The heart in action. The Mighty Heart in Action 2022-10-08
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Gulliver's Travels, written by Jonathan Swift in 1726, is a satirical novel that tells the story of Lemuel Gulliver, a ship's surgeon who, through a series of misadventures, ends up visiting four different fantastical societies. One of these societies is inhabited by a race of intelligent horses called the Houyhnhnms.
The Houyhnhnms are a highly advanced and rational species, in contrast to the degraded and irrational human-like creatures known as the Yahoos that also inhabit their world. Gulliver becomes the servant of a Houyhnhnm master, who he refers to as "my dear horse," and learns to communicate with them through their language, which consists mainly of whinnying and other horse-like noises.
The Houyhnhnms are depicted as being superior to humans in many ways. They are rational, logical, and highly moral, and they live in a society that is free from the problems of human society, such as war, corruption, and deceit. They are also physically superior, with faster reflexes and stronger bodies than humans.
Despite their superiority, the Houyhnhnms are not portrayed as perfect beings. They are shown to be somewhat lacking in emotion and imagination, and they are unable to comprehend many of the complexities of human nature. This is exemplified in their treatment of the Yahoos, whom they see as little more than beasts of burden and who are treated cruelly as a result.
Overall, the Houyhnhnms in Gulliver's Travels serve as a commentary on the nature of intelligence and morality. Swift is using them to argue that reason and rationality alone do not necessarily lead to a better society, and that the human capacity for emotion and imagination is an important part of what makes us human. He is also suggesting that the pursuit of perfection can sometimes lead to a lack of understanding and compassion for those who are different from us.
The heart: Anatomy, how it works, and more
When people discuss inanimate objects or even abstract concepts, they use terms such as "Her election campaign still has a pulse" and "The team's chances flat-lined when it lost its star player" to describe whether the thing in question is "alive" or not. For one thing, the initiation of the "beating" of the heart is controlled by special cardiac myocytes, or heart-muscle cells, called pacemaker cells. An action potential is a reversible change of this membrane potential resulting from a "ripple effect" — an activation of currents generated by the sudden diffusion of ions across the membrane lowers the electrochemical gradient. These disks are highly folded potions of cell membrane which increases the surface area connecting two cells and reduces the electrical resistance between cells, thus allowing them to act more as one unit. Relative Refractory Period: The period during which increased stimulation can generate another action potential. The Purkinje fibers spread from the interventricular septum, into the papillary muscles, which project inward from the ventricular walls, and then continue downward to the apex of the heart. Next, in ventricular systole, we see the blood reach the ventricles before being ejected out of the heart and into circulation of the body.
Anatomy and Function of the Heart's Electrical System
The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract. In other words, certain conditions can disrupt the steady-state membrane ion imbalance and allow ions to flow in large numbers in the direction they "want" to go — in other words, against the pump. They coordinate the signal so that the atria and ventricles do not contract at the same time. The innervation of these systems allows them to alter the firing rate of nodal cells and therefore alter heart rate. While this ratio rightly leaves most of the heart available to carry out work, it also means that a defect in the cells forming the cardiac conduction system can be difficult for the organ to circumvent using alternative conduction pathways, of which there are only so many.
Depolarization and Repolarization of Heart Action Potential Explained
These are the largest veins in the body. What effect will it have on heart rate? About 70 percent of the entering blood flows directly into the ventricles through the atrioventricular opening before the atrial walls contract. The degree of murmur indicates the degree of valvular damage, which can be repaired with surgery. This is why the differences in conduction velocity and pacemaker rate can be used as a diagnostic tool to see which pacemaker cell is not working properly in the heart. The Bundle of His separates into two branches, interventricular bundles in the interventricular septum, with the left bundle branch stimulating the left ventricle and the right bundle branch stimulating the right ventricle. The Bundle of His separates into two branches, interventricular bundles to then activate Purkinje fibers, specialized cardiomyocytes that act as pacemaker cells.
The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart. How does the heart beat? Na + ions rush into the cell, causing a rapid increase in membrane potential to around +30mV, where the channels become inactive. This allows an impulse travels to all parts of the heart when any portion of this net is stimulated. Phase 4 of the cardiac muscle cell potential is called the diastolic interval, because this period corresponds to diastole, or the interval between contractions of heart muscle. Every time you hear or feel the thump of your heartbeat, this is the end of the heart contracting, which as called systole.
When the nerve impulses reach their endings, these fibers secrete acetylcholine, which causes a decrease in S-A and A-V nodal activity. The heart enables the body to eliminate the unwanted carbon dioxide. The bundle of His divides into right and left pathways, called bundle branches, to stimulate the right and left ventricles. Veins have thinner walls than arteries. Cardiac muscle cells are also connected by specialized regions of membrane called intercalated disks. In an EKG, the P wave represents atrial depolarization, the PR interval represents a delay in the AV node depolarization and partially atrial repolarization, the QRS complex represents depolarization in the left and right ventricles, and the T wave represents ventricular repolarization. The bottom right image contrasts the action potential profile of a cardiac myocyte to contraction, and the bottom left contrasts a skeletal muscle cell action potential profile to contraction.
Nodal cells are excitable tissue that undergoes depolarization, which facilitates the subsequent contraction of the heart. Nodal Cell Action Potential Profile This diagram illustrates the action potential profile of a nodal cell within the heart, with time plotted against membrane potential. Of the ions that influence heart action, the most important are potassium K+ and calcium Ca++ ions. PNS stimulation is represented through an increase in vagal stimulation. Diastole, systole, and blood pressure Each heartbeat has two parts: Diastole: The ventricles relax and fill with blood as the atria contract, emptying all blood into the ventricles.
When the cardiac impulse reaches the ventricular fibers, they are stimulated to depolarize rapidly. Action Potential Generation The SA node can undergo spontaneous depolarization, which is the reason the SA node is considered the primary pacemaker for the heart. It all starts with something called an action potential, in this case a cardiac action potential. Under normal cardiac conditions, the SA node is the first to depolarize, demonstrating a conduction velocity of 0. Skeletal Muscle Now that we have discussed the unique cell types of the heart, we can compare the properties of the contractile cardiac myocytes to the contractile skeletal muscle cells you have likely learned about in past Human Physiology courses. Five phases are recognized for the action potential in the heart that encompasses spontaneous depolarization of the SA node, eventual depolarization of the ventricles with the entry of Na+ into the cell, the release of Ca+2 from the SR to cause myocardial contraction, and eventual repolarization of the cardiomyocytes.
The three distinct phases of a nodal cell action potential; the pre-potential yellow , de-polarization red , and re-polarization blue. There, impulses are slowed down for a very short period, then continue down the conduction pathway via the bundle of His into the ventricles. This results in the membrane potential reaching threshold and initiates depolarization at a quicker rate. The answer is The Mighty Heart. As you may have surmised, the contractile cells do the work of pumping blood under the influence of the conducting cells that deliver the signal to contract.