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73-483: The Frank-Starling mechanism occurs as the result of the length-tension relationship observed in striated muscle, including for example skeletal muscles , arthropod muscle and cardiac (heart) muscle . As striated muscle is stretched, active tension is created by altering the overlap of thick and thin filaments. The greatest isometric active tension is developed when a muscle is at its optimal length. In most relaxed skeletal muscle fibers, passive elastic properties maintain

146-417: A complex interface region known as the musculotendinous junction also known as the myotendinous junction , an area specialised for the primary transmission of force. At the muscle-tendon interface, force is transmitted from the sarcomeres in the muscle cells to the tendon. Muscles and tendons develop in close association, and after their joining at the myotendinous junction they constitute a dynamic unit for

219-471: A full professor (Ordinariat). Then he returned to Munich to continue this work. Carl J. Wiggers visited Frank’s laboratory in 1912 and found Frank a ‘‘brilliant analyst, a skillful systematist, a talented mathematician, and a creative thinker...’’, but secretive and difficult to work with. Wiggers returned to the US in the fall of 1912 having ‘smuggled’ copies of some of Frank’s equipment out with him, and published

292-558: A higher capability for electrochemical transmission of action potentials and a rapid level of calcium release and uptake by the sarcoplasmic reticulum. The fast twitch fibers rely on a well-developed, anaerobic , short term, glycolytic system for energy transfer and can contract and develop tension at 2–3 times the rate of slow twitch fibers. Fast twitch muscles are much better at generating short bursts of strength or speed than slow muscles, and so fatigue more quickly. The slow twitch fibers generate energy for ATP re-synthesis by means of

365-757: A higher density of capillaries . However, muscle cells cannot divide to produce new cells, and as a result there are fewer muscle cells in an adult than in a newborn. There are a number of terms used in the naming of muscles including those relating to size, shape, action, location, their orientation, and their number of heads. Broadly there are two types of muscle fiber: Type I , which is slow, and Type II which are fast. Type II has two divisions of type IIA (oxidative), and type IIX (glycolytic), giving three main fiber types. These fibers have relatively distinct metabolic, contractile, and motor unit properties. The table below differentiates these types of properties. These types of properties—while they are partly dependent on

438-404: A length-tension diagram from his data. Starling's data and associated diagrams, provided evidence that the length of the muscle fibers, and resulting tension, altered the systolic pressure. Skeletal muscle Skeletal muscle (commonly referred to as muscle ) is one of the three types of vertebrate muscle tissue , the other being cardiac muscle and smooth muscle . They are part of

511-462: A long term system of aerobic energy transfer. These mainly include the ATPase type I and MHC type I fibers. They tend to have a low activity level of ATPase, a slower speed of contraction with a less well developed glycolytic capacity. Fibers that become slow-twitch develop greater numbers of mitochondria and capillaries making them better for prolonged work. Individual muscles tend to be

584-417: A mixture of various fiber types, but their proportions vary depending on the actions of that muscle. For instance, in humans, the quadriceps muscles contain ~52% type I fibers, while the soleus is ~80% type I. The orbicularis oculi muscle of the eye is only ~15% type I. Motor units within the muscle, however, have minimal variation between the fibers of that unit. It is this fact that makes

657-468: A muscle, and are often termed as muscle fibers . A single muscle such as the biceps in a young adult male contains around 253,000 muscle fibers. Skeletal muscle fibers are multinucleated with the nuclei often referred to as myonuclei . This occurs during myogenesis with the fusion of myoblasts each contributing a nucleus. Fusion depends on muscle-specific proteins known as fusogens called myomaker and myomerger . Many nuclei are needed by

730-456: A number of different environmental factors. This plasticity can, arguably, be the strongest evolutionary advantage among organisms with muscle. In fish, different fiber types are expressed at different water temperatures. Cold temperatures require more efficient metabolism within muscle and fatigue resistance is important. While in more tropical environments, fast powerful movements (from higher fast-twitch proportions) may prove more beneficial in

803-463: A reliance on glycolytic enzymes. Fibers can also be classified on their twitch capabilities, into fast and slow twitch. These traits largely, but not completely, overlap the classifications based on color, ATPase, or MHC ( myosin heavy chain ). Some authors define a fast twitch fiber as one in which the myosin can split ATP very quickly. These mainly include the ATPase type II and MHC type II fibers. However, fast twitch fibers also demonstrate

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876-684: A student bit the dust in the examination in Physiology'. Frank continued to work in Munich until his enforced retirement in 1934 due to his opposition to the Nazi regime. Frank's initial research was related to fat absorption. But in his postdoctoral work ( Habilitationsschrift ) Frank investigated the isometric and isotonic contractile behaviour of the heart and it is this work that he is best known for. Frank's work on this topic preceded that of Ernest Starling , but both are usually credited with providing

949-483: A tendon. Multipennate muscles have fibers that are oriented at multiple angles along the force-generating axis, and this is the most general and most common architecture. Muscle fibers grow when exercised and shrink when not in use. This is due to the fact that exercise stimulates the increase in myofibrils which increase the overall size of muscle cells. Well exercised muscles can not only add more size but can also develop more mitochondria , myoglobin , glycogen and

1022-400: Is a predominance of type II fibers utilizing glycolytic metabolism. Because of the discrepancy in fast twitch fibers compared to humans, chimpanzees outperform humans in power related tests. Humans, however, will do better at exercise in aerobic range requiring large metabolic costs such as walking (bipedalism). Across species, certain gene sequences have been preserved, but do not always have

1095-405: Is a slow twitch-fiber that can sustain longer contractions ( tonic ).   In lobsters, muscles in different body parts vary in the muscle fiber type proportions based on the purpose of the muscle group. In the early development of vertebrate embryos, growth and formation of muscle happens in successive waves or phases of myogenesis . The myosin heavy chain isotype is a major determinant of

1168-529: Is associated with a reduced compliance, or increased stiffness, of the ventricle wall. This reduced compliance results in an inadequate filling of the ventricle and a decrease in the end-diastolic volume. The decreased end-diastolic volume then leads to a reduction in stroke volume because of the Frank-Starling mechanism. The Frank–Starling law is named after the two physiologists, Otto Frank and Ernest Henry Starling . However, neither Frank nor Starling

1241-499: Is attached to other organelles such as the mitochondria by intermediate filaments in the cytoskeleton. The costamere attaches the sarcomere to the sarcolemma. Every single organelle and macromolecule of a muscle fiber is arranged to ensure that it meets desired functions. The cell membrane is called the sarcolemma with the cytoplasm known as the sarcoplasm . In the sarcoplasm are the myofibrils. The myofibrils are long protein bundles about one micrometer in diameter. Pressed against

1314-505: Is expressed in other mammals, so is still accurately seen (along with IIB) in the literature. Non human fiber types include true IIb fibers, IIc, IId, etc. Further fiber typing methods are less formally delineated, and exist on more of a spectrum. They tend to be focused more on metabolic and functional capacities (i.e., oxidative vs. glycolytic , fast vs. slow contraction time). As noted above, fiber typing by ATPase or MHC does not directly measure or dictate these parameters. However, many of

1387-399: Is not the same as ATPase fiber typing. Almost all multicellular animals depend on muscles to move. Generally, muscular systems of most multicellular animals comprise both slow-twitch and fast-twitch muscle fibers, though the proportions of each fiber type can vary across organisms and environments. The ability to shift their phenotypic fiber type proportions through training and responding to

1460-469: Is of functional importance because it serves to adapt left ventricular output to right ventricular output. If this mechanism did not exist and the right and left cardiac outputs were not equivalent, blood would accumulate in the pulmonary circulation (were the right ventricle producing more output than the left) or the systemic circulation (were the left ventricle producing more output than the right). Premature ventricular contraction causes early emptying of

1533-404: Is preceded by the formation of connective tissue frameworks, usually formed from the somatic lateral plate mesoderm . Myoblasts follow chemical signals to the appropriate locations, where they fuse into elongated multinucleated skeletal muscle cells. Between the tenth and the eighteenth weeks of gestation, all muscle cells have fast myosin heavy chains; two myotube types become distinguished in

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1606-572: Is surrounded by a type of connective tissue layer of fascia . Muscle fibers are formed from the fusion of developmental myoblasts in a process known as myogenesis resulting in long multinucleated cells. In these cells the nuclei , termed myonuclei , are located along the inside of the cell membrane . Muscle fibers also have multiple mitochondria to meet energy needs. Muscle fibers are in turn composed of myofibrils . The myofibrils are composed of actin and myosin filaments called myofilaments , repeated in units called sarcomeres, which are

1679-412: Is thought to be a decrease in the spacing between thick and thin filaments, when a cardiac muscle is stretched, allowing an increased number of cross-bridges to form. The force that any single cardiac muscle cell generates is related to the sarcomere length at the time of muscle cell activation by calcium. The stretch on the individual cell, caused by ventricular filling, determines the sarcomere length of

1752-457: Is used in fiber typing vs. MHC typing, and some ATPase types actually contain multiple MHC types. Also, a subtype B or b is not expressed in humans by either method . Early researchers believed humans to express a MHC IIb, which led to the ATPase classification of IIB. However, later research showed that the human MHC IIb was in fact IIx, indicating that the IIB is better named IIX. IIb

1825-437: Is very variable and depends directly upon blood filling and thereby expanding the heart chambers. In the human heart, maximal force is generated with an initial sarcomere length of 2.2 micrometers, a length which is rarely exceeded in a normal heart. Initial lengths larger or smaller than this optimal value will decrease the force the muscle can achieve. For longer sarcomere lengths, this is the result of there being less overlap of

1898-735: The Physiologisches Institut in Leipzig . There in 1892 he completed his doctoral studies ( Promotion ). Subsequently, from 1894 Frank worked as an assistant in Carl von Voit 's Physiological Institute in Munich where he studied cardiac function using approaches derived from earlier thermodynamic analyses of skeletal muscle contraction . His work on the behaviour of heart muscle was the topic of his post doctoral work. In 1902 he became an Extraordinary Professor and from 1905 to 1908 he undertook further work on this topic before becoming

1971-449: The erector spinae and small vertebral muscles, and are innervated by the dorsal rami of the spinal nerves . All other muscles, including those of the limbs are hypaxial, and innervated by the ventral rami of the spinal nerves. During development, myoblasts (muscle progenitor cells) either remain in the somite to form muscles associated with the vertebral column or migrate out into the body to form all other muscles. Myoblast migration

2044-538: The left ventricle (LV) into the aorta . Since the next ventricular contraction occurs at its regular time, the filling time for the LV increases, causing an increased LV end-diastolic volume. Due to the Frank–Starling mechanism, the next ventricular contraction is more forceful, leading to the ejection of the larger than normal volume of blood, and bringing the LV end-systolic volume back to baseline. Diastolic dysfunction

2117-528: The myofibrils , causing a greater number of actin - myosin cross-bridges to form within the muscle. Specifically, the sensitivity of troponin for binding Ca increases and there is an increased release of Ca from the sarcoplasmic reticulum . In addition, stretch of cardiac myocytes increases the releasability of Ca from the internal store, the sarcoplasmic reticulum , as shown by an increase in Ca spark rate upon axial stretch of single cardiac myocytes. Finally, there

2190-458: The pectoral , and abdominal muscles ; intrinsic and extrinsic muscles are subdivisions of muscle groups in the hand , foot , tongue , and extraocular muscles of the eye . Muscles are also grouped into compartments including four groups in the arm , and the four groups in the leg . Apart from the contractile part of a muscle consisting of its fibers, a muscle contains a non-contractile part of dense fibrous connective tissue that makes up

2263-580: The sarcolemma . The myonuclei are quite uniformly arranged along the fiber with each nucleus having its own myonuclear domain where it is responsible for supporting the volume of cytoplasm in that particular section of the myofiber. A group of muscle stem cells known as myosatellite cells , also satellite cells are found between the basement membrane and the sarcolemma of muscle fibers. These cells are normally quiescent but can be activated by exercise or pathology to provide additional myonuclei for muscle growth or repair. Muscles attach to tendons in

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2336-436: The tendon at each end. The tendons attach the muscles to bones to give skeletal movement. The length of a muscle includes the tendons. Connective tissue is present in all muscles as deep fascia . Deep fascia specialises within muscles to enclose each muscle fiber as endomysium ; each muscle fascicle as perimysium , and each individual muscle as epimysium . Together these layers are called mysia . Deep fascia also separates

2409-465: The voluntary muscular system and typically are attached by tendons to bones of a skeleton . The skeletal muscle cells are much longer than in the other types of muscle tissue, and are also known as muscle fibers . The tissue of a skeletal muscle is striated – having a striped appearance due to the arrangement of the sarcomeres . A skeletal muscle contains multiple fascicles – bundles of muscle fibers. Each individual fiber, and each muscle

2482-537: The Wiggers Diagram in the US; arguably one of the most notorious cases of intellectual piracy ever documented. despite this Wiggers and Frank seem to have maintained cordial relations subsequently. Frank appears to have been a demanding teacher and Richard Bing , an Editor of the Journal of Molecular and Cellular Cardiology, who studied with Frank, recalled him as '...a holy terror, hating mediocrity, and many

2555-438: The associated related changes, not a change in fiber type. There are numerous methods employed for fiber-typing, and confusion between the methods is common among non-experts. Two commonly confused methods are histochemical staining for myosin ATPase activity and immunohistochemical staining for myosin heavy chain (MHC) type. Myosin ATPase activity is commonly—and correctly—referred to as simply "fiber type", and results from

2628-443: The basic functional, contractile units of the muscle fiber necessary for muscle contraction . Muscles are predominantly powered by the oxidation of fats and carbohydrates , but anaerobic chemical reactions are also used, particularly by fast twitch fibers . These chemical reactions produce adenosine triphosphate (ATP) molecules that are used to power the movement of the myosin heads . Skeletal muscle comprises about 35% of

2701-668: The body of humans by weight. The functions of skeletal muscle include producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. Skeletal muscle is also an endocrine organ . Under different physiological conditions, subsets of 654 different proteins as well as lipids, amino acids, metabolites and small RNAs are found in the secretome of skeletal muscles. Skeletal muscles are substantially composed of multinucleated contractile muscle fibers (myocytes). However, considerable numbers of resident and infiltrating mononuclear cells are also present in skeletal muscles. In terms of volume, myocytes make up

2774-408: The developing fetus – both expressing fast chains but one expressing fast and slow chains. Between 10 and 40 per cent of the fibers express the slow myosin chain. Otto Frank (physiologist) Otto Frank (21 June 1865 – 12 November 1944) was a Grand Duchy of Hesse born medical doctor and physiologist who made contributions to cardiac physiology and cardiology . The Frank–Starling law of

2847-545: The direct assaying of ATPase activity under various conditions (e.g. pH ). Myosin heavy chain staining is most accurately referred to as "MHC fiber type", e.g. "MHC IIa fibers", and results from determination of different MHC isoforms . These methods are closely related physiologically, as the MHC type is the primary determinant of ATPase activity. However, neither of these typing methods is directly metabolic in nature; they do not directly address oxidative or glycolytic capacity of

2920-531: The environment has served organisms well when placed in changing environments either requiring short explosive movements (higher fast twitch proportion) or long duration of movement (higher slow twitch proportion) to survive. Bodybuilding has shown that changes in muscle mass and force production can change in a matter of months. Some examples of this variation are described below. American lobster , Homarus americanus , has three fiber types including fast twitch fibers, slow-twitch and slow-tonic fibers. Slow-tonic

2993-399: The fascicles can vary in their relationship to one another, and to their tendons. These variations are seen in fusiform , strap , and convergent muscles . A convergent muscle has a triangular or fan-shape as the fibers converge at its insertion and are fanned out broadly at the origin. A less common example of a parallel muscle is a circular muscle such as the orbicularis oculi , in which

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3066-438: The fiber. When "type I" or "type II" fibers are referred to generically, this most accurately refers to the sum of numerical fiber types (I vs. II) as assessed by myosin ATPase activity staining (e.g. "type II" fibers refers to type IIA + type IIAX + type IIXA ... etc.). Below is a table showing the relationship between these two methods, limited to fiber types found in humans. Subtype capitalization

3139-461: The fibers are longitudinally arranged, but create a circle from origin to insertion. These different architectures, can cause variations in the tension that a muscle can create between its tendons. The fibers in pennate muscles run at an angle to the axis of force generation. This pennation angle reduces the effective force of any individual fiber, as it is effectively pulling off-axis. However, because of this angle, more fibers can be packed into

3212-593: The fibers of a skeletal muscle. It is thought that by performing endurance type events for a sustained period of time, some of the type IIX fibers transform into type IIA fibers. However, there is no consensus on the subject. It may well be that the type IIX fibers show enhancements of the oxidative capacity after high intensity endurance training which brings them to a level at which they are able to perform oxidative metabolism as effectively as slow twitch fibers of untrained subjects. This would be brought about by an increase in mitochondrial size and number and

3285-434: The fibres. Therefore the force (pressure) generated by the cardiac muscle fibres is related to the end-diastolic volume of the left and right ventricles as determined by complexities of the force-sarcomere length relationship. Due to the intrinsic property of myocardium that is responsible for the Frank-Starling mechanism, the heart can automatically accommodate an increase in venous return, at any heart rate. The mechanism

3358-529: The foundations of what is termed the Frank–Starling law of the heart . This law states that "Within physiological limits, the force of contraction is directly proportional to the initial length of the muscle fiber". Frank also undertook important work into the physiological basis of the arterial pulse waveform and may have coined the term essential hypertension in 1911. His work on the Windkessel extended

3431-510: The great majority of skeletal muscle. Skeletal muscle myocytes are usually very large, being about 2–3 cm long and 100 μm in diameter. By comparison, the mononuclear cells in muscles are much smaller. Some of the mononuclear cells in muscles are endothelial cells (which are about 50–70 μm long, 10–30 μm wide and 0.1–10 μm thick), macrophages (21 μm in diameter) and neutrophils (12-15 μm in diameter). However, in terms of nuclei present in skeletal muscle, myocyte nuclei may be only half of

3504-403: The groups of muscles into muscle compartments. Two types of sensory receptors found in muscles are muscle spindles , and Golgi tendon organs . Muscle spindles are stretch receptors located in the muscle belly. Golgi tendon organs are proprioceptors located at the myotendinous junction that inform of a muscle's tension . Skeletal muscle cells are the individual contractile cells within

3577-833: The heart is named after him and Ernest Starling . (Friedrich Wilhelm Ferdinand) Otto Frank was born in Groß-Umstadt and was the son of Georg Frank (1838–1907), a doctor of medicine and a practicing physician, and Mathilde Lindenborn (1841–1906). Otto Frank was married to Theres Schuster in a Catholic wedding in Munich. Otto Frank studied medicine in Munich and Kiel between 1884 and 1889 (approbation in Munich 1889). During 1889 to 1891 he undertook training in mathematics, chemistry, physics, anatomy and zoology in Heidelberg , Glasgow , Munich and Straßburg . He then worked until 1894 as an assistant to Carl Friedrich Wilhelm Ludwig in

3650-467: The higher end of any sport tend to demonstrate patterns of fiber distribution e.g. endurance athletes show a higher level of type I fibers. Sprint athletes, on the other hand, require large numbers of type IIX fibers. Middle-distance event athletes show approximately equal distribution of the two types. This is also often the case for power athletes such as throwers and jumpers. It has been suggested that various types of exercise can induce changes in

3723-405: The human body, making up around 40% of body weight in healthy young adults. In Western populations, men have on average around 61% more skeletal muscle than women. Most muscles occur in bilaterally-placed pairs to serve both sides of the body. Muscles are often classed as groups of muscles that work together to carry out an action. In the torso there are several major muscle groups including

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3796-432: The inside of the sarcolemma are the unusual flattened myonuclei. Between the myofibrils are the mitochondria . While the muscle fiber does not have smooth endoplasmic cisternae, it contains sarcoplasmic reticulum . The sarcoplasmic reticulum surrounds the myofibrils and holds a reserve of the calcium ions needed to cause a muscle contraction. Periodically, it has dilated end sacs known as terminal cisternae . These cross

3869-549: The long run. In rodents such as rats, the transitory nature of their muscle is highly prevalent. They have high percentage of hybrid muscle fibers and have up to 60% in fast-to-slow transforming muscle. Environmental influences such as diet, exercise and lifestyle types have a pivotal role in proportions of fiber type in humans. Aerobic exercise will shift the proportions towards slow twitch fibers, while explosive powerlifting and sprinting will transition fibers towards fast twitch. In animals, "exercise training" will look more like

3942-438: The muscle fiber from one side to the other. In between two terminal cisternae is a tubular infolding called a transverse tubule (T tubule). T tubules are the pathways for action potentials to signal the sarcoplasmic reticulum to release calcium, causing a muscle contraction. Together, two terminal cisternae and a transverse tubule form a triad . All muscles are derived from paraxial mesoderm . During embryonic development in

4015-433: The muscle fibers length near optimal, as determined usually by the fixed distance between the attachment points of tendons to the bones (or the exoskeleton of arthropods) at either end of the muscle. In contrast, the relaxed sarcomere length of cardiac muscle cells, in a resting ventricle, is lower than the optimal length for contraction. There is no bone to fix sarcomere length in the heart (of any animal) so sarcomere length

4088-468: The neck that show a potential inverse trend of fiber type percentages (one muscle has high percentage of fast twitch, while the complementary muscle will have a higher percentage of slow twitch fibers). The complementary muscles of turtles had similar percentages of fiber types. Chimpanzee muscles are composed of 67% fast-twitch fibers and have a maximum dynamic force and power output 1.35 times higher than human muscles of similar size. Among mammals, there

4161-536: The need for long durations of movement or short explosive movements to escape predators or catch prey. Skeletal muscle exhibits a distinctive banding pattern when viewed under the microscope due to the arrangement of two contractile proteins myosin , and actin – that are two of the myofilaments in the myofibrils . The myosin forms the thick filaments, and actin forms the thin filaments, and are arranged in repeating units called sarcomeres . The interaction of both proteins results in muscle contraction. The sarcomere

4234-491: The nuclei present, while nuclei from resident and infiltrating mononuclear cells make up the other half. Considerable research on skeletal muscle is focused on the muscle fiber cells, the myocytes, as discussed in detail in the first sections, below. However, recently, interest has also focused on the different types of mononuclear cells of skeletal muscle, as well as on the endocrine functions of muscle, described subsequently, below. There are more than 600 skeletal muscles in

4307-612: The others. Most skeletal muscles in a human contain(s) all three types, although in varying proportions. Traditionally, fibers were categorized depending on their varying color, which is a reflection of myoglobin content. Type I fibers appear red due to the high levels of myoglobin. Red muscle fibers tend to have more mitochondria and greater local capillary density. These fibers are more suited for endurance and are slow to fatigue because they use oxidative metabolism to generate ATP ( adenosine triphosphate ). Less oxidative Type II fibers are white due to relatively low myoglobin and

4380-511: The process of somitogenesis the paraxial mesoderm is divided along the embryo 's length to form somites , corresponding to the segmentation of the body most obviously seen in the vertebral column . Each somite has three divisions, sclerotome (which forms vertebrae ), dermatome (which forms skin), and myotome (which forms muscle). The myotome is divided into two sections, the epimere and hypomere, which form epaxial and hypaxial muscles , respectively. The only epaxial muscles in humans are

4453-587: The properties of individual fibers—tend to be relevant and measured at the level of the motor unit, rather than individual fiber. Slow oxidative (type I) fibers contract relatively slowly and use aerobic respiration to produce ATP. Fast oxidative (type IIA) fibers have fast contractions and primarily use aerobic respiration, but because they may switch to anaerobic respiration (glycolysis), can fatigue more quickly than slow oxidative fibers. Fast glycolytic (type IIX) fibers have fast contractions and primarily use anaerobic glycolysis. The FG fibers fatigue more quickly than

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4526-433: The relatively constant cardiac output. More than 30 years before the development of the sliding filament model of muscle contraction and the understanding of the relationship between active tension and sarcomere length, Starling hypothesized in 1914, "the mechanical energy set free in the passage from the resting to the active state is a function of the length of the fiber." Starling used a volume-pressure diagram to construct

4599-463: The same functional purpose. Within the zebrafish embryo, the Prdm1 gene down-regulates the formation of new slow twitch fibers through direct and indirect mechanisms such as Sox6 (indirect). In mice, the Prdm1 gene is present but does not control slow muscle genes in mice through Sox6 . In addition to having a genetic basis, the composition of muscle fiber types is flexible and can vary with

4672-399: The same muscle volume, increasing the physiological cross-sectional area (PCSA). This effect is known as fiber packing, and in terms of force generation, it more than overcomes the efficiency-loss of the off-axis orientation. The trade-off comes in overall speed of muscle shortening and in the total excursion. Overall muscle shortening speed is reduced compared to fiber shortening speed, as is

4745-524: The size principal of motor unit recruitment viable. The total number of skeletal muscle fibers has traditionally been thought not to change. It is believed there are no sex or age differences in fiber distribution; however, proportions of fiber types vary considerably from muscle to muscle and person to person. Among different species there is much variation in the proportions of muscle fiber types. Sedentary men and women (as well as young children) have 45% type II and 55% type I fibers. People at

4818-432: The skeletal muscle cell for the large amounts of proteins and enzymes needed to be produced for the cell's normal functioning. A single muscle fiber can contain from hundreds to thousands of nuclei. A muscle fiber for example in the human biceps with a length of 10 cm can have as many as 3,000 nuclei. Unlike in a non-muscle cell where the nucleus is centrally positioned, the myonucleus is elongated and located close to

4891-526: The specific fiber type. In zebrafish embryos, the first muscle fibers to form are the slow twitch fibers. These cells will undergo migration from their original location to form a monolayer of slow twitch muscle fibers. These muscle fibers undergo further differentiation as the embryo matures. In larger animals, different muscle groups will increasingly require different fiber type proportions within muscle for different purposes. Turtles , such as Trachemys scripta elegans , have complementary muscles within

4964-401: The thin and thick filaments; for shorter sarcomere lengths, the cause is the decreased sensitivity for calcium by the myofilaments . An increase in filling of the ventricle increases the load experienced by each cardiac muscle cells, stretching their sarcomeres toward their optimal length. The stretching sarcomeres augments cardiac muscle contraction by increasing the calcium sensitivity of

5037-423: The total distance of shortening. All of these effects scale with pennation angle; greater angles lead to greater force due to increased fiber packing and PCSA, but with greater losses in shortening speed and excursion. Types of pennate muscle are unipennate , bipennate , and multipennate . A unipennate muscle has similarly angled fibers that are on one side of a tendon. A bipennate muscle has fibers on two sides of

5110-406: The transmission of force from muscle contraction to the skeletal system. Muscle architecture refers to the arrangement of muscle fibers relative to the axis of force generation , which runs from a muscle's origin to its insertion . The usual arrangements are types of parallel , and types of pennate muscle . In parallel muscles, the fascicles run parallel to the axis of force generation, but

5183-449: The various methods are mechanistically linked, while others are correlated in vivo . For instance, ATPase fiber type is related to contraction speed, because high ATPase activity allows faster crossbridge cycling . While ATPase activity is only one component of contraction speed, Type I fibers are "slow", in part, because they have low speeds of ATPase activity in comparison to Type II fibers. However, measuring contraction speed

5256-457: The work of the heart to skeletal muscle mechanics, Frank observed changes in diastolic pressure with varying volumes of the frog ventricle. His data was analyzed on a pressure-volume diagram, which resulted in his description of peak isovolumic pressure and its effects on ventricular volume. Starling experimented on intact mammalian hearts, such as from dogs, to understand why variations in arterial pressure, heart rate, and temperature do not affect

5329-478: Was the first to describe the relationship between the end-diastolic volume and the regulation of cardiac output. The first formulation of the law was theorized by the Italian physiologist Dario Maestrini , who on December 13, 1914, started the first of 19 experiments that led him to formulate the "legge del cuore" . Otto Frank's contributions are derived from his 1895 experiments on frog hearts. In order to relate

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