Spontaneous depolarization of the nodal tissue in the sa node occurs at action potentials per minute:

It is 70-80 action potentials per minute.  The rate of phase 4 depolarization in the SA node sets the Heart rate, The SA node serves as the Pacemaker It has the greatest  automaticity And ability to  spontaneously generate an action potential.  

The reason it is important to understand the basic laws of inheritance are important in understanding patterns of disease transmission and mutations of genes. Many inheritance patterns and characteristics which are important in our everyday lives, such as height, skin color, eye color, and risk of diseases like diabetes, are controlled by many factors that are either genetic, environmental, or both.