Heart Physiology Practice Exam 2025 - Free Heart Physiology Practice Questions and Study Guide

Autorhythmic cells, such as those found in the sinoatrial (SA) node of the heart, display what is known as pacemaker potentials. This phenomenon is characterized by a gradual depolarization during the resting phase, leading to the automatic generation of action potentials without external stimulation.

The unstable resting potentials of autorhythmic cells result from specific ion channel activities, particularly the funny current (I_f) which allows sodium ions to influx that contributes to the slow depolarization during the diastolic phase of the cardiac cycle. As these cells reach a certain threshold, an action potential is triggered, leading to a coordinated contraction of the heart muscle.

This unique ability of autorhythmic cells to generate rhythmic electrical impulses is foundational to the heart's inherent pacing capability, distinguishing them from typical muscle or nerve cells that have stable resting potentials and require a stronger stimulation to initiate an action potential.