1 / 26

Chapter 2-2

Chapter 2-2. THE MUSCLE AND ITS CONTRACTION. the Neuromuscular Junction (NMJ). Skeletal Muscle Innervation. Illustration of the Neuromuscular Junction (NMJ). New Ion Channel Players. Voltage-gated Ca 2+ channel in presynaptic 突触前的 nerve terminal mediates neurotransmitter release

Télécharger la présentation

Chapter 2-2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 2-2 THE MUSCLE AND ITS CONTRACTION

  2. the Neuromuscular Junction (NMJ)

  3. Skeletal Muscle Innervation

  4. Illustration of the Neuromuscular Junction (NMJ)

  5. New Ion Channel Players • Voltage-gated Ca2+ channel • in presynaptic突触前的 nerve terminal • mediates neurotransmitter release • Nicotinic Acetylcholine乙酰胆碱 Receptor Channel • in muscle neuromuscular junction (postsynaptic突触后的 membrane, or end plate) • mediates electrical transmission from nerve to muscle

  6. Nerve Terminal Ca2+ channels • Structurally similar to Na+ channels • Functionally similar to Na+ channels except • activation occurs at more positive potentials • activation and inactivation much slower than Na+ channels

  7. Neuromuscular Transmission Myelin Axon Axon Terminal Skeletal Muscle

  8. - - + + + - - + - + - + - + + + - Look here + - + - + Neuromuscular Transmission: Step by Step Depolarization去极化 of terminal opens Ca channels Nerve action potential invades axon terminal

  9. ACh is released and Diffuses扩散 across synaptic cleft. Ca2+ induces fusion熔合 of vesicles with nerve terminal membrane. ACh ACh Ca2+ ACh Ca2+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ ACh Na+ Na+ Na+ Na+ Na+ Na+ Na+ Nerve terminal Binding of ACh opens channel pore that is permeable to Na+ and K+. K+ K+ K+ K+ K+ Outside Muscle membrane Inside ACh binds to its receptor on the postsynaptic membrane K+ K+ K+ K+ K+ K+ K+ K+

  10. EPP End Plate Potential (EPP) VNa The movement of Na+ and K+ depolarizes muscle membrane potential (EPP) 0 Muscle Membrane Voltage (mV) Threshold Presynaptic terminal -90 mV VK Time (msec) Presynaptic AP Outside Muscle membrane Inside Voltage-gated Na Channels ACh Receptor Channels Inward Rectifier K Channels

  11. Structural Reality

  12. Neuromuscular Transmission • Properties特性 of neuromuscular junction • 1:1 transmission: A chemical transmission which is designed to assure that every presynaptic action potential results in a postsynaptic one • An unidirectional单向性 process • Has a time delay. 20nm/0.5-1ms • Is easily affect by drugs and some factors • The NMJ is a site of considerable clinical importance

  13. NMJ Diseases • Myasthenia Gravis (重症肌无力) • Autoimmunity to ACh receptor • Fewer functional ACh receptors • Low “safety factor” for NM transmission • Lambert-Eaton syndrome(兰伯特-伊顿综合征 ,癌性肌无力综合征 ) • Autoimmunity directed against Ca2+channels • Reduced ACh release • Low “safety factor” for NM transmission

  14. Microstructure of Skeletal Muscle

  15. Skeletal Muscle • Human body contains over 400 skeletal muscles • 40-50% of total body weight • Functions of skeletal muscle • Force production for locomotion运动 and breathing • Force production for postural姿势 support • Heat production during cold stress

  16. Fascicles肌束: bundles, CT(connective tissue结缔组织) covering on each one • Muscle fibers: muscle cells

  17. Structure of Skeletal Muscle:Microstructure • Sarcolemma(肌管系统) • Transverse (T) tubule • Longitudinal tubule (Sarcoplasmic reticulum, SR肌浆网) • Myofibrils(肌原纤维) • Actin肌动蛋白 (thin filament) • Troponin(肌钙蛋白) • Tropomyosin(原肌球蛋白) • Myosin肌球蛋白 (thick filament)

  18. Within the sarcoplasm Triad (三联管) • Transverse tubules • Sarcoplasmic reticulum -Storage sites for calcium • Terminal cisternae - Storage sites for calcium

  19. Microstructure of Skeletal Muscle (myofibril)

  20. Sarcomeres • Sarcomere 肌小节: bundle of alternating thick and thin filaments • Sarcomeres join end to end to form myofibrils • Thousands per fiber, depending on length of muscle • Alternating thick and thin filaments create appearance of striations条痕

  21. Myosin 肌球蛋白 • Myosin head is hinged铰链 • Bends and straightens during contraction

  22. Thick filaments (myosin) • Bundle of myosin proteins shaped like double-headed golf clubs • Myosin heads have two binding sites • Actin binding site forms cross bridge • Nucleotide核苷酸 binding site binds ATP (Myosin ATPase) • Hydrolysis水解 of ATP provides energy to generate power stroke

  23. Thin filaments 原肌球蛋白 肌钙蛋白 肌动蛋白

  24. Thin filaments (actin) • Backbone: two strands of polymerizedglobular actin – fibrous actin • Each actin has myosin binding site • Troponin • Binds Ca2+; regulates muscle contraction • Tropomyosin • Lies in groove of actin helix • Blocks myosin binding • sites in absence of Ca2+

  25. Thick filament: Myosin (head and tail) • Thin filament: Actin, Tropomyosin, Troponin (calcium binding site)

More Related