L6 (L7 by uni) - cardiac electrical activity

Question 1

pathway of the cardiac conduction system

Answer 1

• siniatrial node ; pacemaker , generates APs
• electrical actvity spreads through the atria
• pass onto the AVN- delay
• conduction along the purkinje fibers
• then onto the ventricular endocardium to epicardium

Question 2

cells ( myocytes) in the hearts

Answer 2

-SAN CELLS
AVN cells
Atrial and ventricular cells
purkinje fibers

Question 3

order of the AP generation from myocytes

Answer 3

SAN>AVN>purkinje fibers> atrial and ventricular (no AP)

Question 4

how many AP per min for SAN

Answer 4

80-100APs/min

Question 5

what is teh pacemaker potential by the SAN

Answer 5

the firing rate of AP

- basically the slight increase in the membrane potential in SAN

Question 6

ions responsible for pacemaker potenial

Answer 6

inwards move of Na and Ca
outwards move of K+
- Em rises slowly

Question 7

ions responsible for rapid depol phase of AP

Answer 7

CA influx though VGChannels

Question 8

ion responsible for repolarisation phase

Answer 8

K efflux

Question 9

two ANS control of SAN

Answer 9

-PNS- vagus nerve

SNS - - cardiac sym nerves

Question 10

what NT does the vagus nerve release

Answer 10

ACh at M2 receptors

Question 11

what Nt does the cardiac sym nerves release

Answer 11

NA at B1 receptors

Question 12

intrinsic rate of SAN is 80-100AP/min so why is the HR aorund 60-70bpm

Answer 12

the vagal tone predominates so decreases HR

Question 13

what happens to the HR as PNS activty increase

Answer 13

increases K efflux
- reduces pacemaker potential (longer to reach threshold)
Hr low

Question 14

what happens to the ions and HR as SNS activity increases

Answer 14

increases Na and Ca influcx
-increases pacemkaer potential
-

Question 15

effect of circurlating of adr

Answer 15

INCREASE HR

Question 16

why is there a delay the AVN before it can transmit the electrical activity to the purkinje fibers

Answer 16

so the atria can contract and eject the blood to the ventricles befoer the ventricles depolarisation

Question 17

what will HR be always driven by

Answer 17

fasted pacemaker which is the SAN

Question 18

phases of ventriculae myocyte AP

Answer 18

0: rapid depol
1: half rapid redepol
2: plateau
3: terminal redepol
4: stable resting potential

Question 19

action of ions in the phases of the ventricular myocyte AP

Answer 19

0: NA infux
1: inactivation of Na channels and activ of K channels
2: Ca inlfux and K efflux
3: more K efflux out delayed rectifier

Question 20

what is refractory peroid

Answer 20

time from ininital depol of frist AP to 2nd ap that can be stimulated

Question 21

two kinds of refractory peroids

Answer 21

absolute and relative

Question 22

what is refractory peroid determined by

Answer 22

no of available and recovered Na VGChannels

Question 23

at what volatges can the Na VGchannels can be recovered quickly

Answer 23

recover more faster at more neg voltage

-shorter AP, shorter peroid, quicker to inactivates channels

Question 24

what are cardiac myocytes coupled to

Answer 24

gap junction

Question 25

what are gap junctions

Answer 25

allows passage of + ions between cellls - if there is a charge of gradient

Question 26

what is conduction velocity

Answer 26

determined by the charge graidient

- the karger the gradient and amplitude of current , the faster the CV