Chapter 5: Membrane Potentials and Action Potentials

Question 1

This is the potential difference between the inside and outside of the cell

Answer 1

diffusion potential

Question 2

In normal mammalian nerve fiber, what is the potential difference inside the fiber membrane?

Answer 2

-94 millivolts (as potassium goes out)

+61 millivolts (as sodium goes in)

Question 3

This equation describes the relationship of diffusion potential to the ion concentration difference across a membrane

Answer 3

Nernst equation

Question 4

This is the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane

Answer 4

Nernst potential

Question 5

Give the Nernst equation

Answer 5

Electromotive Force = ±(61/z) (Concentration inside/Concentration outside)

where z is the electrical charge of the ion (e.g., 1+ for K+)

Question 6

What is the Nernst potential if the concentration of the K+ ions inside is 10 times that on the outside?

Answer 6

• 61 mV

* since log of 10 is 1

Question 7

What is the equation used to calculate the diffusion potential when the membrane is permeable to several different ions?

Answer 7

Goldman equation or

Goldmann-Hodgkin-Katz equation

Question 8

What are the most important ions involved in the development of membrane potentials in nerve and muscle fibers, as well as in the neuronal cells?

Answer 8

Sodium, Potassium, Chloride

Question 9

Resting Membrane Potential of Neurons

Answer 9

-60 to -70 mV

Question 10

Resting Membrane Potential of Skeletal Muscle

Answer 10

-85 to -95 mV

Question 11

Resting Membrane Potential of Smooth muscle

Answer 11

-50 to -70 mV

Question 12

Resting Membrane Potential of Cardiac Muscle

Answer 12

-80 to -90 mV

Question 13

Resting Membrane Potential of Hair cells (cochlea)

Answer 13

-15 to -40 mV

Question 14

Resting Membrane Potential of Astrocytes

Answer 14

-80 to -90 mV

Question 15

Resting Membrane Potential of Erythrocytes

Answer 15

-8 to -12 mV

Question 16

Resting Membrane Potential of Photoreceptors

Answer 16

-40 (dark) to -70 (light) mV

Question 17

This is primarily responsible for the signal transmission in neurons

Answer 17

Rapid changes in sodium and potassium ion permeability

Question 18

What is the sign of the electrochemical driving force if the predicted movement of cations is out of the cell?

Answer 18

positive

Question 19

Cations are predicted to move (?outside/inside?) the cell if the electrochemical driving force of cations is negative

Answer 19

inside

Question 20

This pertains to the difference between the membrane potential and equilibrium potential of the ion

Answer 20

electrochemical driving force

Vdf = Vm – Veq

A positive value indicates outward flux of the ion, and a negative value indicates inward flux of
the ion. A typical equilibrium potential for sodium (calculated using the Nernst equation) is +62 millivolts, so the electrochemical driving force for sodium is −65 − 62 = −127 millivolts. This means that a 127-millivolt force attempts to drive sodium into the cell. The equilibrium potential is about −86 millivolts for potassium and about −70 millivolts for chloride; hence, the electrochemical driving forces for these two ions are +21 and +5 millivolts, respectively (and both ions tend to be driven out of the cell).

Question 21

This is the membrane potential where the net flow through any open channels is 0.

Answer 21

equilibrium potential or reversal potential

Question 22

This is known as the reversal potential

Answer 22

equilibrium potential

**When Vm = Veq, there is no net movement of the ion into or out of the cell. Also, the direction of ion flux through the membrane reverses as Vm becomes greater than or less than Veq; hence, the equilibrium potential (Veq) is also called the reversal potential.

Question 23

When measuring the membrane potential, which electrode is place in the extracellular fluid?

Answer 23

indifferent electrode

Question 24

This is the voltage change area at the cell membrane that causes the potential to decrease abruptly to -70 mV as the recording electrode passes through.

Answer 24

electrical dipole layer

Question 25

The resting membrane potential of large nerve fibers when they are not transmitting nerve signals is about:

Answer 25

−70 millivolts

Question 26

What are the large concentration gradients for sodium and potassium across the resting nerve membrane caused by the Na+-K+ pump?

Answer 26

Na+ (outside):142mEq/L
Na+ (inside):14mEq/L
K+ (outside): 4mEq/L
K+ (inside):140mEq/L

The ratios of these two respective ions from the inside to the outside are as follows:
Na inside /Na outside = 0.1
K inside /K outside = 35.0

Question 27

These are protein channels in the nerve membrane through which potassium ions can leak, even in a resting cell

Answer 27

tandem pore domain, potassium channel, or potassium [K+] “leak” channel

Question 28

How much degree of negativity (in mV) is added by the Na-K pump on the inside of the cell membrane?

Answer 28

-4 mV

Question 29

Most of the membrane potential of the cell is due to the diffusion potentials of which ion?

Answer 29

Potassium

**the diffusion potentials alone caused by potassium and sodium diffusion would give a membrane potential of about −86 millivolts, with almost all of this being determined by potassium diffusion. An additional −4 millivolts is then contributed to the membrane potential by the continuously acting electrogenic Na+-K+ pump, and there is a contribution of chloride ions.

Question 30

These are rapid changes in the membrane potential that spread rapidly along the nerve fiber membrane

Answer 30

action potential

Question 31

What stage of the action potential pertains to the resting membrane potential before the action potential begins?

Answer 31

Resting stage

• polarized membrane with -70mV

Question 32

This is the process by which the normal polarized state of −70 millivolts is immediately neutralized by the inflowing, positively charged sodium ions, with the potential rising rapidly in the positive direction

Answer 32

depolarization

Question 33

This is the reestablishment of the normal negative resting membrane potential by the rapid diffusion of potassium ions to the exterior of the cells as the potassium channels open to a greater degree than normal.

Answer 33

repolarization

Question 34

In a normal resting membrane (-70mV) what is which gate of the voltage-gated sodium channel is closed?

Answer 34

activation gate

Question 35

Around what voltage from the resting membrane potential does the voltage-gated sodium channels undergo a sudden conformational change in its activation gate?

Answer 35

-55 mV (activation gate flips all the way to open position)

Question 36

True or False:
The conformational change that flips the activation gate to the open state is a slower process than the conformational change that closes the inactivation gate.

Answer 36

False:
the conformational change that flips the inactivation gate to the closed state is a slower process than the conformational change that opens the activation gate.

Question 37

This is the method used to measure the flow of ions through different voltage-gated protein channels

Answer 37

Voltage Clamp method

Question 38

This toxin blocks sodium channels when applied to the outside of the membrane

Answer 38

tetrodotoxin

Question 39

This ion blocks the potassium channels when applied to the interior of the membrane

Answer 39

tetraethylammonium

Question 40

What causes the potassium channels to close at the end of action potential?

Answer 40

the return of the membrane potential to a negative state

Question 41

What causes the membrane potential to be positive at the action potential onset?

Answer 41

More sodium ions flow to the interior of the fiber than potassium ions to the exterior

Question 42

These are responsible for the negative charge inside the fiber when there is a net deficit of positively charged potassium ions and other positive ions.

Answer 42

Impermeant negative ions

Question 43

These protein channels are known as the slow channels

Answer 43

voltage-gated calcium ion channels

Question 44

These channels play a key role in initiating action potential

Answer 44

voltage-gated sodium ion channels

Question 45

These channels provide more sustained depolarization

Answer 45

voltage-gated calcium ion channels

Question 46

In some types of smooth muscle, the fast sodium channels are hardly present. In these cells, the action potentials are caused almost entirely by the activation of which channels.

Answer 46

slow calcium channels

Question 47

What is expected to change as for the membrane potential of cells in cases of hypocalcemia?

Answer 47

a small increase of the membrane potential from its normal, very negative level

**When there is a deficit of calcium ions, the sodium channels become activated (opened) by a small increase of the membrane potential from its normal, very negative level. Therefore, the nerve fiber becomes highly excitable, sometimes discharging repetitively without provocation, rather than remaining in the resting state

Question 48

This condition can occur in the muscles if the calcium ion concentrations in the ECF falls 50% below normal

Answer 48

Muscle tetany

**due to the spontaneous discharge of peripheral nerves

Question 49

Which ions appear to bind to the exterior surfaces of the sodium channel protein, altering the electrical state of the sodium channel protein, thus altering the voltage level required to open the sodium gate.

Answer 49

calcium ion

Question 50

What type of feedback cycle opens the sodium-channels (?positive/negative?)

Answer 50

positive-feedback cycle

Question 51

This is the level of stimulation that causes the explosive development of action potential (about 15-30 mV of sudden rise in membrane potential)

Answer 51

threshold for stimulation

Question 52

Once an action potential has been elicited at any point on the membrane of a normal fiber, the depolarization process travels over the entire membrane if conditions are right, but it does not travel at all if conditions are not right. This principle is called the:

Answer 52

all-or-nothing principle

Question 53

For continued propagation of an impulse to occur, the ratio of action potential to threshold for excitation must at all times be greater than 1. This “greater than 1” requirement is called the ___________ for propagation

Answer 53

safety factor

Question 54

Which cellular protein pump is strongly stimulated when excess sodium ions accumulate inside the cell membranes?

Answer 54

sodium-potassium pump

Question 55

The plateau of action potential that occurs in heart muscle fibers occurs for as long as ______ second

Answer 55

0.2 to 0.3 second

Question 56

What are the 2 types of channels that contribute to the depolarization process in the heart muscle?

Answer 56

(1) the usual voltage-activated sodium channels, called fast channels; and (2) voltage-activated calcium-sodium
channels (L-type calcium channels), which are slow to open and therefore are called slow channels.

Question 57

This is a drug (an alkaloid neurotoxin found in Liliaceae family) that activates sodium ion channels causing repetitive discharge of excitable tissues

Answer 57

veratridine

**DRUG HAS BEEN TESTED IN MYASTHENIA GRAVIS TO INCREASE MUSCLE RESPONSE TO GIVEN MOTOR NEURON STIMULATION, AND
USED EXPERIMENTALLY TO ALTER SODIUM CHANNEL KINETICS

Question 58

What is the resting membrane potential in the rhythmical control center of the heart?

Answer 58

-60 to -70 mV

**which is not enough voltage to keep the sodium and calcium channels closed; hence, rhythmical or spontaneous depolarization

Question 59

This is the state in action potential wherein increased outflow of potassium ions leaves considerably more negativity inside the fiber drawing the membrane potential nearer to the potassium Nernst potential

Answer 59

hyperpolarization

Question 60

This is the central core of a myelinated fiber

Answer 60

axon

Question 61

This is a viscid intracellular fluid of an axon.

Answer 61

axoplasm

Question 62

This is the lipid substance that make up the multiple layers of Schwann cell membrane surrounding the peripheral nerve axon

Answer 62

sphingomyelin

Question 63

This substance is an excellent electrical insulator that decreases ion flow through the membrane about 5000-fold

Answer 63

sphingomyelin

Question 64

This is the electrical current flow through the surrounding extracellular fluid outside the myelin sheath, as well as through the axoplasm inside the axon from node to node, exciting successive nodes one after another.

Answer 64

saltatory conduction

Question 65

Range of velocity of action potential conduction in nerve fibers

Answer 65

0.25 m/sec in small unmyelinated fibers to as much as 100 m/sec—more than the length of a football field in 1 second—in large myelinated fibers.

Question 66

When electricity is applied with positive and negative electrodes, the excitable membrane becomes stimulated at the _______ electrode.

Answer 66

negative

**negative current from the electrode decreases the voltage on the outside of the membrane to a negative value nearer to the voltage of the negative potential inside the fiber. This effect decreases the electrical voltage across the membrane and allows the sodium channels to open, resulting in an action potential

Question 67

These are local potential changes that fail to elicit an action potential

Answer 67

acute subthreshold potentials

Question 68

What is the cause of refractory periods after action potential is initiated?

Answer 68

inactivation of sodium channels (closing of inactivation gates)

Question 69

The period during which a second action potential cannot be elicited, even with a strong stimulus, is called the:

Answer 69

absolute refractory period (1/2500 second in a large myelinated fiber)

Question 70

Membrane-stabilizing factors can decrease excitability. Which ions are said to be stabilizers?

Answer 70

Calcium ions

**For example, a high extracellular fluid calcium ion concentration decreases membrane permeability to sodium ions and simultaneously reduces excitability.

Question 71

This is known as the ratio of action potential strength to excitability threshold

Answer 71

safety factor

Question 72

Procaine and tetracaine affect which gate of voltage-gated sodium channels?

Answer 72

activation gate

**Most of these agents act directly on the activation gates of the sodium channels, making it much more difficult for these gates to open and thereby reducing membrane excitability.