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 3 layers of connective tissue  Epimysium – surrounds entire muscle  Perimysium – divide muscle into compartments  Endomysium – surrounds individual.

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Presentation on theme: " 3 layers of connective tissue  Epimysium – surrounds entire muscle  Perimysium – divide muscle into compartments  Endomysium – surrounds individual."— Presentation transcript:

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2  3 layers of connective tissue  Epimysium – surrounds entire muscle  Perimysium – divide muscle into compartments  Endomysium – surrounds individual muscle cells  Blood vessels and nerves  Skeletal muscle fibers

3  Multinucleate – Each contains hundreds of nuclei just internal to membrane  Large  Sarcolemma – Cell membrane  Sarcoplasm - cytoplasm

4  The whole fiber must contract simultaneously  Signal to contract must distribute quickly via Transverse Tubules  Transverse Tubules (T Tubules) – narrow tubes that are continuous with the sarcolemma and extend into the sarcoplasm at right angles to the cell surface  Like a belt

5  Myofibril – Cylindrical structures. Each muscle fiber contains hundreds to thousands of myofibrils  Contain a thick and thin filament  Thin Filament – Actin  Thick Filament – Myosin

6  Sliding Filament Theory – Thick and thin filaments slide across each other therefore shortening and causing a contraction.

7  Neuromuscular Junction  Sarcoplasmic Reticulum  Ca (Calcium Ions)  Sarcomere (~10,000/myofibril)  Actin  Myosin  Acetylcholine (ACh)  Troponin  Tropomyosin 2+  Rope around Actin

8 1. ACh is released at Neuromuscular junction 2. Production of action potential along surface of muscle fiber/T tubules 3. Sarcoplasmic reticulum (SR) releases calcium ions that were stored into sarcoplasm 4. Calcium bind to troponin changing oritentaion and exposing active sites of actin. Cross- bridges form when myosin head binds to active site

9 5. Bind, pivot, detach via hydrolysis of ATP (therefore filament sliding and fiber shortens) 6. Action potential ends with ACh break down 7. SR resorbs calcium 8. Active sites recover to prevent cross-bridge 9. Muscle relaxation occurs

10 In a resting sarcomere, the tropomyosin strands cover the active sites on the thin filaments, preventing cross-bridge formation. When calcium ions enter the sarcomere, they bind to troponin, which rotates and swings the tropomyosin away from the active sites. Cross-bridge formation then occurs, and the contraction cycle begins. SARCOPLASMIC RETICULUM Calcium channels open Troponin Nebulin Active site G-actin (thin filament) Tropomyosin strand Myosin tail (thick filament)

11 The contraction cycle, which involves a series of interrelated steps, begins with the arrival of calcium ions within the zone of overlap. Myosin head Troponin Tropomyosin Actin Contraction Cycle Begins

12 Calcium ions bind to troponin, weakening the bond between actin and the troponin– tropomyosin complex. The troponin molecule then changes position, rolling the tropomyosin molecule away from the active sites on actin and allowing interaction with the energized myosin heads. Active-Site Exposure Sarcoplasm Active site

13 Once the active sites are exposed, the energized myosin heads bind to them, forming cross-bridges. Cross-Bridge Formation

14 After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots toward the M line. This action is called the power stroke; when it occurs, the bound ADP and phosphate group are released. Myosin Head Pivoting

15 When another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken. The active site is now exposed and able to form another cross-bridge. Cross-Bridge Detachment

16 Myosin reactivation occurs when the free myosin head splits ATP into ADP and P. The energy released is used to recock the myosin head. Myosin Reactivation

17 Steps in Initiating Muscle Contraction ACh released, binding to receptors Synaptic terminal Motor end plate T tubule Sarcolemma Action potential reaches T tubule Sarcoplasmic reticulum releases Ca 2  Ca 2  Actin Myosin Active site exposure, cross-bridge formation Contraction begins Steps in Muscle Relaxation ACh broken down by AChE Sarcoplasmic reticulum recaptures Ca 2  Active sites covered, no cross-bridge interaction Contraction ends Relaxation occurs, passive return to resting length


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