L14 Resting (Excitable) Cells

Question 1

Currents flow ___ in a direction denoted by the direction of movement of _____ in an electrical field

Answer 1

passively
cations (+)

Question 2

cations (+) in a solution will move by electrodiffusion to the ____

Answer 2

cathode - negative terminal

Question 3

anions (-) in a solution will move by electrodiffusion to the ___

Answer 3

anode - positive terminal

Question 4

where is electroneutrality seen?

Answer 4

in cytosol

in extracellular fluid

Question 5

where is electroneutrality not conserved?

Answer 5

across the width of the membrane - there is charge separation across the bilayer

Question 6

large anions cannot pass through into what?

Answer 6

from intracellular space to extracellular space

Question 7

define membrane potential

Answer 7

potential of the interior of the cell measured relative to the exterior and is Vm

Question 8

what is the resting membrane potential in neurons?

Answer 8

-65 mV

Question 9

what channels do neurons have open?

Answer 9

LOTS of K+ channels open
some Cl- channels open
few Na+ channels open

Question 10

what is the resting membrane potential for skeletal muscle fibers?

Answer 10

-90 mV

Question 11

what channels do skeletal muscle fibers have open?

Answer 11

LOTS of K+ and Cl- channels open

few Na+ channels open

Question 12

what is the resting membrane potential for photoreceptors (rods)?

Answer 12

-40 mV

Question 13

what channels do photoreceptor (rods) have open?

Answer 13

more Na+ channels open than neurons and muscle fibers

Question 14

what is the resting membrane potential of astrocytes?

Answer 14

-40 mV to -90 mV

Question 15

what can alter the resting membrane potential?

Answer 15

small changes in ion flux

Question 16

what ion is more inside the cell and outside the cell

Answer 16

K-inside

Na-outside

Question 17

an influx of Na+ will move the Vm in what direction?

Answer 17

depolarizing

Question 18

an efflux of K+ will move the Vm in what direction?

Answer 18

repolarize

Question 19

what ions are high extracellularly?

Answer 19

Na+
Cl-
Ca2+
bicarb

Question 20

what ions are high intracellularly?

Answer 20

K+

Question 21

what does changing the concentration of K+ outside the cell do?

Answer 21

alters the resting potential - resting potential dependent on K+

Question 22

what happens if you increase the value of [K+]o?

Answer 22

= reduction in the rate of L ion loss from the cell and the interior becomes LESS NEGATIVE because less DF for K ions

Depolarization

Question 23

what happens if you reduce the value of the [K+]o?

Answer 23

=increase in the rate of K ion loss from the cell and the interior becomes more negative because more DF for K ions

Hyperpolarized!

Question 24

in what ways are ions transported?

Answer 24

by passive and active means

Question 25

how do ions pass through membrane ion channels?

Answer 25

electrodiffusion

Question 26

how are ions actively transported across the membrane?

Answer 26

by ATPases

Question 27

how are ions also transported?

Answer 27

by antiports and symports

Question 28

what determines the membrane potential?

Answer 28

open channels

Question 29

cell transmembrane potential is affected by what?

Answer 29

• ion channel activity
• type + # of open ion channels
• amount of current passing through while channel is open
• time channels spend in an open state
• frequency of channel openings
• maintain by pump/transporter activity

Question 30

every ion channel has a probability of being___

Answer 30

open

Question 31

what is the probability of channel opening (Po)?

Answer 31

the fraction of the total time of observation that the channel is in the open state

Question 32

what acts as capacitor?

Answer 32

bilayer component

Question 33

what acts as a conductor?

Answer 33

open ion channel

Question 34

what do electrochemical gradients drive?

Answer 34

passive ion flux

Question 35

how is equilibrium established at a selectively permeable membrane?

Answer 35

diffusion force = electrical force

Question 36

each ion has its own_____

Answer 36

electrochemical gradient

Question 37

what is the formula for Nernst Equation:

Answer 37

E= RT/ zF ln [ion outside]/[ion inside]

gives you the equilibrium potential for any ion

Question 38

what is the total ionic current across the resting membrane?

Answer 38

zero

Question 39

what is Channelopathies?

Answer 39

dysfunctional ion channels

Question 40

what is cytotoxic edema?

Answer 40

affects grey matter cells more than white matter

Question 41

what is vasogenic edema?

Answer 41

blood vessels become permeable and the fluid accumulates in the extracellular space causing further damage

Question 42

what does resting membrane potential (Vm) depend on

Answer 42

# of open channels for ions
conductances of the open ion channels
equilibrium potentials for ions