Cardiovascular control 1

Question 1

what happens to the membrane potential when there is an impermeable membrane

Answer 1

2 different conc KCl on differnt sides

device measures chemical concentration? - chem conc gradient - no potential difference because no movement of ions

Question 2

what happens to the membrane potential when the membrane is selectively permeable to K

Answer 2

no cl movement - no membrane potential
K move down conc gradient and take +ve charge - charge builds up so repels K ions
conc grad balanced by electrical gradient at equilibrium
no net movement of ions
this is the membrane potential

Question 3

what is the driving force

Answer 3

the difference between concentration and electrical gradient

Question 4

what happens, looking at K, to driving force when membrane is open to K

Answer 4

it is 0 at equilibrium

Question 5

describe the resting membrane potential

Answer 5

depends on flow of K
predict in ideal situations - Nerst eqn
if only permeable to K, potential across it will equal Ek
solve nerst eqn for K

Question 6

action of the Na/K ATPase

Answer 6

pump k out, Na in - against conc gradients
needs ATP to drive
doesn’t contribute to mem potentialmaintains conc gradient

Question 7

why does teh RMP change

Answer 7

depends on relative permeabilities of the ions

Question 8

EK and Ena

Answer 8

-80

+66mV

Question 9

when is the mem potential similar to Ena

Answer 9

when mem selectively permeable to Na

during upstroke

Question 10

what does the Goldman-Hodgkin-katz equation do

Answer 10

take into consideration the relative permeability to the membrane at a particular time

Question 11

length of nerve AP

Answer 11

2ms

Question 12

what happens in a nerve AP

Answer 12

if threshold is reached upstroke is fired because of a large opening of Na channels and so increase of permeability, big conc grad so na enter cell depolarising it
towards Ena
not quite Ena - channels close quickly more K channel open - k out of cell
repolarise

Question 13

compare teh cardiac AP to the nervous AP

Answer 13

longer, 200-300ms - allows control of strength of heart beat
long slow contraction = efficient pumping

Question 14

cardiac refractory period

Answer 14

Na channel inactivation
more repolarised the cell gets , ie more -ve, smaller stimulus needed
more channels recovered and can be activated
longer than in skeletal muscle - not possible to rexcite until full contraction, muscle is electrically inert
allow heart to fill before next contraction - not possible to be tetanised

Question 15

when is refractory period in skeletal muscle

Answer 15

early in contraction phase

re stimulation and summation possible

Question 16

phases of the ventricle AP

Answer 16

phase 0 - upstroke 
1 - early repolarisation 
2 - plateau 
3 - repolarisation 
4 - RMP, diastole period

Question 17

describe upstroke

Answer 17

increase in Pna
Na channels open 
influx of Na 
depolarisation 
poteential towards Ena

Question 18

describe the early repolarisation

Answer 18

small
opening of channel give rise to transient outward current Pto
this is carried by K ions
brief opening and closing of channels
cause efflux of K ions out of the cell to repolarise

Question 19

what happens simultaneously to Pto

Answer 19

increase Pca
ca important for Ca induced ca release - important for contraction
rapid increase in opening of channels
ca current updates rapidly but upstroke caused by Pna
Ca channels still open during platau - don’t change quickly