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Chapter 11– Muscular Tissue

Chapter 11– Muscular Tissue. 11- 1. Ch. 11 Study Guide. Critically read Chapter 11 pp. 402-418 before 11.5 section (Behavior of whole muscles) Comprehend Terminology (those in bold in the textbook) within the reading scope above

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Chapter 11– Muscular Tissue

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  1. Chapter 11– Muscular Tissue 11-1

  2. Ch. 11 Study Guide Critically read Chapter 11 pp. 402-418 before 11.5 section (Behavior of whole muscles) Comprehend Terminology (those in bold in the textbook) within the reading scope above Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions (within the reading scope above) Do end-of-chapter questions— Testing Your Recall— 1-5, 7, 13-16 True or False– 1-2, 4-5

  3. § 11.0-- Introduction to Muscle • Movement is a fundamental characteristic of all living things • In animals, muscular tissues capable of shortening– How (molecular mechanism)? • Three types of muscle tissue-- • Focuses of this chapter– structure, contraction, and metabolism of skeletal muscle at the cellular/molecular levels 11-3

  4. § 11.1--Characteristics of ALL Muscle Cells Changes-- • Responsiveness (excitability) • Respond to stimuli with electrical changes; in what cells? • Conductivity • 2 Purposes– more than a local electrical change; leading to muscle contraction Consequences– of muscles • Contractility–shortens when stimulated; pull on bones and other tissues • Extensibility-- capable of being stretched; in other cells— What happen? • Elasticity-- returns to its original resting length after being stretched 11-4

  5. § Skeletal Muscle • Def. -- Voluntary striated muscle usually attached to bones Explanation-- • Striations -- (Fig. 11.1) • What are they? • Voluntary – why? Under conscious control • A typical skeletal muscle cell/muscle fiber– length: 3-30 cm long; 100 micrometer in diameter 11-5

  6. Figure 11.1 (cell) 11-6

  7. Connective Tissue-- • C.T. attachments between muscle and bone • Endomysium (surrounds each muscle fiber), • ___________ ( . . . fascicle) • ___________ (. . . whole muscle; grades into fascia (CT sheet)) • to bones (may/may not via tendon) • Collagen fibers (include those structures listed above) are extensible and elastic • stretches slightly and recoils when released • Advantage of stretching– protect m. from injury; recoiling of m. help to return to resting length 11-7

  8. § 11.2 Microscopic Anatomy Of Skeletal Muscle– Key words:Multinucleate, Striations, Voluntary 11-8

  9. Fig. 11.2– ONE skeletal muscle fiber-- A (#1) B--Myofibrils (protein bundles) SR T-tubule C--3 types of myofilaments (proteins) 11-9

  10. § Skeletal muscle fiber (#2) • Muscle fiber – one skeletal muscle cell • Myofibril–forming an internal subdivision of a cardiac or skeletal muscle cell • Myofilament– a protein microfilament responsible for the contraction of a muscle cell; • 3 kinds— ?? 11-10

  11. § Skeletal muscle fiber (#3) • Sarcoplasm (cytoplasm) is filled with • Myofibrils • Glycogen– purpose? • Pigment (myoglobin)—binding oxygen • Sarcoplasmic reticulum= smooth ER • network around each myofibril; function? Store calcium • terminal cisternae– • triad = 11-11

  12. Skeletal Muscle Fibers #4 • Multiple flattened nucleiinside cell membrane • fusion of multiple myoblasts during development • Sarcolemma– plasma membrane; having tubular infoldings (transverse (T) tubules) that penetrate the interior of the cell • carry electric current to interior of the cell • This current signals the SR when to release calcium ions into cytoplasm 11-12

  13. § Three kinds of myofilament – 1. Thick Filaments • Each thick filament is made of 200 to 500 ________ molecules– each in turn has • 2 entwined polypeptides (the heads similar to golf clubs) for each myosin molecule • Arranged in a bundle of “golf clubs” with heads directed outward in a spiral array around the bundled tails • Central area of the thick filament is a _________ with no heads (of myosin molecules) Fig. 11.3 a, b, d 11-13

  14. SINGLE MYOSIN MOLECULE Myosin molecules to form thick filament—see next slide 11-14

  15. (partial view) Full picture of the thick filament—see next slide 11-15

  16. Overlap of Thick and Thin Filaments 11-16

  17. Three kinds of myofilament – 2. Thin Filaments (Fig. 11.3c) • (in red) 2 intertwined strands (fibrous (F) actin) • Each bead is a globular (G) actinwith an active site; capable of binding the head of a __________ • (in white) Groove holds ____________ molecules • each can block 6 or 7 active sites of G actins • (in yellow) calcium-binding _________molecule on each tropomyosin molecule A blow-up image in the next slide 11-17

  18. F actin Two interwined chains (F actins; in red) are shown. 11-18

  19. Three kinds of myofilament – 3. Elastic Filaments (Fig. 11.5) • Springy proteins called ________________ • Anchor each thick filament to Z disc • Prevents overstretching of sarcomere Fig. 11.5 11-19

  20. 3 kinds of myofilament in three colors— Purple ones— _____________ filaments Red ones— ____________ filaments Green ones-- _____________ filaments Sarcomere I band A band I band H band Thick filament Titin Thin filament M line Elastic filament Z disc Z disc (b) 11-20

  21. § Contractile & Regulatory Proteins • Myosin and actin are contractile proteins; do the work of shortening the muscle fiber • ________________ and _____________ are regulatory proteins; Function-- 11-21

  22. § Striations = Organization of Filaments • Striations-- Dark A bands alternating with lighter I bands • A bandis thick filament region— Dark/Light (Circle one) • central H band area is lighter, contains no thin filaments • I bandis thin filament region— Dark/Light (Circle one) • bisected by Z disc protein, anchoring elastic and thin filaments • from one Z disc (Z line) to the next is a sarcomere (Fig. 11.5) 11-22

  23. SARCOMERE– contractile unit in a striated muscle fiber; extending from one Z disc to the next Z disc 11-23

  24. § Relaxed & Contracted Sarcomeres • Muscle cells shorten because their individual Sarco________________ shorten • Details-- • Do myofilaments change length? Yes/No • Z discs/sarcomeres? Yes/No • Eventually pulling on sarcolemma (cell mem.) via proteins (especially dystrophin) Fig. 11.4 11-24

  25. Exterior of the muscle cell 11-25

  26. § 11.3--Nerve-Muscle Relationships • Skeletal muscles are innervated by somatic motor neurons • Where are motor neurons’ cell bodies? In ____________________________ • Axons reach these muscle fibers • At its distal end, each axon branches about 200 times; each branch reaches a different fiber (cell) • Each motor neuron and all the muscle fibers it innervates are called a _______________ Fig. 11.6 11-26

  27. Motor neuron originated from— A G F B E C H D A, B, C, D; E, F, G, H 11-27

  28. Motor Units (Fig. 11.7—next slide) • Def.A motor neuron and the muscle fibers it innervates • A muscle (whole muscle) is innervated by _________ motor units; advantages? • Where are the muscle fibers innervated by one motor neuron? • Small motor units--Fine control • small motor units contain as few as 3-6 muscle fibers per nerve fiber • Example– eye muscle • Large motor units--Strength control • gastrocnemius muscle has 1000 fibers per nerve fiber 11-28

  29. 11-29

  30. § Neuromuscular Junctions (NMJ)- 1 • Functional connection between nerve fiber and target cell called synapse; if the target cell is a muscle fiber, the synapse is called NMJ • Neurotransmitter(acetylcholine/ACh) released from nerve fiber stimulates muscle cell • Components of NMJ– Fig. 11.7 (next slide) • A-synaptic knob (with vesicles present; B) • C-synaptic cleft (a tiny gap) • D-motor end plate • E-junctional folds 11-30

  31. The Neuromuscular Junction- 2 A. B. D. Motor end plate C. E. 11-31

  32. § Neuromuscular Junctions- 3 Components of NMJ: A) synaptic knob-- a swollen end of a nerve fiber B) synaptic vesicles-- ________________ C) synaptic cleft--tiny gap _________________________________ D) motor end plate— depression region of sarcolemma where a ______________ rests Features– increases surface area for Ach receptors and contains Acetylcholinesterase E) junctional folds— infoldings in sarcolemma; many Ach receptors present here too 11-32

  33. Neuromuscular Toxins on Muscle: • Spastic paralysis (& possible suffocation) • Symptom: a continual contraction of the muscle • Caused by pesticides (cholinesterase inhibitors) • Mechanism: binds to acetylcholinesterase and prevents it from degrading ACh • Tetanus (lockjaw)is another spastic paralysis caused by toxin of Clostridiumtetanibacteria • blocks glycine release in the spinal cord and causes overstimulation of the muscles • Flaccid paralysis(limp muscles, cannot contract) due to curare that competes with Ach receptor sites • respiratory arrest (thoracic muscles cannot contract) 11-33

  34. § Electrically excitable cells • In what specific cells? • At rest, plasma membrane is charged • difference in charge across the membrane = resting membrane potential(-90 mV in cells) • Why? • Stimulation opens ion gates in membrane • When strong enough, results in action potential production • Details • Depolarization-- Na+ ion gates open; sodium ions enter • Repolarization followed-- K+ rushes out of cell • An action potential spreads— • Where? Cell surface of nerve fibers/sarcolemma 11-34

  35. § Muscle Contraction and Relaxation • Four phases involved in this process • A. excitation= nerve action potentials lead to action potentials in muscle fiber • B. excitation-contraction coupling= action potentials on the sarcolemma activate myofilaments • C. contraction = shortening of muscle fiber • D. relaxation = return to resting length • Images will be used to demonstrate the steps of each of these actions 11-35

  36. A. Excitation (steps 1-5)– These events link action potentials in the nerve fiber to the generation of action potentials in the muscle fiber. 11-36

  37. Steps 1-2 of excitation • Nerve signal opens voltage-gated Calcium channels. Calcium stimulates exocytosis of synaptic vesicles containing _____; then ACh release into synaptic cleft 11-37

  38. Steps 3-4 of excitation Na+ goes in first Binding of ACh to receptor proteins opens Na+ and K+ channels resulting in an end-plate potential (EPP), RMP from -90mV to +75mV and back to -90mV 11-38

  39. Step 5 of excitation Voltage change in end-plate region (EPP) opens nearby voltage-gated channels producing an action potential (cell?) 11-39

  40. B. Excitation-Contraction Coupling (steps 6-9)– These events link action potentials in the muscle fiber to the release and binding of calcium ions 11-40

  41. Steps 6-7-- excitation-contraction coupling Action potential spreading over sarcolemma and down T-tubules, causing calcium gates to open in SR; Purpose?Calcium enters . . . Triad? 11-41

  42. Steps 8-9-- excitation-contraction coupling Thin Filament • Calcium released by SR binds to ___________ • Troponin-tropomyosin complex changes shape and exposes _____________on actin filaments 11-42

  43. C. Contraction (steps 10-13)– The sliding filament mechanism of contraction 11-43

  44. Steps 10-11-- Contraction • Myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and “cocking” it into an extended position • It binds to actin active site forming a cross-bridge 11-44

  45. Steps 12-13-- Contraction • Step 13--With the binding of more ATP, the myosin head releases and extends to attach to a new active site • Step 12--myosin head releases ADP/phosphate as it pulls the thin filament past the thick one #13 #12 11-45

  46. D. Relaxation of a muscle fiber (steps 14-18)– These events lead from the cessation of a nerve signal to the release of thin filaments by myosin 11-46

  47. Steps 14-15-- Relaxation Nerve stimulation ceases and acetylcholinesterase removes ACh from receptors. Stimulation of the muscle cell ceases. 11-47

  48. Step 16-- Relaxation • Active transport needed to pump calcium back into SR (ATP needed) • Calcium binds to _____________ • ATP is needed for muscle relaxation (as well as muscle contraction) 11-48

  49. Steps 17-18-- Relaxation Step 17: ATP binding-- • Loss of calcium from sarcoplasm moves troponin-tropomyosin complex over active sites ATP binding and the cross bridge detaches Step 18: Muscle fiber returns to resting length 11-49

  50. § Impact of calcium ions in muscle contraction 11-50

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