Since pennate fibers insert at an angle, the anatomical cross-sectional area cannot be used as in parallel fibered muscles. Instead, the physiological cross-sectional area (PCSA) must be used for pennate muscles. Pennate muscles can be further divided into uni-, bi- or multipennate. Fiber angle of a pennate muscle.
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PCSA increases with pennation angle, and with muscle length. In a pennate muscle, PCSA is always larger than ACSA. In a non-pennate muscle, it coincides with ACSA.
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Climacosphenia is a genus of marine pennate diatoms in the order Fragilariophyceae.
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Thalassionema nitzschioides is a type of phytoplankton belonging to the pennate diatom group.
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Climacosphenia elegans is a species of marine pennate diatoms in the order Fragilariophyceae.
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This is because the angle between the anatomical and physiological cross-section planes (angle between blue line and green line in figure 1) coincides with Φ, by definition. # ACSA of a non-pennate muscle with the same force as the pennate muscle.In a non- pennate muscle, ACSA = Muscle force / Specific tension, and Muscle force = PCSA2 × Specific tension, hence PCSA2 = Muscle force / Specific tension = ACSA. This implies that, in a muscle such as that in figure 1A, PCSA2 coincides with ACSA.
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Asterionella is a genus of pennate freshwater diatoms. They are frequently found in star-shaped colonies of individuals.
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The extensor digitorum longus is a pennate muscle, situated at the lateral part of the front of the leg.
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In a non-pennate muscle the fibers are parallel to the longitudinal axis, and therefore PCSA and ACSA coincide.
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Diatoms are mostly non-motile; however, sperm found in some species can be flagellated, though motility is usually limited to a gliding motion. In centric diatoms, the small male gametes have one flagellum while the female gametes are large and non-motile (oogamous). Conversely, in pennate diatoms both gametes lack flagella (isoogamous). Certain araphid species, that is pennate diatoms without a raphe (seam), have been documented as anisogamous and are, therefore, considered to represent a transitional stage between centric and raphid pennate diatoms, diatoms with a raphe.
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The muscle architecture of pennate muscles, such as the human quadriceps, is highly plastic and strongly influences contractile properties. Changes to pennate muscle architectural properties, such as pennation angle and thereby the PCSA, can alter the muscle’s force producing capabilities as well as the AGR at which the muscle operates. Parallelogram models predict that total PCSA of bipennate muscles increases in proportion to sin(θpennation) while total force exerted on the associated aponeurosis decreases with cos(θpennation). This theorizes that pennate muscle force generation increases until a 45 degree pennation angle is achieved.
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Blazevich et al. predict the increase in pennation angle seen after eccentric or concentric training allow the pennate muscle to attach more fibers to the associated aponeurosis as well as increase PCSA and AGR. Architectural modifications to pennate muscles shift the position at which the muscle operates on the force-velocity and force-length curves to regions best suited for the muscle’s function. An increase in pennation angle theoretically increases both the PCSA and AGR of a given pennate muscle, allowing the muscle to generate higher forces while operating at higher optimal speeds.
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If all the fascicles are on the same side of the tendon, the pennate muscle is called unipennate (Fig. 1A). Examples of this include certain muscles in the hand. If there are fascicles on both sides of the central tendon, the pennate muscle is called bipennate (Fig. 1B). The rectus femoris, a large muscle in the quadriceps, is typical.
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Fragilariopsis kerguelensis, is a pennate diatom native to the Southern Ocean. It has been characterized as "the most abundant diatom in the Antarctic Seas".
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If the central tendon branches within a pennate muscle, the muscle is called multipennate (Fig. 1C), as seen in the deltoid muscle in the shoulder.
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Frontiers in microbiology, 8: 1239. . 50px Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Selections from Ernst Haeckel's 1904 Kunstformen der Natur (Art Forms of Nature), showing pennate (left) and centric (right) frustules. Diatoms are divided into two groups that are distinguished by the shape of the frustule: the centric diatoms and the pennate diatoms.
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Fragilaria gracilis is a species of freshwater pennate diatoms. F. gracilis is reported from many parts of Europe, in Sweden even as one of the dominant freshwater diatom taxa.
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This is more often observed in freshwater and pennate diatoms like Pseudo- nitzschia. There is contradictory evidence regarding the presence or absence of a resting stage in Pseudo-nitzschia.
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The pennation angle of the rotator cuff myofibers, the angle at which fibers connect to the associated tendon, affects the contractile properties and function of the whole pennate muscle. For example, the pennation angle determines the architectural gear ratio at which a pennate muscle operates. A large initial pennation angle results in a large AGR and velocity amplification. A 2011 study on human cadaveric shoulders suggests tendon tears may affect the pennation angle of the rotator cuff muscles.
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Golden skiffia's numbers were dramatically reduced within a year, likely due to competition from X. maculatus. Golden skiffia is likely a benthic feeder, as indicated by gut contents dominated by pennate diatoms.
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Unlike in parallel muscles, pennate fibers are at an angle to the force-generating axis (pennation angle) and usually insert into a central tendon. Because of this structure, fewer sarcomeres can be found in series, resulting in a shorter fiber length. This further allows for more fibers to be present in a given muscle; however, a trade-off exists between the number of fibers present and force transmission. The force produced by pennate muscles is greater than the force produced by parallel muscles.
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Nitzschia is a common pennate marine diatom. In the scientific literature, this genus, named after Christian Ludwig Nitzsch, is sometimes termed Nitzchia, and it has many species described, which all have a similar morphology.
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Fragilariopsis cylindrus is a pennate sea-ice diatom that is found native in the Argentine Sea and Antarctic waters, with a pH of 8.1-8.4. It is regarded as an indicator species for polar water.
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2 The model results show the more a muscle bulges in dorsoventral height, the further the muscle fibers shorten, therefore providing a higher Architectural gear ratio. In pennate muscles, segments with higher pennation angles put out less force per shortening muscle fiber. Therefore, the architectural gear ratio of a pennate muscle is higher than the architectural gear ratio of spindle like muscles (e.g. fusiform). A smaller fiber length neutralizes this higher architectural gear ratio if the muscle fibers must be squeezed into the same space.
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The third type of pennate subgroup is known as the multipennate architecture. These muscles, such as the deltoid muscle in the shoulder of humans, have fibers that are oriented at multiple angles along the force-generating axis.
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Figure 1 Pennate muscle fiber arrangements: A, unipennate; B, bipennate; C, multipennate In muscle tissue, 10-100 endomysium- sheathed muscle fibers are organized into perimysium-wrapped bundles known as fascicles. Each muscle is composed of a number of fascicles grouped together by a sleeve of connective tissue, known as an epimysium. In a pennate muscle, aponeuroses run along each side of the muscle and attach to the tendon. The fascicles attach to the aponeuroses and form an angle (the pennation angle) to the load axis of the muscle.
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Figure 1 Pennate muscle fiber arrangements. The green lines represent PCSA; the blue lines represent ACSA In muscle physiology, physiological cross- sectional area (PCSA) is the area of the cross section of a muscle perpendicular to its fibers, generally at its largest point. It is typically used to describe the contraction properties of pennate muscles.Strength and cross-sectional area of human skeletal muscle It is not the same as the anatomical cross-sectional area (ACSA), which is the area of the crossection of a muscle perpendicular to its longitudinal axis.
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Fluxes are in T mol Si y−1 (28 million metric tons of silicon per year) Pennate diatom from an Arctic meltpond, infected with two chytrid-like [zoo-]sporangium fungal pathogens (in false-colour red). Scale bar = 10 µm.
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The apex of the lamina is acuminate-obtuse and often unequal. The base of the lamina is attenuate, amplexicaul, and often decurrent. Three longitudinal veins run along the lamina on each side of the midrib. Pennate veins are indistinct.
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Pennate veins are inconspicuous. Tendrils are very short and stiff, rarely exceeding 4 cm in length. Unlike most other species in the genus, N. campanulata produces only one type of pitcher. As the specific epithet suggests, these are campanulate or bell- shaped.
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Pennate muscles, in which the muscle fibers are oriented at an angle to the line of action, typically have two aponeuroses. Muscle fibers connect one to the other, and each aponeurosis thins into a tendon which attaches to bone at the origin or insertion site.
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Like tendons, aponeuroses attached to pennate muscles can be stretched by the forces of muscular contraction, absorbing energy like a spring and returning it when they recoil to unloaded conditions. Also serving as an origin or insertion site for certain muscles e.g latissimus dorsi.
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In most muscles, all the fibers are oriented in the same direction, running in a line from the origin to the insertion. However, In pennate muscles, the individual fibers are oriented at an angle relative to the line of action, attaching to the origin and insertion tendons at each end. Because the contracting fibers are pulling at an angle to the overall action of the muscle, the change in length is smaller, but this same orientation allows for more fibers (thus more force) in a muscle of a given size. Pennate muscles are usually found where their length change is less important than maximum force, such as the rectus femoris.
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In most muscles, all the fibers are oriented in the same direction, running in a line from the origin to the insertion. In pennate muscles, the individual fibers are oriented at an angle relative to the line of action, attaching to the origin and insertion tendons at each end. Because the contracting fibers are pulling at an angle to the overall action of the muscle, the change in length is smaller, but this same orientation allows for more fibers (thus more force) in a muscle of a given size. Pennate muscles are usually found where their length change is less important than maximum force, such as the rectus femoris.
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Bundles of muscle fibers, called fascicles, are covered by the perimysium. Muscle fibers are covered by the endomysium. The gross anatomy of a muscle is the most important indicator of its role in the body. There is an important distinction seen between pennate muscles and other muscles.
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Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the raphes and their shells are typically elongated parallel to these raphes. They generate cell movement through cytoplasm that streams along the raphes, always moving along solid surfaces. Centric diatoms are radially symmetric.
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Architectural gear ratio, also called anatomical gear ratio, (AGR) is a feature of pennate muscle defined by the ratio between the longitudinal strain of the muscle and muscle fiber strain. It is sometimes also defined as the ratio between muscle-shortening velocity and fiber-shortening velocity: AGR = εx/εf where εx = longitudinal strain (or muscle-shortening velocity) and εf is fiber strain (or fiber-shortening velocity). It was originally thought that the distance between aponeuroses did not change during the contraction of a pennate muscle, thus requiring the fibers to rotate as they shorten. However, recent work has shown this is false, and that the degree of fiber angle change varies under different loading conditions.
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Since the position of the large nucleus (dinokaryon), shape of the eye spot, and the number and shape of chloroplasts may vary among species, the most reliable method of identification is to observe tabulation pattern of thecal plate. The most interesting feature of Durinskia is the presence of its tertiary plastid which originated from a pennate diatom. Durinskia’s tertiary plastid is sometimes confused with the tertiary plastid in Peridiniopsis penardii, which originated from a centric diatom since both plastids have four membranes. As a reminder, a plastid is an endosymbiont that has been incorporated into the host as an essential organelle, and a pennate diatom is elongated in valve view whereas a centric diatom is circular.
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The servomotor can be programmed to maintain a given force while allowing the muscle to change length, vice versa, or the muscle may be subject to more complex testing, such as in work loops. When pennate muscles are used, sonomicrometry is often used to accurately determine fiber length during the test.
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Pennate diatom from an Arctic meltpond, infected with two chytrid-like [zoo-]sporangium fungal pathogens (in false-colour red). Scale bar = 10 µm. 50px Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Marine fungi have been observed as far north as the Arctic Ocean.
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Aagaard P, Andersen J, Dyhre-Poulsen P, Leffers A, Wagner A, Magnusson SP, Halkjaer-Kristensen J, Simonsen E. A mechanism for increased contractile strength of human pennate muscle in response to strength training: changes in muscle architecture. J of Physiol. 2001, 534.2: 613-623. A 2001 study, conducted by Aagaard et al.
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The lamina has indistinct longitudinal veins and numerous pennate veins. Tendrils may be up to 60 cm long and 8 mm wide. They are hollow and swollen near the pitcher. Lower pitchers Although most parts of the plant are very large, the pitchers themselves do not rival those of species such as N. rajah.
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The rotator cuff comprises four pennate muscles, the supraspinatus, infraspinatus, subscapularis and teres minor, and their accompanying tendons. These muscles form a cuff around the glenohumeral joint and function to stabilize and manipulate the shoulder.Zuo J, Sano H, Itoi E. Changes in pennation agnle in rotator cuff muscles with torn tendons. J Orthop Sci. 2011.
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Pseudo-nitzschia species are bilaterally symmetrical Pennate diatoms. Cell walls are made up of elongated silica frustules. The silica wall is fairly dense which leads to negative buoyancy, providing a number of advantages. The wall allows the diatoms to sink to avoid light inhibition or nutrient limitations, as well as to protect against grazing zooplankton.
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A pennate or pinnate muscle (also called a penniform muscle) is a muscle with fascicles that attach obliquely (in a slanting position) to its tendon. These types of muscles generally allow higher force production but smaller range of motionFrederick H. Martini, Fundamentals Of Anatomy And Physiology . When a muscle contracts and shortens, the pennation angle increases.
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This plant can show heterophylly: upper leaves can be different from lower leaves. The blade can be more or less elongated, from rounded to lanceolate, with crenate margin. At the base of the petiole there are stipules (5–15 mm long) of various form, from linear and entire stipules to stipules divided in many linear segments, pennate or palmate.
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While the muscle fibers of a fascicle lie parallel to one another, the fascicles themselves can vary in their relationship to one another and to their tendons. The different fiber arrangements produce broad categories of skeletal muscle architectures including longitudinal, pennate, unipennate, bipennate, and multipennate.Lieber, Richard L. (2002) Skeletal muscle structure, function, and plasticity. Wolters Kluwer Health.
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It is not known if P. tricornutum can reproduce sexually. To date no substantial evidence has been found to support sexual reproduction in a laboratory or other setting. Although P. tricornutum can be considered to be an atypical pennate diatom it is one of the main diatom model species. A transformation protocol has been established and RNAi vectors are available.
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Diatomaceous earth as viewed under bright field illumination on a light microscope. This image consists of a mixture of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms suspended in water. The scale is 6.236 pixels/μm, the image is 1.13 by 0.69 mm. Diatoms, and their shells (frustules) as diatomite or diatomaceous earth, are important industrial resources used for fine polishing and liquid filtration.
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One advantage of pennate muscles is that more muscle fibers can be packed in parallel, thus allowing the muscle to produce more force, although the fiber angle to the direction of action means that the maximum force in that direction is somewhat less than the maximum force in the fiber direction. C. Gans (1982). Fiber architecture and muscle function. Exercise & Sports Science Reviews. 10:160–207.
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Muscle architecture is the physical arrangement of muscle fibers at the macroscopic level that determines a muscle’s mechanical function. There are several different muscle architecture types including: parallel, pennate and hydrostats. Force production and gearing vary depending on the different geometries of the muscle. Some parameters used in architectural analysis are muscle length (Lm), fiber length (Lf), pennation angle (θ), and physiological cross-sectional area (PCSA).
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Parallel and pennate (also known as pinnate) are two main types of muscle architecture. A third subcategory, muscular hydrostats, can also be considered. Architecture type is determined by the direction in which the muscle fibers are oriented relative to the force-generating axis. The force produced by a given muscle is proportional to the cross-sectional area, or the number of parallel sarcomeres present.
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This would reduce the force producing capacity of these muscles. However, partial tendon tears, which did not result in a change to pennation in any of the rotator cuff muscles, may not impair the force producing properties of the muscles. Azizi’s observations on variable gearing in pennate muscles further suggests tendon tears will affect the AGR of the supraspinatus and infraspinutus. The greater pennation angle could result in an increased AGR.
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For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (Centrales and Pennales). This classification was extensively overhauled by Round, Crawford and Mann in 1990 who treated the diatoms at a higher rank (division, corresponding to phylum in zoological classification), and promoted the major classification units to classes, maintaining the centric diatoms as a single class Coscinodiscophyceae, but splitting the former pennate diatoms into 2 separate classes, Fragilariophyceae and Bacillariophyceae (the latter older name retained but with an emended definition), between them encompassing 45 orders, the majority of them new. Today (writing at mid 2020) it is recognised that the 1990 system of Round et al. is in need of revision with the advent of newer molecular work, however the best system to replace it is unclear, and current systems in widespread use such as AlgaeBase, the World Register of Marine Species and its contributing database DiatomBase, and the system for "all life" represented in Ruggiero et al.
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The DCM of clear, stratified water is commonly found below the epilimnion. Lake Superior is one of the world's largest freshwater lakes, and in the summer, its DCM ranges from approximately 20 m to 35 m below the surface. Although the epilimnion and DCM are neighbouring layers of water, the species composition of the epilimnion and the DCM differ almost entirely. These differences include the presence of less centric diatoms, more pennate diatoms, cryptophytes, and pyrrophytes at the DCM compared to the epilimnion layer.
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These structures demonstrated pores of sizes characteristic to diatom patterns. When T. pseudonana underwent genome analysis it was found that it encoded a urea cycle, including a higher number of polyamines than most genomes, as well as three distinct silica transport genes. In a phylogenetic study on silica transport genes from 8 diverse groups of diatoms, silica transport was found to generally group with species. This study also found structural differences between the silica transporters of pennate (bilateral symmetry) and centric (radial symmetry) diatoms.
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Pseudo-nitzschia australis is a pennate diatom found in temperate and sub- tropic marine waters, such as off the coast of California and Argentina. This diatom is a Harmful Micro Algae that produces toxic effects on a variety of organisms through its production of domoic acid, a neurotoxin. Toxic effects have been observed in a variety of predatory organisms such as pelicans, sea lions, and humans. If exposed to a high enough dose, these predators will die as a result, and there is no known antidote.
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Durinskia is a genus of dinoflagellate that can be found in freshwater and marine environments. This genus was created to accommodate its type species, Durinskia baltica, after major classification discrepancies were found. While Durinskia species appear to be typical dinoflagellates that are armored with cellulose plates called theca, the presence of a pennate diatom-derived tertiary endosymbiont is their most defining characteristic. This genus is significant to the study of endosymbiotic events and organelle integration since structures and organelle genomes in the tertiary plastids are not reduced.
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The leaves are alternate and pennate (15 to 20 cm long). The flattened petiole is edged by two rows of 25–30 tiny oval leaflets; the leaflets are soon deciduous in dry weather (and during the winter in some areas) leaving the green petioles and branches to photosynthesize. The branches grow double or triple sharp spines long at the axils of the leaves. The flowers are yellow- orange and fragrant, in diameter, growing from a long slender stalk in groups of eight to ten.
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Muscles contain many different systems on which the evolutionary selection of preflex stabilization can operate. The deltoid muscle, for example, consists of at least seven segments with different bone attachments and neural control. Within each muscle segment, there exists a complex internal structure that goes down to one in which each muscle unit consists of a tendon, aponeurosis, and a fascicle of active contractile and passive elements. Another source of variation is in the internal architecture of the fiber orientation relative to a muscle’s line of action, for example, as found in pennate muscles.
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The amoeboid cells of the former combine to form a giant multinucleate organism, while the cells of the latter live separately until food runs out, at which time the amoebae aggregate to form a multicellular migrating "slug" which functions as a single organism. Other organisms may also present amoeboid cells during certain life-cycle stages, e.g., the gametes of some green algae (Zygnematophyceae) and pennate diatoms, the spores (or dispersal phases) of some Mesomycetozoea,Taylor, J. W. & Berbee, M. L. (2014). Fungi from PCR to Genomics: The Spreading Revolution in Evolutionary Biology.
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Most centric and araphid pennate diatoms are nonmotile, and their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on turbulent mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or the ability to grow in colonial chains. These adaptations increase their surface area to volume ratio and drag, allowing them to stay suspended in the water column longer.
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Diatomaceous earth is a soft, siliceous, sedimentary rock made up of microfossils in the form of the frustules (shells) of single cell diatoms. This sample consists of a mixture of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms. This image of diatomaceous earth particles in water is at a scale of 6.236 pixels/μm, the entire image covers a region of approximately 1.13 by 0.69 mm. Microfossils are fossils that are generally between 0.001mm and 1 mm in size, the study of which requires the use of light or electron microscopy.
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Individual cells may regulate buoyancy via an ionic pump. Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive mucilage secreted through the raphe (an elongated slit in the valve face). In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to. Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; mucilage pads, stalks or tubes; amorphous masses of mucilage; or by threads of chitin (polysaccharide), which are secreted through strutted processes of the cell.
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Diatoms have two distinct shapes: a few (centric diatoms) are radially symmetric, while most (pennate diatoms) are broadly bilaterally symmetric. A unique feature of diatom anatomy is that they are surrounded by a cell wall made of silica (hydrated silicon dioxide), called a frustule. These frustules have structural coloration due to their photonic nanostructure, prompting them to be described as "jewels of the sea" and "living opals". Movement in diatoms primarily occurs passively as a result of both water currents and wind-induced water turbulence; however, male gametes of centric diatoms have flagella, permitting active movement for seeking female gametes.
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It was first noticed that these flies carried "nuptial gifts" of silk by Baron Karl von Osten-Sacken. Empididae show diverse mating systems, ranging from species in which males aggregate in mating swarms, and compete for choosing females to sex-role reversed species in which females do aggregate and compete for the attention of choosing males. In some species, such as the North American species Rhamphomyia longicuada, competition for the food provided by males is so strong that females have developed elaborate ornaments, including feathery "pennate" scales on their legs, darkened wings, and inflatable abdominal sacs that enhance their attractiveness.
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One proposal, by Linda Medlin and co-workers commencing in 2004, is for some of the centric diatom orders considered more closely related to the pennates to be split off as a new class, Mediophyceae, itself more closely aligned with the pennate diatoms than the remaining centrics. This hypothesis—later designated the Coscinodiscophyceae-Mediophyceae- Bacillariophyceae, or Coscinodiscophyceae+(Mediophyceae+Bacillariophyceae) (CMB) hypothesis—has been accepted by D.G. Mann among others, who uses it as the basis for the classification of diatoms as presented in Adl. et al.'s series of syntheses (2005, 2012, 2019), and also in the Bacillariophyta chapter of the 2017 Handbook of the Protists edited by Archibald et al.
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There has been little use of domoic acid throughout history except for in Japan, where it has been used as an anthelmintic for centuries. Domoic acid was first isolated in 1959 from a species of red algae, Chondria armata, in Japan; commonly referred to as "doumoi" (in Tokunoshima's dialect word) or "hanayanagi". Poisonings in history have been rare, or undocumented; however, it is thought that the increase in human activities is resulting in an increasing frequency of harmful algal blooms along coastlines in recent years. In 2015, the North American pacific coast was heavily impacted by an algal bloom, consisting predominantly of the domoic acid producing pennate diatom, Pseudo-nitzschia.
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Pseudo-nitzschia is a marine planktonic diatom genus that accounts for 4.4% of pennate diatoms found worldwide. Some species are capable of producing the neurotoxin domoic acid (DA), which is responsible for the neurological disorder in humans known as amnesic shellfish poisoning (ASP). Currently, 57 species are known, 27 of which have been shown to produced DA. It was originally hypothesized that only dinoflagellates could produce harmful algal toxins, but a deadly bloom of Pseudo-nitzschia occurred in 1987 in the bays of Prince Edward Island, Canada, and led to an outbreak of ASP. Over 100 people were affected by this outbreak after consuming contaminated mussels; three people died.
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In humans, the soleus is a complex, multi-pennate muscle, usually having a separate (posterior) aponeurosis from the gastrocnemius muscle. A majority of soleus muscle fibers originate from each side of the anterior aponeurosis, attached to the tibia and fibula. Other fibers originate from the posterior (back) surfaces of the head of the fibula and its upper quarter, as well as the middle third of the medial border of the tibia. The fibers originating from the anterior surface of the anterior aponeurosis insert onto the median septum and the fibers originating from the posterior surface of the anterior aponeurosis insert onto the posterior aponeurosis.
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These sites were hypothesized to be a focal region for delivery of tension during muscle contraction. To test the possibility of tensile force transmission via the perimysium, it was experimentally shown that cutting of the aponeurosis in a pennate muscle did not prevent tension generation further along towards the tendon. Also, in a separate study it was clearly demonstrated that the perimysium could transmit force if tendons normally transmitting force from distinct parts of the extensor digitorum longus muscle were cut. Although a lot of evidence may seem to point to lateral force transmission via the perimysium in tension, the experiments were conducted at very high loads.
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In 2004, the entire genome of the centric diatom, Thalassiosira pseudonana (32.4 Mb) was sequenced, followed in 2008 with the sequencing of the pennate diatom, Phaeodactylum tricornutum (27.4 Mb). Comparisons of the two reveal that the P. tricornutum genome includes fewer genes (10,402 opposed to 11,776) than T. pseudonana; no major synteny (gene order) could be detected between the two genomes. T. pseudonana genes show an average of ~1.52 introns per gene as opposed to 0.79 in P. tricornutum, suggesting recent widespread intron gain in the centric diatom. Despite relatively recent evolutionary divergence (90 million years), the extent of molecular divergence between centrics and pennates indicates rapid evolutionary rates within the Bacillariophyceae compared to other eukaryotic groups.
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For these obliquely oriented fibers the strain in the longitudinal direction is greater than the strain in the muscle fiber direction leading to an architectural gear ratio greater than 1. A higher initial angle of orientation and more dorsoventral bulging produces a faster muscle contraction but results in a lower amount of force production. It is hypothesized that animals employ a variable gearing mechanism that allows self-regulation of force and velocity to meet the mechanical demands of the contraction. When a pennate muscle is subjected to a low force, resistance to width changes in the muscle cause it to rotate which consequently produce a higher architectural gear ratio (AGR) (high velocity).
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These fibers are organized into cone-shaped structures and attach to connective tissue sheets known as myosepta; each fiber shows a characteristic dorsoventral (α) and mediolateral (φ) trajectory. The segmented architecture theory predicts that, εx > εf. This phenomenon results in an architectural gear ratio, determined as longitudinal strain divided by fiber strain (εx / εf), greater than one and longitudinal velocity amplification; furthermore, this emergent velocity amplification may be augmented by variable architectural gearing via mesolateral and dorsoventral shape changes, a pattern seen in pennate muscle contractions. A red-to-white gearing ratio (red εf / white εf) captures the combined effect of the longitudinal red muscle fiber and oblique white muscle fiber strains.
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Flagellated lifecycle stages are found in many groups, e.g., many green algae (zoospores and male gametes), bryophytes (male gametes), pteridophytes (male gametes), some gymnosperms (cycads and Ginkgo, as male gametes), centric diatoms (male gametes), brown algae (zoospores and gametes), oomycetes (assexual zoospores and gametes), hyphochytrids (zoospores), labyrinthulomycetes (zoospores), some apicomplexans (gametes), some radiolarians (probably gametes), foraminiferans (gametes), plasmodiophoromycetes (zoospores and gametes), myxogastrids (zoospores), metazoans (male gametes), and chytrid fungi (zoospores and gametes). Flagella or cilia are completely absent in some groups, probably due to a loss rather than being a primitive condition. The loss of cilia occurred in red algae, some green algae (Zygnematophyceae), the gymnosperms except cycads and Ginkgo, angiosperms, pennate diatoms, some apicomplexans, some amoebozoans, in the sperm of some metazoans, and in fungi (except chytrids).
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A 2009 study utilizing magnetic resonance imaging and ultrasonography discovered strain and pennation angle heterogeneity within the medial gastrocnemius pennate muscle during differing modes of contraction. Parameters of fascicle location and contraction type (eccentric or passive), determined the magnitude of strain experienced by differing regions of the MG. Fascicle ends nearest the deep MG aponeurosis (Achilles tendon) showed an increase in strain from the proximal to distal portions of the MG muscle. The converse was seen in the fascicle ends adjacent to the superficial aponeurosis, which decreased in fiber strain from proximal to distal portions of the MG muscle. These trends may have been due to changes in CSA of the muscle at the proximal and distal ends of the MG, resulting in regions of high stress and strain concentration.
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First, the grasshopper fully flexes the lower part of the leg (tibia) against the upper part (femur) by activating the flexor tibiae muscle (the back legs of the grasshopper in the top photograph are in this preparatory position). Second, there is a period of co-contraction in which force builds up in the large, pennate extensor tibiae muscle, but the tibia is kept flexed by the simultaneous contraction of the flexor tibiae muscle. The extensor muscle is much stronger than the flexor muscle, but the latter is aided by specialisations in the joint that give it a large effective mechanical advantage over the former when the tibia is fully flexed. Co-contraction can last for up to half a second, and during this period the extensor muscle shortens and stores elastic strain energy by distorting stiff cuticular structures in the leg.
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