Explain their physiological significance: physiological significance: ca++ needs to be brought into the cell to activate cicr from sr that will increase [ca++]i and activate muscle contraction mechanism, vm remains fairly constant. Ik1 is not very significant because of inward rectifying. Its role is reduced at 0mv and more positive vm. Ito, and ik are actively causing k+ efflux down conc"n gradient and electrical gradient: ca++ influx through l-type channel occurring to offset the k+ channels. Explain why the qrs complex and the t- wave both produce positive deflections in the ecg: describe what the electrical vector of einthoven"s triangle represents. Describe two situations that cause this vector to shift: electrical vector is downwards and to the left of the heart. This is the direction the depolarization is traveling: ventricle hypertrophy and systemic hypertension causes left axis shift, heart may be displaced, in the absence of extracellular calcium, explain what happens to cardiac contraction.