BATHMOTROPISM: WHAT IS IT, ELECTROPHYSIOLOGY, PHYSIOLOGICAL PACEMAKER - ANATOMY AND PHYSIOLOGY - 2025

The term bathmotropism refers to the ability of muscle cells to activate and generate a modification in their electrical balance, from an external stimulus.

Although it is a phenomenon observed in all striated muscle cells, the term is generally used in cardiac electrophysiology. It is synonymous with excitability. Its final effect is the contraction of the heart from the electrical stimulus that generates the excitation.

By OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, The electrocardiogram is just a simplified sample of the complex electrical mechanism that happens in the heart muscle to maintain a coordinated rhythm. This excitability mechanism includes the entry and exit of sodium (Na ⁺), potassium (K ⁺), calcium (Ca ^{+ +}), and chlorine (Cl ^-) ions to small intracellular organs.

The variations in these ions are, in the end, those that achieve the changes necessary to generate the contraction.

What is bathmotropism?

The term bathmotropism or excitability refers to the ability of muscle cells to activate in the face of an electrical stimulus.

It is a property of skeletal muscle that, although it is not specific to cardiac cells, most of the time it refers to the heart's own functionalism.

The end result of this mechanism is cardiac contraction, and any alteration in the process will have repercussions on the rhythm or rate of the heart.

There are clinical conditions that alter cardiac excitability increasing or decreasing it, causing serious complications in the oxygenation of the tissues as well as the formation of obstructive thrombi.

Electrophysiology of cell excitation

Cardiac cells or myocytes have an internal and an external environment separated by a layer called the cell membrane. On both sides of this membrane there are molecules of sodium (Na ⁺), calcium (Ca ^{+ +}), chlorine (Cl ^-) and potassium (K ⁺). The distribution of these ions determines the activity of the cardiomyocyte.

Under basal conditions, when there is no electrical impulse, the ions have a balanced distribution in the cell membrane known as the membrane potential. This arrangement is modified in the presence of an electrical stimulus, causing excitation of the cells and finally causing the muscle to contract.

By BruceBlaus. When using this image in external sources it can be cited as: Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI: 10.15347 / wjm / 2014.010. ISSN 2002-4436.Derivative by Mikael Häggström - File: Blausen_0211_CellMembrane.png, CC BY 3.0, The electrical stimulus that travels through the cell membrane and causes ion redistribution in the heart cell is called the cardiac action potential.

When the electrical stimulus reaches the cell, a process of variation of the ions occurs in the internal cell environment. This happens because the electrical impulse makes the cell more permeable, thus allowing the entry and exit of Na ⁺, K ⁺, Ca ^{+ +} and Cl ^- ions.

Excitation occurs when the internal cell environment reaches a lower value than the external environment. This process causes the cell's electrical charge to change, which is known as depolarization.

By OpenStax - https://cnx.org/contents/:/Preface, CC BY 4.0, To understand the electrophysiological process that activates cardiomyocytes, or cardiac muscle cells, a model was created that divides the mechanism into five phases.

Cardiomyocyte action potential

The electrophysiological process that occurs in cardiac muscle cells is different from that of any other muscle cell. For your understanding, it has been divided into 5 phases numbered from 0 to 4.

From Action_potential2.svg: * Action_potential.png: User: Quasarderivative work: Mnokel (talk) derivative work: Silvia3 (talk) - Action_potential2.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php? curid = 10524435

- Phase 4: it is the resting stage of the cell, the ions are balanced and the cellular electrical charge is at baseline values. Cardiomyocytes are ready to receive an electrical stimulus.

- Phase 0: at this time cell depolarization begins, that is, the cell becomes permeable to Na ⁺ ions, opening specific channels for this element. In this way, the electrical charge of the internal cell environment decreases.

- Phase 1: it is the phase in which Na ⁺ stops entering the cell and there is movement of K + ions to the outside through specialized channels of the cell membrane. A small increase in internal load occurs.

- Phase 2: also known as plateau. It begins with a flow of Ca ^{+ +} ions into the cell, which causes it to return to the electrical charge of the first phase. The flow of K ⁺ to the outside is maintained but occurs slowly.

- Phase 3: is the cell repolarization process. In other words, the cell begins to balance its external and internal load to return to the state of rest of the fourth phase.

Physiological pacemaker

The specialized cells of the sino-atrial or sino-atrial node have the ability to generate action potentials automatically. This process causes the electrical impulses that travel through the conduction cells.

The automatic mechanism of the sino-atrial node is unique and different from that of the rest of the myocytes, and its activity is essential to maintain the heart rhythm.

Fundamental properties of the heart

The heart is made up of normal skeletal muscle cells and specialized cells. Some of these cells have the ability to transmit electrical impulses and others, such as those of the sino-atrial node, are capable of producing automatic stimuli that trigger electrical discharges.

Cardiac cells have functional properties that are known as fundamental properties of the heart.

By OCAL (OpenClipart) - http://www.clker.com/clipart-myocardiocyte.html, CC0, These properties were described in 1897 by scientist Theodor Wilhelm Engelman after more than 20 years of experimentation, in which he made very important discoveries that were essential for the understanding of cardiac electro-physiology that we know today.

The key properties of cardiac functionalism are:

- Chronotropism, is synonymous with automatism and refers to those specialized cells that are capable of generating the necessary changes to trigger the electrical impulse in a rhythmic way. It is the characteristic of the so-called physiological pacemaker (sino-atrial node).

- Bathmotropism, is the ease of the heart cell to get excited.

- Dromotropism, refers to the ability of cardiac cells to conduct the electrical impulse and generate contraction.

- Inotropism, is the ability of the heart muscle to contract. It is synonymous with contractility.

- Lusitropism, is the term that describes the muscle relaxation stage. Previously it was thought that it was only the lack of contractility due to electrical stimulation. However, the term was included in 1982 as a fundamental property of cardiac function, since it was shown to be an energy-intensive process, in addition to an important change in cell biology.

References

1. Shih, HT (1994). Anatomy of the action potential in the heart. Texas Heart Institute journal. Taken from: ncbi.nlm.nih.gov
2. Francis, J. (2016). Practical cardiac electrophysiology. Indian Pacing and Electrophysiology Journal. Taken from: ncbi.nlm.nih.gov
3. Oberman, R; Bhardwaj, A. (2018). Physiology, Cardiac. StatPearls Treasure Island. Taken from: ncbi.nlm.nih.gov
4. Bartos, D. C; Grandi, E; Ripplinger, CM (2015). Ion Channels in the Heart. Comprehensive Physiology. Taken from: ncbi.nlm.nih.gov
5. Hund, T. J; Rudy, Y. (2000). Determinants of excitability in cardiac myocytes: mechanistic investigation of memory effect. Biophysical journal.
6. Jabbour, F; Kanmanthareddy, A. (2019). Sinus Node Dysfunction. StatPearls Treasure Island. Taken from: ncbi.nlm.nih.gov
7. Hurst J. W; Fye W. B; Zimmer, HG (2006). Theodor Wilhelm Engelmann. Clin Cardiol. Taken from: onlinelibrary.wiley.com
8. Park, D. S; Fishman, GI (2011). The cardiac conduction system. Taken from: ncbi.nlm.nih.gov