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Questions and Answers

What is the most direct consequence of the temporary inactivation of voltage-gated sodium channels during the repolarization phase of a nerve action potential?

The neuron requires a weaker stimulus than normal to reach threshold, making it hypersensitive to new incoming signals.
The neuron is unable of responding to another stimulus, regardless of the strength, allowing the action potential to propagate unidirectionally. (correct)
The neuron immediately repolarizes to its resting membrane potential without an after-hyperpolarization phase.
The neuron can propagate signals more rapidly due to the reduced ion flow across the membrane.

During the rising phase of a nerve action potential, if the concentration of extracellular sodium ions was significantly reduced, what would be the most immediate effect?

The neuron would still depolarize, but the rate of depolarization would decrease. (correct)
The neuron would depolarize more rapidly due to the enhanced activity of the sodium-potassium pump.
The neuron would rapidly hyperpolarize due to the increased efflux of potassium ions.
The neuron would not be able to reach the threshold potential, preventing the initiation of an action potential.

How would the introduction of a drug that selectively blocks leaky potassium channels affect the resting membrane potential (RMP) of a neuron?

The RMP would become more negative, hyperpolarizing the neuron due to increased sodium influx.
The RMP would oscillate wildly as the sodium-potassium pump attempts to compensate for the blockage.
The RMP would become less negative, depolarizing the neuron due to decreased potassium efflux. (correct)
There would be no change in the RMP because leaky potassium channels only affect repolarization.

If the sodium-potassium pump in a neuron suddenly ceased to function, what long-term effect would this have on the neuron's ability to generate action potentials?

The neuron would initially fire more action potentials, but eventually, the ion gradients would dissipate, and the neuron would become unable to fire. (B) Signup and view all the answers

What is the most likely effect on nerve action potentials, if voltage-gated potassium channels were to open sooner than normal during an action potential?

The repolarization phase would occur more rapidly, potentially shortening the action potential and leading to a pronounced after-hyperpolarization. (A) Signup and view all the answers

How does the interplay between voltage-gated ion channels and the Na+/K+ pump contribute to neuronal signaling?

Voltage-gated ion channels generate the action potential, whereas the Na+/K+ pump re-establishes the resting membrane potential after depolarization and repolarization. (B) Signup and view all the answers

A neuron's resting membrane potential (RMP) is measured to be -60mV after an injury. Based on this information, what is the most likely effect on the neuron's excitability?

The neuron's excitability will increase because the membrane is depolarized, bringing it closer to the threshold for firing an action potential. (C) Signup and view all the answers

Using a modified Goldman equation, how would increasing extracellular $K^+$ concentration from 10 mM to 20 mM affect the resting membrane potential, assuming all other ion concentrations and permeabilities remain constant?

It would cause a depolarization of the membrane, shifting the resting membrane potential to a more positive value. (A) Signup and view all the answers

In a scenario where the permeability of $Na^+$ ions dramatically increases relative to $K^+$ ions, what immediate effect would this have on the neuron's membrane potential, according to the principles underlying the Goldman equation?

The membrane potential would move closer to the Nernst potential for $Na^+$. (B) Signup and view all the answers

What would be the direct impact on the resting membrane potential if the $Na^+$/$K^+$ pump were fully inhibited?

The resting membrane potential would gradually depolarize as ion gradients dissipate. (B) Signup and view all the answers

How does the relative number of leaky potassium ($K^+$) channels compared to leaky sodium ($Na^+$) channels affect the resting membrane potential?

The higher number of leaky $K^+$ channels primarily dictates the resting membrane potential, pulling it closer to the equilibrium potential of $K^+$. (C) Signup and view all the answers

What is the significance of the Nernst equation in the context of neuronal membrane potential?

It predicts the equilibrium potential for a specific ion based on its concentration gradient across the membrane. (D) Signup and view all the answers

Given an ion with an intracellular concentration of 140 mM and an extracellular concentration of 4 mM, what would be the approximate Nernst potential at physiological temperature, assuming the ion is positively charged?

-94 mV (A) Signup and view all the answers

If a neuronal membrane was exclusively permeable to sodium ions ($Na^+$), and the intracellular concentration of $Na^+$ is 14 mM while the extracellular concentration is 142 mM, what would be the resting membrane potential, according to the Nernst equation?

61 mV (A) Signup and view all the answers

How does the presence of both potassium ($K^+$) and sodium ($Na^+$) leaky channels complicate the calculation of the resting membrane potential, compared to a scenario where only one type of channel is present?

It requires considering the relative permeabilities of both $K^+$ and $Na^+$ and their respective electrochemical gradients, rather than relying solely on the Nernst equation for a single ion. (C) Signup and view all the answers

How would the resting membrane potential be affected if the permeability of sodium ions ($Na^+$) across the cell membrane drastically increased, while other factors remain constant?

The resting membrane potential would become less negative, moving closer to 0 mV. (D) Signup and view all the answers

If the $Na^+/K^+$ pump were completely inhibited, what is the most likely long-term effect on the resting membrane potential of a neuron?

The resting membrane potential would gradually depolarize as ion gradients dissipate. (A) Signup and view all the answers

Which alteration to the parameters within the Goldman equation would result in a more negative calculated resting membrane potential?

Decreasing the extracellular concentration of $K^+$ (C) Signup and view all the answers

How does the presence of protein anions within the intracellular fluid contribute to the establishment of the resting membrane potential?

They contribute to the net negative charge inside the cell, preventing complete equilibrium of potassium ions. (C) Signup and view all the answers

Consider a hypothetical neuron where the relative permeability of $Na^+$ to $K^+$ is 1:1 instead of the typical 1:100. How would this change impact the resting membrane potential, assuming all other factors remain constant?

The resting membrane potential would become more positive, shifting closer to the $Na^+$ equilibrium potential. (A) Signup and view all the answers

A researcher discovers a new ion channel that is selectively permeable to large, negatively charged molecules only found inside the cell. How would the activation of these channels likely affect the resting membrane potential?

Cause a slight depolarization due to to movement of negative charge out of the cell. (D) Signup and view all the answers

How would the resting membrane potential of a neuron be affected if the extracellular potassium concentration was artificially increased?

The neuron would depolarize, potentially leading to increased excitability. (D) Signup and view all the answers

In a hypothetical scenario, a drug selectively blocks the leaky potassium channels in a neuron. What immediate effect would this have on the neuron's resting membrane potential?

Initially depolarize very slightly due to the change in ionic conductance, before other compensatory mechanisms take place. (A) Signup and view all the answers

How does hypercalcemia affect the voltage sensor of ion channels, and what is the resulting effect on neuronal excitability?

Hypercalcemia decreases the sensitivity of the voltage sensor; therefore, gates do not open as easily, reducing excitability. (B) Signup and view all the answers

Which of the following scenarios would most likely result in increased neuronal excitability?

A shift in the resting membrane potential from -90mV to -86mV. (A) Signup and view all the answers

How do local anesthetics work at the molecular level to prevent pain?

By reversibly blocking voltage-gated sodium channels at peripheral nerve endings. (A) Signup and view all the answers

In the context of action potential propagation, what is the primary role of the Nodes of Ranvier?

To serve as sites where action potentials are regenerated via saltatory conduction. (C) Signup and view all the answers

A patient presents with muscle weakness and is diagnosed with hyperkalemic periodic paralysis. What is the underlying physiological mechanism causing these symptoms?

Elevated extracellular potassium depolarizes the muscle cells, inactivating sodium channels and preventing action potential generation. (C) Signup and view all the answers

An individual with Cushing's syndrome may experience muscle weakness due to electrolyte imbalances. Which of the following electrolyte disturbances is most likely to contribute to this symptom?

Hypokalemia (D) Signup and view all the answers

Which of the following glial cell types is primarily responsible for the myelination of axons in the central nervous system?

Oligodendrocytes (C) Signup and view all the answers

What is the most likely physiological cause of 'Saturday night paralysis,' where a person experiences temporary paralysis of skeletal muscles after prolonged compression of a limb?

Pressure-induced block of nerve conduction in motor nerves, leading to temporary paralysis. (C) Signup and view all the answers

In demyelinating diseases like Multiple Sclerosis and Guillain-Barré syndrome, loss of myelin leads to neuronal dysfunction. What is the MOST direct consequence of myelin loss on the electrical properties of neurons?

Leakage of K+ through voltage-gated channels, causing hyperpolarization and conduction failure. (A) Signup and view all the answers

The myelin sheath is crucial for rapid nerve conduction. Which cellular mechanism is MOST directly compromised by autoimmune reactions targeting myelin protein zero (P0) and PMP22?

Saltatory conduction, by increasing the length constant and speed of action potential propagation. (B) Signup and view all the answers

Mutations in myelin protein genes, as seen in Charcot-Marie-Tooth disease, lead to axonal degeneration. Which of the following is the MOST likely mechanism by which defective myelin causes axonal damage?

Disrupted trophic support from glial cells, leading to axonal starvation and atrophy. (B) Signup and view all the answers

Consider a neuron at rest. How would the resting membrane potential be affected if the extracellular concentration of K+ ions ([K+]o) were suddenly increased significantly?

The resting membrane potential would become more positive, depolarizing the cell. (B) Signup and view all the answers

A researcher is studying the effect of different ions on the resting membrane potential of a neuron. Which of the following changes would MOST likely result in a more negative (hyperpolarized) resting membrane potential?

Increasing the permeability of the membrane to K+. (B) Signup and view all the answers

During the repolarization phase of an action potential, voltage-gated K+ channels open, allowing K+ ions to flow out of the cell. What direct effect does this K+ efflux have on the neuron's membrane potential?

It makes the membrane potential more negative, moving it towards the K+ equilibrium potential. (D) Signup and view all the answers

The threshold for generating an action potential is a critical concept in neurophysiology. What is the MOST accurate description of the action potential threshold?

The level of depolarization at which the positive feedback loop for sodium influx becomes self-sustaining, triggering a full action potential. (B) Signup and view all the answers

Following an action potential, there is a brief period of hyperpolarization known as the after-hyperpolarization. Which ionic event is MOST directly responsible for this after-hyperpolarization?

Continued efflux of potassium ions through voltage-gated channels that remain open longer than necessary. (C) Signup and view all the answers

Flashcards

Resting Membrane Potential (RMP)

The electrical potential difference across a nerve cell membrane when it is not transmitting a signal.

Depolarization

A rapid change in membrane potential, from negative to positive, initiating an electrical signal.

Overshoot

The point during an action potential when the inside of the cell becomes more positive than the outside.