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Muscle Contraction

Muscle Contraction. D escribe movement and maintenance of posture in terms of antagonistic muscle action. Gross and microscopic structure of skeletal muscle. The ultrastructure of a myofibril. The sliding-filament theory of muscle contraction.

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Muscle Contraction

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  1. Muscle Contraction Describe movement and maintenance of posture in terms of antagonistic muscle action. Gross and microscopic structure of skeletal muscle. The ultrastructure of a myofibril. The sliding-filament theory of muscle contraction. Muscles as effectors. The structure, location and general properties of slow and fast skeletal muscle fibres.

  2. Antagonistic muscle action • Muscles exert a pulling force when contracted but cannot push so an antagonistic (opposite) pair of muscles is needed e.g. biceps and triceps • Flexors- muscles that bend a limb • Extensors- muscles that straighten a limb • Isometric contraction- antagonistic muscles in the leg have to both contract a little to exert the right amount of tension to remain upright

  3. Skeletal muscle • Muscle attached to the bones of the body • Also known as voluntary muscle because the person has control over when these muscles are contracted and therefore when they bring about movement • Because of its appearance it is also know as striated or striped muscle

  4. Structure of skeletal muscle • Muscle fibre is surrounded by plasma membrane called the sarcolemma • Cytoplasm in muscle fibre is called sarcoplasm and contains many mitochondria • It is not made up of individual cells but is more like several cells joined together, so it has many nuclei • Myofibrils cause the muscle to appear striped

  5. The structure of a myofibril • Muscle fibres are made up of myofibrils • They contain two different types of filaments: • Thick filaments, myosin • Thin filaments, actin

  6. Sliding-filament theory • When muscles contract the myofibrils get shorter. This happens because the filaments slide over each other

  7. Slow and fast muscle fibres • Slow-twitch fibres- used during aerobic exercise such as long distance running. They appear red because they contain a lot of myoglobin which is a pigment that stores oxygen • Fast-twitch fibres- used for intensive, short length exercise such as sprinting. Are whiter because they contain much less myoglobin. They produce their ATP from anaerobic respiration

  8. Questions • What are skeletal muscles also know as? • What are the two different filaments myofibril contain? • Which of these is thick and which is thin? • Draw a quick diagram of the structure of a myofibril • Name two differences between slow-twitch and fast-twitch muscles • Why do we need antagonistic pairs of muscles?

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