Contraction and rigor mortis
which indicate an intimate connection of the postmortem rigor with the antemortem muscular contractions. Various Forms of RigorThe numerous studies. Muscle Contraction & Rigor Mortis – 50 Informal Points a nerve; links nervous system to muscular system), causing the release of Ca+2 from the sarcoplasmic. Rigor mortis or postmortem rigidity, the third stage of death, is one of the recognizable signs of In rigor mortis myosin heads continue binding with the active sites of actin proteins via adenosine diphosphate (ADP), muscles, which is directly related to the difference in glycogen levels and different types of muscle fibers.
In fact, the already loose calcium ions are brought back into the sarcoplasmic reticulum. Finally, the myosin and actin are unable to bind, thereby contracting, because the myosin active sites need calcium ions to be exposed.
ATP originates from three sources; the phosphagen system, glycogen-lactic acid system, and aerobic respiration. In the phosphagen system, muscle cells store a compound called creatine phosphate in order to replenish the ATP supply quickly.
The enzyme creatine kinase breaks the phosphate from this compound and the phosphate is added to ADP. This source of ATP can only sustain muscle contraction for 8 to 10 seconds.
The glycogen-lactic acid uses the muscles' supply of glycogen. Through anaerobic metabolism, the glycogen is broken down and creates ATP and the byproduct lactic acid. This method does not require oxygen and is able to supply more ATP than the phosphagen sytem, but occurs at a slower rate.
Finally, the aerobic respiration allows glucose to be broken down into carbon dioxide and water in the presence of oxygen. The glucose supplies come from the muscles, the liver, food, and fatty acid.
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This method creates the most ATP and for extended periods of time, but takes the most time. Death terminates aerobic respiration because the circulation system has ceased. As stated above, these sources only provide a small amount of ATP. This lack of ATP disables the myosin heads from detaching from the actin. Meanwhile, calcium ions leak from extracellular fluid and the sarcoplasmic reticulum, which is unable to recall the ions, into the muscle fiber.
As part of the process of decomposition, the myosin heads are degraded by the enzymes, allowing the muscle contraction to release and the body to relax. Following this, the muscles stiffen in rigor mortis. All muscles in the body are affected.Muscles, part 1 - Muscle Cells: Crash Course A&P #21
Starting between two and six hours following death, rigor mortis begins with the eyelids, neck, and jaw. The sequence may be due to different lactic acid levels among different muscles, which is directly related to the difference in glycogen levels and different types of muscle fibers.
Rigor mortis then spreads to the other muscles, including the internal organs, within the next four to six hours. The onset of rigor mortis is affected by the individual's age, sex, physical condition, and muscular build.
Rigor mortis may not be perceivable in many infant and child corpses due to their smaller muscle mass. The onset of rigor mortis and its resolution partially determine the tenderness of meat.
Electrical stimulation also may create quite a lot of microscopic damage, somewhat equivalent to whacking a steak on the block with a heavy beater. Whacking steaks makes them tender but spoils their shape and appearance, but the same tenderizing effect may be achieved in a more sneaky fashion microscopically without upsetting anyone unless they measure the cooking losses, which may be increased by electrical stimulation.
Aging or conditioning All traditional butchers know that beef taste and tenderness are improved by aging or conditioning, although this vital fact is cheerfully ignored by many cut-price supermarkets intent on off-loading mountains of bright red meat as fast as they can.
Meat tenderness and taste definitely are improved if carcasses or vacuum packed cuts are conditioned after slaughter but, paradoxically, beef is quite tender just two hours after slaughter, and several days of conditioning are required to recover this degree of tenderness.
After this point, the beef becomes progressively better, with a higher temperature allowing a faster rate of conditioning. Gains in tenderness from conditioning are particularly important in grass-fed beef. When beef is from youthful animals without risk of being cold shortened, then lack of conditioning is a serious cause of beef toughness.
In early research, it was though that increased tenderness might originate from the breakdown of rigor bonds between thick and thin filaments, but now this appears unlikely, because increased tenderness during conditioning still occurs when sarcomeres are at a stretched length that virtually eliminates any overlap of thick and thin filaments.
Another factor that contributes to the increased tenderness of conditioned meat may be an increase in ionic strength that solubilizes myofibrillar proteins, particularly those of the thick filament. Calcium-activated protease Calpain is an enzyme located in the cytosol. It slowly disrupts Z lines by releasing alpha actinin, a protein that holds the thin filaments into the Z line.
This makes an important contribution to meat conditioning, but many aspects of the calpain system still are unknown. Calpains occur in all vertebrate cells, where they are involved in general purpose enzymatic activity related to maintenance of cell shape and the response of cells to hormones.
Also there are other enzymes inside the muscle fibre which might be involved in the conditioning effect. Cathepsin B and D occur in lysosomes suicide bags to destroy unhappy cells and parts of the sarcoplasmic reticulum.
Rigor mortis - Wikipedia
Acid phosphatase is another enzyme that has been found inside muscle fibres. The enhancement of meat taste and aroma during conditioning still is not fully understood. Conditioning causes changes in a number of water-soluble compounds that affect meat taste, including free amino acids, metabolites of ATP, organic acids and sugars. Free amino acids released by aminopeptidase activity are increased during the conditioning of pork, chicken and beef, although the changes in beef are less than anticipated.
Some of us are worried that conditioning might be reduced by factors in modern animal production, such as the genetic selection for rapid growth rate. Even animals that are growing very rapidly have a balance between the synthesis of new tissue anabolism and the break-down of worn or damaged tissue components catabolism.
Thus, a young animal with rapid growth has much more anabolism than catabolism. But when it reaches its full adult size, anabolism and catabolism are equal. If selection for rapid growth has been achieved by decreasing catabolism as well as increasing anabolism, then we may find that we have weakened the system responsible for the favourable effects of conditioning.
Perhaps we are worrying about nothing and there is no problem, but that is what the cod fishermen said about over-fishing, right up until the time that the cod disappeared.