A 63year old mansuddenly felt a crushing pain beneath his sternum. He became weakand began to sweat profusely. He called 911 and was taken to thehospital where it was confirmed that he had suffered a heart attackdue to occlusion in a major coronary artery.

1.When a coronaryartery is occluded, the K+concentration risesin theinterstitial fluid of the ischemic region of the myocardium.What effect does the elevated K+concentration haveon the resting membrane potential of the myocardial cells in theischemic zone?

A. Increases the resting membranepotential(hyperpolarizes the restingmembrane potential)

B. Decreases the resting membranepotential (depolarizes the restingmembrane potential)

C. Has noeffect on the resting membrane potential

2.What effect doesthischangeinresting membranepotential have on the propagation of the cardiacimpulse?

A. Theupstroke of the action potential will be steeper thannormal

B. Propagation of the actionpotential will be slower than normal

C. Morevoltage-sensitive Na+channels will beactivated

D. Theamplitude of the action potential will beincrease

The patient hadcardiac rhythm disturbances withinminutes after he felt the chest pain. He was given ananti-arrhythmic drug that inactivated many ofthe fast Na+channelsin the heart.

3.What effect wouldthe anti-arrhythmic drug have on the restingmembrane potential of the myocardial cells?

A. It willhave very little effect on the resting membranepotential

B. It willdepolarize the resting membrane potential

C. It willhyperpolarize the resting membrane potential

4.​Whateffect would this drug have on the action potentialin the SAnode?

A. It willincrease the slope of the Ifcomponent of theaction potential

B. It willdiminish the amplitude of the action potential

C. Itwill increase the duration of theaction potential at the SA node

D. It willhave very little effect on the action potential at the SAnode

Soon after thepatient arrived at the hospital, the activity in the vagus nervefibers to the heart increased reflexively.

5.Whatelectrophysiological effects would increased vagal activityhave on thecells of the SA Node?

1.It will increaseheart rate

2.It will decreasethe slope of the Ifcomponent of theaction potential

3.It will depolarizethe resting membrane potential

4.It will increasecellular levels of cAMP