Membrane potential changes in an isolated cardiac muscle cell are recorded along with ion movements across the cell membrane (see graph below). Which of the following ion sequences corresponds to regions 1-2-3 on the graph, respectively?

Question

Membrane potential changes in an isolated cardiac muscle cell are recorded along with ion movements across the cell membrane (see graph below).  Which of the following ion sequences corresponds to regions 1-2-3 on the graph, respectively?

Quizplus · Accepted Answer

11ec160b_3ca4_1457_9249_ff6e43a78dce_MD0001_00 The action potential of ventricular and non-nodal conduction cells within the heart consists of four phases. In sum, the cardiac myocyte action potential includes the following three key events: Na⁺ ion influx (corresponding to the red curve on the ion conductivity graph); Ca⁺⁺ ion influx (corresponding to the blue curve on the ion conductivity graph); and decreased K⁺ permeability during the action potential upstroke (corresponding to the green curve on the ion conductivity graph). (Choices A, C, D, and E) The other ion sequences listed do not correlate with the action potential phases observed in cardiac myocytes. Educational Objective: The cardiac myocyte action potential consists of rapid depolarization (phase 0), initial rapid repolarization (phase 1), plateau (phase 2), late rapid repolarization (phase 3), and resting potential (phase 4). The action potential is associated with increased membrane permeability to Na⁺ and Ca⁺⁺ and decreased permeability to K⁺.

Membrane Potential Changes in an Isolated Cardiac Muscle Cell Are