Excitable Cells and AP

Question 1

resting membrane potential

Answer 1

negative value

excess of negative charges inside compared to outside

Question 2

how does the electical gradient arise?

Answer 2

1. large gradients of Na+ and K+
2. relative permeability of the membrane to those ions

Question 3

Nernst Equation

Answer 3

-60 x log [Xi/Xo]

Question 4

what happens if increase extracellular K?

Answer 4

equilibrium potential will become less negative/depolarize

Question 5

what happens if you increase intracellular K

Answer 5

eq potential will increase/become more negative

hyperpolarize

Question 6

K equilibrium potential

Answer 6

-88 mV

more on inside than outside

Question 7

equilibrium potential of Na

Answer 7

+60 mV

more on outside than inside

if suddenly very permeale to Na (AP) it moves very positive very fast

Question 8

permeability to a given ion

Answer 8

depends n number of channels and conductance of channels

Question 9

GHK equation

Goldman-Hodgkin-Katz

Answer 9

used to determine the potential across a cell’s membrane taking into acct all of the ions that are permeant

start w Nernst and add permeability factor for K

Question 10

what happens when increase K permeability at rest

Answer 10

hyper polarizes

drives membrane potential closer to Keq (-88)

Question 11

Na/K ATPase

Answer 11

ubiquitously expressed in cell membranes

maintains gradient of Na and K

3 Na out for 2 K in

energy consuming

Question 12

Na/Ca exchanger

Answer 12

in muscle cells

3 Na in and 1 Ca out down electrochemical gradients

reversible dep on voltage

maintains low intracellular Ca2+ levels

Question 13

Ca2+ pump

Answer 13

expressed in muscle cells

pumps Ca2+ out with ATP

maintains low intracelular Ca2+ levels

Question 14

passive membrane resistors

Answer 14

ion channels

resist flow but allows it to move

Question 15

passive membrane capacitor

Answer 15

stores charge

2 conductors sep by insulatior

con = ECF, ICF

ions = cell membrane

charge builds up and can store it

Question 16

passive membrane as circuit

Answer 16

1. current charges capacitor (+ to mem and displaces + on the other side
2. current moves through both capacitor and ion channel (new SS - charges begin to leave through resistor)
3. at SS, current moves only through channel (resisotor)

voltage change is linear and can be predicted by Ohm’s law

Question 17

ionic basis of action potential

Answer 17

increase Na+ perm - rushes in, increase voltage to positive

incrase K+ perm - brings gradually back to negative

K channel is delayed rectifier - voltage gated!

Question 18

depolarization

Answer 18

when sodium channels open

outward current (bc Na+ in)

Question 19

hyperpolarization

Answer 19

when K channels open

inward current repolarizes the membrane

Question 20

VG - Na channels

Answer 20

closed - open (Na in) - inactivated (stuck and can’t activate - have to repolarize to open) - closed

Question 21

VG - K channels

Answer 21

delayed rectifiers

single gate - open and closed

open SLOWER

activated at more depolarized P

stays open until back to resting membrane potential

Question 22

rising phages

Answer 22

FEED FORWARD

stim –> depol membrane –> Na channels open –> inward current –> depol mem further

Question 23

falling phase

Answer 23

depol membrnae –> open VG K+ channels –> repolarize membrane –> return to Vrest

Question 24

overshoot

Answer 24

voltage about 0 mV

Question 25

amplitude

Answer 25

voltage from V rest to peak

Question 26

threshold potential

Answer 26

voltage you begin to activate Na+ channels

Question 27

absolute refractory period

Answer 27

if deliver 2nd stim - get NOTHING Na+ channels are inactivated - can't be opened, no response until "closed"

Question 28

relative refractory period

Answer 28

get response but it's blunted cell has increased K+ permeability compared to rest - if fire Na+ channels, response will be smaller

Question 29

action potential conduction

Answer 29

Question 30

length constant

Answer 30

proportional to rm/ri resistance - how currnet will spread and voltage will change higher length constant - current can spread farther

Question 31

time constant

Answer 31

time at which voltage is 63% of max increase membrane capacitance or resitance --\> increased time constant

Question 32

inactive membrane

Answer 32

Na channels closed

Question 33

electrotonic spread

Answer 33

spread of electrotonic current to inactive membrnae brings inactive membrane to AP threshold

Question 34

r (i)

Answer 34

internal resistance - affects length constant (and therefore conduction velocity)

Question 35

r(m)

Answer 35

membrane resistances - affects length const and therefore conduction velocity

Question 36

factiors that influence conduction velocity

Answer 36

length const time const available Na current

Question 37

diameter of axon

Answer 37

increased diameter = really fast decrease r(i) --\> longer length constant