2.1

Question 1

different pace maker frequency of the conducting cells of the heart

Answer 1

SA= 70-80 BPM
AV= 40-60 BPM
Bundle and Purkinje fibers= 20-40

Question 2

what makes the SA node being able to generate AP spontaneously?

Answer 2

1. Hyperpolarization to -50 mV activates the funny current (If) -> influx of Na+ through HCN channel -> slowly depolarize the cell

Question 3

what is the next stage after the funny current?

Answer 3

when we reach -40 mV -> T-Type VDCCs opens -> Ca++ enters the cell (and also some Na+)

Question 4

what is the next stage after the Ca++ entering the cell via T-Type VDCCs?

Answer 4

we reach -25mV -> L-Type VDCCs opens -> more Ca++ enters the cell

Question 5

what are HCN channels?

Answer 5

Hyperpolarization activated Cyclic Nucleotide gated channels, responsuble for the funny current
cAMP bound to HCN channels increase openning of the channels

Question 6

which drug can inhibit HCN channels?

Answer 6

Ivabradine

Question 7

which channels in the heart are open in response to Ach? what will happen?

Answer 7

GIRK

responsible for Hyperpolarization -> decreased HR

Question 8

which parameters are the main target of symp and parasymp activity on the heart?

Answer 8

• minimun diastolic potential (most negative Em value)

- slope of the prepotential (symp will cause the slope to be stiiffer, hence faster depolarization

Question 9

Symp NS effects of the heart? (how)

Answer 9

NE/E -> B1 R -> Gs -> [cAMP] ↑

result is positive chronotropic effect. HR ↑

Question 10

Parasymp NS effects of the heart? (how)

Answer 10

Ach -> M2 R -> Gi a subunit -> cAMP ↓
and Gi b,g subunits -> GIRK ↑
result is negative chronotropic effect. HR ↓

Question 11

what factors effect the conduction velocity?

Answer 11

1. size of the inward current

2. resistance

Question 12

why does the condactance in the Purkinje fibers very high?

Answer 12

they have very large diameter

Question 13

where can we find the slowest conductance in the heart and why?

Answer 13

AV node = 0.02-0.05 m/s

bcs we want to delay ventricular contraction -> allow time for ventricular filling

Question 14

why does it take 100 ms btw AV node to the bundle branches?

Answer 14

1. electrical insulation (fibeous skeleton)

2. smaall diameter conducting tissued

Question 15

how long does it take for the transmission btw SA node to the furthest ventricular tissue?

Answer 15

about 200 ms

Question 16

root of condution by order?

Answer 16

SA -> AV -> Bundle of Hiss -> Bundle Branches -> Purkinje Fibers -> Ventriculat Myocytes

Question 17

what is the last region to depolarize?

Answer 17

Epicardium of the ventricles

Question 18

what does Dromotropic mean?

Answer 18

somthing that effects the conducting velocity

Question 19

NS effects on impulse conduction?

Answer 19

Symp= positive Dromotropic effect
Para= negative Dromotropic effect

Question 20

How does the Sympathetic NS controls the heart?

Answer 20

Increases L-Type VDCC
Increases funny current
NE -> B1 R -> Gs -> [cAMP]

Question 21

Right vagus effects

Answer 21

SA node

Question 22

Left vagus effects

Answer 22

AV node

Question 23

How does the Parasympathetic NS control the heart?

Answer 23

Increases K+ permeability ->hyperpolarization