See [ Facts About Performance Boosters ]. Anaerobic glycolysis - Glycolysis is the initial way of utilizing glucose in all cells, and is used exclusively by certain cells to provide ATP when insufficient oxygen is available for aerobic metabolism. Glycolysis doesn't produce much ATP in comparison to aerobic metabolism, but it has the advantage that it doesn't require oxygen. In addition, glycolysis occurs in the cytoplasm, not the mitochondria.
So it is used by cells which are responsible for quick bursts of speed or strength. Like most chemical reactions, glycolysis slows down as its product, pyruvic acid, builds up. In order to extend glycolysis the pyruvic acid is converted to lactic acid in a process known as fermentation. Lactic acid itself eventually builds up, slowing metabolism and contributing to muscle fatigue. Ultimately the lactic acid must be reconverted to pyruvic acid and metabolized aerobically, either in the muscle cell itself, or in the liver.
The oxygen which is "borrowed" by anaerobic glycolysis is called oxygen debt and must be paid back. Oxygen debt is partly oxygen reserves in the lungs, tissues, and myoglobin in the lungs alactacid oxygen debt.
But mostly it is the amount of oxygen which will be required to metabolize the lactic acid produced. Strength training increases the myofilaments in muscle cells and therefore the number of crossbridge attachments which can form. Training does not increase the number of muscle cells in any real way. Sometimes a cell will tear and split resulting in two cells when healed. Lactic acid removal by the cardiovascular system improves with training which increases the anaerobic capacity.
Even so, the glycolysis-lactic acid system can produce ATP for active muscle cells for only about a minute and a half. Aerobic metabolism - ultimately, the product of glycolysis, pyruvic acid, must be metabolized aerobically.
Aerobic metabolism is performed exclusively in the mitochondria. Pyruvic acid is converted to a molecule called an acetyl group and put into a pathway known as the Krebs Cycle. Energy is released in the form of ATP and, especially, as high energy electrons.
As previously discussed, the contraction of skeletal muscle fibers is triggered by signaling from a motor neuron. Each muscle fiber is innervated by only one motor neuron but a single motor neuron can innervate multiple muscle fibers.
A motor unit is defined a single motor neuron and all of the muscle fibers innervated by it Figure The size of a motor unit dictates its function. A small motor unit, composed of a motor neuron and only a few muscle fibers, permits very fine motor control of a muscle. For example, the extraocular eye muscles have thousands of muscle fibers with every 5 — 10 fibers supplied by a single motor neuron; this allows for exquisite control of eye movements so that both eyes can quickly focus on an object.
Small motor units are also involved in the many fine movements of the fingers and thumb of the hand for grasping, texting, etc. The large motor units of the thigh muscles or back muscles, where a single motor neuron will supply thousands of muscle fibers in a muscle, are representative of this type of activity. Most muscles in the human body have a mixture of small and large motor units which gives the nervous system a wide range of control over the muscle. The smaller motor units in a muscle have motor neurons that are more excitable.
Initial activation of these smaller motor units results in a relatively small degree of tension generated in a muscle.
As more strength is needed, larger motor units are enlisted to generate more tension. This process of bringing on additional motor units to produce more tension is known as recruitment. This process allows a muscle such as the biceps brachii to pick up a feather with minimal force generation versus picking up a heavy weight which requires a much greater amount of force generation.
When necessary, the maximal number of motor units in a muscle can be recruited simultaneously, producing the maximum force of contraction for that muscle, but this cannot last for very long because of the energy requirements to sustain the contraction.
To prevent complete muscle fatigue, motor units are generally not all simultaneously active, but instead some motor units rest while others are active, which allows for longer muscle contractions.
The nervous system thus uses recruitment as a mechanism to efficiently utilize a skeletal muscle. As discussed previously, when a skeletal muscle fiber contracts, myosin heads attach to actin to form cross-bridges followed by the thin filaments sliding over the thick filaments as the heads pull the actin, and this results in sarcomere shortening, creating the tension of the muscle contraction.
The cross-bridges can only form where thin and thick filaments overlap; thus, the length of the sarcomere has a direct influence on the force generated when the sarcomere shortens. This is called the length-tension relationship.
The ideal length of a sarcomere to produce maximal tension occurs at 80 percent to percent of its resting length, with percent being the state where the medial edges of the thin filaments are just at the most-medial myosin heads of the thick filaments Figure This length maximizes the overlap of actin-binding sites and myosin heads.
If a sarcomere is stretched past the ideal length beyond percent , thick and thin filaments do not fully overlap, which results in less tension produced. Skeletal muscle MP is the location of the skin area above the muscle in which an electrical pulse applied transcutaneously evokes a muscle twitch with the least injected current. In other words, it represents the skin area above the muscle where the motor threshold is the lowest for a given electrical input [].
What is a multiple motor unit summation? Category: automotive motorcycles. Quick Reference. The combined effect of a number of motor units acting within a muscle at any given time. See also recruitment, spatial summation. What is treppe? Medical Definition of treppe. How are muscles activated? What are graded responses? What is the difference between treppe and wave summation? What is treppe what causes it in vivo?
What controls the force of muscle contraction? How do you calculate Tetanizing frequency? Why is a motor unit important? How does the motor unit work? This addition is termed summation. Within a muscle summation can occur across motor units to recruit more muscle fibers, and also within motor units by increasing the frequency of contraction.
When a weak signal is sent by the central nervous system to contract a muscle, the smaller motor units, being more excitable than the larger ones, are stimulated first. As the strength of the signal increases, more and larger motor units are excited. The largest motor units have as much as 50 times the contractile strength as the smaller ones; thus, as more and larger motor units are activated, the force of muscle contraction becomes progressively stronger.
A concept known as the size principle allows for a gradation of muscle force during weak contraction to occur in small steps, which become progressively larger as greater amounts of force are required. For skeletal muscles, the force exerted by the muscle can be controlled by varying the frequency at which action potentials are sent to muscle fibers. Action potentials do not arrive at muscles synchronously, and, during a contraction, only a certain percentage of the fibers in the muscle will be contracting at any given time.
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