EX1; Excitable Cells; Electricity

Question 1

The electrical charge difference between the inside and outside of a cell is what

Answer 1

voltage

Question 2

The voltage of a resting cell is steady, therefore the plasma membrane must have what

Answer 2

resistance

Question 3

When a resistance changes, ions cross the membrane and this is what

Answer 3

current

Question 4

This is the reciprocal of resistance

Answer 4

conductance

Question 5

These two things are membrane properties

Answer 5

conductance and resistance

Question 6

There is a higher concentration of solutes in 1 but why is there no voltage difference

Answer 6

because the number of cations in 1 is the same as the number of anions in 1; and vice versa

Question 7

Something causes permeability to increase, therefore X+ moves down the concentration gradient from 1 to 2, 1 aquires a negative charge and 2 aquires positive; but the movement of X+ stops before the concentration is equal, why?

Answer 7

a charge difference develops (voltage); the system attains an equilibrium state

the concentration difference and voltage difference are directed oppositely

Question 8

What does the Nernst equation describe

Answer 8

it relates the voltage difference between 1 and 2 and the concentration difference between 1 and 2

Question 9

What is the Nernst equation

Answer 9

Ex= (58/z) log10 ([X1]/[X2])

z = valence

Question 10

What does the Nernst equation yield

Answer 10

the equilibrium potential or a single ionic species

Question 11

This is the voltage across a cell membrane that exactly balances the force in the concentration gradient of a permeable ion

Answer 11

equilibrium potential

Question 12

What is a diffusion potential and what does it mean to be transient

Answer 12

they are due to asymmetic ion flow - an imbalance in the flow of an ion or several ions between two compartments

they can disappear over time

Question 13

What is an example of a transient diffusion potential

Answer 13

A membrane is equally permeable to Na and Cl, but Cl moves faster, therefore bringing the negative chage more into one compartment, one having an excess positive charge is a diffusion potential; eventually they will equal out

Question 14

A diffusion potential can or cannot be maintained at a steady level over time

Answer 14

can be

Question 15

What is an example of a steady diffusion potential

Answer 15

membrane becomes permeable to only K, the one compartment will have a high postive charge and the other a high negative chage; the change in voltage will slow the subsequent diffusion; when the concentration force is balanced by the electrical force diffusion potential stops changing

Question 16

There is a high concentration of what inside the cell

Answer 16

K+

Question 17

There is a higher concentration of what outside the cell

Answer 17

Na+

Question 18

The membrane of a resting cell is most permeable to what ion

Answer 18

K+

Question 19

What is the Pk/P(Na) ration

Answer 19

around 60; K+ ions diffuse across a typical membrane 60 times more readuly than Na+ when the cell is at rest

Question 20

Equilibrium is reached with the force in the concentration gradient for K+ ions to move out of the cell is balanced by what

Answer 20

the opposing force in electrical gradient which favors keeping K+ ions inside the cell

Question 21

This keeps the resting membrane potential slightly lower than Ek

Answer 21

Na+ diffuses into cell down both its concentration gradient and electrical gradient

Question 22

What is the flow of ions when a cell is at rest

Answer 22

K+ ions diffuse out

Na+ ions diffuse in

Question 23

The resting membrane potential is what; is not a transient diffusion potential

Answer 23

steady

Question 24

The resting potential is not due to the instantaneous movement of ions, it is due to what

Answer 24

the fact the ions have moved across the membrane (specifically K+)

Question 25

This protein moves K+ ions back into the cell and Na+ ions out of the cell when it is at rest; requires ATP

Answer 25

Na+/K+ ATPase pump

Question 26

A change of the membrane potential toward 0mV is referred to as what

Answer 26

depolarization (or hypopolarization)

Question 27

A change in the membrane potential away from 0mV, in the negative voltage direction is referred to as what

Answer 27

repolarization

Question 28

An increase in membrane potential from the resting value (more negative toward resting potential; -70mV) is referred to as what

Answer 28

hyperpolarization

Question 29

What is the resting potential

Answer 29

-70mV

Question 30

True or False

The Na/K ATPase pump maintian concentration gradients for Na and K across membrane

Answer 30

True

Question 31

What does the active transport via the Na/K ATPase pump counteract

Answer 31

the passive diffusion of ions; keeping the resting potential

Question 32

The Na/K ATP-ase pump is an example of what

Answer 32

homeostasis

Question 33

True or False

The number of ions that are required to cross the membrane, which results in large changes in the membrane potential is extremelly small compared to the total number of ions

Answer 33

True

Question 34

True or False

The extracellular and intracellular concentrations of the ions that cross living cell plasma membranes, remain essentially unchanged, even during periods of intense excitation

Answer 34

True