Conduction system of the heart and the mechanisms that are involved in the rhythm control.
The automimic nervous system plays a vital role in regulating cardiac activity. An Intrinsic cardiac conduction system controls basic heart rhythm. This system is comprised of specialized cells (noncontractile cardiac) that initiate and distribute impulses through the heart eventually leading to depolarization and contraction in a sequential manner (Fedele et al, 2020). The sequence of heart excitation: an electrical impulse travel from the higher regions of the brain through the brain stem towards the Sinoatrial node (SA), then depolarization wave (the impulse) travel via gap junctions and passes through the internodal pathway towards atrioventricular node (AV). A slight delay of about 0.1 seconds allows atria to complete contraction. Then it travels through the atrioventricular (AV) bundle (bundle of His) and eventually passes to the Purkinje fibers. It completes the sequence by contracting and depolarizing ventricles, leading to blood ejection from the heart. Cardiac pacemaker cells are found in the SA and AV nodes. This pacemaker cell set the heart's rhythm, and they have a fast depolarization rate (Marieb et al, 2018, p.686). Rhythm of the heart can be increased or decreased due to internal or external environmental stressors. For example, the toxic external environment initially may lead to an increased heart rate and the rate of respiration. An internal stressor can be an acid-base balance that may lead to either state, the excitatory or the inhibitory, increasing or decreasing the heart rate and the rate of respiration. Control of the heart rate is done through the sympathetic nervous system (SNS) or the parasympathetic nervous system (PNS) of the autonomic nervous system (ANS). The SNS is the excitatory system and the PNS is inhibitory system. These systems provide the homeostatic balance of to body by either increasing the heart rate or decreasing it due to a stressor.
The heart rate is controlled by the autonomic nervous system (ANS). The ANS is involuntary, and it is under subconscious control. Internal or external environmental stressors influence the heart rhythm. These stressors either increase or decrease the heart rate. This mechanism has to operate with precision because our life depends on it. There are two nervous systems that are involved in that, the sympathetic nervous system (SNS) or parasympathetic nervous system (PNS), the former is excitatory, fight and fly, and the latter is inhibitory, the rest and digest. When either external or internal stressors activate receptors, these systems respond accordingly. Stressor could also be an emotion. Heart rate is controlled by the nervous system, but the endocrine system is also involved in that (Marieb et al, 2018, p.698). For example, when anxiety or an exercise is a stressor, the sympathetic nervous fibers of SNS release neurotransmitter norepinephrine (NE) that causes the SA node to increase heart contractility (Gordan et al, 2015, p.208). The PNS opposes the SNS and reduces the heart rate. We are under control of this system when for example we are in relax mode, and the stressful situation has passed. These responses are mediated by the neurotransmitter acetylcholine (Ach) and mediated by potassium channels (Gordan et al, 2015, p.207).
References
Fedele, L., & Brand, T. (2020). The Intrinsic Cardiac Nervous System and Its Role in Cardiac Pacemaking and Conduction. Journal of cardiovascular development and disease, 7(4), 54. https://doi.org/10.3390/jcdd7040054
Gordan, R., Gwathmey, J. K., & Xie, L. H. (2015). Autonomic and endocrine control of cardiovascular function. World journal of cardiology, 7 (4), 204–214. https://doi.org/10.4330/wjc.v7.i4.204
Marieb, E. N. (2018). The function of blood and its constituents. In Human Anatomy and Physiology (pp. 685–700). Pearson
