Chapter 12-4 Passive Forces & Active Forces

Front 1

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

Back 1

Both Passive and active

Front 2

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

Back 2

Chemical and

Electrical gradients

Front 3

What do positive and negative charge do to one another?

Back 3

Attract

Front 4

What happens if nothing separates positive and negative charges?

Back 4

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

Front 5

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

Back 5

Current

Front 6

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

Back 6

How easily the ions can cross the membrane

Front 7

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

Back 7

Resistance

Front 8

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

Back 8

Because few ions can cross the membrane

Front 9

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

Back 9

Because ions flow across the membrane

Front 10

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

Back 10

Electrical gradients

Front 11

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

Back 11

Electrochemical gradient

Front 12

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

Back 12

The electrochemical gradients for K+ and Na+

Front 13

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

Back 13

Potassium (K+) ions

Front 14

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

Back 14

Drive them out of the cell

Front 15

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

Back 15

It opposes movement

Front 16

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

Back 16

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

Front 17

What are k+ repelled by?

Back 17

The positive charges on the outside of the plasma membrane

Front 18

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

Back 18

Chemical gradient

Front 19

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

Back 19

Electrical gradient

Front 20

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

Back 20

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

Front 21

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

Back 21

Equilibrium potential

Front 22

What is the mV for equilibrium for potassium ions?

Back 22

-90mV

Front 23

What is the mV for resting membrane potential?

Back 23

-70mV

Front 24

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

Back 24

Na+ leaking continuously into the cell

Front 25

What does the equilibrium indicate?

Back 25

An ion's contribution to the resting membrane potential

Front 26

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

Back 26

Sodium Ion (Na+)

Front 27

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

Back 27

A strong chemical gradient is driving it into the cell

Front 28

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

Back 28

Negative charges

Front 29

What two things drive Na+ into the cell?

Back 29

Both electrical forces and chemical forces

Front 30

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 30

Reverse the electrical gradient

Front 31

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 31

Any further net movement of Na+ into the cell.

Front 32

What is mV for the equilibrium potential for Na+?

Back 32

+66mV

Front 33

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

Back 33

Low

Front 34

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

Back 34

It ejects them as fast as they cross the membrane

Front 35

What is an electrochemical gradient a form of?

Back 35

Potential energy

Front 36

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

Back 36

Position,

Charged,

Behind

Front 37

What would diffusion do without a plasma membrane?

Back 37

eliminate all electrochemical gradients

Front 38

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

Back 38

sudden and dramatic ion movement

Front 39

What does a stimulus that opens sodium on channels trigger?

Back 39

A rush of Na+ into the cell

Front 40

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

Back 40

No

Front 41

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

Back 41

Electrochemical gradient

Front 42

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

Back 42

Sodium,

Potassium

Front 43

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

Back 43

ATP

Front 44

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

Back 44

Sodium-potassium ATPase

Front 45

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

Back 45

3 intracellular sodium ions

Front 46

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

Back 46

2 extracellular potassium ions

Front 47

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

Back 47

As quickly as they enter the cell

Front 48

Why does the resting membrane potential remain stable?

Back 48

Because the ionic concentration gradient are mainteined