Neuroscience: Cell Membrane Channels

Questions and Answers

What happens at the axon hillock before propagation of the action potential?

It converts electrical signals into chemical signals.

It generates an action potential which propagates down the axon. (correct)

It stabilizes the resting membrane potential.

It generates multiple action potentials simultaneously.

What defines conduction velocity in the context of action potential propagation?

The distance between nodes of Ranvier.

The time it takes for a neurotransmitter to bind to receptors.

The strength of the stimulus applied to the neuron.

The speed at which an action potential is propagated. (correct)

Which factor does NOT affect conduction velocity?

The presence of myelin insulation.

The internal resistance of the axon.

The diameter of the axon.

The frequency of the action potentials. (correct)

How does myelin affect the propagation of action potentials?

It facilitates saltatory conduction at the nodes. Signup and view all the answers

What is the primary function of ion channels in neuronal membranes?

To control the movement of ions across the membrane Signup and view all the answers

What is the primary reason that larger diameter axons can conduct action potentials faster?

They have reduced internal resistance to charge flow. Signup and view all the answers

What is the term for the process where action potentials appear to jump along myelinated axons?

Saltatory conduction Signup and view all the answers

Which property distinguishes voltage-gated channels from passive channels?

They can open or close in response to voltage changes Signup and view all the answers

How do positive ions affect the membrane potential when sodium channels open?

They cause the membrane potential to become more positive Signup and view all the answers

What factor does NOT determine the selectivity of an ion channel?

The energy level of the ion Signup and view all the answers

During an action potential, what initiates the opening of voltage-gated channels?

Change in voltage across the membrane Signup and view all the answers

Which type of ion channel is primarily responsible for continuous ion flow?

Passive (leakage) channels Signup and view all the answers

What is the typical resting membrane potential of a neuronal cell?

-70 mV Signup and view all the answers

What happens to the potassium channels during a nerve impulse?

They begin to open after sodium channels close Signup and view all the answers

Which of the following statements about integral proteins is false?

They are found only in the cell nucleus Signup and view all the answers

What is the typical value for the resting membrane potential?

-70 millivolts Signup and view all the answers

The sodium-potassium pump moves sodium and potassium in which direction relative to their gradients?

Against their gradients Signup and view all the answers

What provides the energy needed for the sodium-potassium pump to operate?

ATP Signup and view all the answers

Where is the action potential generated in a neuron?

At the axon hillock Signup and view all the answers

How much does the membrane need to depolarize to reach threshold at the axon hillock?

15 millivolts Signup and view all the answers

What happens if a weak stimulus at the axon hillock does not reach the threshold?

No action potential is produced Signup and view all the answers

What is another name for an action potential?

Nerve impulse Signup and view all the answers

Do action potentials always maintain the same amplitude and duration?

Yes, they are consistent Signup and view all the answers

What initiates the action potential at the axon hillock?

The density of voltage-gated sodium channels Signup and view all the answers

What happens to sodium voltage-gated channels when the threshold is reached?

They open fully and allow sodium influx Signup and view all the answers

During which phase of the action potential is potassium permeability the greatest?

During repolarization Signup and view all the answers

When does potassium permeability begin to decrease slowly during the action potential?

During repolarization Signup and view all the answers

What is the absolute refractory period?

The period when sodium channels are inactive and no action potential can be generated Signup and view all the answers

Why can't a neuron generate another action potential during the absolute refractory period?

Sodium cannot enter through inactive channels while potassium continues to exit Signup and view all the answers

What defines the relative refractory period?

A time where action potentials can be generated but require a higher depolarizing stimulus Signup and view all the answers

Which diagram phase corresponds to depolarization?

Peak Signup and view all the answers

Which option describes hyperpolarization?

The membrane potential becomes more negative than resting potential Signup and view all the answers

During which phase does the cell initially begin to repolarize?

Initiation of repolarization phase Signup and view all the answers

Which of these statements is true about an action potential?

Action potentials are all-or-nothing events, regardless of stimulus strength Signup and view all the answers

What defines the threshold membrane potential?

It is the point where depolarization becomes regenerative. Signup and view all the answers

Which processes interrupt the positive feedback loop during the rising phase of the action potential?

Inactivation of voltage-gated sodium channels and opening of voltage-gated potassium channels. Signup and view all the answers

What are the two gates associated with voltage-gated sodium channels?

A voltage-sensitive gate and a time-sensitive inactivation gate. Signup and view all the answers

What occurs at the peak of the action potential regarding voltage-gated sodium channels?

They begin to inactivate, reducing inward sodium flow. Signup and view all the answers

When do voltage-gated potassium channels begin to open?

About the time the action potential reaches its peak. Signup and view all the answers

What results from the opening of voltage-gated potassium channels?

Potassium exits the cell, leading to repolarization. Signup and view all the answers

What happens during the process of repolarization?

Sodium permeability decreases and potassium permeability increases. Signup and view all the answers

What is hyperpolarization in relation to the action potential?

It occurs when potassium continues to exit the cell past the resting potential. Signup and view all the answers

During which phase does sodium permeability increase rapidly?

During the rising phase of the action potential. Signup and view all the answers

During which phase does sodium permeability decrease rapidly?

During the peak of the action potential. Signup and view all the answers

Study Notes

Functions of Cell Membrane Channels

Ion channels are responsible for controlling the movement of ions across the neuronal membrane.
Four main properties of ion channels include selectivity, being either passive or active, regional location, and functional uniqueness.
Ion channels are composed of integral proteins.

Selectivity and Mechanism of Ion Channels

Selectivity depends on the charge of the ion (positive or negative), the size of the ion, and the ion's ability to attract and hold water.
Passive ion channels (leakage channels) are always open, while active channels can open or close based on conditions.

Resting Membrane Potential

The resting neuronal cell membrane is more positive outside than inside, with a typical membrane potential value of -70 mV.
When at rest, voltage-gated channels are closed; depolarization triggers their opening during an action potential.

Action Potential Dynamics

An action potential (or nerve impulse) is initiated at the axon hillock, where voltage-gated sodium channels are concentrated.
Threshold is reached when depolarization of approximately 15 mV occurs, resulting in an all-or-none response.

Ion Channel Behavior During Action Potential

Sodium voltage-gated channels open rapidly, leading to an increase in sodium permeability; this promotes further depolarization.
The positive feedback loop sustaining depolarization is interrupted by sodium channel inactivation and potassium channel opening.
At the peak of the action potential, sodium channels begin inactivation, resulting in reduced inward sodium flow.

Repolarization and Hyperpolarization

Repolarization occurs when potassium ions exit the cell, decreasing membrane potential toward resting levels.
Hyperpolarization can happen when potassium channels remain open beyond the resting potential, leading to a more negative value.

Refractory Periods

The absolute refractory period occurs right after an action potential, during which a new action potential cannot occur due to many inactive sodium channels.
The relative refractory period allows for the generation of another action potential only if the stimulus is sufficiently strong, due to some inactive sodium channels and open potassium channels.

Action Potential Propagation

Once initiated, action potentials propagate down the axon through depolarization of adjacent membrane areas.
Conduction velocity is influenced by axon diameter and myelination; larger diameters and myelination typically increase conduction speed.
In myelinated axons, action potentials appear to jump between nodes (nodes of Ranvier) in a process called saltatory conduction, enhancing propagation efficiency.

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Description

Explore the crucial roles of ion channels in neuronal membranes through this quiz. Understand their properties, selectivity mechanisms, and how they contribute to resting membrane potential and action potential dynamics. Test your knowledge on how these elements interact within the nervous system.