Resting membrane potential

Question 1

What is the role of neurons/nerve cells?

Answer 1

They are the building blocks of the nervous system

Question 2

What are the structures of a neuron?

Answer 2

Dendrites, Cell body, Axon, Axon terminal

Question 3

What is the flow of electrical signals through a neuron?

Answer 3

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

Question 4

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

Answer 4

Synaptic potential

Question 5

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

Answer 5

Action potential

Moves through axon

Question 6

What does the cell body do?

Answer 6

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

Question 7

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

Answer 7

An action potential

Question 8

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

Answer 8

By chemical signals

Synapses

Question 9

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

Answer 9

Electrical signals

Dendrites, cell body and axon

Question 10

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

Answer 10

50-70 mV

It is in the cytoplasm

Question 11

How was the rest membrane potential first discovered?

Answer 11

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)

Question 12

Why was a squid giant axon used?

Answer 12

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

Question 13

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

Answer 13

The vast majority of cells do

Question 14

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

Answer 14

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

Question 15

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

Answer 15

It makes the cell excitable

Question 16

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

Answer 16

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

Question 17

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

Answer 17

Microelectrode recording and patch-clamp

Question 18

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

Answer 18

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.

Question 19

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

Answer 19

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

Question 20

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

Answer 20

Ions are moving in solution

In wire it is electrons moving

Question 21

By convention, what is the potential outside the cell?

Answer 21

Defined as zero

Question 22

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

Answer 22

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)

Question 23

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

Answer 23

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

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

Question 24

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

Answer 24

By the Na+/K+ pump

Question 25

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

Answer 25

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

Question 26

What are the two main types of ion channels?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

There are many leak K+ channels but very few leak Na+ channels K+ is 40 times more permeable through the cell membrane than Na+

Question 29

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

Answer 29

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

Question 30

What is an equilibrium potential?

Answer 30

It is where the net flow of ions is zero

Question 31

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

Answer 31

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

Question 32

How can the equilibrium potential be calculated for each ion?

Answer 32

Using the nernst equation

Question 33

What is the nernst equation?

Answer 33

61.5mV * (log[conc_ion_outside])/conc_ion_inside

Question 34

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

Answer 34

``` K+ = -80mV Na+ = +60mV ```

Question 35

Why is the potential for Na+ positive?

Answer 35

There are more Na+ ions inside the cell than outside

Question 36

Why is the potential for the K+ negative?

Answer 36

There are less ions inside the cell than outside

Question 37

What assumption does the nernst equation make?

Answer 37

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

Question 38

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

Answer 38

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

Question 39

What do the glia cells do?

Answer 39

Supporting cells to the neurons

Question 40

What is the resting membrane potential of glia cells?

Answer 40

-80mV

Question 41

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

Answer 41

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

Question 42

What can the range of RMP of a cell be?

Answer 42

Between -80mV and +60mV

Question 43

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+?

Answer 43

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

Question 44

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

Answer 44

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

Question 45

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+?

Answer 45

The Goldman equation

Question 46

What is the simplified Goldman equation?

Answer 46

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

Question 47

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

Answer 47

If the permeability ratio changes then the RMP changes

Question 48

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

Answer 48

Na/K pump non-gated (leak) Na and K channels