EXPH 365 1st Edition Lecture 7 Skeletal Muscle structure and function3 types of muscle tissue- Cardiac (involuntary)- Smooth muscles (involuntary)- Skeletal muscle (voluntary)Skeletal muscle - Striated fibers with different structures and functions- Needed for movement- Strengthens jointsProperties- Extensibility and elasticity - Irritable (it responds)- Contractibility (can only PULL) (shorten)Muscle Organization- Muscle belly—big large central portion of muscle- Fascicles (bundles) big circles- Smaller circles are FIBERS—or muscle cell (myocytes), they are like threads, they are not round (hair like) - Myofibrils—rod-like strands that run entire length of muscle, where all the size change occursMuscle connective tissue- Tendono Fibrous cord that consists primarily of collagen o Attach muscle to bone- Fasciao Thickest sheet that covers muscle and divides muscle into different partso Provides protection- Epimysiumo Covers the bellyo Transfers force- Perimysiumo Covers muscle bundleso Keeps them in classo Pathway for blood and nerves- EndomysiumThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Covers muscle fiberso Pathway for capillaries and nerveso Insulator for neurological activity - Sarcolemma o Cell wall, very thino Underneath Endomysiumo Thin plasma membrane o Nervous stimulation penetrates through it as well as blood for nutrientsMuscle Fibers (cells)- Contained inside the sarcolemma- 1-3 inches long- Inside sarcolemma is nucleus (multinuclear) o Area that one nucleus controls is NUCLEAR DOMAIN- Mitochondria - Sarcoplasmic reticulum (SR)o Storage place for calcium—vital for muscle contraction- T-Tubules- Myofibrils- contractile proteinso Actin- THIN and lihgto Myosin-thick and darko Alterations of these make the muscle appear to be striped o SARCOMERE- functional unit of a muscle One unit of the actin/myosin bands Aligned in a series from z line to z line (flat disc)- Sarcoplasm – fluid inside cell - M line connects thick filaments- A band (anisotropic) - I band (Isotropic)- H zone (no contraction area)Sliding filament theory- How sarcomeres contract- Series of Eventso A nerve sends a chemical signal to muscle o The signal creates an electrical impulse (action potential) that travels around the entire sarcolemma and down the t-tubules (cannot penetrate sarcolemma because made of fatand fat doesn’t let electricity flow through)o The signal travels into the sarcoplasmic reticulum and calcium is releasedo The calcium opens up the binding sites on ACTINo Myosin binds to the sites and performs the power stroke causing the filaments to slide past each other  REQUIRES ATPo Cross bridge—actin and myosin join together and glide past each other  During muscle activation each cross bridge undergoes repeated but independentcycles of attachment and detachment to actin Takes thousands of times to shorten the sarcomere Z lines come closer together Actin