The importance of the heart cannot go understated. It is an incredible little muscle that contracts and relaxes tens of thousands of times a day and delivers essential oxygen, nutrients and hormones to our body tissues. Perhaps one of the most remarkable aspects of the heart is that all this work is done without us even thinking about it. The heart possesses three very unique qualities that allow it to function the way that it does.
- Automaticity is the heart’s ability to create electrical impulses without help or stimulation from an outside source [1]. These electrical impulses are made in the Sinoatrial (SA) node, the atrioventricular (AV) node and the Purkinje fibers. Each of these areas of the heart produces electrical impulses but at varying rates. The SA node produces impulses at 60-100 per minute, while the AC node produces impulses from 40-60 per minute. The Purkinje fibers have the slowest rate at 20-40 impulses per minute. The formation of impulses occurs when a cardiac cell depolarizes or changes from a negative resting membrane potential to positive [2]. This depolarization happens due to a rapid influx of positive ions, namely sodium, potassium and calcium, into the cells. This constant shift of ions allows the heart to depolarize and create electrical impulses without any outside stimulation.
- Conductivity allows the cells to take the impulses created through depolarization and transmit or pass them to the cells next to them. While everyone’s biology is slightly different, the heart’s conduction pathways all follow a general path. Impulses begin in the heart’s SA node and travel to the AV node through the internodal pathways and Bachmans Bundle. After a brief pause in the AV node, impulses pass through to the AV bundle, also called the bundle of His, and eventually to the left and right bundle branches and the Purkinje Fibers.
- Contractility is the cardiac cells’ ability to shorten in response to the electrical impulses as they pass through the cells [1]. Contraction of the cells that make up the chambers in the heart compresses the blood filling those chambers, forcing it through the vasculature and creating a pulse.
These three unique attributes of the heart – automaticity, conductivity and contractility – allow us to perform our daily activities and tasks without giving so much as a second thought through impulse creation, electrical conduction and cardiac squeeze.
References
1. Booth K, O’Brien T. Electrocardiography for Healthcare Professionals: 5th Edition. McGraw Hill Education. 2019.
2. Cosstanzo LS. Physiology: Sixth Edition. Elsevier. 2018.
