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
View Full Document