Dr. Karius' Action Potential lecture

Question 1

Why do cells expand a huge amount of energy maintaining the membrane potential?

Answer 1

to store energy

Question 2

What characteristics of the pore channel allow it to control flow?

Answer 2

charge of its amino acids
size of the pore
can open/close

Question 3

pore channels can be controlled by

Answer 3

voltage changes
chemical binding
mechanical deformation

Question 4

a “closed” channel has done what?

Answer 4

undergone a conformational change

Question 5

inactivation and closure

Answer 5

inactivation is also a conformational change that cuts off pore movement but it’s not the same thing as closure because its not able to directly open from the inactivated state

Question 6

The usual order for channels is

Answer 6

Open –> Inactivation —> Closed

Question 7

What controls the direction in which ions flow?

Answer 7

the gradient

Question 8

Voltage gated channels are used by

Answer 8

Na and K

Question 9

ClC1 channels are used by

Answer 9

Cl- open at rest, closes with depolarization

Question 10

K-leak channels are active when?

Answer 10

at rest

Question 11

What happens to chlorine channels during depolarization?

Answer 11

they close

Question 12

What channels are open at rest? What channels are closed at rest?

Answer 12

Na/K symporters, K leaky, and Cl- are all operational at rest

Na+ and K voltage gated channels are closed at rest

Question 13

K+ leaky channel
When open?
What opens/closes?
Ion?
Inactivation?

Answer 13

open at rest/always
constitutive
K
No inactivation

Question 14

ClC1 channels

When open?
What opens/closes?
Ion?
Inactivation?

Answer 14

open at rest
depolarization closes
Cl
Maybe inactivation?

Question 15

Voltage gated Na

When open?
What opens/closes?
Ion?
Inactivation?

Answer 15

closed at rest, open during action potentiall
Opens during depolarization
Yes can be inactivated

Question 16

voltage gated K channel

When open?
What opens/closes?
Ion?
Inactivation?

Answer 16

Closed at rest, opens during action potential
Opens during depolarization
K
Yes can be inactivated

Question 17

The single highest user of ATP in the body is

Answer 17

the 3Na/2K pump, huge amounts of energy are

Question 18

A local response is the

Answer 18

subthreshold

Question 19

what is a subthreshold response?

Answer 19

a membrane depolarization that doesn’t achieve threshold

Question 20

a sub-threshold is graded

Answer 20

they get larger with each new stimuli

Question 21

what happens to local potentials after the stimulus is achieved?

Answer 21

they die away

Question 22

Local responses have what kind of characteristic the further away they get from the site of stimulation?

Answer 22

they decay

Question 23

Definition of excitable cells =

Answer 23

cells in which an action potential can be induced

Question 24

there are ____ changes responsible for closing/opening a pore channel

Answer 24

2: both sides have to undergo a conformational change

Question 25

"excitable cells": definition is restricted to

Answer 25

neurons skeletal muscle cardiac muscle smooth muscle

Question 26

parts of an action potential:

Answer 26

subthreshold--> action potential (Depolarization) --> Repolarization--> hyperpolarization

Question 27

After voltage gated ion channels are fully open, what two events occur?

Answer 27

sodium enters the cell and will make the Vm positive, overshooting the nernst potential

Question 28

what happens during repolarization?

Answer 28

Na gates become inactivated and K gates are opening they open slowly K leaves cell the cell repolarizes

Question 29

how does the Na channel close?

Answer 29

repolarization has to achieve -90mV

Question 30

What are the ionic events that produce the rapid unsweep of the action potential, repolarization, and the re-establishment of the resting Vm? rapid upsweep

Answer 30

this is depolarization opening of voltage gated sodium channels allowing sodium influx

Question 31

What are the ionic events that produce the rapid unsweep of the action potential, repolarization, and the re-establishment of the resting Vm? repolarization

Answer 31

opening of voltage gated sodium channels and K-efflux/inactivation of sodium channels

Question 32

What are the ionic events that produce the rapid unsweep of the action potential, repolarization, and the re-establishment of the resting Vm? resting

Answer 32

Na/K ATPase re-establishes resting concentrations

Question 33

Threshold =

Answer 33

the Vm at which ALL the Na channels have opened

Question 34

How does an action potential's "shape" change during stimulus?

Answer 34

it doesnt. it's just all or nothing

Question 35

how can you increase or decrease the amount of Na going into a cell during an action potential?

Answer 35

you cant: you have to make new channels or change the Na concentration

Question 36

Refractory period.... ABSOLUTE refractory period Relative Refractory period

Answer 36

the period after an action potential in which it is impossible or more difficult to elicit a second action potential AR: impossible to get a 2nd AP. Na channels open but inactivated RR: more difficult to get a 2nd ap, some Na channels back to closer state

Question 37

What is the role of the Na/K ATPase?

Answer 37

restablishes the resting gradient

Question 38

the absolute refractory period makes up what "chunk" of the action potential?

Answer 38

the subthreshold, the depolarizaation, and a large portion of the repolarization

Question 39

the relative refractory period makes up what portion of the action potential?

Answer 39

a chunk of the repolarization and the hyperpolarization period

Question 40

Why don't sodium channels close immediately after depolarization?

Answer 40

because the Vm is +

Question 41

Voltage inactivation =

Answer 41

depolarization block something is maintaining the Vm in (+) and it doesn't get a chance to return to resting Vm it's more or less stuck in the AR stage

Question 42

Subthresholds versus action potential propagation

Answer 42

Subthresholds die away the further they get from the origin of stimulus action potentials do NOT die away

Question 43

Propagation of the action potential (4 parts)

Answer 43

1) action potential goes along axon allowing Na influx 2) Na diffuses to other regions 3) those regions of the membrane are brought to threshold 4) action potential propagated

Question 44

bigger/more myelinated axons ---->

Answer 44

faster the conduction

Question 45

Node of Ranvier

Answer 45

points where myelination are missing

Question 46

Where are the Na/K channels located on a myelinated axon?

Answer 46

at the nodes

Question 47

Myelin does what

Answer 47

it doesn't allow the sodium to diffuse away, so it maintains the signal

Question 48

What happens to sodium in an axon without myelination?

Answer 48

the sodium can leak out

Question 49

subthreshold versus action potential: which is graded?

Answer 49

subthreshold, not AP | AP is All or None

Question 50

how do ST and AP change with time?

Answer 50

ST die away, AP do not have a change in amplitude

Question 51

how do ST and AP change with distance?

Answer 51

ST die away, APs do not have a change in amplitude

Question 52

# Define the following: Saltatory conduction

Answer 52

in myelinated neurons, the action potential appears to hop from node of ranvier to node with little loss of Sodium in between: VERY FAST

Question 53

# Define the following: Propagation

Answer 53

an action potential in one part of the membrane is sufficient to depolarize the neighboring membrane to threshold

Question 54

# Define the following: Depolarization block

Answer 54

External force causes membrane potential to remain depolarized for longer periods of time: voltage gated sodium channels "stuck" in the inactive state

Question 55

Define the time of the AR in an AP

Answer 55

beginning of AP to middle of repolarization

Question 56

Define the time of the RR in an AP

Answer 56

End of ARP to some time after end of AP

Question 57

RR and AR periods differ when they occur but also how they can be induced

Answer 57

during a AR a second AP cannot be induced no matter what during a RR a second one can be induced with increasing stimulus

Question 58

Mechanism of AR versus RR

Answer 58

in AR, all votage gated Na channels are either open or inactive in RR, enough voltage gated Na channels have moved from inactive to closed state for a second potential to be induced