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Chapter 6

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Natural Science
NATS 1610
Barbara Czaban

Living Body Notes: Chapter 6 -Muscular tissue is composed of cells called muscle fibers • Contractile (forcefully shorten in response to external stimulation) -3 Types of muscle • Skeletal: interacts with the skeleton to move the body (most of the body’s muscle tissue) (Voluntary) • Smooth: Walls of hollow organs and of tubes (EX. Blood Vessels) (Involuntary) • Cardiac: Found only in the heart and contracts without stimulation (No Control, Involuntary) -Skeletal Muscle Diagram (Major muscles in the body) PAGE 105 -Skeletal muscles are made up of bunches of myofibrils • Myofibrils: threadlike structures in a muscle fiber that contain the units of contraction • Tendons make joints more stable by keeping adjoining bones aligned • Fluid filled sacs called bursae help reduce the friction between bones • Tendon Sheaths: elongated bursae folded around the tendon (found in fingers, wrists, knees) -Origin: is attached to the bone and stays relatively motionless during movement -The other end of the muscle is the insertion -Motor neuron axons: in a nerve leading from spinal chord -Each basic unit of contraction is a sarcomere • Each myofibril is divided into bands o Dark bands are called Z bands (Mark the end of each sarcomere) o Filaments are arranged in overlapping array  Thick filaments: made of bundles of Myosin (tail and double head  Thin filaments: two strands of beads (Actin, tropomyosin, troponin) o everything runs the same way -Sliding filament mechanism: explains how interactions between thick and thin filaments allow muscle fibers to contract (cross bridge interaction between actin and myosin) • during a contraction all the myosin fibers stay in the same place o they use power strokes to slide actin filaments over them, toward sarcomere centre o each power stroke is powered by ATP • Rigor mortis: stiffness of death • At cross bridges, myosin filaments bind to actin filaments (requires calcium) • During contraction, cycles of myosin/actin unbinding and rebinding -Skeletal muscle contraction cycle 1. ATP binds to myosin head: myosin is energized 2. Energized myosin-ADP binds to actin: forming cross bridge binding, binding bwteen myosin and actin requires calcium 3. ADP and Pi are released and myosin head “swivels” towards centre of sarcomere (power stroke): actin filaments slides as head swivels back to previous conformation a. If more ATP is available, myosin releases actin as fresh ATP binds to myosin b. If no more ATP, myosin and actin do not detach (Rigor mortis) -Motor Neuron: carries commands to muscle fibers, travels to a muscle and issues signals that trigger or halt contraction of the sarcomeres in the muscle fibers • T Tub
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