Neuroscience Chapter on Membrane Potentials

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Questions and Answers

Which of the following statements accurately describes the role of myelination in conduction velocity?

Myelination allows the action potential to jump between nodes, increasing speed. (correct)

Myelination only affects the conduction velocity of Group C fibers.

Myelination reduces the need for voltage-gated Na+ channels along the entire axon.

Myelination increases conduction velocity by allowing continuous conduction.

How does the diameter of nerve fibers affect their conduction velocity?

Larger diameter fibers transmit impulses faster than smaller ones due to reduced resistance. (correct)

Larger diameter fibers have slower conduction velocities than smaller ones.

Conduction velocity is independent of the diameter of nerve fibers.

Only myelinated fibers show a correlation between diameter and conduction velocity.

What clinical symptoms may indicate impaired action potential propagation?

Improved muscular coordination and clarity of speech

Visual disturbances, weakness, and loss of muscular control (correct)

Increased sensory perception in visceral organs

Enhanced reaction times during physical activity

What is the primary effect of local anesthetics on action potentials?

They block voltage-gated Na+ channels, preventing action potential generation. Signup and view all the answers

Which of the following fibers would be expected to transmit action potentials at the slowest rate?

Group C fibers as they are unmyelinated with the smallest diameter Signup and view all the answers

What happens to the membrane potential during hyperpolarization?

It becomes more negative than resting potential. Signup and view all the answers

Which statement accurately describes the nature of graded potentials?

They are short-lived and localized changes in membrane potential. Signup and view all the answers

What triggers the generation of graded potentials in neurons?

The binding of neurotransmitters to specific receptors. Signup and view all the answers

How do action potentials differ from graded potentials?

Action potentials do not decay over distance, unlike graded potentials. Signup and view all the answers

In what specific locations do action potentials primarily occur?

In muscle cells and axons of neurons. Signup and view all the answers

Which of the following options correctly describes the factors influencing the spread of graded potentials?

The strength of the stimulus affects how far the current flows. Signup and view all the answers

What change in ion concentration typically occurs during depolarization?

Sodium ions efflux decreases. Signup and view all the answers

What effect does hyperpolarization have on a neuron's ability to fire an impulse?

It decreases the probability of firing an impulse. Signup and view all the answers

What primarily resets the electrical conditions after repolarization during an action potential?

Na+/K+ pumps restoring ionic conditions Signup and view all the answers

What must occur for an axon to produce an action potential?

Membrane depolarization to threshold voltage Signup and view all the answers

What characterizes the all-or-none phenomenon of action potentials?

Action potentials either occur completely or do not occur at all Signup and view all the answers

How does the propagation of an action potential occur along an unmyelinated axon?

By continuous depolarization and repolarization of each segment Signup and view all the answers

Which of the following statements about sodium ion influx during an action potential is true?

Na+ influx begins the positive feedback cycle of depolarization Signup and view all the answers

What happens to sodium channels immediately after an action potential is initiated?

They inactivate and cannot reopen until repolarization occurs Signup and view all the answers

What is the consequence of depolarizing the membrane by 15 to 20 mV?

Threshold for an action potential is reached Signup and view all the answers

Which ion is primarily involved in the depolarization phase of an action potential?

Sodium ions (Na+) Signup and view all the answers

During the action potential propagation in myelinated axons, where does the action potential occur?

At the nodes of Ranvier Signup and view all the answers

How does the central nervous system differentiate between a weak and strong stimulus?

By the frequency of action potentials received per second. Signup and view all the answers

What occurs during the absolute refractory period?

Another action potential is not possible. Signup and view all the answers

Which of the following best describes the relationship between axon diameter and conduction velocity?

Larger-diameter fibers have lower resistance to current flow, resulting in faster conduction speeds. Signup and view all the answers

What does the relative refractory period coincide with?

The repolarization phase of the action potential. Signup and view all the answers

What defines the all-or-none principle in action potentials?

Action potentials will occur regardless of stimulus strength. Signup and view all the answers

What primarily dictates the conduction velocity of action potentials in neurons?

The presence of myelin sheaths surrounding the axon. Signup and view all the answers

Which of the following statements about action potentials is accurate?

All action potentials are identical regardless of the stimulus intensity. Signup and view all the answers

What is the main factor that prevents a neuron from responding to a new stimulus during the absolute refractory period?

The inactivation of voltage-gated Na+ channels. Signup and view all the answers

How does the frequency of action potentials relate to the intensity of the stimulus?

Higher frequency indicates stronger stimuli. Signup and view all the answers

What phenomenon occurs when the inside of the membrane becomes less negative than the resting membrane potential?

Depolarization Signup and view all the answers

Which ions' concentration difference is crucial in generating the resting membrane potential?

Na+ and K+ Signup and view all the answers

What is the expected result of an increase in membrane permeability to Na+ ions?

Depolarization of the membrane Signup and view all the answers

What type of signal is produced when the membrane potential changes over short distances?

Graded potential Signup and view all the answers

What ultimately balances the K+ leakage from the cell to establish a negative membrane potential?

Electrical gradient for K+ entry Signup and view all the answers

What occurs during hyperpolarization of a membrane?

Inside of the cell becomes more negative Signup and view all the answers

In the context of membrane potential changes, what is the role of protein anions?

Contribute to the negative charge inside the cell Signup and view all the answers

What best describes the relationship between graded potentials and action potentials?

Graded potentials can trigger action potentials if they reach a certain threshold Signup and view all the answers

Which statement accurately describes the resting membrane potential?

It is primarily determined by potassium ion concentration Signup and view all the answers

What mechanism allows for the generation of action potentials based on membrane permeability changes?

Rapid voltage-gated ion channels activation Signup and view all the answers

Study Notes

Membrane Potential Changes

Membrane potential can change when the ion concentrations across the membrane change or when the membrane permeability to ions changes.
These changes can produce two types of signals: graded potentials and action potentials.
Graded potentials are short-lived, localized changes in membrane potential that act over short distances.
Action potentials are long-distance signals that travel down the axon of a neuron.

Hyperpolarization and Depolarization

Hyperpolarization is an increase in membrane potential, making the inside of the membrane more negative than the resting membrane potential.
Hyperpolarization decreases the probability of producing an impulse.
Depolarization is a decrease in membrane potential, making the inside of the membrane less negative than the resting membrane potential.
Depolarization increases the probability of producing an impulse.

Graded Potentials

Graded potentials are triggered by a stimulus that opens gated ion channels, resulting in depolarization or sometimes hyperpolarization.
The strength of the stimulus determines the magnitude of the voltage change and the distance the current flows.
Graded potentials decay over short distances.

Action Potentials

Action potentials are the principle way neurons send signals and are the means of long-distance neural communication in muscles and axons.
They involve a brief reversal of membrane potential with a change in voltage of approximately 100 mV.
Action potentials do not decay over distance like graded potentials.
They involve the opening of specific voltage-gated channels.

Generating an Action Potential

An action potential is generated when the membrane is depolarized to a threshold voltage.
The threshold voltage is typically 15-20 mV above the resting membrane potential.
At threshold, Na+ permeability increases and Na+ influx exceeds K+ efflux, initiating a positive feedback cycle.

All-or-None Phenomenon

An action potential either happens completely or not at all.
This is known as the "all-or-none" principle.

Propagation of an Action Potential

Propagation allows the action potential to be transmitted from its origin down the entire axon length towards the terminals.
Na+ influx through voltage gates in one membrane area cause local currents that open Na+ voltage gates in adjacent membrane areas.
This leads to depolarization of that area, which in turn causes depolarization in the next area.

Refractory Periods

A refractory period is a time when a neuron cannot trigger another action potential.
Absolute refractory period: No new action potential can be generated during this period, as voltage-gated Na+ channels are open.
Relative refractory period: Follows the absolute refractory period; most Na+ channels are reset, but a stronger stimulus is required to trigger an action potential.

Conduction Velocity

The speed of action potential propagation varies depending on the axon diameter and the degree of myelination.
Axon diameter: Larger diameter axons have less resistance to local current flow and therefore conduct impulses faster.
Myelination: Myelin sheaths insulate and prevent leakage of charge, making conduction faster.

Types of Nerve Fibers

Nerve fibers are classified into three groups based on their diameter, degree of myelination, and speed of conduction:
- Group A fibers: Largest diameter, myelinated, transmit at ~300 mph.
- Group B fibers: Medium diameter, lightly myelinated, transmit at ~30 mph
- Group C fibers: Smallest diameter, unmyelinated, transmit at ~2 mph.

Impaired AP Impulse Propagation

Impaired action potential impulse propagation can be caused by a number of factors like local anesthetics, cold temperatures, or continuous pressure that interrupts blood flow to neurons.

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Description

Explore the dynamics of membrane potential changes in neurons. This quiz covers graded and action potentials, along with hyperpolarization and depolarization. Test your knowledge on how these phenomena impact neuronal signaling.