13. Cardiac AP & Conduction

Question 1

what is the order an AP spreads in the heart

Answer 1

SA node

AV node

bundle of his

R/L bundle branches

purkinje fibers

Question 2

where is AP generated most frequently in the heart

Answer 2

SA node

= pacemaker

Question 3

what is overdrive suppression

Answer 3

higher freq of SA node firing suppress other pacemakers (like AV node)

aka: SA node trigger AP in AV before it can fire itself

*something wrong with the SA node- then AV node will take over

Question 4

what are the pacemaker qualities of the AV node & purkinje fibers

Answer 4

AV node: less freq that SA node

purkinje fibers: least freq, asynchronous contraction

Question 5

rate the velocity of the fibers of the heart

Answer 5

purkinje > atrial/ventricular M > AV

depends on fiber diameters - larger = faster

Question 6

which part of the heart contracts milisecs before the other side

Answer 6

RA before LA

endocardium before epicardium

RV epicardium before LV epicadium

Question 7

why is it preferred that the endocardium contract prior to the epicardium

Answer 7

b/c want to push blood up and out

Question 8

what is the current at phase 0 & 1

Answer 8

Na current

-Vg Na channels open for depol

Question 9

what is the reason for the rapid/partial repol at the peak of phase 1

Answer 9

transient outward K+ current

Question 10

what phase is a result of L-type Ca channels opening

Answer 10

phase 2 & 3

slow to open and reapin open for specific amount of time & then close (–> causing transition to phase 3)

Question 11

what is inward rectifying current

Answer 11

Vg-K channels that are open at RMP & close and particular Vg (phase 2)

-open again in phase 3 & slow to close

Question 12

What current denotes phase 3 only

Answer 12

rapid K & slow K current

Vg gated contribute to repol

Question 13

what current accounts for phase 4

Answer 13

K leak channels

Question 14

what is the funny Na current

Answer 14

rise in mem potential

open after certain repol vg reached & close at threshold

-lead to continous, rhythmic firing

Question 15

what are the characteristics of the Vg Na channels

Answer 15

quick to open & quick to close at threshold

have activation gate (opened at threshold)

& inactivation gate (close quickly after activation gate opens –> will not allow another AP until it opens again = Abs refractory period)

Question 16

when do L type Ca channels open and clsoe

Answer 16

open at threshold - high current

-and slow down (start closing) –> complete closure at end of phase 2

Question 17

when does transient outward K current happen

Answer 17

K channels open at phase 0 & close rapidly to get the peak at phase 1

-makes sure mem. potential doesnt overshoot

Question 18

What happens when vg K channel current peaks

Answer 18

transition from phase 2 to phase 3

Question 19

What are the steps of the inward rectifying current (starting from before threshold)

Answer 19

1. open - let K out of cell
2. —> cell depol & channels close in phase 0 to help maintain phase 2
3. —> open again at particular Vg to help with phase 3

Question 20

What currents contribute to phase 2

Answer 20

=Ca current in

K current out

inward rectifying current (closed channels)

Question 21

when does contraction happen in relation to AP

Answer 21

slightly delayed - so happens after AP

to help get Ca to M cells, etc

Question 22

what happens to K leak channels during phase 2

Answer 22

increased outward current

Question 23

how is phase 4 of SA/AV nodes different from other APs

Answer 23

gradually depol unti reaching threshold (funny Na current)

= intrinsic, spontaneous depol –> = pace maker

Question 24

what happens in phase 0 of the SA/AV nodes

Answer 24

Vg Ca open –> depol (NOT Na)

close rectifiers (Vg K channels)

Question 25

what channels are open/closed during phase 3 of the SA/AV node

Answer 25

close - Vg Ca open- Vg K (rectifier & traditional)

Question 26

what is the cause of the absolute refactory period (ARP)

Answer 26

inactivation gates of Na channel closed

Question 27

when can you have an AP during RRP? What will the AP look like

Answer 27

w/ greater stimulus = smaller/weaker

Question 28

what is SNP

Answer 28

as you repolarize, inactivation gates eventually reset - so these channels can fire even if not completley repolarized ==\> dont need as much stimulus bc youre already close to threshold -AP will still be smaller/weaker tho

Question 29

how can arrythmias occur

Answer 29

in beats are happening too closely -rapid firing of APs

Question 30

what is the chonotropic effect determined by

Answer 30

depolarization of phase 4 faster = + chonotropic slower = - chonotropic =effect changes in HR

Question 31

what can be determined by slope of phase 0

Answer 31

dromotropic effects = effect speed of conduction steeper slope = quicker conduction

Question 32

what is inotropic

Answer 32

effect strength of M contraction

Question 33

what is lusitropic

Answer 33

effect rate of M relaxation

Question 34

what occurs in parasym stimuluation of the SA/AV node

Answer 34

neg chronotropic effect: slower funny Na current & **_hyperpo_**l of SA node by _increasing outward K current_ (Ach K channels) neg dromotropic effect: _decrease inward Ca current_ & increase outward K current (Ach K channels)

Question 35

what happens with sym stimulus of the SA/AV nodes

Answer 35

pos chronotropic effect: more rapid opening of funny Na channels pos dromotropic effect: increased inward Ca current