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Membrane potential & action potential & ion channels & ion transporters

35 important questions on Membrane potential & action potential & ion channels & ion transporters

What are the three categories of potentials?

Receptor potential
Synaptic potential
Action potential

What are the requirements of electrical signalling?

Fast
Cross long distances
Should not lose strength over distance

What is the difference between passive and active responses?

Passive responses are below the threshold and active responses exceed the threshold.

What happens to the action potential if you give a stronger stimulus (when the first one already exceeded the threshold)?

Nothing happens, the action potential is an all or nothing response so the amplitude remains the same.

What happens with passive conductance?

It will decay over distance

The resting membrane potential is based on two principles in physics, what are these?

Diffusion of particles
Electrical forces between electrical charges

What are the key players in excitability of neurons?

Potassium, sodium, chloride, and calcium

If ions start moving to the outer side of the membrane, what force generates?

The electrical force

What happens to the membrane potential if you increase the concentration of extracellular potassium?

The membrane starts to depolarize

If you look to the relation between action potential and reversal potential, what can you conclude?

The action potential is nothing more than moving in between the two reversal potentials.

What are the two types of proteins that can move ions over the cell membrane?

Ion transporters and ion channels

What is the main difference between ion transporters and ion channels?

Ion channels do not require any ATP, ions can diffuse down their concentration gradient.

What happens to the sodium flux if you reduce the extracellular concentration of potassium?

The sodium flux will also be reduced because with the Na+/K+ these are translocated but if there is no K+, also Na+ cannot be transported.

What are exchangers? What are the two types?

Exchangers are a type of ion transporters. These do not require ATP, they use the electrical gradient of other ions as an energy source.
The two types are antiporters and co-transporters.

What are the requirements to study excitability of neurons?

Nerve cells that produce action potentials and is experimentally good accessible --> giant axons of the squid

What is the voltage-clamp technique?

The wanted membrane voltage is set at a controlled level, if the membrane voltage of the real axon is different then you know that there is a current. The difference between the desired and real membrane potential is the current that flows through the axon.

What can you measure with a current clamp?

How the membrane changes to different currents.

How can you determine if current consists of two separate currents?

Use specific solutions (specific ions will not flow, because they are not there)
Use toxins (blocking specific channels)

What happens if you inhale/inject TTX (or eat it, it is located in Pufferfish which is a Japanese delicacy)?

Sodium channels are blocked.

What is the patch-clamp technique?

You can measure the current flowing through one channel.

What is a cell-attached recording?

A type of the patch-clamp method in which you can record single ion channel currents.

What is whole-cell recording?

A type of the patch-clamp method which allows measurements of electrical potential and currents from the entire cell.

When is the chance to be in an open state higher for ion channels?

At depolarized levels.

What is special about Na-channels?

There are fast activation and slow inactivation gates. The activation gates open and then Na can move into the cell. After a while the inactivation gates close the channel again and then Na cannot move into the cell anymore.

When are the fast activation gates of Na channels open? And when are they closed?

The fast activation gates of Na channels are open during depolarization and closed during hyperpolarization (repolarization phase).

Why are the activation gates faster than the inactivation gates?

Because the channel first needs to be opened. If the inactivation would be faster, the channel would never be opened and thus useless.

What is the key component in the excitability of neurons?

Ion channels

What happens to the membrane when there is input (synaptic stimulation)?

The membrane starts to depolarize. If the threshold is reached, an action potential is generated.

What is the rapid rise phase (depolarization phase)?

The Na-channels will open. At the beginning of the phase not all the channels are open, at the end they are. The Na that moves inside of the cell depolarizes the membrane which opens more Na-channels

What happens to the membrane is the K-channels open?

The membrane starts to hyperpolarize because the positive K ions move out of the cell.

What is the repolarizing phase?

The combination of shutting down Na-channels (slow inactivation gates) and the opening of K-channels.

What is special about the soma?

The soma has a higher expression of Na-channels, so it is more sensitive to depolarization.

How is an action potential propagated?

Passive flow: Na ions diffuse away from point of stimulation
Active flow: the opening and closing of the channels to give a new impuls to the passive flow and the signal will not die out.

What are nodes of Ranvier?

The spots on the axons that are not myelinated. Na-channels are highly localized here.

What is wrong with patients with multiple sclerosis?

They do not have myelin sheets so their signals die out.

The question on the page originate from the summary of the following study material:

Neurosciences

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