Action potential

Question 1

factors increasing speed of conduction of neurons?

Answer 1

presence of myelin
increased heat
increased axon thickness

Question 2

why are channels selectively permeable?

Answer 2

due to shape and chemical properties

Question 3

two types of ____ gated ion channels?

Answer 3

ligand and voltage gated

Question 4

channel for water?

Answer 4

aquaporins.

Question 5

describe equilibrium when an electrical field is applied?

Answer 5

equilibrium between voltage AND concentration is established

Question 6

describe nernst equation

Answer 6

measures ionic equilibrium potential

• potential difference when equilibrium (voltage and conc) is reached when the membrane is permeable to one ion
• depends on relative concs and ionic charge

Question 7

describe goldman equation

Answer 7

measures membrane potential

• potential difference when equilibrium (voltage and conc) is reached when the membrane is permeable to multiplie ions
• depends on relative concs and permeability

Question 8

what two membrane proteins set resting membrane potential?

Answer 8

two pore domain potassium pump and Na/K-ATPase

Question 9

what is resting membrane potential

Answer 9

-65mV

Question 10

describe how Na/K-ATPase works

Answer 10

• 3 intracellular Na bind
• Pi attaches
• conformational change and release
• extracellular K bind
• pi releases
• conformational change
• -> membrane potential nears EK+

Question 11

4 types of K channels?

Answer 11

2 pore domain potassium channels
voltage gated K channels
inward rectifying K channels
calcium activated K channels

Question 12

describe 2 pore domain channels

Answer 12

have 2 pore loop domains, which are open, contributing to ongoing K+ channel

Question 13

describe voltage gated K channels

Answer 13

delayed rectifier

• open some time after membrane reaches a certain voltage
• returns to resting potential

Question 14

describe voltage gated sodium channels

Answer 14

closed at -65mV
open at -40mV for 1ms
inactivate at -65mV (globular protein blocks)
returns

Question 15

pros and cons of passive conduction?

Answer 15

doesnt require energy but strength of AP reduces (since its done by diffusion)

Question 16

pros and cons of active conduction?

Answer 16

requires energy, but propagates

Question 17

describe depolarisation to threshold

Answer 17

membrane potential increases due to physically Na channels opening or due to inheritance somewhere in the cell

Question 18

during resting membrane potential, what controls the membrane potential?

Answer 18

Na/K-ATPase and two pore domain potassium pumps

Question 19

what happens during rapid depolarisation

Answer 19

membrane potential increases, voltage gated sodium channels open FOR ONE MS; sodium enters cell, increases membrane potential (positive feedback)

Question 20

what happens during repolarisation?

Answer 20

voltage gated sodium channels close. only K2p channels open, so membrane potential falls.

Question 21

what happens in hyperpolarisation

Answer 21

voltage gated (delayed rectifier) K channels open

Question 22

what happens during absolute refractory period

Answer 22

Na+ channels are inactivated (globular protein blocks channel), limiting second AP from firing for atleast 1ms

Question 23

describe relativle refractory period

Answer 23

voltage gated potassium channels close

Question 24

are channel openings stoichastic?

Answer 24

yes

Question 25

where is the threshold reached? why?

Answer 25

axon hillock/spike initiation zone

because Na+ channels are open the most here and hence its easiest to reach threshold.

Question 26

why do APs propagate in one direction?

Answer 26

inactivated sodium channels prevent back propagation of AP

Question 27

in terms of axons and the myelin sheath, where are sodium channels most densely found?

Answer 27

in the nodes of ranvier

Question 28

describe saltatory conduction

Answer 28

AP’s jump from node to node

Question 29

why is saltatory conduction quicker than when there’s no myelin

Answer 29

AP’s dont have to happen constantly, only in nodes

Question 30

what happens if the nodes are too far apart?

Answer 30

strength of AP will decline as ions have to diffuse intracellularly to get to the node

Question 31

what happens when you inject a current and

• it doesnt reach threshold
• reaches threshold?

Answer 31

doesnt reach threshold = no AP

reaches threshold - frequency proportional to strength of injected current