Action Potentials

Question 1

what is depolarisation?

Answer 1

when the membrane potential becomes less negative

Question 2

what is hyperpolarisation?

Answer 2

the membrane potential becomes more negative

Question 3

what causes a change in membrane potential?

Answer 3

ionic movements across the membrane

Question 4

what two things determine the change in membrane potential?

Answer 4

direction of movement of the ion

charge on the ion

Question 5

what direction is influx?

Answer 5

into the cell

Question 6

what direction is efflux?

Answer 6

out of the cell

Question 7

what drives passive movement of an ion through a channel?

Answer 7

its electrochemical gradient

Question 8

when does movement of sodium ions occur?

Answer 8

in response to the opening of sodium selective channels on the cell membrane

Question 9

what direction does sodium flow and why?

Answer 9

into a cell

its concentration and electrical gradients are inward

Question 10

what is the value of the membrane potential and what represents this?

Answer 10

Vm = -70mV

Question 11

what is the equilibrium potential for sodium?

Answer 11

Ena = +60mV

Question 12

what is the driving force for sodium influx and when does sodium move into the cell?

Answer 12

Vm - Ena

when this is negative

Question 13

what is Ina?

Answer 13

the current carried by sodium ions

Ina = gna(Vm-Ena)

Question 14

what is Gna?

Answer 14

the sodium conductance

Question 15

when does movement of potassium occur?

Answer 15

in response to the opening of potassium selective channels

Question 16

which direction does K move in and why?

Answer 16

outwardly

its concentration gradient is outwards and greater than its inwards electrochemical gradient

Question 17

what is the equilibrium potential for potassium?

Answer 17

Ek = -100mV

Question 18

what is the driving force for K+ efflux?

Answer 18

Vm-Ek

moves outward when positive

Question 19

what are ion channels?

Answer 19

proteins that span the lipid bilayer forming pathways for selected ions

Question 20

what states do ion channels have and cycle between?

Answer 20

open (o) and closed (c)

Question 21

name two types of gated ion channels and state what opens them

Answer 21

voltage gated ion channels (opened by changes in membrane voltage)

ligand gated ion channels (opened when chemicals bind)

Question 22

what ion channels are responsible for the action potential in neurons?

Answer 22

voltage gated ion channels (VGICs)

voltage gated sodium and voltage gated potassium channels

Question 23

opening of which channel causes Vm to depolarise?

Answer 23

voltage gated sodium channels

Question 24

opening of which channel causes Vm to hyperpolarise?

Answer 24

voltage gated potassium channels

Question 25

what is an action potential?

Answer 25

a brief electrical signal in which the polarity of the membrane is momentarily reversed

Question 26

when is an action potential generated?

Answer 26

when the stimulus reaches threshold

Question 27

what does opening of a few sodium channels cause and what is this an example of?

Answer 27

the opening of further channels positive feedback

Question 28

what does opening of a few potassium channels cause and what is this an example of?

Answer 28

closing of channels negative feedback

Question 29

what happens to sodium channels during maintained depolarisation?

Answer 29

they enter a non-conducting inactivated state

Question 30

how does a sodium channel enter its closed state?

Answer 30

when repolarisation occurs

Question 31

what is the absolute refractory period?

Answer 31

no stimulus can elicit a second AP all sodium channels inactivated

Question 32

what is the relative refractory period?

Answer 32

a very strong stimulus may be able to elicit a second AP

Question 33

what substance surrounds axons?

Answer 33

myelin

Question 34

what produces myelin in the PNS?

Answer 34

schwann cells many surround a single axon

Question 35

what produces myelin in the CNS?

Answer 35

oligodendrocytes one surrounds many axons

Question 36

what are oligodendrocytes and schwann cells?

Answer 36

types of macroglia

Question 37

is conduction faster in a myelinated axon or non myelinated axon?

Answer 37

myelinated