Question

Sympathomimetics cause all of the following EXCEPT:

A. opening of Na+ channels

B. increased electrical Refractory Period

C. increased velocity of action potentials through the AV Node

D. tachycardia

E. increased myocardial contractility

Answer 1

B. increased electrical Refractory Period

Sympathomimetics refers to the drug which mimic the sympathetic activation of the heart and blood circulations via release of  the norepinephrines from sympathetic nerves. It triggers the heart stimulation via activation of the beta-adrenoreceptors and the activation of beta-adrenoreceptors causes subsequent activation of the alpha-adrenoreceptors which causes the myocardial muscle contraction and vasoconstriction; results into higher heart rate (tachycardia). It also causes the increased cardiac stimulation. However, the sympathetic activation also cause the shortening of the refractory period(refractory period refers to the adjusting of stimulus and reduces the action potential sent per minute) and opens the Na+ channels thus accelerate the action potential specially thorugh the AV node.