Heart rate node, where the faster pacemaker cells driving the self-generated rhythmic firing and responsible for the heart's autorhythmicity are located. For endurance athletes at the elite level, it is not unusual to have a resting heart rate between 33 and 50 bpm. The "maximum heart rate" (HR) is the highest heart rate an individual can achieve without severe problems through exercise stress, and generally decreases with age. Since HR varies by individual, the most accurate way of measuring any single person's HR is via a cardiac stress test. In this test, a person is subjected to controlled physiologic stress (generally by
Cardiac neural crest cells Cardiac neural crest cells Neural crest cells are a group of temporary, multipotent (can give rise to some other types of cells but not all) cells that are pinched off during the formation of the neural tube (precursor to the spinal cord and brain) and therefore are found at the dorsal (top) region of the neural tube during development. They are derived from the ectoderm germ layer, but are sometimes called the fourth germ layer because they are so important and give rise to so many other types of cells. They migrate throughout the body and create a large number