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UMass Amherst BIOLOGY 152 - Muscles and Skeletons

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Lecture 12 Outline of Last Lecture a. Homeostasis continued i. Countercurrent b. Energy Requirements Outline of Current Lecture II. Types of Skeletons a. Hydrostatic Skeletons b. Exoskeletons c. Endoskeletons III. Muscle Cell Structure IV. Sliding Filament Model Current Lecture **Clicker Question** Which of these statements might be correct? • Answer = A whale sized snake would use less energy than a whale •reptiles have less body mass than mammals •so even if the snake and the whale were the same size, the whale would still use more energy because it is a mammal and has more body mass •the reptiles tend to fall below the line, and the mammals tend to fall along or above the line, so in general, at a given body mass is that reptiles would use less energy than mammals •A would be true if the statement was flipped (an elephant sized pigeon would use more energy than a pigeon sized elephant) •reptiles use less energy because they’re exothermic !Comparative Physiology of a Few Systems 1. muscles/skeletons 2. respiration/circulation 3. nervous system 4. maybe the immune system Bio 152 1!!!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !!!Muscles/Skeletons today Types of skeletons 1. hydrostatic 2. endoskeletons (humans/mammals) 3. exoskeletons (arthropods) !Hydrostatic Skeletons •the majority of animals rely on this type of skeleton •sea anemones •pods coming off the sea worm (and other invertebrates) •elephant trunk •human tongue •tube feet of sea urchins and sea stars •very limited for movement with large bodies •they’re good for movement in a lot of different directions, not as limited as the fixed skeleton because they don’t have to have joints •can’t lift as much weight in general •relies on the fact that water is not particularly compressible—can have a water filled tube circled with muscle and move it around easily !Exoskeletons •key innovation in arthropod ancestor •helped spectacular diversification •better protection: made of chitin (glucose/carbohydrate) •most important limitation = growth •organisms with exoskeletons must shed them when they want to get bigger (like the fruit fly) •when they molt, they are open to predation because of soft outside (exoskeleton provides protection) •can’t do continuous growth, must do it in stages •breaks are harder to repair, a cut in exoskeleton can lead to desiccation •can’t grow as big !Limits of an exoskeleton: •think of a cube •as the cube gets larger, the weight of it increases cubically •as the tube that supports it gets bigger, its ability to hold things only increases by the power of two (think of tube like a leg) •so as an ant gets bigger, the legs can’t support it •would need huge legs which would make it difficult to move !Endoskeletons •vertebrate endoskeleton: bones and joints •allow for continuous growth •relatively strong!•more limited in movement than hydrostatic but about the same as exoskeleton •bones, cartilage, tendons, ligaments •change in angles between bones is key to the movement •can be repaired easily •can support much larger organisms !Movement •muscles contract pulling on skeletal tissues •skeletal muscles tend to come in pairs •set of muscles that pulls bone one way when it contracts, and a set that pulls them the other way (flexor and extensor) •hydrostatic skeletons use a similar system but these muscles are either circular or longitudinal muscles !**Clicker Question** Against which incompressible structure do the circular and longitudinal muscles of earthworms work? •Answer = Hydrostatic skeleton !The hydrostatic skeleton is inside a worm, and they use bristles along the outside for traction. 2 sets of muscles (circular and longitudinal) work in a system •when they’re thin, the circular muscles are contracted and the diameter gets smaller and the organism gets thinner •when the longitudinal muscles are contracted, then the diameter increases and the organism gets wider (circular muscle relaxed) !**Clicker Question** If you were to disable the circular muscle contraction which stage would be impaired? •Answer = stage B (it also wouldn’t be able to move) !Muscle Cell Structure Types of muscles: •striated muscles — because of the striped pattern •skeletal: for movement •cardiac: heart •smooth: in charge of blood vessels, digestion and •A closer look at striated skeletal muscle •-bundle of muscle fibers composed of: •muscle fibers (single cells, multi nucleated) — have stem cells that grow together and keep all their nuclei and mitochondria •within this cell you have myofibril •Inside the myofibril •each myofibril is circled by the sarcoplasmic reticulum (loaded with calcium which leads to contraction but more on this later) •they are then broken down into sarcomeres •made up of mostly actin (thin filaments) and myosin (thick filaments)!•they are arrayed between 2 z discs or z-line !**Clicker Question** What is a muscle fiber? A. A single cell of a muscle B. A group of muscle cells that make up the same muscle group C. The myosin that makes up the contractile unit of a muscle cell D. The connective tissue outer covering of a muscle •Answer = A — muscle fiber is always a SINGLE CELL !Sarcomere organization Actin and myosin proteins actin makes thin filaments myosin (has head groups on it) and makes thick filaments myosin can bind to actin myosin uses ATP to make a “power stroke” !**Clicker Question** Myosin from a rabbit will bind to actin from an amoeba. Myosin from animals will even bind plant actin. What does this suggest about the evolution of the structures of actin and myosin? •The binding sides of actin and myosin are strongly conserved throughout evolution. !The Sliding Filament Model when the muscle contracts the thick filaments move along the thin filaments (actin) : the z-discs get closer together *movie showing rabbit muscle — adding ATP to the muscle causing it to contract The cycle of actin/myosin based contraction — the sliding filament model 1. Note when bound to ATP the affinity of actin is low, ATP binding causes the myosin to let go of the actin 2. ATP hydrolysis and ADP Pi still attached to the myosin — myosin has been phosphorylated here 3. Myosin ADP+Pi has high affinity for actin and


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UMass Amherst BIOLOGY 152 - Muscles and Skeletons

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