topic 2

Question 1

what cells does the heart contain

Answer 1

contractile cells (myocytes) and conducting cells

Question 2

what are conducting cells responsible for and where are they located

Answer 2

impulse genration and pacemaker activity
located in SA node of R atrium

Question 3

types of action potentials and location

Answer 3

-fast response action potential (atrial and ventricular myocytes)
-slow response action potentials (SA node and AV node)

Question 4

5 phases of fast response action potentials

Answer 4

1) phase 0 - upstroke - Na+ current
2) phase 1 - partial repolarisation - K+ current
3) phase 2 - plateau - Ca2+ current
4) phase 3 - complete repolarisation - K+ current
5) phase 4 resting membrane potential

Question 5

duration of fast response action potential

Answer 5

200ms

Question 6

3 phases of slow response action potientials

Answer 6

1) phase 4 - pacemaker potential - automatic depolarisation (funny channels open so Na+ (and little K+) enter cell
2)phase 0 - depolarisation - one threshold reached, T type and L type Ca2+ channels open
3)phase3 - repolarisation - K+ channels open so K+ leaves cell so returns to membrane potential

Question 7

duration of slow response action potentials

Answer 7

400ms

Question 8

differences between fast and slow response action potentials

Answer 8

-slow response lack phase 1 & 2 (partial repolarisation and plate)
-resting Em (phase 4) is more negative in fast response
-amplitude of action potential is greater in fast response
-conduction velocity is slower and more likely to be blocked in slow response nodal tissues than fast response myocardium

Question 9

mechanism of pacemaker potential

Answer 9

• pacemaker cells (SA node) have automaticity so spontaneously depolarise generating AP

Question 10

key ions that play a role in action potential generation

Answer 10

Na+, K+, Ca2+

Question 11

ion channels involved in development of pacemaker potential

Answer 11

1) funny current
2) T type Ca2+ channels
3) L type Ca2+ channels
4)voltage gated K+ channels
5) GIRK channels

Question 12

If current

Answer 12

-mediated by hyperpolarization-activated cyclic nucleotide gated cation channels (4 isoforms), in heart its HCN1 or HCN4

-activated by hyperpolarizatio
-allows Na+ or K+ inside cell but Na+ dominates
-Na+ causes gradual depolarisation
<-50mV, influx of Na+ slowly depolarises nodal cells