potentials

Question 1

how is the potential differences across a membrane achieved?

Answer 1

distribution of ions
(Na+, K+)

Question 2

what is meant by resting potential?

Answer 2

• neurone is not carrying a nerve impulse
• inside of neurone negatively charged with respect to outside
• approximately -70mV
• membrane is polarised

Question 3

what is the role of the sodium potassium ion pump?

Answer 3

uses ATP to pump 3 sodium ions out of the cell and 2 potassium ions into the cell
- net movement of one cation outwards

Question 4

…… potassium ion channels allow K+ out by facilitated diffusion
…… sodium ion channels allow Na+ in by facilitated diffusion

Answer 4

many
fewer

Question 5

how do metabolic poisons work?

Answer 5

blocks respiratory pathways and prevent formation of ATP so K+/Na+ pump cannot function

Question 6

describe how the resting potential of a neurone is maintained (2)

Answer 6

• active transport of Na+ out and K+ in
• membrane less permeable to Na+
• less Na+ come in and more K+ leave

Question 7

what are voltage gated channels?

Answer 7

open or close depending on potential differences across membrane

Question 8

during an action potential, the voltage gated Na+ channels open which changes …………..

Answer 8

permeability of membrane so Na+ ions rush into the axon

Question 9

what happens when the sodium channels open?

Answer 9

• depolarisation
• Na+ enter and membrane becomes more positive

Question 10

what is the change in voltage for depolarisation?

Answer 10

-70 to +40mV

Question 11

describe depolarisation

Answer 11

• Na+ channels open
• increased Na+ ions diffuse in
• triggers more channels to open and more Na+ to enter

Question 12

what is meant by an action potential?

Answer 12

when the neurone’s voltage increases beyond a set point from the resting potential, generating a nervous impulse

Question 13

when will an action potential be generated?

Answer 13

if a threshold is reached
-55mV

Question 14

describe repolarisation

Answer 14

• Na+ channels close
• no more Na+ entering but K+ still leaving so voltage decreases

Question 15

describe hyperpolarisation

Answer 15

• more K+ channels are open
• voltage becomes more negative than resting potential

Question 16

why is there no stimulation in the refractory period?

Answer 16

• ensures discrete impulses are produced separately
• ensure action potential travels in one direction
• limits number of impulse transmission which prevents overreaction

Question 17

what is the status of the K+ and Na+ channels at resting potential?

Answer 17

closed

Question 18

when do Na+ channels open?

Answer 18

depolarisation

Question 19

when do K+ channels open?

Answer 19

repolarisation

Question 20

what is meant by the all or nothing principle?

Answer 20

a stimulus only causes voltage gated ion channels to open if it exceeds the threshold level
- all Na+ channels open if threshold reaches
- all action potentials are always same size (level of depolarisation is always +40mV) no matter the stimulus intensity

Question 21

what is the difference between intense and weak stimuli?

Answer 21

intense stimuli cause many frequent action potentials