6.5 - 6.7

Question 1

The predominate ions in the extracellular fluid are ___, and the predominant ions in the intracellular fluid are ___.

Answer 1

Na+ and Cl-;

K+ and phosphate compounds

Question 2

T/F: A fundamental physical principle is that charges of the same type (such as 2 + charges) attract e/o, while charges of opposite types (+ and -) repel e/o.

Answer 2

F

Question 3

The units of electrical potential in biological systems are milli-___.

Answer 3

volts

Question 4

The movement of electrical charges is called ___.

Answer 4

current

Question 5

All cells under resting conditions have a voltage different bt the inside and outside of the PM, which is referred as the ___.

Answer 5

resting membrane potential

Question 6

The resting membrane potential holds steady ___.

Answer 6

unless changes in electrical current alter the potential

Question 7

A difference in the amount of electrical charge bt 2 points in space is defined as a difference in electrical ___.

Answer 7

potential (or voltage)

Question 8

The equilibrium potential is the membrane potential at which the ___ and ___ forces on an ion are equal in magnitude and opposite in direction.

Answer 8

concentration; electrical

Question 9

The electrical potential difference bt 2 area tends to make the charges flow, thus producing a ___.

Answer 9

current

Question 10

At a resting membrane potential of -70mV, both the concentration and electrical gradients favor inward movement of ___, whereas the concentration and electrical gradients are in opposite directions.

Answer 10

Na+; K+

Question 11

By convention, when describing a cell’s membrane potential the ___ of the cell is assigned a value of 0, and the voltage is defined as the + or - charge of the ___ of the cell.

Answer 11

outside; inside

Question 12

At rest, the membrane potential is close to the K+ equilibrium potential because ___ channels in the PM are much more available for K+ than Na+.

Answer 12

leak

Question 13

T/F: Most cells have resting membrane potentials that are negative on the inside compared to the outside.

Answer 13

T

Question 14

T/F: In most cells, the Na+/K+ ATPase pump makes a small electrogenic contribution to creating the negative resting membrane potential.

Answer 14

T (moving 3 Na+ out of the cell in exchange for moving 2 K+ into the cell has a small direct effect to make the inside if the membrane more negative on resting cells)

Question 15

Arrange the events in order from no membrane potential to a steady negative resting membrane potential, start with the Na+/K+ ATPase pump.

Answer 15

• The Na+/K+ ATPase pump moves Na+ out of the cell and K+ into the cell, setting up concentration gradients across the membrane
• Due to a permeability difference, there is a greater net movement of K+ out of the cell than Na+ into the cell
• The membrane potential becomes negative, approaching the K+ equilibrium potential
• equal leaks of Na+ and K+ are offset by the continued activity of the Na+/K+ ATPase pump

Question 16

The equilibrium potential of an ion is the ___.

Answer 16

membrane potential at which ion flux due to the membrane potential is equal and opposite to the flux due to the concentration gradient

Question 17

The capability is a cell to produce electrical signals through the action of a voltage-gated ion channel is called ___.

Answer 17

excitability

Question 18

In an experiment with an artificial cell, the equilibrium potentials for ions X+, Y- and Z+ are +50 mV, -50 mV, and +5 mV, respectively. If the cell is equally permeable to ions X+ and Y-, but 10 times more permeable to ion Z+ than to ion Y-, which statement is most likely true?

Answer 18

All three ions have higher concentrations outside the cell than inside, and the resting membrane potential is positive.
(The cations must be higher outside than in because the equilibrium potentials are positive and the anion must be higher outside than in because the equilibrium potential is negative. Because Z+ is the most permeable by far, the resting membrane potential will be closest to its equilibrium potential while the other two will offset each other.)

Question 19

The resting potential of a cell is largely determined by the movement of potassium and sodium down their concentration gradients through ion channels that are always open in the membrane. The channels ate called ___ channels.

Answer 19

leak

Question 20

What is true about graded potentials?

Answer 20

the flow of charge decreases with distance

Question 21

Which is true regarding the effect of the Na+/K+ ATPase pump on the membrane potential of excitable cells?

Answer 21

The pump has a minor electrogenic effect that directly contributes to the negative value of the resting membrane potential.

Question 22

Summation occurs when ___.

Answer 22

additional stimuli cause graded potentials to occur in a neuron before the graded potentials from previous stimuli have died away

Question 23

At rest, the membrane potential is maintained at a value of ___. In addition, , the inward and outward leak of positive ions is equal even though there is a greater permeability to ___.

Answer 23

-70 mV; K+

Question 24

The ability is nerve and muscle cells to produce changes in membrane voltage in response to a stimulus is known as ___.

Answer 24

excitability

Question 25

The contributions of Na+, K+ and Cl- to the overall membrane potential are mainly a function of their ___.

Answer 25

concentration gradients and relative permeabilities

Question 26

T/F: Graded potentials are “all-or-none,” meaning that the change in the membrane potential is the same size regardless of the size of the stimulating event.

Answer 26

F

Question 27

The permeability of a resting plasma membrane is greater for ___ than it is for ___; therefore, a net negative membrane potential develops.

Answer 27

potassium; sodium

Question 28

An action potential ___.

Answer 28

• is an all-or-none event
• is conducted wo decrement
• occurs very rapidly

Question 29

A membrane ion channel operated by the binding of a specific molecule to the channel protein is said to be ___-gated.

Answer 29

ligand

Question 30

An ion channel that opens in response to a change in the membrane potential of the cell is called a ___ channel.

Answer 30

voltage-gated

Question 31

Which is a true statement regarding the voltage-gated Na+ and K+ channels that mediate neuronal action potentials?

Answer 31

The Na+ channels have inactivation gates, but the K+ channels do not.

Question 32

The repolarization phase of a neuronal action potential is produced primarily by the ___.

Answer 32

efflux of K+

Question 33

When voltage-gated K+ channels are slow to close, the membrane potential is bt the normal resting potential and the K+ equilibrium potential, The phase of the action potential is known as the ___ phase.

Answer 33

afterhyperpolarization

Question 34

Mechanically gated ion channels open is response to ___.

Answer 34

physical deformation of the PM

Question 35

The continuous action of the membrane Na+/K+ ATPase pumps prevents the cellular accumulation of ___ and loss of ___.

Answer 35

Na+; K+

Question 36

What channel is the most important for giving a membrane the ability to generate action potentials?

Answer 36

voltage-gated channels

Question 37

Stimuli that are strong enough to depolarize the membrane to generate an action potential are known as ___ stimuli.

Answer 37

threshold

Question 38

When a neuronal membrane is depolarized by a stimulus, which voltage-gated channel typically opens the fastest?

Answer 38

Na+ channels

Question 39

A stimulus that causes a graded depolarization that is too small to generate an action potential is called a ___ stimulus.

Answer 39

subthreshold

Question 40

The closing of voltage-gated K+ channels during repolarization of an action potential is an example of ___ feedback; the opening of Na+ channels during the depolarizing phase of an action potential is an example of ___ feedback.

Answer 40

negative; positive

Question 41

T/F: A large number of ions are required to cause the large fluctuation in membrane potential during an action potential; without the action of the Na+/K+ ATPase pump, the concentration gradients for Na+ and K+ would be significantly altered by a single action potential.

Answer 41

F (tiny numbers of the ions cross the membrane during an action potential)

Question 42

Threshold stimuli ___.

Answer 42

elevate the membrane potential sufficiently to generate an action potential

Question 43

A subthreshold stimulus to a neuron ___.

Answer 43

• depolarizes the local membrane potential briefly before it returns to the resting potential
• does not generate an action potential

Question 44

Describing an action potential as “all-or-none” means that ___.

Answer 44

stimuli are either suprathreshold (action potential occurs) or subthreshold (no action potential); action potentials are graded

Question 45

Afterhyperpolarization is the phase of a neuron’s action potential where the cell’s membrane potential ___ the normal resting potential because of a persistent current through slowly closing voltage-gated ___ channels.

Answer 45

falls below; K+

Question 46

True statements about the movement of ions during an action potential:

Answer 46

• the number of ions that cross the membrane during an action potential is extremely small compared to the total number of ions in the cell
• with repeated action potentials, concentration gradients for Na+ and K+ would eventually dissipate wo the action of the Na+/K+ ATPase pump

Question 47

The absolute refractory period of a neuronal membrane ___.

Answer 47

is dependent on the length of time it takes Na+ channels to recover from inactivation

Question 48

A subthreshold potential is best described as a ___.

Answer 48

weak depolarization

Question 49

An action potential is either generated because a stimulus is suprathreshold, or is not generated because the stimulus is subthreshold. This property of action potentials is referred to as the ___-___-___ property.

Answer 49

all-or-none

Question 50

What 4 statements are true during the relative refractory period?

Answer 50

• K+ is continuing to flow out of the cell
• voltage-gated K+ channels are resetting to the closed position
• voltage-gated Na+ channels are resetting from the inactivated to the closed position
• some voltage-gated Na+ channels are closed while some are inactivated

Question 51

During action potential propagation, when an action potential is occurring in one patch of membrane what induces the neighboring patch of membrane to depolarize to threshold?

Answer 51

The flow of local positive current from the depolarized patch to the neighboring patch of membrane.

Question 52

After the initiation of an action potential in a given region of a neuronal membrane, there is a period of time during which a second action potential cannot be stimulated no matter how strong the stimulus. This is called the ___ ___ period.

Answer 52

absolute refractory

Question 53

Action potentials tend to travel in only one direction along an axon for which two reasons?

Answer 53

• They begin propagating at one end of an axon, and not in the middle
• Refractoriness of the region of membrane where an action potential has just occurred prevents a propagating action potential from reversing direction

Question 54

A subthreshold stimulus to a neuron ___. (2)

Answer 54

• depolarizes the local membrane potential briefly before it returns to the resting potential
• does not generate an action potential

Question 55

During the relative refractory period of an axon ___.

Answer 55

voltage-gated Na+ channels change from the inactivated state to the closed state

Question 56

Events of action potential propagation in order.

Answer 56

1. generation of an initial action potential
2. generation of a local current in membrane adjacent to the initial action potential
3. depolarization of plasma membrane adjacent to initial action potential
4. threshold reached in adjacent areas of the membrane
5. generation if next action potential

Question 57

The only direction of action potential propagation is away from a region of membrane that has recently been active. This is because a membrane area that has just undergone an action potential is ___ and cannot immediately undergo another.

Answer 57

refractory

Question 58

Propagation of an action potential down a myelinated axon in which the action potential appears to “jump” from node to node is called ___ ___.

Answer 58

saltatory conduction

Question 59

The period of time following an action potential during which only stronger than normal stimuli can initiate a second action potential is termed the ___ ___ period of the action potential.

Answer 59

relative refractory

Question 60

Which of these explains why an action potential is able to propagate along the full length of an axon?

Answer 60

Action potentials are regenerated in each patch of membrane by depolarizing local currents arriving from previously-depolarized patches of membrane.

Question 61

Potentials that are generated in the sensory receptors at the peripheral ends of the neurons, which are at the ends farthest from the CNS, are called ___.

Answer 61

receptor potentials

Question 62

T/F: If an action potential was started in the middle of an axon it could only propagate in one direction—away from the cell body.

Answer 62

F (they move one way because they start at one end)

Question 63

Receptor potentials ___.

Answer 63

are graded potentials in afferent neurons