The heart is by far the most resilient and efficient muscle in the body. While definitively characterized as an organ, I use the word "muscle" to emphasize the fact that the heart is entirely composed of highly specialized striated cardiac muscular tissue. The human heart never takes a rest, never pauses to recuperate energy, and will function at a peak level of efficiency for years if proper care is taken to ensure that it remains healthy and unburdened by the many preventable risk factors which contribute to CHD.
How long do you think you would be able to continously open and close your hand as though attempting to crack a walnut? Five minutes... fifteen at most? There is no question that your heart undertakes the enormity of this task, without so much as a split second's hesitation, throughout the entire duration of your life. This is due to a variety of factors, which will be discussed in the following section.
Muscle Power:
There are three types of muscular tissue in the human body. Smooth muscles form a protective barrier around certain organs and may be found in the linings of the digestive tract and blood vessels. These muscles are said to be involuntary, or outside the realm of conscious control. Skeletal muscles line your bones and are most often subject to voluntary control mechanisms. As such, skeletal muscular tissue is better suited for strenuous work than is smooth muscular tissue. Cardiac muscle is highly specialized and can only be found in the heart. It combines features of both smooth and skeletal muscular tissue. While cardiac muscle cannot be voluntarily controlled, it is able to perform with the same power and efficiency as skeletal muscle.
Interestingly, cardiac tissue does not require signals from the nervous system to contract. The brain plays a role in dictating heart rate, but the heart will continue to beat even if all nervous system functions are completely impaired, providing that it is supplied with an adequate supply oxygen and nutients.
The secret to this automated mechanism resides in the heart's electrical conduction system. Cells in the heart are affected by polar atoms, which can be positively or negatively charged. When cells in cardiac tissue are inundated by sodium, calcium and potassium ions (atoms which have an unequal number of protons and electrons), a dance of give-and-take takes place, as the body naturally seeks to maintain homeostasis, or a state of internal equilibrium. When the cells inside the heart contain more positively charged ions than the area surrounding the outside of cardiac cells, the condition will seek to reverse itself. Negatively charged ions will rush into heart cells to compensate for the "disequilibrum", while positively charged ions seek to rush out, until a critical threshold is reached and the flow is once again reversed. It is this reversal of flow which generates the electrical spark which causes cardiac cells to contract, and therefore the heart to beat.
