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UT Arlington BIOL 2457 - Mandibular joint- skeletal muscle tissue

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BIOL 2457 1st Edition Lecture 18Outline of Last Lecture The skeletal system: lower limb Outline of Current LectureSKELETAL SYSTEM: joints Temporomandibular Joint Combined hinge and planar joint formed by the mandible and the temporal bone Only movable joint between skull bones Only the mandible movesShoulder Joint  Ball-and-socket joint formed by the head of the humerus and the scapula More freedom of movement than any other joint of the bodyBursa a small fluid-filled sac lined by synovial membrane inner capillary layer of slimy synovial fluid highly innervated (very painful) reduces friction of soft tissue around a joint allows free movement found around most joints of the body  most common in feet called bunionsElbow Joint  Hinge joint formed by the humerus, the ulna, and the radiusHip Joint  Ball-and-socket joint formed by the femur and the hip boneKnee Joint Largest and most complex joint of the body Modified hinge jointAging  May result in decreased production of synovial fluid The articular cartilage becomes thinner Ligaments shorten and lose some of their flexibility Osteoarthritis is partially age-related Stretching and aerobic exercises are helpful in minimizing the effects of aging Help to maintain the effective functioning of ligaments, tendons, muscles, synovial fluid, and articular cartilageJoints  Joints may be replaced surgically with artificial joints Most commonly replaced are the hips, knees, and shoulders Hip Replacements Partial hip replacements involve only the femur Total hip replacements involve both the acetabulum and head of the femur Knee Replacements Actually a resurfacing of cartilage and may be partial or total Potential complications of arthroplasty include infection, blood clots, loosening or dislocation of the replacement components, and nerve injuryOverview of Muscular Tissues  Types of Muscular Tissue Skeletal Cardiac Smooth Skeletal Muscle Tissue So named because most skeletal muscles move bones Skeletal muscle tissue is striated: Alternating light and dark bands (striations) as seen when examined with a microscope Skeletal muscle tissue works mainly in a voluntary manner Its activity can be consciously controlled Most skeletal muscles also are controlled subconsciously to some extent Ex: the diaphragm alternately contracts and relaxes without conscious control Cardiac Muscle Tissue Found only in the walls of the heart Striated like skeletal muscle Action is involuntary Contraction and relaxation of the heart is not consciously controlled Contraction of the heart is autorhythmic and initiated by a node of tissue called the “pacemaker” Smooth Muscle Tissue Located in the walls of hollow internal structures Blood vessels, airways, and many organs Lacks the striations of skeletal and cardiac muscle tissue Usually involuntary Functions of Muscular Tissue Producing Body Movements Walking and running Stabilizing Body Positions Posture Moving Substances Within the Body Heart muscle pumping blood Moving substances in the digestive tract Generating heat Contracting muscle produces heat Shivering increases heat production Properties of Muscular Tissue Properties that enable muscle to function and contribute to homeostasis Excitability Ability to respond to stimuli Contractility Ability to contract forcefully when stimulated Extensibility Ability to stretch without being damaged Elasticity Ability to return to an original lengthSkeletal muscle tissue  Connective Tissue Components Fascia Dense sheet or broad band of irregular connective tissue that surrounds muscles Epimysium The outermost layer Separates 10-100 muscle fibers into bundles called fascicles Perimysium Surrounds numerous bundles of fascicles Endomysium Separates individual muscle fibers from one another Tendon Cord that attach a muscle to a bone Aponeurosis Broad, flattened tendon Nerve and Blood Supply Neurons that stimulate skeletal muscle to contract are somatic motor neurons The axon of a somatic motor neuron typically branches many times Each branch extending to a different skeletal muscle fiber Each muscle fiber is in close contact with one or more capillaries Microscopic Anatomy The number of skeletal muscle fibers is set before you are born Most of these cells last a lifetime Muscle growth occurs by hypertrophy An enlargement of existing muscle fibers Testosterone and human growth hormone stimulate hypertrophy Satellite cells retain the capacity to regenerate damaged muscle fibers Sarcolemma The plasma membrane of a muscle cell Transverse (T) tubules Connect the plasma membrane to the interior of the cell Muscle action potentials travel through the T tubules Ensure that action potential excites all parts of the muscle fiber at the same time Sarcoplasm, the cytoplasm of a muscle fiber Sarcoplasm includes glycogen used for synthesis of ATP anda red-colored protein called myoglobin which binds oxygen molecules Myoglobin releases oxygen when it is needed for ATP production Myofibrils Thread-like structures which have a contractile function Sarcoplasmic reticulum (SR) Membranous sacs which encircles each myofibril Stores calcium ions (Ca2+) Release of Ca2+ triggers muscle contraction Filaments Function in the contractile process Two types of filaments (Thick and Thin) There are two thin filaments for every thick filament Sarcomeres Compartments of arranged filaments Basic functional unit of a myofibril Z discs Separate one sarcomere from the next Thick and thin filaments overlap one another A band Darker middle part of the sarcomere Thick and thin filaments overlap I band Lighter, contains thin filaments but no thick filaments Z discs pass through the center of each I band H zone Center of each A band which contains thick but no thin filaments M line Supporting proteins that hold the thick filaments together in the H zone Muscle Proteins Myofibrils are built from three kinds of proteins Contractile proteins Generate force during contraction Regulatory proteins Switch the contraction process on and off Structural proteins Align the thick and thin filaments


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