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Fundamentals of Neuroscience > Membranes and Cell Excitation > Flashcards

Membranes and Cell Excitation Flashcards

1
Q

An electrical signal involves…

A

.a change in the balance of positive and negative charges

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2
Q

Name 5 important charged particles

A

Na+, K+, Cl-, Ca2+ and protein side chains

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3
Q

What controls ion movement inside and outside of a cell?

A

The membrane

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4
Q

What generates an electrical signal?

A

The transfer of ions through ion channels

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5
Q

What maintains gradients?

A

Ion pumps

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6
Q

Describe lipid bilayer permeability

A

Impermeable to most molecules, including ions

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7
Q

The inside of a cell contains…

A

an excess of anions and therefore there is a negative membrane potential (Em)

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8
Q

What is the voltage inside the cell called?

A

Membrane potential (Em)

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9
Q

What is the membrane potential of a neurone?

A

-65mV

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10
Q

What determines membrane potential?

A

The balance of charges

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11
Q

What type of process is ion movement?

A

Passive

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12
Q

Which ion channels are permeant?

A

Na+, K+, Ca2+, Cl-

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13
Q

What controls membrane potential?

A

Membrane proteins

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14
Q

Name the three types of gated channels

A

Non-gated, voltage, ligand

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15
Q

What are non-gated channels also known as?

A

Leak channels

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16
Q

What do voltage-gated channels do?

A

Generate action potentials

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17
Q

What do ligand-gated channels do?

A

Generate membrane potential changes at synapses

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18
Q

What type of cells are neurones?

A

Excitable cells

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19
Q

Neurones have a resting membrane potential of…

A

-60mV to -70mV

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20
Q

What factors influence ion movement across the cell membrane?

A

Unequal ion distribution of ions creating a chemical gradient
Electrical force when ions are attracted or repelled by the voltage inside the cell.

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21
Q

What determines membrane permeability?

A

The number of ion channels for a particular ion. Therefore ions which move more easily through the membrane, have a higher number of ion channels within the membrane.

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22
Q

What do efflux and influx mean?

A 
Efflux = movement out
Influx = movement in
23
Q

Define equilibrium

A

An ion is in equilibrium when chemical gradient and electrical force are in balance

24
Q

What is equilibrium potential abbreviated to?

A

Eion

25
Q

What does the Nernst equation do?

A

Defines the voltage at which the ion is at equilibrium

26
Q

What is happening at equilibrium potential?

A

The amount of efflux = influx. This is the voltage the cell needs to be at for there to be no net movement of the ions.

27
Q

What is different between Eion and Em

A

Eion is a constant, Em can vary

28
Q

What is ionic driving force?

A

the net force resulting from chemical and electrical influences.

Em - Eion

29
Q

Explain ionic driving force

A

The force that drives the ion across the membrane when Em is not equal to Eion

30
Q

In a neurone, what influences Em?

A

Na+ and K+

31
Q

What ion equilibriums does Em rest between?

A

EK and ENa

32
Q

How do we calculate Em?

A

The Goldman equation

33
Q

What is Em dependent on?

A

Relative permeabilities (Pion)

34
Q

Compare the relative permeabilities of Na and K

A

PK is 40x bigger than PNa

35
Q

Why is Em closer to EK?

A

Because of the difference in permeabilities

36
Q

What is happening at -65mV in a neurone?

A

Driving force acting on both Na+ and K+
Na+ influx
K+ efflux

37
Q

What is making Na+ move in?

A

Chemical gradient and electrical force

38
Q

What is making K+ move out?

A

Chemical gradient, but electrical force is making K+ move in. K+ doesnt move in however since the chemical gradient is greater than the electrical force moving in therefore the driving force is effluxing.

39
Q

What ensures Em of -65mV is at rest?

A

Na+ influx = K+ efflux

40
Q

Compare the driving force of Na+ and K+

A 
Na+ = large
K+ = small
41
Q

Compare the permeability to Na+ and K+

A 
Na+ = small
K+ = large
42
Q

Do ion pumps control Em?

A

No, they maintain concentration in the long term

43
Q

What does the sodium-potassium pump do?

A

Exchanges internal Na+ for external K+

against concentration gradient

44
Q

Is K+ higher conc on intracellular or extracellular?

A

intracellular

45
Q

Is Na+ conc higher intracellular or extracellular?

A

Extracellular

46
Q

What is the value for Ek?

A

-80mV

47
Q

What is the value for ENa?

A

+62mV

48
Q

When is the driving force for an ion >0?

A

whenever Em is different than the equilibrium potential of that ion

49
Q

How is the resting membrane potential maintained?

A

By a large driving force of Na+ coupled with a low permeability
-small driving force of K+ with a large permeability

50
Q

How does the sodium-potassium pump work?

A
  • catalyses ATP breakdown
  • exchanges internal Na+ for external K+
  • against conc gradients (active transport)
  • operate in background constantly
  • not for controlling Em
51
Q

How is the Resting membrane potential generated?

A
  • K+ leak channels open and therefore since [K] greater inside the cell, this leads to K efflux
  • [Na] lower inside cell and fewer Na channels in membrane therefore K efflux > Na Influx
  • Em becomes negatively charged
  • Voltage < 0 and therefore an electrical force is generated so the negative Em causes a drive for K and Na ions to move into the cell
  • K efflux > K influx so K ions still move out and thus the electrical force gets stronger.
  • Results in Em being closer to Ek
  • Eventually Em has no net movement as K efflux = Na influx so voltage is set at -65mV
52
Q

What causes Em at rest to be closer to Ek than ENa?

A

Ek = -80mV ENa = +62mV

Since K efflux > Na influx as membrane is more permeable to K ions.
K efflux is trying to bring Em to -80mV whereas Na influx tries to bring Em to +62mV

At rest Pk = 40 x PNa so Em is closer to Ek.

53
Q

Why can the chemical gradient of resting membrane potential be considered as a constant?

A

Over short time scales, Changes in concentration are extremely small and hence the chemical gradient is almost constant.

Fundamentals of Neuroscience (16 decks)

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