Membranes and Cell Excitation

Question 1

An electrical signal involves…

Answer 1

.a change in the balance of positive and negative charges

Question 2

Name 5 important charged particles

Answer 2

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

Question 3

What controls ion movement inside and outside of a cell?

Answer 3

The membrane

Question 4

What generates an electrical signal?

Answer 4

The transfer of ions through ion channels

Question 5

What maintains gradients?

Answer 5

Ion pumps

Question 6

Describe lipid bilayer permeability

Answer 6

Impermeable to most molecules, including ions

Question 7

The inside of a cell contains…

Answer 7

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

Question 8

What is the voltage inside the cell called?

Answer 8

Membrane potential (Em)

Question 9

What is the membrane potential of a neurone?

Answer 9

-65mV

Question 10

What determines membrane potential?

Answer 10

The balance of charges

Question 11

What type of process is ion movement?

Answer 11

Passive

Question 12

Which ion channels are permeant?

Answer 12

Na+, K+, Ca2+, Cl-

Question 13

What controls membrane potential?

Answer 13

Membrane proteins

Question 14

Name the three types of gated channels

Answer 14

Non-gated, voltage, ligand

Question 15

What are non-gated channels also known as?

Answer 15

Leak channels

Question 16

What do voltage-gated channels do?

Answer 16

Generate action potentials

Question 17

What do ligand-gated channels do?

Answer 17

Generate membrane potential changes at synapses

Question 18

What type of cells are neurones?

Answer 18

Excitable cells

Question 19

Neurones have a resting membrane potential of…

Answer 19

-60mV to -70mV

Question 20

What factors influence ion movement across the cell membrane?

Answer 20

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

Question 21

What determines membrane permeability?

Answer 21

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.

Question 22

What do efflux and influx mean?

Answer 22

Efflux = movement out
Influx = movement in

Question 23

Define equilibrium

Answer 23

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

Question 24

What is equilibrium potential abbreviated to?

Answer 24

Eion

Question 25

What does the Nernst equation do?

Answer 25

Defines the voltage at which the ion is at equilibrium

Question 26

What is happening at equilibrium potential?

Answer 26

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.

Question 27

What is different between Eion and Em

Answer 27

Eion is a constant, Em can vary

Question 28

What is ionic driving force?

Answer 28

the net force resulting from chemical and electrical influences. Em - Eion

Question 29

Explain ionic driving force

Answer 29

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

Question 30

In a neurone, what influences Em?

Answer 30

Na+ and K+

Question 31

What ion equilibriums does Em rest between?

Answer 31

EK and ENa

Question 32

How do we calculate Em?

Answer 32

The Goldman equation

Question 33

What is Em dependent on?

Answer 33

Relative permeabilities (Pion)

Question 34

Compare the relative permeabilities of Na and K

Answer 34

PK is 40x bigger than PNa

Question 35

Why is Em closer to EK?

Answer 35

Because of the difference in permeabilities

Question 36

What is happening at -65mV in a neurone?

Answer 36

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

Question 37

What is making Na+ move in?

Answer 37

Chemical gradient and electrical force

Question 38

What is making K+ move out?

Answer 38

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.

Question 39

What ensures Em of -65mV is at rest?

Answer 39

Na+ influx = K+ efflux

Question 40

Compare the driving force of Na+ and K+

Answer 40

``` Na+ = large K+ = small ```

Question 41

Compare the permeability to Na+ and K+

Answer 41

``` Na+ = small K+ = large ```

Question 42

Do ion pumps control Em?

Answer 42

No, they maintain concentration in the long term

Question 43

What does the sodium-potassium pump do?

Answer 43

Exchanges internal Na+ for external K+ | against concentration gradient

Question 44

Is K+ higher conc on intracellular or extracellular?

Answer 44

intracellular

Question 45

Is Na+ conc higher intracellular or extracellular?

Answer 45

Extracellular

Question 46

What is the value for Ek?

Answer 46

-80mV

Question 47

What is the value for ENa?

Answer 47

+62mV

Question 48

When is the driving force for an ion >0?

Answer 48

whenever Em is different than the equilibrium potential of that ion

Question 49

How is the resting membrane potential maintained?

Answer 49

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

Question 50

How does the sodium-potassium pump work?

Answer 50

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

Question 51

How is the Resting membrane potential generated?

Answer 51

- 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

Question 52

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

Answer 52

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.

Question 53

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

Answer 53

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