Muscular System: Structure of Skeletal Muscle PDF

# Muscular System: Structure of Skeletal Muscle **CN 12, Plate 24, see also 7** **1.** Color (b) and (c) the same color. Note that the myofibrils (1), seen in full length as well as in cross sections of the muscle belly, receive the same color as the A band in the diagram below. The large arrow be...

# Muscular System: Structure of Skeletal Muscle **CN 12, Plate 24, see also 7** **1.** Color (b) and (c) the same color. Note that the myofibrils (1), seen in full length as well as in cross sections of the muscle belly, receive the same color as the A band in the diagram below. The large arrow below the myofibril points to the magnified view of the myofibril showing its various bands and lines. **2.** Color the diagrams below, describing the contraction of the myofibrils. Note that the H band (h) falls in the center of the A band and is colored separately. Note also that the Z line (l) falls in the center of the I band and is colored separately. **3.** Note that the sarcomere (*) and its arrows are to be colored gray. ## Diagram of Skeletal Muscle **Tendon** **Epimysium (Muscle Belly)** **Perimysium (Fascicle)** **Endomysium (Muscle Fiber)** **Myofibril** **I Band** **A Band** **H Band** **Sarcomere** **Z Line** **Actin** **Myosin** **Cross Bridges** ## Diagram of Sarcomere **I band** **A band** **I band** **Z line** **Z line** **Z line** **Sarcomere** * * * ## Skeletal muscle structure A skeletal muscle consists of bundles (fascicles) of muscle cells (fibers) each wrapped in their connective tissue sheath (epimysium, perimysium, endomysium, respectively). As the skeletal muscle approaches its attachment site, the muscle fibers end; and connective tissue continues on as the tendon. A muscle cell consists of several nuclei administering a mass of myofibrils in the cytoplasm (sarcoplasm) within boundaries of a cell membrane (sarcolemma). Myofibrils have been shown to be a collection of myofilaments arranged in a pattern. The basic unit of this pattern is the sarcomere (*). Within the sarcomere, the dark and light areas are called bands (I, A, H), and these are created by the relative arrangements of the filaments actin (k) and myosin (L). When a skeletal muscle fiber contracts, the actin filaments within a sarcomere slide toward each other, past the myosin filaments, breaking and remaking cross bridges. The myosin filaments do not move. Therefore, one would expect the A bands to have a constant length during contraction, while the I and H bands would shorten. In this way, the Z lines are brought closer together, and the overall muscle cell length shortens by about one-third of its resting length. * * * # Neuromuscular Junction Biochemical Pathway ## Diagram of Neuromuscular Junction **Neuron** **Muscle** **Muscle Fiber** **Synaptic Cleft** **Space or Gap** **Muscle End Plate** **(with ACh receptors)** **Neuron (Cell)** **Synaptic Vesicle (organelle)** **Neurotransmitter Acetylcholine (ACh)** **Nerves** **Muscle** **Opening of T. Tubule** **Muscle Fiber** **Myofibril (organelle)** **S.R.** **T. Tubule** **1.** Signal starts action potential on the neural cell. **2.** A.P arrives at the synaptic vesicle. **3.** Synaptic vesicle fuses with cell membrane and dumps ACh into synaptic gap. **4.** ACh moves across the space and binds to the receptor on the muscle cell. This causes the cell membrane to allow ions to move across → action potential. * * * # Questions **3.** The other name for muscle fiber is? Muscle cell. **4.** In your model, how many muscle fibers do you have? 9. **5.** Identify 4 structures found inside of the muscle fiber. - myofibrils - sarcoplasmic reticulum - sarcoplasma - T tubule **6.** One of the most unique structures found inside a muscle fiber is the myofibril. This myofibril is actually made up of 2 filaments. What are the names of these filaments? * Actin * Myosin **7.** A muscle fascicle is a bundle of what? Muscle Fibers. **8.** How many muscle fascicles do you have in your model? 3. **9.** The 3 different connective tissues in a muscle are what? * Epimysium * Perimysium * Endomysium **10.** For each connective tissue listed in 9, state what it surrounds. * Epimysium surrounds muscle. * Perimysium surrounds fascicle. * Endomysium surrounds muscle fibers. **11.** Where is a sarcolemma found? What is this structure? Found around a muscle fiber; the cell membrane. **12.** From the smallest to largest order all terms found in italics in this lab. This must include the 4 structures listed in 3 and the 2 structures listed in 4. * Muscle fiber * Endomysium * Perimysium * Epimysium * Actin * Myosin * Sarcolemma * T tubule * Myofibrils * Sarcoplasmic reticulum * Sarcoplasma * Cell * Muscle * Fascicle.