Muscle & Muscle Tissue
Types of Muscle Tissue Skeletal Are striated Controlled voluntarily Tires easily
Types of Muscle cont. Smooth Walls of visceral organs Force fluids through internal channels Not voluntary Not striated
Cardiac Found only in the heart Striated Not voluntary
Muscle structure Made up of 4 connective tissue Epimysium Fascicle Perimysium Endomysium
Gross Anatomy of a Skeletal Muscle Epimysium Outermost layer Connective tissue surrounding the entire muscle tapers at end to form tendon
Fascicle Inside the muscle are discrete areas of muscle tissue
Perimysium Connective tissue surrounding each fascicle
Endomysium Thin connective tissue surrounding each muscle fiber (cell) Smallest unit of muscle visible without a microscope
Skeletal Muscle Muscles always contract actively Can extend only passively Ability to move a bone part in opposite directions requires that muscles be attached to the skeleton Tire easily Bundle of long fibers running the length of the muscle Each fiber is a single cell with many nuclei & consists of bundles of smaller myofibrils arranged longitudinally
Muscle Fiber Single muscle cell Cylindrical in structure Surrounded by membrane capable of excitation & impulse propagation Contains muscle fiber bundles called myofibrils
Sarcolemma Delicate sheath (cell membrane) Made up of lipid molecules Transport nutrients & synthesizes proteins Sodium/potassium pump Maintain shape of muscle cell
Sarcoplasm Aqueous substance – cytoplasm Surrounds myofibrils House the mitochondria Houses blood vessels, glycogen & nerve endings
Myofibrils Fibers functional unit Threadlike structure within muscle fiber Contains sarcomeres at intervals Made up of 2 protein fibers – microfilaments
Sarcoplasmic Reticulum Specialized endoplasmic reticulum Function is to store calcium and release it on demand when a muscle fiber is stimulated to contract Initiates muscle contraction at the sarcomere
Sarcomere Segment of myofibril Composed of 2 contractile proteins Actin Myosin Sarcomeres are separated by Z lines
Sarcomere Has a dark band – A band The A band has light zone called the H band (this disappears when contracted) Center of the H band is the M line
Sarcomere I band contains Actin Length varies with the start of muscle contraction
Myofilaments Protein fibers Composed of 2 filaments Actin – thin Myosin - thick Divided into bands which alternate light and dark
Thick filaments A bands are dark areas Dark areas represent thick filaments 2 thick filament dark areas are connected by the M line Consist of myosin & ATPase Enzyme splits ATP to generate the power of muscle contractions
Thin filaments I band Light areas contain thin filaments Made up of actin, troponin and tropomyosin