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z:2017 - Biosci 107 2/2 > Resting membrane potential > Flashcards

Resting membrane potential Flashcards

1
Q

What is the role of neurons/nerve cells?

A

They are the building blocks of the nervous system

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2
Q

What are the structures of a neuron?

A

Dendrites, Cell body, Axon, Axon terminal

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3
Q

What is the flow of electrical signals through a neuron?

A

From the dendrite, to the cell body along the axon and transferred to other cells by axon terminals

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4
Q

What kind of electrical signal flows from the dendrite to the cell body?

A

Synaptic potential

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5
Q

What kind of electrical signal flows from the cell body to other cells? What does the signal move through?

A

Action potential

Moves through axon

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6
Q

What does the cell body do?

A

Integrates the synaptic potentials and makes a decision whether to respond or not respond

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7
Q

If a cell body decides to respond to a synaptic potential, what does it produce?

A

An action potential

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8
Q

How is information received and transferred between nerve cells? What structure is involved in this?

A

By chemical signals

Synapses

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9
Q

How is information transferred through a nerve cell? What structures are involved in this?

A

Electrical signals

Dendrites, cell body and axon

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10
Q

What is the resting membrane potential of a neuron? Where is the voltage difference within the cell?

A

50-70 mV

It is in the cytoplasm

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11
Q

How was the rest membrane potential first discovered?

A

By getting a squid giant axon and an electrode and measuring the voltage difference between the squid giant axon and the reference node (in the air FYI)

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12
Q

Why was a squid giant axon used?

A

Because most animals have an axon with a diameter of 20-30µm which is too small for an electrode, squid giant axon is 500µm so electrode can fit much easier

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13
Q

Do all cells in the body have a negative membrane potential?

A

The vast majority of cells do

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14
Q

What happens when the electrical potential of the cell changes? Explain

A

It depends on the cell type. Only neurons, muscle cells and some endocrine cells can suddenly respond with a short change of this potential

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15
Q

If a cell is able to respond to a short/transient change in potential, what does this make it?

A

It makes the cell excitable

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16
Q

What does being excitable mean? What is the difference between an excitable and unexcitable cell?

A

It means that the membrane potential can change

Excitable = membrane potential can change and produce an action potential

Unexcitable = resting membrane potential is stable so no action potential

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17
Q

What are the two method for measuring the intracellular potential of cells?

A

Microelectrode recording and patch-clamp

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18
Q

How does the microelectrode recording technique work? What information does it record?

A

A glass microelectrode, with a tip size of less than 1 micron with a hole in it is filled with a salt solution to conduct electricity, is inserted inside the cell and the voltage difference between a reference electrode is measured

Measure the resting membrane potential, action potential, synaptic potentials etc.

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19
Q

What does the patch clamp technique? what does it measure?

A

A glass microelectrode, with a tip size of 2-3 micron with a hole in it filled with a salt solution to conduct electricity, are attached to the cell membrane and is broken by using a negative pressure creates a bridge between the inside of the cell and the pipette

Voltage changes and current

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20
Q

When we talk about charge moving in a cell, what is physically moving? How is this different from a copper wire?

A

Ions are moving in solution

In wire it is electrons moving

21
Q

By convention, what is the potential outside the cell?

A

Defined as zero

22
Q

What creates the resting membrane potential to be lower than the extracellular fluid?

A

Unequal concentration of Na+ and K+

Unequal permeability of the cell membrane to these ions

Electrogenic action of the Na-K pump (smaller contribution FYI)

23
Q

Outside and inside the cell, what is the concentration of Na+ and K+?

A

Outside: Na+ = 150mM, K+ = 5mM

Inside: Na+ = 15mM, K+ = 100mM

24
Q

How are the concentration gradients (i.e. the different concentration) of K+ and Na+ maintained?

A

By the Na+/K+ pump

25
Q

How does the Na+/K+ pump contribute to the overall negative charge of the RMP?

A

It pumps out 3 Na+ for 2K+ pumped in. This results in a net loss of 1+ charge

26
Q

What are the two main types of ion channels?

A

Non-gated channels (i.e. leak channels) and gated channels (voltage-gated, chemically-gated, mechanically-gated etc.)

27
Q

What is the difference between an non-gated and a gated ion channel?

A

Non-gated ion channel are always open (therefore there are always particles moving through them) but gated ion channels only open when stimulated

28
Q

What is unique about the cell membrane of neurons that contributes to the RMP? How does this influence the permeability of these ions?

A

There are many leak K+ channels but very few leak Na+ channels

K+ is 40 times more permeable through the cell membrane than Na+

29
Q

How does the unequal concentrations and unequal cell membrane permeability to Na+ and K+ affect ion movement? What does this result in?

A

Na+ has a very low permeability so its new ion flow is very low

However K+ moves with its electrical gradient into the cell and then moves out with it concentration gradient (i.e. concentration and electrical gradient work in opposite directions)

Creates an equilibrium potential

30
Q

What is an equilibrium potential?

A

It is where the net flow of ions is zero

31
Q

How is the net flow of ions zero if there are concentration and electrical gradients?

A

Na+ have very low permeability so it does not move into the cell, it is only pumped out by Na+/K+ pumps

K+ diffuses out of the cell at the same rate as it is electrically attracted into it therefore electrochemical gradient is net zero

32
Q

How can the equilibrium potential be calculated for each ion?

A

Using the nernst equation

33
Q

What is the nernst equation?

A

61.5mV * (log[conc_ion_outside])/conc_ion_inside

34
Q

What are the equilibrium potential for Na+ and K+ in mammals?

A 
K+ = -80mV
Na+ = +60mV
35
Q

Why is the potential for Na+ positive?

A

There are more Na+ ions inside the cell than outside

36
Q

Why is the potential for the K+ negative?

A

There are less ions inside the cell than outside

37
Q

What assumption does the nernst equation make?

A

That a cell membrane is only permeable to one ion (i.e. has only one type of leak channels)

38
Q

Is the assumption the nernst equation makes normally valid? When is there an exception?

A

It is not normally true as neurons have both Na and K leak channel (40 times more K FYI)

However the Glia cells only have leak channels for K so it is valid then

39
Q

What do the glia cells do?

A

Supporting cells to the neurons

40
Q

What is the resting membrane potential of glia cells?

A

-80mV

41
Q

What is the rule for how a cell can shift its equilibrium potential?

A

the higher the permeability of the cell membrane to a particular ion, the greater the ability of this ion to shift the RMP towards its equilibrium potential

42
Q

What can the range of RMP of a cell be?

A

Between -80mV and +60mV

43
Q

Knowing the range of the RMP and the rule for how a cell can shift it equilibrium potential, why is the RMP of nerve cells at rest somewhere closer to the equilibrium potential of K+?

A

K+ has a much higher permeability than Na+ therefore the RMP is closer to the K+ equilibrium potential. However because there are some Na+ leak channels there is a slight lower permeability of K+ so due to the equilibrium potential rule, the RMP is not quite at the K+ equilibrium potential

44
Q

Why are the nerve cells more positive than the glia cells?

A

Because in nerve cells there is a small contribution of + charge from the Na+ therefore it is not at the K+ resting membrane potential but glia cells doesn’t have any Na+ therefore at the K+ resting potential

45
Q

What is the equation that takes into account both the concentration gradients and the relative permeability of the resting cell membrane of both K+ and Na+?

A

The Goldman equation

46
Q

What is the simplified Goldman equation?

A

permeability = p
o = outside
i = inside
61.5mV * log( { p[K+_o] + p[Na+_o] } / { p[K+_i] + p[Na+_i] } )

47
Q

What property does the Goldman equation tell us about the cell membrane?

A

If the permeability ratio changes then the RMP changes

48
Q

What does the concentration gradient depend on? What does the RMP depend on?

A

Na/K pump

non-gated (leak) Na and K channels

z:2017 - Biosci 107 2/2 (16 decks)

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