Question

fill in the blank question

the built-in structure of the heart that rhythmically sets off a wave of electrical excitation is called the

Explanation:

Identify the key physiological function

The question asks for the built-in structure of the heart that rhythmically sets off a wave of electrical excitation. This refers to the heart's natural pacemaker.

Determine the anatomical term

The primary structure responsible for initiating this rhythmic electrical impulse in a healthy heart is the sinoatrial node (SA node), which functions as the cardiac pacemaker. Based on standard introductory anatomy and physiology fill-in-the-blank questions, the term "pacemaker" directly completes this definition.

Answer:

The built-in structure of the heart that rhythmically sets off a wave of electrical excitation is called the <blank>pacemaker</blank>.