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Introduction to Muscle Anatomy Types of Muscle 1. Skeletal Longitudinal Cells View – Elongated – Multi nucleated Notice striations and nuclei – Striated – striped appearance around outside of cell. – Voluntary – Produces powerful contractions – Tires easily, needs rest (fatigue). Cross Section – Covers bony skeleton Notice nuclei (motility) around outside of cell. Skeletal Muscle Composite Sketch 2. Smooth – Spindle-shaped Cell – Single nucleus in each cell – No Striations – Involuntary – Slow, sustained contractions – In hollow visceral Cross organs Section (stomach, Nucleus is in center respiratory bladder, of cell. Cells much passages) smaller. Smooth Muscle Composite Sketch 3. Cardiac (Heart) – Branched cell – Contain intercalated discs – Single nucleus in each cell – Striations – Involuntary – Steady, constant contractions – Never tires Cardiac Muscle Composite Sketch Muscle Functions • Produce movement – locomotion & manipulation – Help blood move through veins & food thru small intestines • Maintain posture • Stabilize joints • Body temp homeostasis – Shivering: movement produces heat energy Axon of neuron Muscle Requirements Motor end plate (terminus) • Demands continuous oxygen/nutrient supply. – Lots of arteries/capillaries to muscle. • Each muscle cell w/ its own nerve ending controlling its activity. • Produce much metabolic waste due to constant activity. Muscle Attachments • Most muscles span joints • Attaches to bone in two places: (video) 1. Insertion: the moveable bone • Bicep insertion is the radius 2. Origin: the stationary bone • bicep originates in two different places in scapula • Attachment types 1. Direct: attaches right onto bone - ex. intercostal muscles of ribs 2. Indirect: via tendon or aponeurosis (sheet-like tendon) to connect to bone - leaves bone markings such as tubercle Muscle Organization Muscles are complex bundled structures: fibers within fibers Muscle organization Muscle (organ) Fascicle Muscle fiber (cell) Myofibril Sarcomere Myofilaments: Actin & Myosin Muscle Fibers • A Muscle Fiber = Muscle Cell • HUGE cell: – 10 - 100m in diameter – can be hundreds of centimeters long (created by cytoplasmic fusion of multiple embryonic cells) – extends the length of the muscle • Main content: bundles of proteins (actin and myosin) • Multinucleated – to maintain high rate of protein synthesis. – Muscle fiber nucleus = myonucleus Insulation of Muscles •Muscle cells must be insulated from one another by specialized membranes •Muscle cells work electrically – if not insulated, nerves cannot control individual muscles. • Epimysium surrounds entire muscle – Dense CT that merges with tendon – Epi = outer – Mys = muscle • Perimysium surrounds muscle fascicles – Peri = around – Within a muscle fascicle are many muscle fibers • Endomysium surrounds muscle fiber – Endo = within Structural Terminology Associated with Muscle Fibers Prefixes: myo, mys, and sarco all refer to muscle • Sarcoplasmic Reticulum = Smooth ER of muscle (regulates calcium levels for muscle contraction) • Sarcoplasm = Cytoplasm – To maintain ATP production during cellular respiration, contains high amounts of: • mitochondria • glycosomes that store sugar • oxygen binding protein called myoglobin • Sarcolemma = Plasma Membrane • T tubules - The sarcolemma of muscle cells are not just on the outside, rather forms tubes that dive into the muscle cells • Myosin and Actin= muscle proteins that create muscle cytoskeletal filaments for contraction myofibril Sarcoplasmic Reticulum T-tubule sarcolemma Myosin (red) and Actin (blue) Microstructures • Each muscle fiber (muscle cell), is composed of many myofibrils. – Organized system of cytoskeleton filaments of actin and myosin proteins that do the actual contracting – Myofibrils are NOT CELLS – A sarcomere is one segment of a myofibril (muscle segments). – The series of sarcomeres produce the striated appearance of muscles Muscle Fiber Sarcomere Sarcomere organization • Myofibril composed of repeating series of sarcomeres with dark A and light I bands. • I bands intersected by Z discs mark the outer edges of each sarcomere. • Contraction happens within one sarcomere. Sarcomere Banding Pattern How do muscle contract? Let’s sketch the sarcomere together and discuss the sliding filament model of muscle contraction
