Cardiac Muscle Contration and Relaxation (Essay Sample)

CARDIAC MUSCLE CONTRATION AND RELAXATION
Student’s Name
Physiology: Heart Physiology, Essay
October 18, 2014
The cardiac muscle makes a huge percentage of the mammalian heart. This feature enables the heart perform its primary role with ease and efficiency. As an organ whose primary function is to nourish the whole body, unique characteristics distinct to this heart is a necessity. As such, this paper talks about the cardiac muscle, their contraction and relaxation, and the features that aid the cardiac muscle perform its function in the diastolic and systolic phases of the heartbeat.
At the cellular level, contraction of the cardiac muscle follows a particular chain of events. When the action potential reaches the cardiac muscle fibers, it depolarizes the transverse tubules. The dehydro-pyridine receptors (DHPR) facilitate calcium influx into the cardiac fiber. Increase in calcium concentration stimulates the release of more calcium from the sarcoplasmic reticulum and the mitochondria. This process is called calcium-induced calcium release. The calcium released via the ryanodine receptors (RhR) stimulates the cardiac muscle. For uniform heart contraction, the cardiac fibers have intercalated discs. Intercalated discs are cellular membranes of the cardiac muscles that form a complex meshwork between the muscle fibers to allow communication gaps between the cells called gap junctions. This feature fastens cardiac stimulation and helps in uniformity of the heart contraction.[Kim Barret, Heddwen Brooks, Scott Boitano and Susan Barman, Ganong’s Review of Medical Physiology, (New York: McGraw-Hill Lange, 2010), 107.] [Ibid.] [Arthur Guyton and John Hall, Textbook of Medical Physiology, (Philadelphia: Elsevier Saunders, 2006), 103.]
Cardiac contraction, likewise, follows a detailed process at the organ level. Firstly, it is
important to appreciate that the heart is myogenic. It means that the ignition of the heartbeat does not require nervous stimulation. Located in the sinus venosum of the right atrium is the S.A node. It starts the pulse by sending impulses through intermodal pathways to the A.V node at the crux of the heart. Impulse is then transmitted to the A.V bundle of His. From the bundle, the impulse is transmitted to the Purkinje fibers to the ventricular walls and then to the other parts of the heart. This conducting system is vastly distributed in the heart so as to ensure rapid and uniform heart beats in the whole organ.[Guyton, Textbook of Medical Physiology, 116.] [Ibid.] [Ibid.]
During relaxation, the heart does not just relax and let in the blood. Contrary to the general assumption, the relaxation of all muscles is an energy requiring process. Cardiac muscle is dependent on the calcium ions; therefore, reduced calcium ion concentration reduces the muscle stimulation. The ions are pumped against their concentration gradient back into the sarcoplasmic reticulum via active transport. This procedure requires energy in the form of ATP. Once most of the ions are pumped back, the cardiac muscle relaxes. Calcium action in cardiac contraction is a safety measure, which safeguards the heart from diseases such as tetanus. It executes this thorough increasing the relative refractive property. During this plateau period, the heart muscle cannot get stimulated further even if an action potential was to pass th...