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CORE Block 4 > Membrane potentials, action potentials, and synaptic transmission > Flashcards

Membrane potentials, action potentials, and synaptic transmission Flashcards

1
Q

What is Vm when there is no charge imbalance on either side of the cell membrane?

A

It is 0

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2
Q

Describe the two forces fighting each other in movement of K+ across the cell membrane.

A
  • concentration gradient makes K+ want to leave the cell
  • electrical gradient makes K+ want to enter the cell (naturally more negative inside_
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3
Q

What is diffusion potential,equilibrium potential, or nernst potential?

A

They all mean the same thing: membrane potential is set up to counterbalance the diffusion-driven movement of ions across the membrane.

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4
Q

Under what conditions do we arrive at equilibrium potential?

A

When we have the same charge inside and outside the cell

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5
Q

How do membrane potential and equilibrium potential differ?

A

Membrane potential refers to the whole cell, and equilibrium potential refers to the ion type.

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6
Q

Why do K+ and Cl- normally not move from or to the cell on their own?

A

Their equilibirum potentials are very close to the membrane potential.

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7
Q

Under what conditions is there a driving force on an ion?

A

When Vm does not equal Ex (membrane potential and equilibrium potential of an ion, X)

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8
Q

How do we calculate driving force?

A

Vm - Ex (membrane potential - equilibrium potential)

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9
Q

Under what conditions is there a net movement of cations into and out of the cell?

A

Vm > Ex, net movement out of the cell

Vm < Ex, net movement into the cell

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10
Q

What does an electrochemical gradient mean?

A

It means the movement of ions depends both on concentration and charge.

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11
Q

Under what conditions is there a net movement of anions into and out of the cell?

A

Vm > Ex, movement into the cell

Vm < Ex, movement out of the cell

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12
Q

Describe equilbrium potential for positive versus negative ions.

A

It is not the same for any ion. Cannot generalize one ion type having a negative or positive Ex.

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13
Q

When pumping rate of Na is much larger than that of K, how do Vm and Ek relate?

A

They will be equal, because the membrane is selectively permeable to Na.

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14
Q

What relationship does the GHK equation describe?

A

It relates the pumping rate of multiple ions to the Vm and the equilibrium potential of the ions.

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15
Q

Why does the cell end up with a negative membrane potential?

A

Because the cell is more permeable to potassium than to sodium.

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16
Q

Compare the contributions of K and Na equilibrium potentials to the membrane potential.

A

Ek contributes more to the Vm than does ENa.

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17
Q

Why do lethal injection contain potassium chloride?

A

The membrane is highly sensitive to changes in the potassium gradient. Increased potassium concentration depolarizes the membrane of neurons so that they stop functioning.

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18
Q

What does P stand for?

A

Absolute ionic permeability

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19
Q

What does alpha stand for

A

Relative ionic permeability

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20
Q

What components do you need to get a membrane potential?

A
  • selective permeability
  • ion gradients set up by ion pumps
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21
Q

What is needed of Vm to get an action potential?

A

It needs to change and to not be constant

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22
Q

What is the change in Vm called?

A

An action potential

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23
Q

What phase of the action potential must the stimulus reach in order for depolarization to be possible?

A

The threshold

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24
Q

List the different phases of the action potential.

A
  • resting potential
  • rising phase
  • overshoot
  • falling phase
  • undershoot
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25
Q

What did Bernstein propose about action potentials?

A

He proposed that the membrane was permeable to K+ at rest and that AP was a transient breakdown of selectivity no create a non-selective barrier

26
Q

How can an action potential be recorded?

A

One microelectrode stimulates the neuron and another microelectrode records the membrane potential. We see that a certain height of stimulus is required to overcome the threshold and actually depolarize the membrane.

27
Q

What does it mean for action potentials to be all or none?

A

For a given set of conditions, they always reach the same amplitude.

28
Q

What do changes in Vm represent?

A

Membrane potential changes represent change in relative ion permeability and gradient changes. (however gradient changes do not happen fast enough, so Vm changes really only reflect changes in alpha, or relative ion permeability)

29
Q

How did scientists determine that the action potential occurs in the axon of a neuron?

A

They measured Vm with electrodes in the axon

30
Q

What did Hodgkin and Katz show the action potential was dependent on?

A

They showed that as Na+ concentration increased, so did the action potential amplitude, just like it is dependent on equilibrium potential of Na+

31
Q

What is the sodium hypothesis of action potentials?

A

The membrane becomes transiently Na+-selective, and this change is driven by changes in Vm. (must be, because equilibrium potential for an ion does not change unless in different cell types)

32
Q

How did Hodgkin and Huxley analyze time- and voltage-dependence of the current of action potentials?

A

They used a voltage clamp which controls the voltage in order to make the membrane have the same Vm as a control. They showed that during an action potential, Na+ goes into the cell and K+ leaves the cell, along their concentration gradients set up by pumps.

33
Q

Why do voltage-gated K+ channels need Vm to become more positive in order to be opened?

A

Because the equilibrium potential of K+ is negative, it will only flow out of the cell when the Vm becomes more positive.

34
Q

Which conductanes of the Vm do Na+ and K+ contribute to?

A

Na+ conductance is higher and contributes to depolarization, and K+ conductance is lower and contributes to repolarization and hyperpolarization. (K+ out of cell comes after Na+ into cell. Na+ into cell contributes to more positive Vm_

35
Q

What are the properties of action potential ionic conductances?

A
  • Na+ conductance: voltage dependent, rapid gating, and inactivates
  • K+ conductance: voltage dependent, slower gating (delayed rectifier), no inactivation (stays open for hyperpolarization)
36
Q

How did the calculated AP by Hodgkin and Huxley relate to the real AP?

A

It was very close.

37
Q

Why is the refractory period necessary?

A

Because Na+ channels need to inactivate after closing in order for a new AP to be triggered,

38
Q

Compare absolute and relative refractory periods.

A

Absolute is at the top of the AP and makes a second response impossible regardless of strength or duration of stimulus. Relative refractory period still allows for a new reponse, but the stimulus must be stronger.

39
Q

How does axon diameter affect action potential?

A

The larger the axon diameter, the faster the action potential is propagated.

40
Q

What does the refractory period allow for?

A

The single direction propagation of the action potential.

41
Q

At what structure is signal of action potential regenerated?

A

At the Node of Ranvier.

42
Q

What is the role of myelination in the conduction of action potential along the axon?

A

Myelination acts as insulation to affect AP velocity by making the AP “jump” and move faster so they don’t have to travel the full distance. This allows the sodium to move faster.

43
Q

Describe the ion channels involved in AP propagation.

A
  • discrete transmembrane proteins that undergo voltage-driven conformational changes
  • in the open state of the channel, an ion-selective transmembrane pore is formed and the ion travels down its electrochemical gradient.
44
Q

Describe the state of the Na+ channel when the K+ channel becomes open.

A

When the K+ channel becomes open, the Na+ channel is becoming inactivated. The K+ channel never is inactivated, just either closed or opened.

45
Q

What is the downside of measuring single Na+ or K+ channels?

A

There is a lot of background noise recorded.

46
Q

Describe the crystal structure of the voltage-gated channel.

A

4 subunits with a central pore.

-voltage sensor helix that moves in response to a change in transmembrane voltage

47
Q

What factors change the graphical shape of action potentials?

A

number and properties of channels

48
Q

What is the stimulus that initiates an action potential?

A

It occurs at the synapse where two cells come together and a neurotransmitter is received by the receiving cell.

49
Q

What is the receiving structure of the post-synaptic neuron?

A

Dendrite

50
Q

What event causes the release of synaptic vesicles from the pre-synaptic neuron?

A

Voltage-dependent Ca2+ channels respond to the action potential, causing an influx of calcium into the cell and help fuse the vesicles with the membrane, causing the neurotransmitter to be released into the synaptic cleft.

51
Q

What happens to the neurotransmitter once it binds to receptors on the surface of the post-synaptic neuron?

A

They can either be degraded or taken back up by the pre-synaptic neuron.

52
Q

Excitatory versus inhibitory synapse

A
  • excitatory: causes depolarization and postsynaptic cell passes threshold and causes an action potential
  • inhibitory: hyperpolarization results, preventing an action potential
53
Q

What model was used to elucidate excitatory and inhibitory synapses?

A

frog neuromuscular junction

54
Q

How does the GHK equation describe excitatory vs inhbitory synaptic transmission?

A
  • excitatory neurotransmitters increase nonselective cation permeability, increasing relative permeability to 1, leading to depolarization
  • inhibitory neurotransmitters increase anion permeability (Vm moves closer to equilibirum potential for Cl-), making it harder to depolarize the membrane
55
Q

What are some excitatory transmitters?

A

acetylcholine, serotonin, glutamate

56
Q

What are some inhibitory transmitters?

A

GABA, glycine

57
Q

How do we know there is a smaller and delayed response away from localization of a stimulus?

A

The delay in response time increases as a function of the distance from the end plate

58
Q

Quantal release of ACh

A

This is how we know there are specific amounts of neurotransmitters released from the neuron, because the number of veiscle peaks do not change under the same conditions.

59
Q

How does acetylcholine cause an AP in the post-synaptic neuron?

A

At the neuromuscular junction, ACh interacts with the nicotinic acetylcholine receptor AChR. The receptor undergoes a conformational change in the presence of ACh, opening a cation-selective transmembrane pore

60
Q

What is an IPSP?

A

Inhibitory post-synaptic potential. Inhibitory transmitters drive Vm to Cl- equilibrium potential which is either resting potential or more negative, making it harder for the stimulus to reach threshold.

61
Q

Why would the same cell have both inhibitory and excitatory responses?

A

Since the only output of an excitable cell is an all-or-nothing potential, multiple inputs allow integration of responses. It is sort of like a check and balance system

CORE Block 4 (8 decks)

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