Chapter 17, Problem 8CYR

Summary Introduction

To review:

Whether the following statements are true or false. Also, rectify the false statements.

a. The rapid depolarization phase of the contractile cell action potential is due to the opening of voltage-gated potassium ion channels.

b. Pacemaker cells lack a distinct plateau phase.

c. The plateau phase in contractile cells is due to the influx of calcium ions through calcium ion channels.

d. The repolarization of the contractile cell is due to the potassium ions rushing into the cell through potassium ion channels.

e. Open sodium ion channels cause hyperpolarization in pacemaker cells, which triggers the HCN channels to open and begins a new action potential.

Introduction:

The action potentials are generated in the myocardium or the heart muscles due to the opening of Na⁺ (sodium ion) channels. The Na⁺ are positively-charged and are present in a lower concentration inside the cells as compared to the outside. When the Na⁺ channels open, the Na⁺ rush inside the cells due to the concentration gradient. This makes the inner membrane of the cell temporarily positive. This phase is called the depolarized phase. After a few seconds, the Na⁺ channels close and the K⁺ (potassium ion) channels open. The K⁺ are present in ahigher concentration inside the cells as compared to outside. Hence, the K⁺ move out of the cells and the inner cell membrane again becomes negative. This stage is called the repolarized state of the cell.