated limb. *Flexion followed by extension* - While **flexion** is the primary action, it is not typically followed immediately by extension within the same limb in a simple withdrawal reflex. - If a coordinated movement were to occur, such as shifting weight, the **crossed extensor reflex** would involve extension in the opposite limb. *Not applicable* - The withdrawal reflex involves a clear and defined muscle action which is **flexion**, making "not applicable" incorrect. - This reflex is a fundamental component of the nervous system's response to noxious stimuli.

Q: ATPase activity is present in

Myosin. ***Myosin*** - Myosin heads possess intrinsic **ATPase activity**, meaning they can hydrolyze ATP into ADP and inorganic phosphate. - This **ATP hydrolysis** provides the energy required for the **power stroke** during muscle contraction, detaching the myosin head from actin. *Actin* - Actin filaments themselves do not have ATPase activity. - Actin's primary role is to form the **thin filaments** and bind to myosin heads during contraction. *Actin during interaction with myosin* - While actin interacts with myosin, it does not acquire ATPase activity. - The **myosin head**, not actin, is responsible for ATP hydrolysis during this interaction. *None of the options* - This option is incorrect because **myosin** clearly possesses ATPase activity, which is crucial for muscle function.

Q: Which of the following fiber types is classically categorized as Group B nerve fibers?

Sympathetic preganglionic. ***Sympathetic preganglionic*** - **Group B nerve fibers** are **myelinated preganglionic autonomic fibers** with intermediate diameter (3-15 μm) and moderate conduction velocity (3-15 m/s) - Both **sympathetic and parasympathetic preganglionic fibers** are classified as Group B fibers - **Sympathetic preganglionic** neurons are the classical example, originating from T1-L2 spinal segments and synapsing in paravertebral or prevertebral ganglia *Sympathetic postganglionic* - These are **unmyelinated Group C fibers** with slow conduction velocity (0.5-2 m/s) - They extend from ganglia to target organs *Parasympathetic preganglionic* - These are also **Group B fibers** (myelinated preganglionic) - However, **sympathetic preganglionic** is the more commonly cited classical example in standard classifications - They originate from cranial nerves (III, VII, IX, X) and sacral segments (S2-S4) *Parasympathetic postganglionic* - These are **unmyelinated Group C fibers** with the slowest conduction velocities - Short fibers extending from ganglia near or within target organs to effector cells

Q: Which type of nerve fibers are responsible for carrying joint position and vibration sense?

A-beta fibers. ***A-beta fibers*** - **A-beta fibers** are **large-diameter, myelinated** sensory fibers that conduct impulses rapidly. - They are primarily responsible for transmitting **light touch, pressure, joint position (proprioception), and vibration sense**. - **This is the correct answer** because A-beta fibers carry **BOTH joint position AND vibration sense together**. *A-alpha fibers* - **A-alpha fibers** are the **largest and fastest** conducting nerve fibers. - They include **motor nerves to skeletal muscles** and **sensory fibers from muscle spindles (Ia) and Golgi tendon organs (Ib)**. - While Ia fibers (A-alpha) do carry **proprioception from muscle spindles**, they do **NOT carry vibration sense**. - The question asks for fibers carrying **BOTH** joint position **AND** vibration sense, making A-beta the correct answer. *C fibers* - **C fibers** are **small-diameter, unmyelinated** nerve fibers with **slow conduction velocities**. - They are responsible for transmitting **dull, aching pain, temperature, and crude touch**. *A-delta fibers* - **A-delta fibers** are **small-diameter, thinly myelinated** nerve fibers with an intermediate conduction velocity. - They primarily transmit **sharp, fast pain** and **cold temperature sensations**.

Q: What is a key difference between smooth muscle and skeletal muscle physiology?

Troponin is absent in smooth muscle.. ***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.

Q: When the tension in a muscle fibre is maximum, its length is called?

Optimum length. ***Optimum length*** - This is the muscle length at which the **maximum number of cross-bridges** can form between actin and myosin filaments. - At this length, the sarcomere allows for the **greatest overlap** of thick and thin filaments without excessive stretching or compression, leading to peak tension generation. *Equilibrium length* - This term usually refers to the **resting length** of a muscle fiber when no external forces are acting upon it. - At equilibrium, the tension generated by the muscle may not necessarily be at its maximum. *Initial length* - This is a general term that refers to the **starting length** of a muscle fiber before it contracts or is stretched. - It does not specifically denote the length at which maximum tension is achieved. *None of the options* - This option is incorrect because **optimum length** accurately describes the muscle length yielding maximum tension.

Q: Tetanic contraction is due to accumulation of?

Ca 2+ . ***Ca 2+ *** - **Tetanic contraction** results from a rapid succession of muscle stimulations, leading to the sustained elevation of **intracellular calcium (Ca 2+ )** levels. - This persistent high Ca 2+ 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 Ca 2+ 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 Ca 2+ release required for tetanic contraction.

Question 1

Most common type of calcium channels of skeletal muscles is?

Accepted Answer

L-type

Answer

N-type

Answer

T-type

Answer

R-type

Question 2

What is the primary action observed in the withdrawal reflex?

Accepted Answer

Flexion

Answer

Extension

Answer

Flexion followed by extension

Answer

Not applicable

Question 3

ATPase activity is present in

Accepted Answer

Myosin

Answer

Actin

Answer

Actin during interaction with myosin

Answer

None of the options

Question 4

Which of the following fiber types is classically categorized as Group B nerve fibers?

Accepted Answer

Sympathetic preganglionic

Answer

Sympathetic postganglionic

Answer

Parasympathetic preganglionic

Answer

Parasympathetic post ganglionic

Question 5

Which type of nerve fibers are responsible for carrying joint position and vibration sense?

Accepted Answer

A-beta fibers

Answer

A-alpha fibers

Answer

C fibers

Answer

A-delta fibers

Question 6

What is the primary factor that determines the resting membrane potential in a nerve fiber?

Accepted Answer

Is primarily determined by the equilibrium potential of potassium ions.

Answer

Is equal to the resting potential of cardiac muscle fibers.

Answer

Can be accurately measured using intracellular electrodes.

Answer

Increases with elevated extracellular potassium concentration.

Question 7

What is a key difference between smooth muscle and skeletal muscle physiology?

Accepted Answer

Troponin is absent in smooth muscle.

Answer

Calcium is required for contraction.

Answer

Myosin is essential for contraction.

Answer

Potassium is required for contraction.

Question 8

A man slept with his head over his forearm. The next morning, he complains of tingling and numbness over the forearm. If this were primarily due to hypoxia affecting nerve fibers, which of the following statements about nerve fiber sensitivity to hypoxia is correct?

Accepted Answer

B fibers are most sensitive to hypoxia, followed by A fibers, and C fibers are least sensitive.

Answer

All nerve fibers are equally sensitive to hypoxia.

Answer

C fibers are most sensitive to hypoxia, followed by B fibers, and A fibers are least sensitive.

Answer

A fibers are most sensitive to hypoxia, followed by B fibers, and C fibers are least sensitive.

Question 9

When the tension in a muscle fibre is maximum, its length is called?

Accepted Answer

Optimum length

Answer

None of the options

Answer

Initial length

Answer

Equilibrium length

Question 10

Tetanic contraction is due to accumulation of?

Accepted Answer

Ca<sup>2+</sup>

Answer

Na+

Answer

K+

Answer

Cl<sup>-</sup>

Nerve and Muscle Physiology — MCQs

Nerve and Muscle Physiology — MCQs

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