Origin and conduction of cardiac impulse

Question 1

where does excitation of the heart normally originate

Answer 1

SA NODE

Question 2

where is the sa node located

Answer 2

right atrium close to where the sperior vena cava enters

Question 3

what takes the membrane potential to a threshold

Answer 3

the spontaneous pacemaker potential and everytime its reached an AP. is generated

Question 4

what is the pacemaker potential due to

Answer 4

the funny current
decrease in k+ efflux
ca+ influx

Question 5

funny current

Answer 5

a depolarising cation current mainly due to slow Na+ INFLUX through HCN channels (hyperpolarisation-activated cyclic nucleotide-gated)

Question 6

what happens once the threshold is reached

Answer 6

the rising phase of action potential is caused by opening of long lasting voltage gate ca+ channels

Question 7

what occurs during the rising ohase

Answer 7

ca+ influx
decreased k+ efflux
funny current

Question 8

falling phase

Answer 8

repolarisation
activation of k+ channels resulting in k+ efflux

Question 9

what is the falling phase caused by

Answer 9

inactivation of l type ca+ channels and activation of k+ channels

Question 10

where is the av node located

Answer 10

base of right attrium

Question 11

what is the only poiint of electrical contact between atria and ventricles

Answer 11

av node

Question 12

do the cells of the av node have a slow conducting veolicty

Answer 12

yes

Question 13

spread of excitation

Answer 13

sa node to av node where it is delayed
bundle of his and its bracnhes and network of purkinje fibres allow rapid spread to ventricles

Question 14

phase 0 in contractile myocytes

Answer 14

fast na+ influx

Question 15

phase 1

Answer 15

closure of na+ channels
k+ efflux

Question 16

phase 2

Answer 16

mainly ca+ influx

Question 17

phase 3

Answer 17

closure of ca+
k+ efflux

Question 18

phase 4

Answer 18

resting membrane potential

Question 19

plateau phasw

Answer 19

membrane potential maintained

Question 20

what is the plateau phase mainly duw o

Answer 20

influx of ca+

Question 21

falling phase

Answer 21

inactivation of ca+ and activation of k+- k+ efflux

Question 22

what signals atrial depolarisaton

Answer 22

p waveh

Question 23

what signals ventricular depolarisation

Answer 23

QRS complex

Question 24

pr interval

Answer 24

largely av nodal delay

Question 25

when does ventricular systole occur

Answer 25

st segment

Question 26

when does diastole occur

Answer 26

tp interval

Question 27

neurotransmitter in parasympathetic supply

Answer 27

ach acting through m2 muscarinic receptors