Recent orders
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THE CONTRACTION AND RELAXATION OF CARDIAC FIBERS
THE CONTRACTION AND RELAXATION OF CARDIAC FIBERS
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Introduction
Contraction is always controlled by the central nervous system (CNS), which is comprised of the brain as well as the spinal cord. The brain always controls voluntary muscle contractions, while, on the other hand, the spinal cord controls involuntary reflexes. Cardiac fibers usually undergo a series of the coordinated contraction through calcium-induced calcium release, which is conducted through intercalated discs.
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According to previous research, that calcium and not potassium is the main determinant of myocardial contractility became evident when Ebashi and Kodama described troponin, as well as regulatory proteins in the thin filament, were discovered to be crucial for micromolar calcium concentrations to be able to activate the contractile proteins of skeletal muscle in vitro. Thus, in Cardiac muscles, contraction occurs via a phenomenon referred to as excitation-contraction coupling (ECC). The phenomenon illustrates the entire conversion process of an electrical stimulus into a mechanical response from neurons. An inward flux of the existing extracellular calcium ions in cardiac muscle through calcium channels on the T-tubules usually sustains the depolarization of cardiac muscle cells for longer duration. Thus, contraction in cardiac muscle happens through the model of contraction known as sliding filament. In this case, there is sliding of myosin filaments along actin filaments in order to lengthen or shorten the muscle fiber for contraction and relaxation.
Various changes in relaxation and contractility can be viewed as functional responses developing rapidly in general, over a duration of a few seconds or minutes. The responses are affected by mechanisms such as altered calcium fluxes as well as post-translational phosphorylations. In the process of the plateau phase of the action potential, calcium ions usually flow down a steep concentration gradient and gradually enters the myocyte. Most of this calcium then enters through the L-type channels, strategically located primarily at sarcolemmal/sarcoplasmic reticulum junctions.
Another example of research done previously shows that the transcriptional regulation modifies myocardial contractility, and was done 1962. In this case, ATPase activity was discovered to be depressed in myofibrils that were isolated from failing hearts. The influx of calcium then triggers the release of more calcium from the sarcoplasmic reticulum via ryanodine receptors. The calcium-triggered calcium release is in contrast to skeletal muscle, whereby the action potential directly triggers the release of calcium. Intracellular calcium, which at this juncture is free, interacts with the C subunit of troponin. Consequently, it leads to a configuration change in the troponin complex, allowing the interaction of actin with myosin. Cross bridge cycling takes place, resulting to the shortening of the sarcomere and the resultant muscular contraction. As the intracellular calcium concentrations are exhausted during repolarization, calcium then dissociates from troponin with the decrease of intracellular calcium concentration, resulting in relaxation.
Conclusion
The strength of a cardiac contraction may be varied through increasing the amount of free intracellular calcium. This can be done by altering the sensitivity of the myofilaments to calcium, or both. The latter takes place while stretching of the myofilaments. Myofilament calcium sensitivity reduces due to acidosis. High concentrations of magnesium and phosphate also impair cardiac function. In the meanwhile, catecholamines activates beta-adrenergic receptors found in the heart to produce a G-protein mediated increase in cAMP and the enhanced activity of protein kinase which is cAMP-dependent. This results to the phosphorylation of calcium membrane channels, facilitating calcium entry into the cell. Phosphorylation of myosin also occurs in this juncture and increases the rate of cross bridge cycling. Catecholamines increase the rate of calcium re-uptake into the sarcoplasmic reticulum, thus aiding relaxation.
Bibliography
Alpert, Nelson. In Myofibrillar Adenosine Triphosphatase Activity in Congestive Heart
Failure, 940–946. Am J Physiol, 1962.Ebashi, Sesturo, and Arthur Kodama. In A New Protein Factor Promoting Aggregation of
Tropomyosin, 107–108. Tokyo: J Biochem, 1965.
Political and economic condition of Republic of Kazakhstan
Political and economic condition of Republic of Kazakhstan
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Foreign direct investment is attainable where there is a good business relationship between the investing companies or parent company and its subsidiary company located abroad (Anthony, 1993). The main factors which will determine if a foreign direct investment can take place are the political and economic prospects of the foreign country. This paper discusses the economic and political status of the Republic of Kazakhstan.
The transition to market economy is a journey that started 17 years ago from the former soviet economy to a free market economy. After independence from the Soviet Union in 1991, the high rate of inflation and economic decline that was witnessed in the early parts of 1990’s Kazakhstan engaged itself into a series of political, economic and social reforms. Currently the economic reforms are geared towards diversifying the economy more particular is to remove the economic reliance on natural resources and focus on developing other key sectors of the economy, investment included.
Foreign investment in Kazakhstan economy has increased because investors are attracted to the country by the fact that economy of the country has be experiencing tremendous growth, evidence is shown by figures which show that about eighty percent of all capital inflows that went to the central Asia region were direct towards the country’s economy with the European Union topping the list in terms of source of investments. Arromdee (1992), in his studies show that this sharp raises in foreign investment is due to the economic reforms made, stable institutions that have being set up and the development experienced in the banking sector (Arromdee, 1992).
Both the developed, developing and under developed countries are caught in a neck to neck competition for foreign direct investment to go into their countries. Thus the need to promote each individual’s country investment opportunities that can be tapped by potential foreign investors.
Recommendation for improvements
Kazakhstan should take the advantage of its strategic location which put it at a better place to become the center of business in central Asia with ready markets form Russia and China. To gain competitive advantage over other country Kazakhstan should focus on creating conducive business environment together with political stability and increase the incentive granted their local companies that want to participate in direct investment abroad. All this will be attainable if there will be zero tolerance to corruption cases, improving of the education standards and the logistical infrastructure.
Political institution should be strengthen by instituting professional training for government officials, engaging the local government in the developments of clusters, design a process to ensure that the political environment is transparent in its deal and consistent, institute professional civil service with transparent rules and performance based promotion.
References
Anthony, J., 1993, “Equilibrium Locations of Vertically Linked Industries,” CEP Discussion Papers dp0137, Centre for Economic Performance, LSE.
Arromdee, V., 1992, “State Characteristics and the Location of Foreign Direct Investment Within the United States , Coughlin, Terza .