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The immediate source of energy for muscular contraction is the high-energy phosphate compound called adenosine triphosphate (ATP). Although ATP is not the only energy-carrying molecule in the cell, it is the most important one, and without sufficient amounts of ATP most cells die quickly. The three main parts of an ATP molecule are: an adenine portion, a ribose portion, and three phosphates linked together. The formation of ATP occurs by combining adenosine diphosphate (ADP) and inorganic phosphate (Pi). This formation requires a large amount of energy to and it is called a high-energy bond. In order for a muscle to contract, the enzyme ATPase breaks the ATP bond and releases energy which is used to do work. ATP is the energy produced from the breakdown of food into a useable form of energy required by cells. Muscle cells store limited amounts of ATP. Therefore, because muscular exercise requires a constant supply of ATP to provide the energy needed for contraction, metabolic pathways must exist in the cell to be able to produce ATP rapidly.
Muscle cells can produce ATP by three metabolic pathways: creatine phosphate (CP), formation of ATP, formation of ATP through the degragation of glucose or glycogen (glycolysis), and oxidative formation of ATP. The formation of ATP through the CP pathway or glycolysis is called anaerobic metabolism because they do not use oxygen. Oxidative formation of ATP by the use of oxygen is called aerobic metabolism. As rapidly as ATP is broken down to ADP and Pi during exercise, ATP is reformed through the CP reaction. However, muscle cells only contain small amounts of CP, so the total amount of ATP formed through this action is limited. The combination of stored ATP and CP is called the ATP-CP system and provides energy for muscle contraction during short-term high-intensity exercise.
CP is reformed only while you are recovering from exercise. For this process to occur, there has to be ATP present. A second metabolic pathway capable of producing ATP rapidly without the involvement of oxygen is called glycolysis. Glycolysis involves the breakdown of glucose or glycogen to form two molecules of pyruvic acid or lactic acid. Glycolysis is an anaerobic pathway used to transfer energy from glucose to rejoin Pi to ADP. Glycolysis produces a net gain of two molecules of ATP and two molecules of pyruvic or lactic acid.
Although the end result of glycolysis is energy producing, you must add ATP at two points at the beginning of the pathway. In conclusion, glycolysis is the breakdown of glucose or glycogen into pyruvic or lactic acid with the net production of two or three ATP. This depends on whether the pathway began with glucose or glycogen. Since oxygen is not directly involved in glycolysis, the pathway is considered anaerobic. However, in the presence of oxygen in the mitochondria, pyruvate can participate in the aerobic production of ATP. In addition to being an anaerobic pathway capable of producing ATP without oxygen, glycolysis is the first step in the aerobic degragation of carbohydrates. Although several factors serve to control glycolysis, the most important rate-limiting enzyme in glycolysis is phosphofructokinase (PFK).
PFK is located near the beginning of glycolysis. When exercise begins, ADP/Pi levels rise and enhance PFK activity, which serves to increase the rate of glycolysis. In contrast, at rest when cellular ATP levels are high, PFK activity is inhibited and glycolytic activity is slowed. Further, high cellular levels of free fatty acids also inhibit PFK activity. Similar to the control of the ATP-CP system, regulation of PFK activity operates through negative feedback. Another important regulating enzyme in glycolysis is phosphorylase, which is responsible for degrading glycogen to glucose. This reaction provides the glycolytic pathway with the necessary glucose at the origin of the pathway. At the beginning of exercise, calcium is released from the sarcoplasmic reticulum in muscle.
This rise in sarcoplasmic calcium concentration indirectly activates phosphorylase which immediately begins to break down glycogen to glucose for entry into glycolysis. In addition, phosphorylase activity is stimulated by high levels of the hormone epinephrine. Epinephrine, released at a faster rate during heavy exercise, results in the formation of cyclic AMP. It is cyclic AMP, not epinephrine, that directly activates phosphorylase. Therefore, the influence of epinephrine on phosphorylase is indirect. It is important to emphasize the interaction of anaerobic and aerobic metabolic pathways in the production of ATP during exercise.
Although it is common to hear someone speak of aerobic versus anaerobic exercise, in reality the energy to perform most types of exercise comes from a combination of anaerobic/aerobic sources. The contribution of anaerobic ATP production is greater in short-term high-intensity activities, while aerobic metabolism is mainly found in longer activities. In conclusion, the shorter the activity, the greater the contribution of anaerobic energy production. The longer the activity, the greater the contribution of aerobic energy production. Aerobic Respiration is the metabolic process that generates ATP in association with a chemiosmotic process driven by a respiratory chain that depends on the use of oxygen as the ultimate ele ctron acceptor. Water is the ultimate reduced end product and this process occurs in the mitochondria where ATP is made by oxidative phosphorylation.
In mitochondria tricarborylic acid cycle activity and fatty acid oxidation provide most of the reducing equivalents that fuel this process but reducing equivalents released by metabolite oxidation reactions in the cytosol can be shuttled into mitochondria to supply a small proportion of ATP needs. The abdominal muscles help to maintain the trunk, maintain posture and compress the contents of the abdomen. There are four different sets of abdominal muscles involved. The first is the rectus abdominus. This is the straight muscle of the abdomen. It is medial, and it is divided into segments laterally by connective tissue.
The rectus abdominus flexes and rotates the trunk and compresses the abdomen. The external obliques are the most superficial of the lateral muscles. Its fibres run obliquely from the ribs to the linea alba. The linea alba is the midline seam of connective tissue which binds all of the abdominal muscles. The external obliques flex and laterally flexes the trunk, and compresses the abdomen. The internal obliques are deep to the external obliques.
The fibres run at right angles to the externals, which increases the strength of the muscular abdominal wall. The internal obliques flex and laterally flexes the trunk, and as well assists in compressing the abdomen. The transversus abdominus is the deepest of the lateral muscles. Its fibers run transversely from the ribs and top of the ox coxa to the linea alba. The only function it has is to compress the abdomen. When performing a regular crunch exercise, you can hit all four of the abdominal muscles discussed. There is no abdominal exercise that is better than the rest, but it is important that you switch exercises every so often.
The reason for this is due to the fact that each exercise hits the abdomen in a different way and in order to prevent your muscles from adapting, you must not only increase intensity, but the exercise as well. Muscular contraction is a complex process involving a number of cellular proteins and energy production systems. The final result is a sliding of attin over myosin, which causes the muscle to shorten and therefore develop tension. The process of muscular contraction is best explained by the sliding filament theory of contraction; muscle fibres contract by a shortening of their myofibrils, which results in a reduction of distance from Z line to Z line. As the sarcomeres shorten in length, the A bands do not shorten but move closer together. However, the I bands decrease in length.
Filament sliding occurs due to the action of the numerous cross-bridges extending out like arms from myosin and attaching on the actin filament. The head of the myosin cross-bridge is oriented in opposite directions on either end of the sarcomeres. This orientation of cross-bridges is such that when they attach to actin on each side of the sarcomeres they can pull the actin from each side towards the center. The energy from contraction comes from the breakdown of ATP by the enzyme ATPase. The breakdown of ATP to ADP and Pi and the release of energy serves to energize the myosin cross bridges. The ATP released energy is used to cock the myosin cross-bridges, which in turn pull the actin molecules over myosin and shortens the muscle.
A single contraction cycle, or power stroke of all the cross-bridges in a muscle would shorten the muscle by one percent of its resting length. Since the muscles can shorten up to sixty percent of their resting length, it is clear that the contraction cycle must be repeated over and over again. In order for this to occur, the cross-bridges must detach from actin after each power stroke, resume their original position and then re-attach to actin for another power stroke. Relaxed muscles are easily stretched which demonstrates that at rest, actin and myosin are not attached. The regulation of a muscle contraction is a function of two proteins called troponin and tropomyosin, which are located on the actin molecule. The actin filament is formed from many smaller protein pub units arranged in a double row and twisted. Tropomyosin is a thin molecule that lives in a grove between the double row of actin.
Troponin is attached directly to the tropomyosin. They work together to regulate the attachment of the actin and myosin cross-bridges. In a relaxed muscle, tropomyosin blocks the active sides on the actin molecule where the myosin cross-bridges must attach in order for contraction to occur. The trigger of contraction to occur is linked to the release of stored calcium from the sarcoplasmic reticulum. Most of this calcium is stored within expanded portions of the sarcoplasmic reticulum. In a relaxed muscle the concentration in the saroplasm is very low. However, when a nerve impulse arrives at the mernomuscular junction it travels down the transverse tubules to the sarcoplasmic reticulum and causes a release of calcium. Some of this calcium binds to troponin, which causes a position change in tropomyosin such that the active sites on the actin are uncovered.
The energy released from the breakdown of ATP cocks the myosin cross-bridges. This energized cross-bridge then attaches to the active sites on actin and contraction occurs. Attachment of fresh ATP to the myosin cross-bridges allo ....
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