membrane and action potentials

Question 1

what is the resting membrane potential in a typical nerve cell

Answer 1

-70 mV

Question 2

what is the sodium equilibrium potential

Answer 2

+60 mV

Question 3

what is the potassium equilibrium potential

Answer 3

-90 mV

Question 4

what is equilibrium potential

Answer 4

when the conc. gradient and electrical gradient balance out each other (equilibrium)and no net movement of ion occurs, the potential that would exist at this equilibrium is known as the equilibrium potential

Question 5

what is the relative membrane permeabilities of sodium and potassium ions

Answer 5

Na+: 100
K+:1

Question 6

what is the value for the sodium, potassium and chloride ion concentrations inside and outside the cell

Answer 6

inside and outside:
Na+ : 15 mM,150mM
K+ :150 mM, 5 mM
Cl- : 7 mM,110 mM

Question 7

what is the Nernst equation for calculating equilibrium potential

Answer 7

Eion= 61 log 10 [ion]o/[ion]i

Question 8

state the Goldman-Hodgkin-Katz equation to calculate membrane potential

Answer 8

Em= 61 log Pk [K+]o+ PNa [Na+]o/Pk [K+]i + PNa [Na+]i

log base 10, Pk=1 PNa=0.01

Question 9

why are the resting membrane potential and potassium equilibrium potential not identical?

Answer 9

Due to the slight inward leak of Na+ into the cell (down the Na+-electrochemical gradient)

increases membrane potential from Ek

Question 10

The plasma membranes of all cells are polarised electrically
true or false

Answer 10

true

Question 11

The plasma membranes of all cells are electrically neutral

  true or false

Answer 11

false

Question 12

concentration gradient for Na+ is outward/inward

Answer 12

inward

Question 13

concentration gradient for K+ is outward/inward

Answer 13

outward

Question 14

At resting potential the membrane is ___ times more permeable to K+ than Na+.

Answer 14

100

Question 15

At resting potential the membrane is 100x more permeable to __ than __

Answer 15

K+, Na+

Question 16

The 2 opposing forces acting on K+:
______ gradient -tending to move K+ out of the cell
_______ gradient -tending to move K+ into the cell)

Answer 16

concentration, electrical

Question 17

the Na+-K+ pump generates a hyperpolarizing current

true or false

Answer 17

true

3 +ve go out for 2 in, net 1+ve goes out- leaves -ve overall charge in

Question 18

what is depolarization

Answer 18

the inside of cell becomes less negative ( more +ve)

Question 19

what is hyperpolarization

Answer 19

the inside of the cell becomes more negative

Question 20

Na+ selective ion channel effects the membrane potential by

Answer 20

Depolarization

Inward current: Vm is driven toward ENa+:becomes more +ve

Question 21

K+ selective ion channel effects the membrane potential by

Answer 21

Hyperpolarization

Outward current:Vm is driven to EK+: becomes more -ve

Question 22

what is neuronal action potential

Answer 22

they are electrical signals which momentarily reverse the polarity of the nerve cell membrane

Question 23

what is threshold

Answer 23

To generate an action potential, the cell needs to reach threshold

about -55 mV, they are all or none

Question 24

what is upstroke and downstroke

Answer 24

upstroke: rise during depolarization till 0 mV
downstroke: fall from 0 mV during hyperpolarization

Question 25

what is overshoot and undershoot

Answer 25

overshoot: peak of action potential from 0 mV undershoot: fall of action potential from resting potential

Question 26

Na+ ion channel in its closed stage is

Answer 26

non- conducting | inactivation gate is open, activation gate is closed

Question 27

Na+ ion channel in its open stage is

Answer 27

conducting

Question 28

Na+ ion channel in its inactivated stage is

Answer 28

non-conducting | inactivation gate is closed, activation gate is open ## Footnote this allows for a refractory period

Question 29

what is an absolute refractory period?

Answer 29

no stimulus can elicit a secondary action potential ## Footnote all Na+ channels are inactivated and membrane is depolarized and repolarized

Question 30

what is a relative refractory period?

Answer 30

a stronger than normal stimulus may elicit a secondary action potential ## Footnote some Na+ channels are closed not inactivated now, and membrane is hyperpolarized

Question 31

how does an impulse propagate in a myelinated nerve fibre?

Answer 31

saltatory conduction ## Footnote it "jumps" from each node- nodes of raniver--> occurs due to local current flow

Question 32

how does an impulse propagate in a un-myelinated nerve fibre?

Answer 32

contiguous conduction or passive conduction

Question 33

List the 3 types of gated ion channels

Answer 33

.membrane voltage: voltage-gated ion channels (VGICs) .chemical substances:ligand-gated ion channels (LGICs) .physical stimuli e.g., mechanical, thermal

Question 34

The ion channels responsible for the action potential in neurones are ____ gated ion channels

Answer 34

voltage

Question 35

Driving force for Na+ influx

Answer 35

-130 mV | Vm- ENa+= -70-60=-130 mV ## Footnote since its negative causes inward movement

Question 36

Driving force for K+ efflux

Answer 36

+20 mV | Vm-EK+= -70-(-90)= 20 mV ## Footnote since it's +ve causes outward movement

Question 37

what causes upstroke in action potential

Answer 37

upstroke (depolarizing phase) is mediated by the opening of voltage-activated Na+ channels

Question 38

what causes downstroke in action potential

Answer 38

downstroke is due to the opening of voltage-activated K+ channels and the inactivation of voltage-activated Na+ channels

Question 39

what causes undershoot in action potential

Answer 39

undershoot is due to delayed closure of voltage-activated K+ channels

Question 40

ways to increase passive conduction

Answer 40

* increase diameter of axon * decrease leak of current by insulating material- myelin--> schwann cells in PNS and ogliodendrocytes in CNS | schwann cells and ogliodendrocytres are both types of macroglia

Question 41

how does the activation of Na+ ion channels work?

Answer 41

The activation of Na+ channels is self-reinforcing – the opening of a few channels causes further channels to open, causes further depolarization | positive feedback

Question 42

what causes activation of Na+ ion channels ?

Answer 42

depolarization.

Question 43

how does activation of K+ ion channels work?

Answer 43

The activation of K+ channels is self-limiting – outward movement of K+ causes repolarization which turns off the stimulus for opening This is negative feedback

Question 44

what causes activation of K+ ion channels?

Answer 44

depolarization