Membrane & Action potentials

Question 1

Where do electrical signals start?

Answer 1

They start in the receptor cells

Question 2

What three kinds of electrical potentials are there?

Answer 2

1. Receptor Potential
2. Synaptic potential
3. Action potential

Question 3

Which of the three types of electrical potential is the fastest?

Answer 3

Action potential is the fastest

Synaptic is the second and the third is Receptor potential

Question 4

What are the requirements for electrical signaling between nerve cells?

Answer 4

1. Must be fast
2. Must cross a long distance
3. Should not lose strength

Question 5

What is the nature of the resting potential inside a cell, compared to the extracellular environment?

Answer 5

The nature of the charge is negative ( -65 mV )

Question 6

What happens when you feed a positive current into a nerve cell? What happens if you increase the strength?

Answer 6

The positive current will depolarize the cell until the threshold is met. This translates to an action potential. A stronger positive current does not result in a stronger action potential but leads to multiple action potentials.

Question 7

What would happen if only passive conduction was present?

Answer 7

The charges would diffuse across the cell - the signal becomes weaker the further it goes.

Question 8

What is the benefit of active conduction compared to passive conduction?

Answer 8

The signal does not lose strength over time.

Question 9

What two principles is the resting membrane potential based on?

Answer 9

1. Diffusion of particles (from high concentration to low concentration)
2. Electrical forces between electrical charges (positive and negative forces)

Question 10

What are the four main ions for signal transduction in neurons?

Answer 10

K+ , Na+ , Cl- and Ca2+

Question 11

What happens at the electrochemical equilibrium?

Answer 11

At the equilibrium, the diffusion forces will equal the electrical forces of the ions (K+)
No net movement of K+ ions on either side of the membrane.

Question 12

What is the equilibrium potential?

Answer 12

The potential at the electrochemical equilibrium.

Question 13

Why don’t ion concentrations change, if there are ions flowing in an out constantly, even at a resting membrane potential?

Answer 13

Because the amount of ions creating this flow is very small. About one millionth of the total concentration.
(Small, almost non-detectable shift)

Question 14

What can you use the Nernst equation for?

Answer 14

Calculating the Equilibrium potential.

Question 15

What is the reversal potential?

Answer 15

The reversal potential creates a flow that brings the potential back to the equilibrium if the concentrations deviate.

Question 16

What is hyperpolarization and depolarization, regarding the resting potential?

Answer 16

Hyperpolarization goes under the resting potential (becomes more negative) and depolarization goes above the resting potential (becomes more positive)

Question 17

What factors influence the resting potential?

Answer 17

Concentrations of K+, Na+ and Cl- inside and outside the cell, as well as the membrane permeability for those ions (Ca2+ is NOT found freely inside or outside the cell)

Question 18

What ion channels are leaky on the membrane?

Answer 18

K+ ion channels are leaky.

Na+ channels are closed

Question 19

What ion dominates the resting membrane potential mechanism?

Answer 19

K+ dominates the control of the resting membrane potential.

Question 20

What happens if the extracellular concentration of K+ is increased?

Answer 20

The resting membrane potential is also increased (becomes more positive)

Question 21

Why does K+ dominate the resting membrane potential?

Answer 21

Because the permeability for K+ is much higher than all other ions, at the resting membrane potential.

Question 22

What happens to permeability during an action potential?

Answer 22

The membrane becomes much more permeable for Na+ ions than K+ ions, thus creating an ion flow.

Question 23

What is the function of ion transporters?

Answer 23

It does active transport of ions against the gradient. This costs energy (ATP)

Question 24

What is the function of ion channels?

Answer 24

It allows ions to diffuse down the concentration gradient. Those are selectively permeable for certain ions.

Question 25

Roughly explain how the Na/K ATPase pump works

Answer 25

The enzyme starts with a high affinity for Na+. After 3 Na+ ions bind to the enzyme, ATP phosphorylates the enzyme, which changes configuration and opens the gates on the other side. The affinity changes and the Na+ is released. The enzyme then gets a high affinity for K+. After the K+ bings to the enzyme, it dephosphorylates and changes configuration again, releasing K+ on the other side and gaining a high affinity for Na+ again. (a transport cycle)

Question 26

How much approximate energy does the Na/K ATPase use in the brain?

Answer 26

Around 20 - 40% of the energy consumption in the brain.

Question 27

Why is the efflux of Na+ reduced when external K+ is removed?

Answer 27

Because relatively less K+ will bind to the Na/K ATPase

Question 28

What happens when the ATPase activity is blocked?

Answer 28

The efflux of Na+ is greatly reduced, as the protein cannot get phosphorylated.

Question 29

What is the energy source of Ion exchangers?

Answer 29

The ion gradient op the ions it transports.

Question 30

What ion is (usually) used for Co-transport and anti-port

Answer 30

Na+ is usually used as an "exchange" for other ions.

Question 31

What are the model requirements for studying electrical signaling in nerve cells?

Answer 31

1. Nerve cells that produce action potentials | 2. It is well accessible

Question 32

Why were the first nerve experiments done on squids?

Answer 32

The squid had a giant axon which was easily accessible.

Question 33

What two types of recordings were performed on the squid experiment in the 50s?

Answer 33

1. Voltage clamp - Artificial changes in voltage, induced with current 2. Current clamp - induce a current to see how the voltage changes over time ``` Voltage = amount of mV Current = flow of ions ```

Question 34

What is the difference in duration of how long ion channels are open, for Na+ and K+ channels?

Answer 34

K+ channels are open for a longer amount of time than Na+ channels.

Question 35

Why do Na+ channels remain closed after a brief moment of depolarisation?

Answer 35

The Na+ channels are affected by two mechanisms. The first mechanism is the opening of the channel after depolarisation. After it has been activated, a second mechanism is put in motion, that blocks ions from passing through. It is like a cork on a wine bottle. The Na+ ion channel is open, but inactive and cannot transport Na+ inwards for a brief moment of time, until the "cork" is removed.

Question 36

What are the two components of the Na+ ion channel? (two mechanisms)

Answer 36

1. Fast activation gates - open during depolarisation | 2. Slow inactivation gates - close during depolarisation

Question 37

Why is it important that the inactivation gates in the Na+ ion channel are slower than the fast activation gates?

Answer 37

Because otherwise current will be completely impaired and no flow would happen. With this system, the flow is controlled, as only a small discharge is needed.

Question 38

What is the refractory period?

Answer 38

The period after an action potential, in which no other action potential can happen again

Question 39

Why is there a refractory period?

Answer 39

This has to do with the inactivation of the Na+ channels. After the opening of the channels, the slow inactivation gates cover up the channel and don't let ions through. They keep it covered for some time - during which no flow is possible, even after another depolarisation.

Question 40

What leads to the opening of K+ channels?

Answer 40

A change in the voltage | K+ channels have a (depolarized) voltage sensor

Question 41

What types of ion channel classes are there?

Answer 41

1. Voltage Gated 2. Ligand gated (GTP) 3. Thermosensitive 4. Mechanosensitive

Question 42

Describe Phase 1 of depolarization.

Answer 42

Na+ and K+ channels are closed, but there are some leaky K+ channels

Question 43

Describe Phase 2 of depolarization.

Answer 43

When the membrane gets depolarized, Na+ channels start to open (Permeability for Na+ is increased)

Question 44

Why does the cell become more depolarized during Phase 2 of depolarization?

Answer 44

Because the Na+ channels are starting to open, letting more positive ions inside the cells, thus depolarizing it (positive feedback loop)

Question 45

Describe Phase 3 of depolarization.

Answer 45

Na+ channels are open and a lot of ions flow inside the cells

Question 46

Describe Phase 4 of depolarization.

Answer 46

In Phase 4, Na+ channels are closed by the inactivation gates, and K+ channels open, letting K+ ions flow outside the cell.

Question 47

Describe Phase 5 of depolarization.

Answer 47

:(

Question 48

Where does the initial action potential take place?

Answer 48

It happens at the soma (cell) and NEVER in the middle of the neuron This is because the impulse must go only in one direction

Question 49

What does myelin prevent in terms of ion concentration?

Answer 49

Myelin prevents ion leaks | This is how the ion concentration gradient remains constant, very little to none is lost over a distance.

Question 50

Why is diffusion faster in myelinated axons?

Answer 50

The concentration difference is maintained and the ions will be more "willing" to move towards a low concentration gradient, as the differences remain high (hope this is understandable)