lecture 3: membrane potentials, resting potential

Question 1

why do cells need electrical potential?

Answer 1

• they need electrical potential to be able to transmit information reliably and quickly over a large distance

Question 2

Why are calcium ions important?

Answer 2

• they are important for releasing chemical signals such as neurotransmitters - they are needed to manipulate biochemical pathways

Question 3

what is flux?

Answer 3

flux is the number of molecules that cross a unit area per unit time

Question 4

what is diffusion equilibrium ?

Answer 4

uniform concentration and no further movement here there is no net flux

Question 5

what is ohms law ? what is voltage? what is current? what is resistance?

Answer 5

• Voltage= current x resistance - generated by ions to produce a charge gradient - the current is the movement of ions due to potential - resistance is the barrier that prevents the movement of ions

Question 6

what charge is the resting membrane potential?

Answer 6

• the inside of the cell is negative compared to the outside at rest

Question 7

how are the inside and outside charges separated?

Answer 7

they are separated by a selectively permeable membrane - the concentration of the ions is different on either side

Question 8

what is a diagram of the resting potential of a cell?

Answer 8

Question 9

what are ion channels for?

Answer 9

they are needed to be selective for different ions for example K+, Na+, Cl-, Ca2+

Question 10

what are the two main types of ion channel? explain them :

Answer 10

• voltage dependent : they open by a change in the membrane potential - voltage independent: they are open all of the time (these are needed for the resting potential of the cell)

Question 11

what is the generation of a membrane potential through a selectively permeable membrane with no channels?

Answer 11

there are no channels so no diffusion so concentrations on either side are the same

Question 12

what is the generation of a membrane potential through a selectively permeable membrane with with its membrane permeable to K+ but not Na+? INSERT THE PIC

Answer 12

1. this means K= crosses the membrane down the concentration gradient 2. C2 becomes negative and C1 is positive 3. as one side becomes more positive is repels the excess K+ moving in 4. the electrochemical equilibrium is eventually attained when so much K+ has gathered that no more K+ can move in 5. this makes a stable membrane potential the fluxes are equal but K+ in the C1 is still less than the C2

Question 13

what is the generation of a membrane potential through a selectively permeable membrane with with its membrane permeable to Na+ but not K+?

Answer 13

• in this case the C2 gains positive charge and the C1 becomes negative - At electrical equilibrium the electrical force prevents further diffusion across the membrane - a membrane potential exists - fluxes are equal

Question 14

what are the main differences concerning the membrane being permeable to Na+ or K+ ?

Answer 14

• the sign of the membrane potential will be opposite even thought the concentrations are the same - the selectivity is different - the electrical potential that prevents the diffusion down the ions concentration gradient

Question 15

what is an electrochemical equilibrium ?

Answer 15

this is reached when the concentration gradient is balanced by the electrical gradient

Question 16

what is an equilibrium potential?

Answer 16

the potential that prevents the diffusion down the ions concentration gradient

Question 17

what is the nernst equation?

Answer 17

Question 18

what do the different variables in the nernst equation stand for? R= T= z= F= X= E= C2 = C1=

Answer 18

R= gas constant T= temperature in kelvins z= charge on the ion F= faradays number X= the intercellular and extracellular concentration E= equilibrium potential of the ion C2= inside C1= outside §

Question 19

what does the nernst equation do?

Answer 19

it relates the size of the equilibrium potential of an ion to the size of its concentration gradient

Question 20

what is the main governing factor

Answer 20

it is the permit all the ions that governs the overall membrane potentiality of the membrane

Question 21

what is the real membrane potential for a neurone?

Answer 21

-70mV

Question 22

what is the goldman hodgkin katz voltage equation? how to use it INSERT PIC

Answer 22

this describes the resting membrane potential if a channel is open then the Permeability is 1 if the channel is closed the permeability is 0

Question 23

what are the 2 changes in membrane potential definitions?

Answer 23

• graded potential = change in amplitude - action potential = uniform amplitude (all or nothing)