Neuroscience: Action Potentials and Membrane Dynamics

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Questions and Answers

What is the resting membrane potential typically found in a cell?

$-80$ mV

$-90$ mV

$-70$ mV (correct)

$-60$ mV

What process describes the membrane potential becoming more positive?

Depolarization (correct)

Hyperpolarization

Repolarization

Resting Potential

Which term describes the return of the membrane potential to its resting state after depolarization?

Sodium influx

Repolarization (correct)

Ion equilibrium

Overshoot

During resting potential, which ion is the cell most permeable to?

Potassium Signup and view all the answers

What is the main factor that changes the membrane potential during an action potential?

Changing ion channel permeability Signup and view all the answers

How quickly do the changes in membrane potential during an action potential occur?

Milliseconds Signup and view all the answers

What is hyperpolarization in terms of membrane potential?

Decreasing the resting potential Signup and view all the answers

What defines the rapid change in membrane potential known as an action potential?

A sudden change in membrane permeability to ions Signup and view all the answers

What happens to the sodium channels during the early phase of an action potential?

They activate quickly and then inactivate. Signup and view all the answers

What dictates the flow of potassium ions out of the cell during repolarization?

The concentration gradient and electrical driving force. Signup and view all the answers

What characterizes the voltage-gated potassium channels compared to the voltage-gated sodium channels?

They remain open longer and do not inactivate. Signup and view all the answers

What occurs during the afterhyperpolarization phase of an action potential?

Potassium continues to leave the cell, making the inside more negative. Signup and view all the answers

What leads to the termination of an action potential and the return to resting potential?

The closing of sodium channels. Signup and view all the answers

What is the typical value of the resting membrane potential in a standard cell?

-70 mV Signup and view all the answers

How does the membrane potential change during depolarization?

It becomes more positive. Signup and view all the answers

What initiates the opening of voltage-gated sodium channels?

A neurotransmitter-induced local potential change. Signup and view all the answers

What is the primary mechanism by which the resting membrane potential is maintained?

Potassium leak channels. Signup and view all the answers

Why do sodium channels inactivate after initial opening during depolarization?

To prevent excess sodium from entering the cell. Signup and view all the answers

What primarily causes the graded potentials in neurons?

Neurotransmitter binding to ion channel receptors Signup and view all the answers

What occurs at the trigger zone of a neuron?

Firing of an action potential Signup and view all the answers

Which of the following statements about graded potentials is true?

They decrement in strength as they move from the site of stimulation. Signup and view all the answers

What effect do excitatory neurotransmitters typically have on a neuron's membrane potential?

They cause depolarization by allowing sodium ions to enter. Signup and view all the answers

What is the role of inhibitory neurotransmitters in neuronal signaling?

They can hyperpolarize the membrane by allowing chloride ions to enter. Signup and view all the answers

What happens once the threshold potential is reached in a neuron?

Voltage-gated sodium channels increase sodium permeability. Signup and view all the answers

What characterizes the 'upstroke' phase of an action potential?

Rapid sodium influx into the cell. Signup and view all the answers

How do voltage-gated sodium channels become inactive during an action potential?

An inactivation gate closes the pore. Signup and view all the answers

During the early stages of action potential development, what initial change occurs in the membrane?

Na+ ions start to flow into the cell. Signup and view all the answers

What is meant by the term 'graded' in graded potentials?

They are proportional to the strength of the stimulus. Signup and view all the answers

Why is the location of neurotransmitter binding significant in graded potentials?

It affects the strength of the depolarization signal. Signup and view all the answers

What occurs to the membrane potential when sodium ions flow into the cell?

It becomes less negative or more positive. Signup and view all the answers

What happens after the peak of the action potential is reached?

Potassium channels open and lead to repolarization. Signup and view all the answers

What causes the decrement in strength of graded potentials over distance?

Ion leakage through the membrane. Signup and view all the answers

Study Notes

Definitions and Key Concepts

Resting membrane potential typically ranges from -60 to -90 mV; here illustrated as -70 mV.
Depolarization refers to the membrane potential becoming more positive.
Hyperpolarization is a change that moves the membrane potential in the negative direction from resting potential.
Repolarization involves the return of a depolarized membrane back to its resting state.
Action potential is a rapid change in membrane potential that signals communication between cells.

Mechanism of Action Potentials

Changes in membrane potential are primarily driven by ion permeability.
At rest, cells are more permeable to potassium ions, resulting in a negative membrane potential.
Threshold potential is reached through graded potentials, which are small changes in membrane potential from neurotransmitter binding to ion channels.
Graded potentials can be excitatory (depolarizing) or inhibitory (hyperpolarizing); the effect depends on the type of neurotransmitter.

Local Potentials and Threshold

Local depolarizations can vary in strength based on the number of ligand bindings to receptors.
The signal strength decreases (decrement) as the distance from the initial stimulus increases.
Excitatory neurotransmitters lead to sodium influx, moving the membrane potential closer to threshold, while inhibitory neurotransmitters promote chlorine influx or potassium efflux, hyperpolarizing the neuron.

Initiation of Action Potential

Once the threshold is achieved, sodium permeability increases, allowing sodium ions to rush into the cell.
Voltage-gated sodium channels open in response to a depolarizing signal, initiating a rapid influx of sodium.
Positive feedback mechanism: Initial sodium influx causes more sodium channels to open, rapidly changing the membrane potential towards +30 mV.

Sodium Channel Dynamics

Voltage-gated sodium channels have two gates: an activation (M) gate and an inactivation (H) gate.
At rest, the H gate is open while the M gate is closed. When depolarization occurs, the M gate opens, allowing sodium in, then the H gate closes to stop further sodium influx.

Repolarization Process

After reaching the peak, voltage-gated potassium channels open, allowing potassium to exit the cell.
Potassium’s exit helps restore the negative membrane potential following depolarization.
Delayed opening of potassium channels leads to longer outflows compared to sodium influx, contributing to after-hyperpolarization, which can bring the membrane potential below resting levels.

Return to Resting Potential

Voltage-gated potassium channels close as the membrane potential becomes negative.
Return to resting membrane potential is facilitated by potassium leak channels.
After-hyperpolarization occurs due to prolonged potassium channel activity, causing potential to dip below resting state before stabilizing.

Summary of Action Potential Events

Initiation starts at threshold through neurotransmitter-induced depolarization.
Sequence includes rapid depolarization due to sodium influx, followed by repolarization through potassium efflux, and stabilization back to resting potential.

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Description

Explore the fundamental concepts of action potentials, resting membrane potential, and the mechanisms driving changes in membrane permeability. This quiz covers key definitions like depolarization, hyperpolarization, and graded potentials, crucial for understanding neuronal communication.