Electrophysiological Measurements — MCQs
What is the primary cause of the plateau phase in the cardiac muscle action potential?
Equilibrium potential of calcium is
Which of the following statements about the Na-K pump is false?
Assertion: RMP depends on proteins and phosphate ions. Reason: Diffusion potential can be calculated using nernst equation. Choose the best statement regarding the assertion and reason.
Hyperpolarization is caused by which ions?
Alpha wave on EEG represents -
Identify the modality of intercellular communication shown below.
In multiple sclerosis, slow conduction of motor and sensory pathways is due to?
Cranial nerve 8 palsy is associated with all of the following symptoms except:
Which of the following types of nerve fibers are primarily responsible for transmitting slow, dull, and chronic pain sensations?
Electrophysiological Measurements Indian Medical PG Practice Questions and MCQs
Question 1: What is the primary cause of the plateau phase in the cardiac muscle action potential?
- A. The movement of fewer sodium ions across the cell membrane
- B. The calcium channels remaining open longer than the sodium channels (Correct Answer)
- C. The increased membrane permeability to potassium ion
- D. A decrease in the amount of calcium diffusing across the membrane
Explanation: ***The calcium channels remaining open longer than the sodium channels*** - The **plateau phase** (Phase 2) of the cardiac action potential is primarily due to the sustained influx of **calcium ions** through long-lasting L-type calcium channels. - This **calcium influx** balances the efflux of potassium ions, maintaining depolarization for an extended period, which is crucial for effective cardiac contraction and preventing tetany. *The movement of fewer sodium ions across the cell membrane* - The rapid influx of **sodium ions** is responsible for the rapid depolarization (Phase 0) of the cardiac action potential, not the plateau phase. - **Sodium channels** inactivate quickly, contributing to repolarization rather than sustained depolarization. *The increased membrane permeability to potassium ion* - Increased permeability to **potassium ions** (efflux) is mainly responsible for repolarization (Phase 3) of the cardiac action potential, bringing the membrane potential back to its resting state. - During the plateau phase, potassium efflux is partially balanced by calcium influx. *A decrease in the amount of calcium diffusing across the membrane* - A decrease in **calcium diffusion** would lead to a shorter plateau phase or more rapid repolarization, not an sustained plateau. - The **sustained influx of calcium** is the defining characteristic of the plateau.
Question 2: Equilibrium potential of calcium is
- A. +130mV (Correct Answer)
- B. -32mV
- C. +65mV
- D. -95mV
Explanation: ***+130mV*** - The **equilibrium potential** for an ion is the **membrane potential** at which the net movement of that ion across the membrane is zero, even if there is a concentration gradient. - Due to the significantly higher extracellular concentration of **calcium ions (Ca2+)** relative to the intracellular concentration, a large positive membrane potential is required to prevent Ca2+ influx. *-32mV* - This value does not represent the typical **equilibrium potential** for any major physiological ion like sodium, potassium, chloride, or calcium in mammalian cells. - Equilibrium potentials are highly dependent on the **concentration gradients** of the specific ion. *+65mV* - This value is close to the typical **equilibrium potential for sodium (Na+)**, which is approximately +60 to +70 mV in many cells, due to its outward concentration gradient. - **Calcium's equilibrium potential** is much more positive than sodium's due to its larger concentration gradient and its divalent charge. *-95mV* - This value is close to the typical **equilibrium potential for potassium (K+)**, which is approximately -90 to -95 mV, reflecting the movement of potassium out of the cell. - The **equilibrium potential for calcium** is highly positive, whereas this negative value suggests an inward current for a positively charged ion.
Question 3: Which of the following statements about the Na-K pump is false?
- A. It is not directly involved in the generation of action potentials.
- B. It is electrogenic
- C. It needs ATP for its functioning
- D. It is located on the apical membrane of cell (Correct Answer)
Explanation: ***It is located on the apical membrane of cell*** - The **Na-K pump**, or **Na+/K+-ATPase**, is primarily located on the **basolateral membrane** of epithelial cells, not **apical membrane**. - Its strategic placement on the basolateral membrane is crucial for maintaining cellular polarity and driving transepithelial transport processes, such as reabsorption in the kidneys. *It is electrogenic* - The Na-K pump is indeed **electrogenic** because it transports three **Na+ ions** out of the cell for every two **K+ ions** pumped in. - This unequal charge distribution creates a net movement of one positive charge out of the cell, contributing to the **resting membrane potential**. *It is not directly involved in the generation of action potentials.* - While the Na-K pump is essential for **maintaining the ion gradients** necessary for **action potentials**, it is not directly involved in their rapid depolarization or repolarization phases. - Action potentials are primarily generated by the rapid opening and closing of **voltage-gated ion channels** (e.g., Na+ and K+ channels). *It needs ATP for its functioning* - The Na-K pump is an **active transport mechanism** that moves ions against their concentration gradients, requiring **energy in the form of ATP hydrolysis**. - This **ATP-dependent process** ensures the continuous maintenance of the Na+ and K+ gradients, crucial for various cellular functions, including nerve impulse transmission and muscle contraction.
Question 4: Assertion: RMP depends on proteins and phosphate ions. Reason: Diffusion potential can be calculated using nernst equation. Choose the best statement regarding the assertion and reason.
- A. Assertion false, Reason true
- B. Both true, Reason is the explanation of assertion
- C. Assertion true, Reason false
- D. Both true, Reason is not the explanation of assertion (Correct Answer)
Explanation: ***Both true, Reason is not the explanation of assertion*** - The **Assertion is TRUE**: The resting membrane potential (RMP) does depend on intracellular **proteins and phosphate ions**, which are large, non-diffusible anions that remain trapped inside the cell. These molecules contribute significantly to the **net negative charge** of the intracellular compartment and create the **Gibbs-Donnan effect**. At physiological pH, most intracellular proteins are negatively charged, and phosphate ions (HPO₄²⁻, H₂PO₄⁻) are major intracellular anions. While the primary determinants of RMP are the concentration gradients and membrane permeabilities of K⁺, Na⁺, and Cl⁻ ions, the presence of non-diffusible anions (proteins and phosphates) is essential for establishing the baseline negative intracellular environment. - The **Reason is TRUE**: The **Nernst equation** (E = RT/zF × ln[ion]out/[ion]in) is indeed used to calculate the **equilibrium potential** (also called diffusion potential) for a single permeable ion. This equation determines the membrane potential at which the electrical gradient exactly balances the concentration gradient for that specific ion, resulting in no net ion movement. - **However, the Reason does NOT explain the Assertion**: The Nernst equation calculates equilibrium potentials for diffusible ions like K⁺, Na⁺, and Cl⁻. It does NOT explain the contribution of **non-diffusible** anions (proteins and phosphates) to the RMP. The actual RMP, which involves multiple ions with different permeabilities, is calculated using the **Goldman-Hodgkin-Katz (GHK) equation**, not the Nernst equation. The two statements are independently true but address different aspects of membrane potential physiology. *Assertion false, Reason true* - This is **incorrect** because the assertion is actually TRUE. Intracellular proteins and phosphate ions do contribute to the RMP by providing fixed negative charges that influence the distribution of diffusible ions and create the electrochemical environment necessary for RMP establishment. *Both true, Reason is the explanation of assertion* - This is **incorrect** because while both statements are true, the Nernst equation (Reason) does not explain how proteins and phosphate ions contribute to RMP (Assertion). The Nernst equation applies only to permeable ions, whereas proteins and phosphates are impermeant molecules whose role is explained by the Gibbs-Donnan equilibrium and their contribution to fixed negative charges. *Assertion true, Reason false* - This is **incorrect** because the reason is TRUE. The Nernst equation is a fundamental and valid equation in membrane physiology that accurately calculates the equilibrium potential for any permeable ion based on its concentration gradient.
Question 5: Hyperpolarization is caused by which ions?
- A. K+ (Correct Answer)
- B. Na+
- C. HCO3-
- D. Ca2+
Explanation: ***K+*** - **Efflux of K+ ions** out of the cell makes the inside of the cell more negative, leading to **hyperpolarization**. - This efflux is typically mediated by **voltage-gated potassium channels** opening, or by activation of **GABA-A** or **glycine receptors** that increase K+ conductance. *Na+* - **Influx of Na+ ions** into the cell makes the inside of the cell more positive, causing **depolarization**, not hyperpolarization. - This influx is responsible for the **rising phase of an action potential**. *Ca2+* - **Influx of Ca2+ ions** into the cell also contributes to **depolarization** and can trigger various intracellular processes. - Ca2+ influx is crucial for **neurotransmitter release** and muscle contraction, but not for hyperpolarization. *HCO3-* - Bicarbonate ions (**HCO3-**) play a significant role in **maintaining pH balance** in the body and are involved in various physiological processes. - While ion channels can conduct HCO3-, their movement is not typically the primary cause of cell membrane hyperpolarization.
Question 6: Alpha wave on EEG represents -
- A. Awake and fully alert
- B. Awake with eyes open
- C. Awake with eyes closed with mind wandering (Correct Answer)
- D. Deep sleep
Explanation: ***Awake with eyes closed with mind wandering*** - **Alpha waves** are characteristic of a relaxed, wakeful state when the eyes are closed and the mind is not actively focusing on a task. - They typically have a frequency range of 8-13 Hz and are most prominent over the **occipital lobe**. *Awake and fully alert* - This state is primarily associated with **beta waves** (13-30 Hz) due to active mental engagement and processing. - Alpha waves tend to be attenuated or replaced by beta activity when an individual is fully alert and actively concentrating. *Awake with eyes open* - When a person's eyes are open while awake, **alpha waves** are usually suppressed or "blocked" by visual input and mental processing. - This is known as **alpha blocking** or desynchronization, and the EEG shifts towards lower amplitude, higher frequency beta waves. *Deep sleep* - **Deep sleep** (Stage N3, or slow-wave sleep) is characterized by high-amplitude, low-frequency **delta waves** (0.5-4 Hz). - Alpha waves are not a prominent feature of deep sleep; instead, they are suppressed.
Question 7: Identify the modality of intercellular communication shown below.
- A. Paracrine (Correct Answer)
- B. Autocrine
- C. Synaptic
- D. Gap junction
Explanation: ***Paracrine*** - The image shows a **signaling cell** releasing **signaling molecules** (red dots) into the extracellular space, which then act on a nearby **target cell**. This local signaling is characteristic of paracrine communication. - In **paracrine signaling**, the molecules travel short distances through the interstitial fluid to influence neighboring cells, without entering the bloodstream. *Autocrine* - In **autocrine signaling**, a cell releases signaling molecules that then act on **receptors on the same cell** that produced them. The image clearly depicts communication between two different cells. - The signaling molecules are shown moving from one cell (signaling cell) to another distinct cell (target cell), rather than acting back on the originating cell. *Synaptic* - **Synaptic signaling** involves specialized structures called **synapses** where neurons transmit signals using **neurotransmitters** across a synaptic cleft to a target cell (another neuron, muscle cell, or gland cell). The image does not show a neuronal structure or a synapse. - This type of communication is highly specific to the nervous system and involves electrical impulses followed by chemical transmission, which is not represented here. *Gap junction* - **Gap junction communication** involves direct passage of signaling molecules between adjacent cells through specialized protein channels called **gap junctions**. - The image depicts signaling molecules being released into the extracellular space and binding to receptors on the target cell, rather than passing directly between the cytoplasms of two cells.
Question 8: In multiple sclerosis, slow conduction of motor and sensory pathways is due to?
- A. Loss of myelin sheath (Correct Answer)
- B. Dysfunction of sodium channels
- C. Dysfunction of calcium channels
- D. Defect in the nodes of Ranvier
Explanation: ***Loss of myelin sheath*** - Multiple sclerosis (MS) is characterized by **demyelination**, which is the destruction of the **myelin sheath** surrounding nerve fibers in the central nervous system. - Myelin acts as an electrical insulator, facilitating rapid, **saltatory conduction** of nerve impulses; its loss directly leads to **slowed or blocked signal transmission**. *Dysfunction of sodium channels* - While sodium channel dysfunction can occur secondary to demyelination, it is not the primary cause of slow conduction in MS but rather a downstream effect or an adaptive change. - The initial and fundamental problem leading to slowed conduction in MS is the **loss of the myelin sheath**, which renders the exposed axon less efficient at propagating action potentials. *Dysfunction of calcium channels* - Dysfunction of calcium channels is not the primary pathological mechanism responsible for the slowed conduction in MS. - While calcium dysregulation can play a role in **axonal damage** and neurodegeneration in MS, it is not the direct cause of the characteristic **slowed nerve impulse propagation**. *Defect in the nodes of Ranvier* - The **nodes of Ranvier** are uncovered gaps in the myelin sheath that are crucial for **saltatory conduction**. While their integrity is important, a primary "defect" in the nodes themselves is not the initial cause of slowed conduction in MS. - Slowed conduction occurs because the **myelin surrounding the axons** is lost, leading to longer distances for the action potential to travel and exposing segments of the axon unprepared for continuous conduction.
Question 9: Cranial nerve 8 palsy is associated with all of the following symptoms except:
- A. Gag reflex (Correct Answer)
- B. Hearing loss
- C. Tinnitus
- D. Vertigo
Explanation: ***Gag reflex*** - The **gag reflex** is primarily mediated by the **glossopharyngeal (CN IX)** and **vagus (CN X)** nerves. - CN VIII, the vestibulocochlear nerve, is solely responsible for hearing and balance, and thus has no role in the gag reflex. *Vertigo* - **Vertigo** is a common symptom of CN VIII palsy, specifically involving the **vestibular branch** of the nerve. - Damage to this branch can disrupt the sense of balance and spatial orientation. *Hearing loss* - **Hearing loss** is a hallmark symptom of CN VIII palsy, affecting the **cochlear branch** of the nerve. - This can manifest as conductive, sensorineural, or mixed hearing loss, depending on the specific pathology. *Tinnitus* - **Tinnitus**, the perception of sound when no external sound is present, is frequently associated with CN VIII palsy. - It often accompanies hearing loss and is a common complaint in conditions affecting the auditory system.
Question 10: Which of the following types of nerve fibers are primarily responsible for transmitting slow, dull, and chronic pain sensations?
- A. A-alpha fibers
- B. A-beta fibers
- C. A-delta fibers
- D. C fibers (Correct Answer)
Explanation: ***C fibers*** - These are **unmyelinated**, small-diameter nerve fibers that conduct impulses slowly (0.5-2 m/s). - They are primarily responsible for transmitting **slow, dull, burning, or aching pain** (second pain or chronic pain), as well as temperature sensations and itch. - Their slow conduction velocity results in the delayed, poorly localized pain sensation that persists after initial injury. *A-alpha fibers* - These are the **largest and fastest-conducting** myelinated nerve fibers (70-120 m/s). - They are primarily involved in transmitting **proprioception** (sense of body position) and **motor information** to skeletal muscles. - They do **not transmit pain** signals. *A-beta fibers* - These are **large, myelinated** fibers with a fast conduction velocity (30-70 m/s). - They primarily transmit **touch and pressure sensations**, and can modulate pain perception through the gate control theory. - They are **not nociceptors** and do not directly transmit pain. *A-delta fibers* - These are **small, myelinated** nerve fibers that conduct impulses at 12-30 m/s. - They transmit **fast, sharp, well-localized pain** (first pain or acute pain) and cold sensations. - While they do transmit pain, they are responsible for the **initial sharp pain**, not the slow, dull, chronic pain that defines C fiber function.
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