11+Muscle+Physiology

Muscle Physiology Chapter 10

**__Content Summary __** //Chapter 12 consists of the muscle physiology section of the book. This section covers the wants and needs of the skeletal muscles and how they do what they do in order to achieve their daily needs. The chapter starts off talking about the skeletal muscles in general and moves on from there. The following topics are the mechanisms of contraction, contractions of skeletal muscles, the energy requirements of skeletal muscles, neural control of skeletal muscles, and finally the cardiac and smooth muscle. As you can see the majority of the chapter’s content goes to support and explain the skeletal muscles and their actions and duties. I followed the book in selecting my three topics to go into detail about and selected three of the skeletal muscle topics. The three that were the most interesting to me were the skeletal muscles, the energy requirements of skeletal muscles, and the neural control of the skeletal muscles. //

//Skeletal muscles are very simply attached to the bones by their respective tendons. Every muscle is composed of singular muscle cells that are aligned in a parallel pattern to that of the tendon. To form each muscle there are three layers present. First is the individual muscle cells that are then covered by the endomysium. Following this you have the bundles of fibers called fascicles which are then covered by the layer of perimysium. Then the entire muscle is covered by the epimysium. Another important note is that muscle fibers are striated. The striations that are darker in color are known as the A bands, and those that are lighter are known as the I bands. In between the middle of each I band there is a structure called the Z line. Muscle contractions that occur in vivo are directly as a result of somatic motor neurons. Each somatic motor axon branches off to connect to all of the muscle fibers. This connection, or innervations, is known as a motor unit. The more motor units that are present in a certain area of the body, the more fine the muscle control. // Source (Physiology Book)



//The next subject I found very interesting in this chapter was the energy requirements of skeletal muscles. The skeletal muscles are where the aerobic cell respiration occurs. This is needed because it is essential in the production of ATP which is vital for the cross-bridge activity. Fatty acids play a large role in the energy requirements for skeletal muscles. When cells are at rest or performing light exercise, they obtain majority of their energy from fatty acids. During moderate exercise the cells obtain their energy about equally from fatty acids and glucose. Of course this is when the exercise is still below the lactate level, but not by far. During heavy exercise, the glucose which is stored in the blood plasma becomes increasingly important. There are three main types of muscle fibers. There are the fast-twitch fibers, slow-twitch, and intermediate fibers. The slow-twitch fibers red fibers are made for aerobic respiration and are highly resistant to becoming fatigue. Fast-twitch white fibers are mainly for the purpose of anaerobic respiration. And finally the intermediate fibers that are originally fast-twitch, but can adapt to act like slow-twitch if they see fit and are needed. // Source (Physiology Book)

//The final section that I found to be interesting was the neural control of skeletal muscles. The lower motor neurons, or somatic neurons that innervate the muscles, play a vital role in how the muscles are controlled. The alpha motor neurons are the neurons that innervate the ordinary muscle fibers. On the other hand, the muscle spindles are innervated by the gamma motor neurons. These very muscle spindles act as length detectors in muscles. A spindle is basically intrafusal fibers wrapped around spindles in a parallel pattern. The stretching of the muscle thus stretches the spindle and causes an excitatory response in the sensory endings. // Source (Physiology Book)

[|__Muscle Physiology__]

//The section in this chapter about the needs of the skeletal muscles to be able to perform is a chapter that anyone could learn a thing or two about. The needs of our muscles are very important if we plan on getting around performing daily tasks. Without the proper materials, our muscles would not be able to perform and keep up on a daily basis. The things we eat are important for many reasons, but in this case it could be one of the most important factors of muscle needs that no one really thinks twice about. The three types of muscle cells each need something a little different in order to be able to perform their specific job. I believe in this case, if these things are neglected it could lead to a snowball effect on other actions that the body needs to engage in. The muscles being affected could lead to the inability to exercise or do the other things that we need to do in order to remain alive. //
 * __Application __**

//The sliding filament theory pertains to the process of skeletal muscle contraction. In briefly describing this theory, myosin moves along the filament by repeating a binding and releasing sequence that causes the thick filament to move over the thinner filament. There are seven stages in which this progresses. When completing these stages, the filaments slide and the skeletal muscles contract and release. //
 * __Essential Questions __**

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage One: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> When the impulse gets to the unit, it travels along the axon and enters the muscle through the neuromuscular junction. This will cause calcium channels in the axon membrane to then open. Calcium ions come from extra cellular fluid and move into the axon terminal causing synaptic vessels to fuse with pre synaptic membranes. This causes the release of acetylcholine within the synaptic cleft. As acetylcholine is released it defuses across the gap and attaches itself to the receptors along the sarcolemma and spreads along the muscle fiber. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage Two: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> The action potential spreads quickly along the sarcolemma once it has been generated. This action continues to move deep inside the muscle fiber down to the T tubules and the action potential triggers the release of calcium ions from the sarcoplasmic reticulum. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage Three: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> Calcium is then released from the sarcoplasmic reticulum and actin sites are activated. When calcium ions are released they will begin to bind to Troponin. During this process is when Tropomyosin blocks the binding of actin and that is what causes this series of events to lead to muscle contraction. As calcium ions bind to the Troponin it changes shape, which removes the blocking action of Tropomyosin. Actin active sites are then exposed and allow myosin heads to attach to the site. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage Four: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> Next, myosin heads attach to actin and form cross bridges. Also, ATP is broken down. Myosin binds at this point to the exposed binding sites and through the sliding filament mechanism the muscles contract. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage Five: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> Then the myosin head pulls the Actin filament and ADP and inorganic Phosphate are released. ATP binding allows the myosin to detach and ATP hydrolysis occurs during this time. This recharges the myosin head and then the series starts over again. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage Six: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> Cross bridges detach while new ATP molecules are attaching to the myosin head while the myosin head is in the low-energy configuration. Cross bridge detachment occurs while new ATP attaches itself to the myosin head. New ATP attaches itself to the myosin head during this process. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">Stage Seven: // //<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;"> Now ATP is broken down and used as energy for the other areas including new cross bridge formation. Finally, a drop in stimulus causes the calcium concentrate and this decreases the muscle relaxation. // <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Source One (Physiology Book), [|Source Two]

<span style="color: #df2323; font-family: Verdana,Geneva,sans-serif; font-size: 200%;">[|__Stages of Muscle Contraction__]

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