Pacemaker cells isolated from the SA node generate action po

Pacemaker cells isolated from the SA node generate action potentials at ______ beats per minute. A) 20-40 B) 40-60 C) 80-100 D) 100-140 E) 140-180 The long plateau phase of the cardiac muscle action potential is due to A) movement of fewer sodium ions across the cell membrane into the cell. B) calcium channels remaining open. C) increased membrane permeability to potassium ion. D) decrease in the amount of calcium diffusing across the membrane. E) increased membrane permeability to sodium ions. As a result of the long refractory period in the cardiac action potential, cardiac muscle cannot exhibit A) tonus. B) treppe. C) tetany. D) recruitment. E) fatigue.

Solution

16) Ans. (C) (80-100). Explanation -: Cardiac muscle contraction in animals and humans is initiated by electrical potential known as action potential and its value is mentiones above .

17. Ans (A) Movement of fewer sodium ions across the cell membrane into the cell

18 Ans (C) Tetany Explanation -: In tetany contraction of muscles is involuntary which is cause by disease and other factores which increases action potential of muscle.