Potential oxidative energy sources for muscle include sugars, carbohydrates, fats, and particular amino acids. As just noted, muscle tissue in healthy, fed individuals has significant reserves of glycogen. This fuel source can be supplemented by glucose supplied from the blood; liver glycogen, which can be broken down to glucose and delivered to muscle through the circulation; and fats and amino acids, which exist in muscle as well as in other depots around the body. Further, Continue reading.
Archive for the “Physiology” Category
May
05
2010
 
Skeletal Muscle Functional Anatomy Organizational HierarchyPosted by Rodom in Physiology, Sports MedicineThe structure of skeletal muscle can be considered from a hierarchical perspective (Figure 17-2). A typical skeletal muscle is composed of muscle fascicles, which in him are composed of muscle fibers. Because a fiber is a single multinucleated cell, the terms cell and fiber are used interchangeably. Each fiber is composed of myofibrils arranged in a three- dimensional mosaic pattern (Figure 17-2). Within this structure, the sarcomeres form the basic contractile units of the fiber; they are composed of interdigitating thick and thin myo fIlaments.
This hierarchical organization of muscle is achieved with several connective tissue membranes. The connective tissue that surrounds an entire muscle is called the epimysium (i.e., on top of muscle); the membrane that binds groups of fibers into fascides is called the perimysium (i.e., around muscle). Two separate membranes surround the interior milieu of individual muscle fibers (Figure 17-3). The outermost membrane is most frequently referred to as the basement membrane. The basement membrane is not a membrane in the usual sense. Rather than having the normal structure of a lipid bilayer, the basement membrane is a loose collection of glycoproteins and collagen network. It is freely permeable to proteins, solutes, and other metabolites. An additional thin elastic membrane is found just beneath the basement membrane and is termed the
plasma membrane or sarcolemma. The plasma membrane is, in fact, the true cell boundary.
At a muscle fiber’s resting length, the plasma membrane has the morphological characteristic of small indentations termed caveolae. The caveolae provide additional length during fiber stretching. Muscle fiber lengths extend approximately 10 —15% during normal physical activity. The caveolae allow this lengthening to occur without damaging the plasma membrane. Compared to the basement membrane, the plasma membrane is much more selective to ions, solutes, and substrates crossing it. An intact plasma membrane is of critical importance to cell function. This membrane maintains the proper acid—base balance of the fiber, allowing it to contract repeatedly during exercise. The membrane is involved in propagating an action potential that will lead to muscle contraction. The membrane also transports metabolites from the blood in the capillaries to the center cytosol of the muscle fiber. Many metabolites that can be used as a fuel for exercise, such as lactic acid and glucose, are transported by specific transporter mechanisms. Also, the plasma membrane has, at the neuromuscular junction, an even more elaborate region of functional folds than elsewhere along the fiber. This elaboration helps the transmission of an action potential from the nerve to the muscle fiber.
Wedged between the basement membrane and plasma membrane are cells known as satellite cells, which are discussed further below. Interior to the plasma membrane is the cytoplasm (i.e., cytosol), which is rich in soluble proteins, myofilaments, and true myonuclei, as well as stored high-energy intermediates (ATE PC), substrates (glycogen and lipids), enzymes of metabolism, mitochondrial protein, ribosomes for protein synthesis, and so on.
True myanuclei and satellite cells are of fundamental importance for the growth and development of muscle, for the adaptive capacity of skeletal muscle to various forms of training or disuse, and for the recovery from exercise-induced or traumatic injury. When muscle fibers are viewed longitudinally with a light microscope, the nuclear material appears to be located along the peripheral edge of the
The structure of skeletal muscle can be considered from a hierarchical perspective:  Levels of Organization of Skeletal muscle A typical skeletal muscle is composed of muscle fascicles, which in turn are composed of muscle fibers. This hierarchical organization of muscle is achieved with several connective tissue membranes. Read more There are 660 skeletal muscles in the adult human being. These muscles constitute approximately 45% of body weight. Based simply on its large relative mass, it is clear that skeletal muscle is not only the largest organ system in the body, but it is also an important tissue for bioenergetic homeostasis during rest and exercise. Skeletal muscle is both the major
Our lives depend on conversions of chemical energy to other forms of energy. These conversions, or transductions, of energy are limited by the two laws of thermodynamics, which apply to physical as well as biological energy transductions.Continue Reading
Mar
06
2010
Glucose Catabolism and Anabolism IntroductionPosted by Rodom in Bioenergetics, Physiology, Sports MedicineSpeed-power activities such as 400-m sprinting, and court and field games such as basketball and football, are energetically driven by the combination of immediate and nonoxidative energy sources. However, the importance of nonoxidative, glycolytic energy sources described in this section extend far beyond a role in sustaining activities lasting a few minutes or less. Continue reading. |
