Chapter 12-4 The Membrane Potential Is The Electrical Potential Of The Cell's Interior To Its Surroundings

Front 1

What do all living cells have that varies from moment to moment depending on the activities of the cell?

Back 1

Membrane potential

Front 2

What is the membrane potential of an unstimulated cell?

Back 2

Resting membrane potential

Front 3

What begins with a change in the resting membrane potential of a neuron?

Back 3

All neural activites

Front 4

What is a typical stimulus that produces a temporary, localized change in the resting membrane potential called?

Back 4

Graded Potential

Front 5

What decreases with distance form the stimulus?

Back 5

The effect of graded potential

Front 6

What is created in the membrane of the axon if the graded potential is large enough?

Back 6

Action potential

Front 7

What is propagated during an action potential along the surface of an axon?

Back 7

Electrical impulse

Front 8

The electrical impulse in action potential does not ___________ as it moves away from its source.

Back 8

Deminish

Front 9

Where does the electrical impulse in action potential travel to?

Back 9

One or more synapses

Front 10

The integration of stimuli at the level of the individual cell is the simplest from of what in the nervous system?

Back 10

Information Processing

Front 11

What two things do the response of the postsynaptic cell receiving the stimuli ultimately depend on?

Back 11

What stimulated receptors do and

What other stimuli are influencing the cell at the same time

Front 12

What processes do you need to understand to know how neurons deal with information and communicate with one another and with peripheral effectors?

Back 12

Resting potential,

Graded potential,

Action Potential,

Synaptic Activity,

Information processing

Front 13

What is the first important concept regarding the membrane potential?

Back 13

The extracellur fluid (ECF) and intracellular fluid (cytosol) differ greatly.

Front 14

What does the extracellular fluid (ECF contain high concentrations of?

Back 14

Sodium ions (Na+) and chloride ions (Cl-)

Front 15

What does intracellular fluid (cytosol) contain high concentrations of?

Back 15

Potassium ions (K+) and negatively charged proteins

Front 16

What is the second important concept regarding the membrane potential?

Back 16

Cells have selectively permeable membranes

Front 17

If the the plasma membrane were freely permeable, diffusion would continue until all the ions were evenly distributed across the membrane and what would exist?

Back 17

State of equilibrium

Front 18

Why does an even distribution across a plasma membrane not occur?

Back 18

Because cells have selectively permeable membranes

Front 19

What portion of the plasma membrane are ions unable to cross freely?

Back 19

Lipid

Front 20

What is the only thing ions can enter or leave the cell through?

Back 20

Membrane channels

Front 21

Many kind of membrane channels exist, each with its own what?

Back 21

Properties

Front 22

Where do ions move through at the resting membrane potential, or membrane potential of an undisturbed cell.

Back 22

Leak channels

Front 23

Leak channels are membrane channels that are always what?

Back 23

open

Front 24

What do sodium potassium exchange pumps move?

Back 24

Specific ions into or out of the cell

Front 25

What is the third important concept regarding the membrane potential?

Back 25

Membrane permeability varies by ion

Front 26

What does not ensure an equal distribution of charges across its plasma membrane?

Back 26

The cell's passive and active transport mechanisms

Front 27

Why does the cell's passive and active transport mechanisms not ensure an equal distribution of charges across its plasma membrane?

Back 27

Because membrane permeability varies by ion

Front 28

What does membrane permeability very by?

Back 28

Ions

Front 29

What forces act across the plasma membrane to determine the membrane potential at any moment?

Back 29

Both Passive and active

Front 30

What to things are involved in the passive forces acting across the plasma membrane?

Back 30

Chemical and

Electrical gradients

Front 31

What do positive and negative charge do to one another?

Back 31

Attract

Front 32

What happens if nothing separates positive and negative charges?

Back 32

Oppositely charged ions will move together and eliminate the potential difference between them

Front 33

What is a movement of charges to eliminate a potential difference called?

Back 33

Current

Front 34

If a barrier (such as a plasma membrane) separates the oppositely charged ions, what does the amount of current depend on?

Back 34

How easily the ions can cross the membrane

Front 35

What is a measure of how much the membrane restricts ion movement called?

Back 35

Resistance

Front 36

If the resistance is high, the current is very small. Why is this?

Back 36

Because few ions can cross the membrane

Front 37

If the resistance is low, the current is very large. Why is this?

Back 37

Because ions flow across the membrane

Front 38

What can either reinforce or oppose the chemical gradient for each ion?

Back 38

Electrical gradients

Front 39

What is the sum of the chemical and electrical forces action on a specific ion across the plasma membrane called?

Back 39

Electrochemical gradient

Front 40

What are the primary factors affecting the resting membrane potential of most cells, including neurons called?

Back 40

The electrochemical gradients for K+ and Na+

Front 41

What is relatively high in intracellular concentration, but very low in extracellular concentration?

Back 41

Potassium (K+) ions

Front 42

Because the potassium ions relatively high in intracellular fluid, their chemical gradients tend to do what?

Back 42

Drive them out of the cell

Front 43

What does the electrical gradient do to the movement of (K+) potassium?

Back 43

It opposes movement

Front 44

Why does the electrical gradient oppose the movement of (K+) potassium?

Back 44

Because (K+) inside the cell are attracted to negatively charges on the inside or the plasma membrane

Front 45

What are k+ repelled by?

Back 45

The positive charges on the outside of the plasma membrane

Front 46

Does the chemical gradient or the electrical gradient have more power?

Back 46

Chemical gradient

Front 47

What weakens the force driving the K+ out of the cell?

Back 47

Electrical gradient

Front 48

What would happen if the plasma membrane were freely permeable to K+ but impermeable to other positively charged ions?

Back 48

Potassium ions would continue to leave the cell until the electrical gradient was as strong as the chemical gradient.

Front 49

What is the membrane potential at which there is no net movement of a particular ion across the plasma membrane called?

Back 49

Equilibrium potential

Front 50

What is the mV for equilibrium for potassium ions?

Back 50

-90mV

Front 51

What is the mV for resting membrane potential?

Back 51

-70mV

Front 52

What is the difference in equilibrium potential and resting potential due to?

Back 52

Na+ leaking continuously into the cell

Front 53

What does the equilibrium indicate?

Back 53

An ion's contribution to the resting membrane potential

Front 54

What concentration is relatively high in extracellular fluid, but extremely low inside the cell?

Back 54

Sodium Ion (Na+)

Front 55

What is the result of having a high concentration of sodium ion (Na+) outside of the cell?

Back 55

A strong chemical gradient is driving it into the cell

Front 56

In addition, the extracellular sodium ions are attracted by the excess of __________ _______ on the inner surface of the plasma membrane

Back 56

Negative charges

Front 57

What two things drive Na+ into the cell?

Back 57

Both electrical forces and chemical forces

Front 58

If the plasma membrane were completely permeable to Na+ the ions would continue to cross until the interior of the cell contains enough excess positive charges to do what?

Back 58

Reverse the electrical gradient

Front 59

Na+ movement across a freely permeable membrane would continue until the interior developed such a strongly positive charge that repulsion between the positive charges would prevent what?

Back 59

Any further net movement of Na+ into the cell.

Front 60

What is mV for the equilibrium potential for Na+?

Back 60

+66mV

Front 61

The resting membrane potential is nowhere near the equilibrium potential because resting membrane permeability to Na+ is very what?

Back 61

Low

Front 62

What do ion pumps in the plasma membrane do to sodium ions?

Back 62

It ejects them as fast as they cross the membrane

Front 63

What is an electrochemical gradient a form of?

Back 63

Potential energy

Front 64

The potential energy is stored energy - the energy of ________, as exists in a stretched spring, a _______ battery, or water ______ a dam.

Back 64

Position,

Charged,

Behind

Front 65

What would diffusion do without a plasma membrane?

Back 65

eliminate all electrochemical gradients

Front 66

What does any stimulus that increases the permeability of the plasma membrane to sodium or potassium ions produce?

Back 66

sudden and dramatic ion movement

Front 67

What does a stimulus that opens sodium on channels trigger?

Back 67

A rush of Na+ into the cell

Front 68

Does the nature of the stimulus determine the amount of ion movement?

Back 68

No

Front 69

What determine the amount of ion movement once the stimulus opens the door?

Back 69

Electrochemical gradient

Front 70

At the normal resting membrane potential, the cell must bail out __________ ions that leak in and recapture _________ ions that leak out.

Back 70

Sodium,

Potassium

Front 71

The "bailing" takes place through the activity of an exchange pump powered by what?

Back 71

ATP

Front 72

The ion pump involved in the "bailing" of sodium ions is the carrier protein called what?

Back 72

Sodium-potassium ATPase

Front 73

How many sodium ions are exchange in the Sodium-potassium pump?

Back 73

3 intracellular sodium ions

Front 74

How many potassium ions are exchanged in the Sodium-potassium pump?

Back 74

2 extracellular potassium ions

Front 75

At what rate are sodium ions ejected from the sodium-potassium pump during normal resting membrane potential?

Back 75

As quickly as they enter the cell

Front 76

Why does the resting membrane potential remain stable?

Back 76

Because the ionic concentration gradient are mainteined

Front 77

Why does the resting potential exist?

Back 77

The cytosol differs from extracellular fluid in chemical and ionic composition,

The plasma membrane is selectively permeable

Front 78

Cells are dynamic structures that continually modify their what?

Back 78

Activities

Front 79

How do cells continually modify specific functions?

Back 79

Either in response to external stimuli or to perform specific functions

Front 80

The membrane potential is equally dynamic, doing what in response to temporary changes in membrane permeability?

Back 80

rising or falling

Front 81

The changes in the membrane a result of what?

Back 81

Opening or closing of specific membrane channels

Front 82

What controls the movement of ions across the plasma membrane?

Back 82

Membrane channels

Front 83

What are the primary determinants of the membrane potential of many cell types, including neurons?

Back 83

Sodium and potassium ions

Front 84

Sodium and potassium ion channels are one of which two things?

Back 84

Passive,

and active

Front 85

Whats another word for passive channel?

Back 85

Leak channels

Front 86

Are leak channels A) Always open B) Always closed or C) they open and close?

Back 86

Always open

Front 87

What can vary with leak channels from moment to moment?

Back 87

It's permeability

Front 88

What makes up the leak channels?

Back 88

Protiens

Front 89

What changes as the proteins that make up the leak channel responds to local conditions?

Back 89

Its shape

Front 90

What are leak channels important in establishing?

Back 90

The normal resting membrane of the cell

Front 91

What do plasma membranes have that open or close in response to specific stimuli?

Back 91

Active channels

Front 92

What is another name for active channels?

Back 92

Gated channels

Front 93

What are the three states in which each gated channel can be in?

Back 93

Closed but capable of opening,

Open (activated),

Closed and incapable of opening (inactivated)

Front 94

What are the threeclasses of gated channels?

Back 94

Chemically gated or ligand-gated channels,

Voltage-gated channels,

Mechanically gated channels

Front 95

Which class of gated channel opens or closes when they bind specific chemicals?

Back 95

Chemically gated channels or ligand-gated channels

Front 96

How class of gated channel has receptors that bind acetycholine (ACH) at the neuromuscular junction?

Back 96

Chemically gated

Front 97

Where are chemically gated channels most abundant?

Back 97

Dendrites and cell body of neuron

Front 98

What occurs most at the dendrites and cell body of a neuron?

Back 98

Synaptic communication

Front 99

Which class of gated channels open or close in response to changes in the membrane potential?

Back 99

Voltage-gated channels

Front 100

A membrane capable of generating and propagating an action potential is called what?

Back 100

Excitable membrane

Front 101

Examples of excitable membranes are the _____ of unipolar and multipolar neurons, and the __________ (including _________) of skeletal muscle cells.

Back 101

Axons,

Sacrolemma,

T-tubules

Front 102

What are the three most important voltage-gated channels for the purposes of this chapter?

Back 102

Sodium channels,

Potassium channels,

Calcium channels

Front 103

What are the two gates of the voltage-gated sodium channels?

Back 103

Activation gate,

Inactivation gate

Front 104

Which voltage-gated sodium channel opens on stimulation, letting sodium ions into the cell?

Back 104

Activation gate

Front 105

Which voltage-gated sodium channel closes to stop the entry of sodium ions?

Back 105

Inactivation gate

Front 106

Which class of gated channels opens or closes in response to physical distortion of the membrane surface?

Back 106

Mechanically gated channels

Front 107

What are mechanically gated channels important in?

Back 107

Sensory receptors that respond to touch, pressure, or vibration

Front 108

Are most gated channels open or closed at the resting potential?

Back 108

Closed

Front 109

When gated channels open, what happens to the rate of ion movement across the plasma membrane, changing the membrane potential?

Back 109

It increases

Front 110

What causes the rate of ion movement across the plasma membrane to increase?

Back 110

A gate channel opening.

Front 111

When a gate channel opens and the rate of the ion movement across the plasma membrane increases, what changes?

Back 111

Membrane potential

Front 112

The distribution of membrane channels ______ from one region of plasma membrane to another.

Back 112

Varies

Front 113

What does the variance of distribution of membranes channels affect?

Back 113

How and where a cell responds to specific stimuli

Front 114

What are wide spread channels on the surfaces of a neuron?

Back 114

Chemically gated sodium channels

Front 115

What channels are abundant on the axon, its branches, and axon terminals?

Back 115

Voltage-gated sodium channels

Front 116

What are voltage-gated sodium channels abundant on?

Back 116

Axon,

Branches,

Axon terminals

Front 117

What channels are typically located only on the dendrites of sensory neurons?

Back 117

Mechanically gated channels

Front 118

Where are mechanically gated channels typically located?

Back 118

Dendrites of sensory neurons

Front 119

What are changes in the membrane potential that cannot spread from the site of stimulation?

Back 119

Graded potentials

Front 120

What is another word for graded potentials?

Back 120

Local potentials

Front 121

A graded potential is produced by any stimulus that does what?

Back 121

Opens a gate channel

Front 122

During graded potential what enters the cell?

Back 122

Sodium ions

Front 123

What are sodium ions that enter the cell during graded potential attracted to?

Back 123

The negative charges along the inner surface of the membrane

Front 124

As additions positively charged sodium ions enter spread out, the membrane potential shifts towards what mV?

Back 124

0

Front 125

What is any shift from the resting membrane potential toward a more positive potential is called what?

Back 125

Depolarization

Front 126

The term depolarization applies to changes in potential from ___ mV to smaller negative values, as well as to membrane potentials above ___ mV.

Back 126

-70,

0

Front 127

During depolarization membrane potential always becomes more what?

Back 127

Positive

Front 128

As the plasma membrane depolarizes, sodium ions are released from where?

Back 128

Its outer surface

Front 129

Where do the sodium ions released from its outer surface, along with other extracellular sodium ions, move toward?

Back 129

Open channels

Front 130

What do the sodium ions released from its outer surface, along with other extracellular sodium ions, that move toward the open channels replace?

Back 130

Ions that have already entered the cell

Front 131

What is the movement of positive charges parallel to the inner and outer surfaces of a membrane clled?

Back 131

Local current

Front 132

In a graded potential, what decreases with distance away from the stimulation site?

Back 132

Degree of depolarization

Front 133

One reason depolarization lessens with distance is because the cytosol offers considerable what?

Back 133

Resistance to ion movement

Front 134

Another reason depolarization lessens with distance is because some of the sodium ions entering cell then do what?

Back 134

Move back out across the membrane through sodium leak channels

Front 135

What is undetectable at some distance from the entry point?

Back 135

The effects on the membrane potential

Front 136

The maximum change in the membrane potential is proportional to the size of what?

Back 136

The stimulus

Front 137

What determines the number of open sodium channels?

Back 137

The size of the stilmulus

Front 138

The more open _________, the more _________ ____ enter the cell?

Back 138

Channels,

Sodium Ions

Front 139

The greater the membrane area affected, and the greater the what?

Back 139

The degree of depolarization

Front 140

What does the membrane potential soon do when a chemical stimulus is removed and a normal membrane permeability is restored?

Back 140

Returns to resting membrane

Front 141

What is the process of restoring the normal resting membrane potential after depolarization called?

Back 141

Repolarization

Front 142

Repolarization typically involves a combination of what two things?

Back 142

Ion movement through membrane channels,

The activities of ion pumps

Front 143

What does opening a gated potassium channel have the opposite effect from?

Back 143

Opening a gated sodium channel

Front 144

What happens to the rate of potassium ion outflow when opening a gated potassium channel?

Back 144

It increases

Front 145

What happens to the interior of a cell during the opening of a potassium gated channel?

Back 145

Loses positive ions

Front 146

What effect does losing positive ions from the interior of the cell have?

Back 146

It becomes more negative?

Front 147

What does the increase of negativity of the resting membrane potential and loss of positive ions produce?

Back 147

Hyperpolarizatoin

Front 148

What distributes the effect to adjacent portions of the plasma membrane during hyperpolarization?

Back 148

Local current

Front 149

A local current distributes the effect of hyperpolarization to adjacent portions of the plasma membrane, and the effect decreases with what?

Back 149

Distance from the open channel or channels

Front 150

Graded potential occur in membranes of many cell types of cells - not just nerve and muscle cells. What are those other cell types?

Back 150

Epithelial cells,

Gland cells,

Adipocytes,

Variety of sensory receptors.

Front 151

Graded potential often trigger specific what?

Back 151

Cell functions

Front 152

An example of graded potential triggering a specific cell function would be when it triggers what at the surface of a gland cell?

Back 152

Exocytosis of secretory vesicles

Front 153

At a neuromuscular junction, what does the graded depolarization of the motor end plate by ACh at trigger?

Back 153

An action potential in adjacent portions of the sarcolemma

Front 154

What does the motor end plate support?

Back 154

Graded potentials

Front 155

What does the sarcolemma consist of?

Back 155

Excitable membrane

Front 156

What channels do excitable membranes have?

Back 156

Voltage-gated channels

Front 157

The effect of graded potential decrease with what?

Back 157

Distance

Front 158

In graded potential, the membrane potential is most changed where?

Back 158

At the site of stimulation

Front 159

How does the effect of graded potential spread due to local currents?

Back 159

Passively

Front 160

Graded potential effect spreads passively due to what?

Back 160

Local currents

Front 161

Can graded potential be involved in both depolarization and hyperpolarization? If not, which one can it be involved in?

Back 161

Both

Front 162

The properties and distribution of the membrane channels involved in graded potential determine what?

Back 162

The nature of the change

Front 163

What increases with stronger stimulus during graded potential?

Back 163

The change in the membrane potential

The affected area