MYOLOGY I. GROSS ANATOMY OF SKELETAL MUSCLEA. Comprised of fasciclesB. Each fascicle is made up of muscle fibers=muscle cells=myofiber C. Each skeletal muscle is an organD. Attachments = dense regular CT; 2 forms1. Tendons: cable like attachments2. Aponeuroses: sheet like attachmentsE. Connective Tissue Wrappings (all are the same type of tissue, names only denote location)1. Entire muscle (composed of fascicles) is surrounded by epimyseium (“on top of muscle tissue”)2. Each fascicle (group of muscle fibers) is surrounded by perimysium3. Each muscle fiber wrapped in endomysium II. MICROSCOPIC ANATOMY OF SKELETAL MUSCLEA. General Microscopic Structure1. Each fiber (cell) is composed of myofibrils2. Each myofibril is composed of myofilimentsa. thick myofilaments: contain the protein myosin (larger diameter)b. thin myofilaments: contain primarily the protein actin (smaller diameter) 3. Muscle cell membrane: sarcolemma (sarc= “muscle”)4. Cytoplasm: sarcoplasm5. It has cellular organelles like lysosomes, ribosomes, and endoplasmic reticulum (called sarcoplasmic reticulum)- Sarcoplasmic reticulum are very branched and smooth (SMOOTH ER)a. function of sarcoplasmic reticulum (SR): stores Calcium ions (Ca++) and releases these ions as needed for muscle contraction6. Transverse tubules (T-tubules)a. function: can conduct a nerve impulse rapidly to the interior of the muscle cell; these also act as a means of getting nutrients into the cell and waste products out. (bidirectional) B. Banding Pattern (Striation Pattern) of a Sarcomere (contractile unitof myofibril) when it is relaxed1. Light bands: I-bands (I - LIGHT)a. thin myofilaments only2. Dark bands: A-bands (A = DARK)a. thick and thin myofilaments 3. Z-line (Z-disc): dark line in the middle of an I-band (demarks a sarcomere)(essentially where the thin myofilaments attach)4. H-zone: a lighter, central region in the middle of an A-banda. only thick myofilaments5. Sarcomere - runs from Z-line to Z-line (functional contractile unit) Sarcomeres shorten during contraction III. CONTRACTION OF SKELETAL MUSCLEA. Sliding Filament Model of Contraction - Muscle stimulated by nerve - Thick and thin myofilaments slide over one another - Length of each sarcomere shortens, muscle contracts (myofilaments do NOT change length)1. Nerve impulse carried from brain/spinal cord to muscle by the axon of a motor neuron2. Axon meets muscle fiber at the neuromuscular junction (myoneural junction) 3. Axon releases a chemical neurotransmitter called acetylcholine which binds to sarcolemma4. A nerve impulse is generated in the sarcolemma and it passes down the T-tubules. As a result, the sarcoplasmic reticulum releases calcium ions (Ca++)5. Calcium ions (Ca++) bind to thin myofilaments a. This helps thick myofilaments attach to the thin myofilaments6. Myofilaments slide over one another; sarcomere shortens; muscle contracts7. When the nerve impulse stops, Ca++ returns to the sarcoplasmic reticulum and the myofilaments slide back to theirresting state Calcium ions are stored in the __________.a. Sarcolemmab. Transverse (T-) tubulesc. Sarcoplasmic reticulum*****d. Myofibrile.
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