The effect of norepinephrine on SA nodal cells is to: (not e) A move the thresho

Question

The effect of norepinephrine on SA nodal cells is to: (not e)

A move the threshold closer to -80 mV

B increase the rate of spontaneous depolarization

C decrease heart rate

D produce bradycardia

E hyperpolarize the pacemaker cells

A drug blocking the influx of calcium would have its greatest effect on which phase of the action potential in a ventricular cardiomyocyte?         (not 3)  

0                                           

1                             

2                             

3

Which sequence correctly represents the succession of action potentials in one heartbeat? (not c)                            

A -AV – SA – bundle branch                         

B - SA – bundle branch – AV                       

C - SA – Purkinje fibers – bundle branch

D - SA - AV - bundle branch

E - AV – Purkinje fibers – bundle branch

Explanation / Answer

1

answer is hyperpolarize the pacemaker cell

norepinephrine is a sympathetic neurotransmittor acts through beta-1 adrenergic receptors stimulate sodium and it is responsible for hyperpolarization increase in the heart rate

2 answer is phase 2

the action potential in ventricular cardiomyocytes begins with rapid upstroke phase 0 opening of sodium channels, phase 1 partial repolarisationand allow pottassium ions and membrane potential centers the plateu phase is in phase 2 allow the calcium ions

so drug blocking  the influx of calcium would have its greatest effect on phase-2 of the action potential in a ventricular cardiomyocyte

answer 3

answer is d

sinoatrial node ----- av node---- av bundle then perkinje fibers

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