Electrical activity of the heart

Question 1

where are the 4 areas of pacemaker cells

Answer 1

SA node
AV bundle
Bundle of His
purkinje fibres

Question 2

how does the action potential spread from the pacemaker cells into the contractile cells

Answer 2

through gap junctions located at the intercalated disks

Question 3

what is the resting membrane potential in a cardiac contractile cell

Answer 3

-90mV

Question 4

what mV is reached when a cardiac cell depolarizes

Answer 4

20mV

Question 5

what is the function of desmosomes in intercalated disks

Answer 5

they weld the two adjacent cells together

Question 6

what is the unstable membrane potential of a cardiac auto-rhythmic cell

Answer 6

starts as -60

Question 7

what gives auto rhythmic cells their ability to generate APs

Answer 7

comes from their unstable membrane potential that starts at -60 and will slowly drift upwards to threshold

Question 8

what are the channels in auto-rhythmic cells that create the pacemaker potential

Answer 8

If channels

Question 9

what are If channels leaky for

Answer 9

NA+ and K+

Question 10

once threshold is reached in an autorhythmic cell what happens next

Answer 10

threshold is reached. IF channels are closed and Ca2+ channels open . Making the cell depolarise further

Question 11

in autorhythmic cells once the cell has depolarised to 20 mV what channels open

Answer 11

K+ channels open and potassium laves the cell, cell repolarises

Question 12

what percentage of heart cells are contractile

Answer 12

99%

Question 13

why does the AV node delay the signal from the SA node

Answer 13

so the atria can finish contracting before the ventricles contract, without this delay all the chambers would squeeze at once and the blood wouldn’t go anywhere.

Question 14

cardiac muscle has a long refractory period therefore it cannot do what

Answer 14

exhibit tetanic contraction

Question 15

Ca2+ entry from outside the cell can regulate contraction of cardiac muscle how is this possible

Answer 15

Ca2 release does not saturate the troponin so regulation of Ca2 release can be used to vary the strength of contraction

Question 16

does the inside or outside of the cell have a higher concentration of K

Answer 16

inside

Question 17

where is there a higher concentration of Na and Ca, inside or outside the cell

Answer 17

outside

Question 18

what does the P wave correspond to in an ECG

Answer 18

atrial depolarization

Question 19

what does the QRS complex correspond to in an ECG

Answer 19

ventricular depolarization

Question 20

what does the T wave correspond to in an ECG

Answer 20

ventricular repolarisation

Question 21

in skeletal muscle contraction what does tropinin bind to

Answer 21

Ca2+

Question 22

what is the purpose of troponin binding to Ca2+ in skeletal muscle

Answer 22

this action causes troponin to pull the tropomyosin away from the actin filament

Question 23

what binds to the active sites on actin

Answer 23

myosin cross bridge heads

Question 24

how long is the cardiac action potential

Answer 24

250msec

Question 25

how long is skeletal muscle action potential

Answer 25

2msec

Question 26

Ca2+ entry from outside the cell can regulate contraction why is this

Answer 26

as Ca2+ release does not saturate the troponin so entry of more calcium can be used to increase the strngth of contraction

Question 27

what would Calcium channel blockers do the force of contraction

Answer 27

decrease

Question 28

what is an example of a cardiac glycocide

Answer 28

digoxin

Question 29

what do cardiac glycosides do to the force of contraction

Answer 29

increase

Question 30

what effect does temperature have on the force of contraction

Answer 30

increases it 10 beats/min/ºC

Question 31

what can too little or too much potassium do to the heart

Answer 31

cause fibrillation and heart block