Membrane Potentials & Action Potentials

Question 1

action potential definition

Answer 1

the propagation of depolarisation (positive change) down the length of the axon

Question 2

how is an action potential achieved?

Answer 2

by movement of ions across the cell membrane to create an ion gradient for more ion movement

Question 3

what happens on an electrical gradient?

Answer 3

opposite charges attract
ions move down an electrical gradient
when ionic charges are balanced, they are at equilibrium

Question 4

what happens in the Na+ & K+ chemical gradient?

Answer 4

Na+ & K+ important in cells

Na+ & K+ move down their chemical gradient - area of high to low concentration

Question 5

purpose & function of a gradient in a cell

Answer 5

for positively charged ions to diffuse into the cell

the phospholipid bilayer blocks the ions, so they require channels to enter the cell

Question 6

4 steps of the action potential

Answer 6

1. resting membrane potential (RMP)
2. depolarisation
3. repolarisation
4. hyperpolarisation

Question 7

step 1: resting membrane potential purpose and function

Answer 7

at rest, resting membrane potential (voltage) @ -70mV

uses an electrochemical gradient

Question 8

why is the RPM -70mV?

Answer 8

cells use the Na+/K+-ATPase pump to pump ions against the electrochemical gradient
there should be a high Na+ concentration OUTSIDE the cell
there should be a high K+ concentration INSIDE the cell

Question 9

purpose & function of voltage-gated ion channels

Answer 9

ions require these channels to move across the membrane
voltage-gated ion channels are gated by voltage
closed when the RPM of cell is -70mV
they only open at certain voltages:
+60mV opens the voltage-gated Na+ channel
+30mV opens the voltage-gated K+ channel

Question 10

step 2. depolarisation structure and function

Answer 10

voltage reaches -60mV to open voltage-gated Na+ channels
Na+ diffuses into cell
cell becomes more positive than the outside
Na+ continues to enter cell until RMP reaches +30mV

Question 11

what happens in early depolarisation?

Answer 11

the membrane voltage changes to -60mV, activating the cell, opening the Na+ voltage-gated channels
the K+ voltage-gated channels are still closed

Question 12

step 3. structure and function of repolarisation

Answer 12

@ +30mV, voltage-gated Na+ channels close & voltage-gated K+ channels open
opening of these channels allows K+ to leave cell down the electrochemical gradient
cell becomes more negative than outside

Question 13

step 4. structure and function of hyperpolarisation

Answer 13

voltage-gated K+ channels begin to close at -40mV
RPM reesstablished
as K+ leaves, the cell becomes more negative than the outside
K+ continues to leave the cell until the RMP reaches -80mV

Question 14

what is the refractory period?

Answer 14

not able to generate another action potential during this period
the voltage-gated Na+ channels are either already open (causing depolarisation) or inactive (during hyper polarisation)