Ion Channels, Resting & Action Potentials

Question 1

Take Homes of Ion Channels Presentation (5)

1. Ion Channels = generate ____ membrane potential and action potential
2. Nernst Equation = electrochemical _____ potential for an ion across cell membrane
3. ______ Equation = steady-state potential for multiple ions across the cell membrane
4. Resting membrane potential = ___mV in many neurons bc neurons are primarily permeable to ___
5. Action Potential Propagation: Unmyelinated axons = ____ conduction; myelinated axons = _____ conduction

Answer 1

1. Ion Channels = generate resting membrane potential and action potential
2. Nernst Equation = electrochemical equilibrium potential for an ion across cell membrane
3. Goldman-Hodgkin-Katz Equation = steady-state potential for multiple ions across the cell membrane
4. Resting membrane potential = -70mV in many neurons bc neurons are primarily permeable to K+
5. Action Potential Propagation: Unmyelinated axons = continuous conduction; myelinated axons = saltatory conduction

Question 2

What are the 3 Gating mechanisms?

Answer 2

1. voltage gated
2. ligand gated
3. mechanical stress gated

Question 3

Selective ion permeability of voltage gated channels is it which 3 ions?

Answer 3

selective to K+, Na+ or Ca2+

Question 4

Selective ion permeability of ligand gated channels is cation selective to ___, ___ and sometimes ___ while anion selective to ___.

Answer 4

cation selective K+, Na+, sometimes Ca2+

anion selective Cl-

Question 5

Channelopathies are

Answer 5

genetic disorders affecting ion channels

Question 6

What Na+ channel is strongly expressed in nociceptive DRG neurons?

Answer 6

NaV1.7

Question 7

NaV1.7 mutations cause _____ of DRG neurons and ______

Answer 7

hyperexcitability; neuropathic pain

Question 8

Nonsense mutations in NaV1.7 result in

Answer 8

complete inability to sense pain (channels not being expressed at all)

Question 9

Delayed rectifier K+ channels open with ______ and close with ______

Answer 9

depolarization; repolarization

Question 10

What generates the falling phase of the action potential?

Answer 10

Delayed rectifier K+ channels

Question 11

What generates the resting membrane potential?

Answer 11

Leakage K+ channels

Question 12

Leakage K+ channels ____ at the resting membrane potential

Answer 12

open

Question 13

What channel inactivation (closing after opening) includes a “ball and chain” protein segment that causes inactivation recovery from inactivation only after neuron repolarizes?

Answer 13

Na+

Question 14

Na+ channel gate ____ with depolarization

Answer 14

open

Question 15

What channel generates the rising phase of the action potential?

Answer 15

voltage gated Na+

Question 16

What are the types of Ca2+ channels? (voltage subsets)

Answer 16

1. High Voltage
   a) L-type
   b) N-type
2. Low Voltage
   c) T-type

Question 17

T/F: In the Ca2+ channels, inactivation time varies based on type

Answer 17

true

Question 18

L-type ca2+ channels are sensitive to _______ and are a part of excitation-contraction coupling in _____

Answer 18

dihydropyridines; skeletal muscle

Question 19

N-type ca2+ channels has a transmitter that releases at the

Answer 19

synapses

Question 20

High voltage activated Ca2+ channels are at a charge of ____ depolarization

Answer 20

-50mV

Question 21

Low voltage activated Ca2+ channels are at a charge of ____ depolarization

Answer 21

5-10mV

Question 22

Which 2 ions flow INTO the cell?

Answer 22

Na+ and Cl-

Question 23

Which 2 ions flow OUT OF the cell?

Answer 23

K+ and A-

Question 24

Ion gradients across cell membranes are maintained by what enzyme?

Answer 24

Na+/K+ ATPase

Question 25

What is the natural charge of the intracellular membrane?

Answer 25

-85mV

Question 26

The equilibrium potential for K+ is

Answer 26

negative

Question 27

In equilibrium potential, the membrane is permeable to ____ ion

Answer 27

one

Question 28

In equilibrium potential, the ion flux is driven in _____ direction by the ________ across membrane

Answer 28

one; chemical gradient

Question 29

In equilibrium potential, flux results in (2)

Answer 29

1. charge difference | 2. voltage across membrane

Question 30

In equilibrium potential, opposite ion flux is driven by

Answer 30

the membrane voltage

Question 31

Electrochemical equilibirum is achieved at the voltage where the 2 fluxes...

Answer 31

balance each other out

Question 32

What are the equilibrium potentials for K+ and Na+?

Answer 32

K+: -90mV | Na+: +50mV

Question 33

What equation tells you what the equilibrium potential is?

Answer 33

Nernst Equation

Question 34

Which leakage channels are ALWAYS open in neurons?

Answer 34

K+

Question 35

Why is the resting potential -70mV instead of -90mV?

Answer 35

Because other channels like Na+ and Cl- are open which make the resting membrane potential a little more positive than the K+ equilibrium potential

Question 36

Generation of the action potential is a

Answer 36

all-or-none event

Question 37

Resting membrane potential

Answer 37

voltage-independent gK; leakage K+ channels

Question 38

Rising phase

Answer 38

activation of gNa; voltage gated Na+ channels (2)

Question 39

Falling phase

Answer 39

inactivation of gNa and activation of gK; inactivation of voltage-gated Na+ channels and delayed rectifier K+ channels (3) and leakage K+ channels

Question 40

Action potential depolarization in one region spreads ______ to neighboring regions

Answer 40

passively

Question 41

Passive depolarization initiates

Answer 41

action potential in neighboring region

Question 42

Myelinated axons include nodes of Ranvier which are separated by

Answer 42

long stretches of myelin

Question 43

Myelin is formed by which glial cells? (2)

Answer 43

oligodendrocytes & Schwann cells

Question 44

What is the internodal distance of Nodes of Ranvier?

Answer 44

1-2mm

Question 45

Saltatory Conduction

Answer 45

action potential depolarization at one node spreads passively to neighboring node 1-2mm distance; rapid propagation velocity

Question 46

Equilibrium potential equation

Answer 46

Vion (mV) = 58/z x log x {ion}0/{ion}i log(10) = 1 log(1) = 0 log (1/10) = -1

Question 47

Na+ equilibrium is ____ if there is a higher concentration of Na+ outside the cell than in

Answer 47

positive

Question 48

Why is it more difficult to generate a 2nd action potential immediately following the generation of an action potential?

Answer 48

1. Na+ channels are inactivated and cannot open to depolarize the neuron 2. Delayed rectifier K+ channels remain open, hyperpolarizing the cell

Question 49

What will happen to an action potential traveling down a myelinated axon when it encounters a demyelinated region of the axon?

Answer 49

block/slowing of action potential example: Multiple Sclerosis