Membrane depolarization and the action potential Flashcards

1
Q

What are the factors that determine whether a presynaptic release will result in propagation of an action potential by postsynaptic cell?

A

Stimulus number
Stimulus magnitude
Excitatory/Inhibitory stimulus
Stimulus location

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2
Q

The release of a neurotransmitter causes a local membrane permeability and allows the flow of ion current and a small, localized depolarization. Will this always result in an action potential?

A

No, action potential will occur if there are voltage-gated channels in the area and only if the depolarization is large enough

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3
Q

The greater the flow of current the greater change in the what of depolarization?

A

Magnitude of depolarization

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4
Q

How is the flow of current related to the depolarization area?

A

Large flow of current = larger area of depolarization

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5
Q

If 2 cells receive the same stimulus, which cell are have a larger ara of depolarization?

A

The cell with the larger length constant

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6
Q

What is the spatial summation of non-propagating depolarization?

A

Overlapping zones of depolarization constructively reinforce one another resulting in greater depolarization

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7
Q

For an action potential to be propagated, what must be present in the zone of depolarization?

A

Axon hillock

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8
Q

What is decremental conduction of depolarization?

A

Postsynpatic membrane depolarizes in response to the presynpatic release of excitatory transmitter but propagation will occur depending on length constant of the cell

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9
Q

If a zone of depolarization overlaps with a high Cl- conductance, what is the result?

A

Reduced propagation of depolarization

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10
Q

What is temporal summation?

A

Post synaptic effects that occur close in time will build on each other to cause depolarization

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11
Q

What is the difference between spatial and temporal summation?

A

Spatial summation is 1 action potential occurring in 2 overlapping sections to create a depolarization

Temporal summation is 2 action potentials occurring in one section to cause depolarization

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12
Q

Signal propagation depends on the density of sensitivity of what channel? Where are these channels most dense?

A

Nav

Axon hillock

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13
Q

During an action potential, membrane potential increases initially due to what?

A

Electrotonic conduction

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14
Q

What is electrotonic conduction?

A

A depolarization zone is caused by a nearby depolarization without a change in membrane conductance

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15
Q

Why do Na+ channels open before K+ channels?

A

Na+ channels open at more negative potentials than K+ channels

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16
Q

At what point in the action potential is the K+ conductance increasing most rapidly?

A

Peak of action potential

17
Q

What causes afterhyperpolarization?

A

K+ conductance is larger than during resting conditions

18
Q

Why is hyperpolarization important?

A

Nav channels deinactivate

19
Q

When K+ channels deinactivate?

A

At resting membrane potential

20
Q

Does electrotonic depolarization rely on voltage-gated channels?

21
Q

The magnitude of depolarization depends on what 2 factors?

A

Magnitude of depolarization at the source (current density) and distance from source (length constant)

22
Q

Are voltage-gated Ca2+ channels located at the axon hillock?

23
Q

Are Ca2+-activated K+ channels located at the axon hillock?

24
Q

Describe the steps of depolarization at the axon hillock with short relative refractory period

A

Electrotonic depolarization opens Nav channels

Nav channels induce action potential

K+ channels open at peak of action potential
Ca2+ voltage-gated channels open (little effect)

Kv & Ca2+ channels inactivate

Exchangers & ATPase return resting membrane potential

25
How is calcium pumped out of the cell?
Na-Ca exchanger | Ca2+-ATPase
26
Describe the steps of depolarization at the axon hillock with long relative refractory period
Electrotonic depolarization opens Nav channels Nav channels induce action potential Ca2+ voltage-gated channels open Ca2+-sensitive K+ channels open (hyperpolarization) Nav channels deinactivate during hyperpolarization Kca2+ channels have prolonged open probability as long as cytosol Ca2+ levels are elevated Kca2+ channels causes prolonged hyperpolarization Exchangers and ATPases return resting membrane potential
27
Do action potentials lose amplitude during spread from soma to terminal? What is this called?
No | Undiminished (reinforced) signal conduction
28
If an action potential occurs at the axon hillock, will it result in an excitatory response?
Yes
29
What are absolute refractory periods?
Duration during which an action potential cannot occur
30
What are relative refractory periods?
Duration during which it takes a stronger than normal stimulus to make an action potential
31
When does the absolute refractory occur?
During activation & inactivation of Nav channels
32
When does the relative refractory period occur?
During membrane hyperpolarization
33
Can action potentials move retrograde? Why or why not?
No because those ion channels are inactivated
34
If a nerve is stimulated between the soma and the terminus which way does the action potential propagate?
Both ways
35
What determines the length constant?
Ratio of membrane resistance to cytoplasm resistance
36
What 2 ways can the length constant be increased (better propagation)?
Decrease cytosolic resistance (increase diameter) Increase membrane resistance (myelination)