Nerve and Muscle Physiology Practice Questions

Q: A 30-year-old patient presents with muscle weakness and fatigue. Which ion channel disorder is MOST COMMONLY responsible for these symptoms?

Potassium channel. ***Potassium channel*** - **Potassium channelopathies** often lead to **muscle weakness and fatigue**, as these channels are critical for muscle cell repolarization and excitability. - Examples include **periodic paralyses**, where abnormal potassium channel function causes episodes of severe muscle weakness [2]. *Sodium channel* - **Sodium channelopathies** usually manifest as **painful myotonia** or **paralysis**, rather than general weakness [2]. - Conditions like **hyperkalemic periodic paralysis** involve sodium channel dysfunction but present distinctly with episodes of flaccid paralysis triggered by high potassium levels [2]. *Calcium channel* - **Calcium channel disorders** are more commonly associated with **neurological symptoms** like ataxia, migraines, or specific muscle diseases like **Lambert-Eaton myasthenic syndrome**, which primarily causes proximal muscle weakness [1]. - Familial hemiplegic migraine is another disorder linked to calcium channel dysfunction [3]. *Chloride channel* - **Chloride channelopathies** are known to cause conditions like **myotonia congenita**, characterized by **muscle stiffness and delayed relaxation** following contraction, not typically general muscle weakness and fatigue [2]. - The reduced chloride conductance leads to hyperexcitability of the muscle membrane.

Q: In cardiac muscles, T-tubules are present at?

Z lines. ***Z lines*** - In **cardiac muscle**, the T-tubules are located at the level of the **Z lines**, which delineate the sarcomere boundaries. - This placement allows for efficient excitation-contraction coupling by bringing the **action potential** into close proximity with the sarcoplasmic reticulum. *A lines* - The **A line** represents the length of the **myosin (thick) filaments** within the sarcomere. - T-tubules are not typically found at the A line; their primary function requires them to be positioned at the ends of the sarcomere. *I lines* - The **I line** (or I band) contains only **actin (thin) filaments** and spans from the edge of the A band to the Z disk. - While I lines are adjacent to Z lines, the precise location for T-tubules in cardiac muscle is at the Z line itself, not the I line. *A-I junction* - The **A-I junction** is the region where the A band (myosin) meets the I band (actin). - In **skeletal muscle**, T-tubules are located at the A-I junction, but in **cardiac muscle**, they are specifically at the Z line.

Q: Spinal cord has how many synapses in golgi tendon reflex?

2 synapses. ***2 synapses*** - The **Golgi tendon reflex** is a **disynaptic** reflex. - It involves an afferent neuron communicating with an interneuron, which then synapses with an efferent neuron. *1 synapse* - A **monosynaptic reflex** involves only one synapse between the afferent and efferent neuron, such as the **stretch reflex**. - The Golgi tendon reflex is more complex in its neuronal pathway. *3 synapses* - While polysynaptic reflexes can involve multiple interneurons, the direct pathway for the Golgi tendon reflex specifically involves two synapses in the spinal cord. - Three synapses would imply an additional interneuronal connection beyond the standard inhibitory interneuron. *4 synapses* - This number of synapses would be present in highly complex or polysynaptic reflexes involving extensive spinal cord processing. - The Golgi tendon reflex is simpler than a polysynaptic reflex that would demand four synapses.

Q: Which of the following statements about myosin is true?

Myosin has ATPase activity.. ***Myosin has ATPase activity.*** - The **myosin head** contains a binding site for **ATP** and possesses **ATPase activity**, which is crucial for muscle contraction. - This **ATPase activity** hydrolyzes ATP into ADP and inorganic phosphate, providing the energy for the **power stroke** during muscle contraction. *Myosin is a thin filament.* - Myosin is the primary component of **thick filaments** in muscle cells. - **Thin filaments** are primarily composed of **actin**, along with regulatory proteins like **tropomyosin** and **troponin**. *Myosin is a calcium-binding protein.* - The primary **calcium-binding protein** in muscle contraction is **troponin C**, which is part of the thin filament complex. - While calcium plays a crucial role in initiating myosin-actin interaction, myosin itself does not directly bind calcium to trigger this interaction. *Myosin covers the active site of actin.* - **Tropomyosin** is the protein that covers the **active sites** on actin filaments, preventing myosin from binding in a resting muscle. - Upon calcium binding to **troponin**, tropomyosin moves away, exposing the active sites for myosin to bind.

Q: Afferents for stretch reflexes are carried by which fibers?

Ia (Group Ia). ***Ia (Group Ia)*** - **Type Ia (Group Ia) afferent fibers** from muscle spindles are the primary sensory receptors that carry information about **muscle stretch and velocity of stretch**. - Type Ia fibers are the **largest diameter** and **fastest conducting sensory fibers** in the peripheral nervous system, ensuring rapid transmission for the monosynaptic stretch reflex. - They synapse directly on alpha motor neurons in the spinal cord, forming the basis of the **stretch reflex (myotatic reflex)**. - **Type II (Group II) afferents** also contribute to stretch reflexes by detecting static muscle length. *Gamma (γ) efferents* - **Gamma motor neurons** are **efferent (motor) fibers**, not afferent (sensory) fibers. - They innervate the **intrafusal muscle fibers** within the muscle spindle to regulate spindle sensitivity. - Their role is motor control of spindle tension, not carrying sensory information from the stretch reflex. *Type B* - **Type B fibers** are **preganglionic autonomic fibers** (sympathetic and parasympathetic). - They are **myelinated** but smaller and slower than Type Ia fibers, and are not involved in somatic stretch reflexes. *Type C* - **Type C fibers** are **unmyelinated**, small-diameter, and the **slowest conducting** nerve fibers. - They primarily transmit **pain (nociception)**, **temperature**, and some **autonomic** signals, not proprioceptive information for stretch reflexes.

Q: In a muscle fiber at rest, the length of the I band is 1 mm and A band is 1.5 mm. What is the length of the sarcomere?

2.5 mm. ***2.5 mm*** - A **sarcomere** is defined as the region between two successive **Z-discs** and is the functional contractile unit of muscle. - Each sarcomere contains: one complete **A band** (1.5 mm) in the center, and **half of each adjacent I band** on either side. - The given **I band length of 1 mm** represents the full I band, so each sarcomere contains two halves of I bands: 0.5 mm + 0.5 mm = 1 mm total. - Therefore, sarcomere length = **A band + two half I-bands** = 1.5 mm + 0.5 mm + 0.5 mm = **2.5 mm**. *0.5 mm* - This value represents only half of the I band length, which is the portion of I band within one sarcomere from one side. - This does not account for the **A band** or the other half of the **I band**, so it grossly underestimates sarcomere length. *3.5 mm* - This incorrect value would result from adding the **A band** to two complete **I bands** (1.5 mm + 1 mm + 1 mm = 3.5 mm). - This is wrong because each sarcomere contains only **two halves** of I bands (totaling one I band), not two complete I bands. *5 mm* - This value has no anatomical basis in sarcomere structure given the measurements provided. - It represents a significant overestimation and misunderstanding of how the **A band** and **I band** components sum to form the sarcomere length.

Q: Dull visceral pain is carried by which type of neurons?

C fibres. ***C fibres*** - **C fibres** are unmyelinated, small-diameter nerve fibres that conduct impulses slowly (0.5-2 m/s). - They are primarily responsible for transmitting **dull, aching, burning, and chronic pain**, including the diffuse, visceral pain often associated with internal organs. - Visceral pain is typically poorly localized and carried predominantly by C fibers. *A delta* - **A-delta (Aδ) fibres** are thinly myelinated, small-diameter nerve fibres that conduct impulses at moderate speeds (5-30 m/s). - They transmit **sharp, localized, and acute pain** (fast pain or "first pain"), which is different from the dull visceral pain described. - These fibers are responsible for the initial sharp sensation of pain. *Aa* - **Aα (alpha) fibres** are large-diameter, heavily myelinated nerve fibres that conduct impulses very rapidly (70-120 m/s). - They are primarily involved in transmitting **proprioception** (sense of body position) and **motor information to skeletal muscles**, not pain. *B* - **B fibres** are lightly myelinated, small-diameter nerve fibres (3-15 m/s), predominantly found in the autonomic nervous system. - They typically transmit **preganglionic autonomic signals** and are not directly involved in the sensation of somatic or visceral pain.

Q: Which type of fibers carry warmth sensation?

C fibers. ***C fibers*** - **C fibers** are **unmyelinated**, slow-conducting nerve fibers responsible for transmitting **dull, aching pain** and **warmth sensations**. - They are also involved in conveying **itching** and some types of **light touch**. *Aα fibers* - **Aα fibers** are **large**, **myelinated** and are primarily involved in transmitting **proprioception** (sense of body position) and **motor information** to skeletal muscles. - They have the **fastest conduction velocity** among peripheral nerve fibers. *Aβ fibers* - **Aβ fibers** are **medium-sized**, **myelinated** fibers that primarily transmit **light touch**, **pressure**, and **vibration** sensations. - They are responsible for discriminative touch and tactile sensations. *Aδ fibers* - **Aδ fibers** (not Aγ) are **small**, **myelinated** fibers that transmit **fast, sharp pain** and **cold** sensations. - They conduct more rapidly than C fibers due to myelination.

Question 1

A 30-year-old patient presents with muscle weakness and fatigue. Which ion channel disorder is MOST COMMONLY responsible for these symptoms?

Accepted Answer

Potassium channel

Answer

Sodium channel

Answer

Calcium channel

Answer

Chloride channel

Question 2

In cardiac muscles, T-tubules are present at?

Accepted Answer

Z lines

Answer

A lines

Answer

I lines

Answer

A-I junction

Question 3

Spinal cord has how many synapses in golgi tendon reflex?

Accepted Answer

2 synapses

Answer

1 synapse

Answer

3 synapses

Answer

4 synapses

Question 4

Which of the following statements about myosin is true?

Accepted Answer

Myosin has ATPase activity.

Answer

Myosin is a thin filament.

Answer

Myosin is a calcium-binding protein.

Answer

Myosin covers the active site of actin.

Question 5

Afferents for stretch reflexes are carried by which fibers?

Accepted Answer

Ia (Group Ia)

Answer

Gamma (γ) efferents

Answer

Type B

Answer

Type C

Question 6

In a muscle fiber at rest, the length of the I band is 1 mm and A band is 1.5 mm. What is the length of the sarcomere?

Accepted Answer

2.5 mm

Answer

0.5 mm

Answer

3.5 mm

Answer

5 mm

Question 7

Which of the following statements accurately describes Type C nerve fibers?

Accepted Answer

They are primarily responsible for transmitting pain and temperature sensations.

Answer

They are involved in motor functions.

Answer

They can transmit both sensory and motor signals.

Answer

They are involved in various types of nerve signal transmission.

Question 8

Dull visceral pain is carried by which type of neurons?

Accepted Answer

C fibres

Answer

A delta

Answer

Aa

Answer

B

Question 9

Which type of fibers carry warmth sensation?

Accepted Answer

C fibers

Answer

Aα fibers

Answer

Aβ fibers

Answer

Aδ fibers

Question 10

Excitability of cells is maximally affected by a change in the concentration of which ion?

Accepted Answer

Ca2+

Answer

Na+

Answer

K+

Answer

Cl-

Nerve and Muscle Physiology — MCQs

Nerve and Muscle Physiology — MCQs

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