1. Muscle Tissue Chapter # 4 6/13/2016 1 Muscular System

2. Muscles  “muscle” = myo- or mys-  sarco- = “flesh” - also refers to muscles 6/13/2016 2 Muscular System

3. Main Functions of Muscles 1.Produce movement 2.Maintain posture & body position 3.Stabilize joints 4.Generate heat Additional: protect organs, valves, dilate pupils, raise hairs 6/13/2016 3 Muscular System

4. Types of Muscle Tissue  Skeletal : voluntary, striated, multinucleated  Cardiac : (heart) striated, involuntary  Smooth : visceral (lines hollow organs), nonstriated, involuntary 6/13/2016 4 Muscular System

5. Special Characteristics  Excitability – can receive and respond to stimuli  Contractility – can shorten forcibly  Extensibility – can be stretched or extended  Elasticity – can recoil and resume resting length after being stretched 6/13/2016 5 Muscular System

6. Gross Anatomy of Skeletal Muscle  1 muscle = 1 organ  Each muscle served by a nerve, artery, & vein (1+)  Rich blood supply – need energy & O 2  Connective tissue sheaths: wraps each cell and reinforce whole muscle  Attachment : (1) directly to bone, (2) by tendons or aponeuroses to bone, cartilage, or other muscles 6/13/2016 6 Muscular System

7. Muscle Muscle cells + blood vessels + nerve fibers Covered by epimysium (connective tissue) Fascicle Bundle of muscle cells Surrounded by perimysium Muscle fiber (cell) Surrounded by endomysium Myofibril Complex organelle Sarcomere Contractile unit Organization of Skeletal Muscle 6/13/2016 7 Muscular System

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9. Anatomy of Muscle Fiber  Multinucleate cell  Up to 30 cm long  Sarcolemma (plasma membrane)  Sarcoplasm (cytoplasm)  Myofibril = rodlike organelle  Contains contractile element ( sarcomeres )  Alternating light (I) and dark (A) bands 6/13/2016 9 Muscular System

10. Sarcomere  Smallest contractile unit of muscle fiber  Region between 2 successive Z discs 6/13/2016 10 Muscular System

11. Sarcomere  Protein myofilaments :  Thick filaments = myosin protein  Thin filaments = actin protein 6/13/2016 11 Muscular System

12. Myofilaments Thick Filaments  Myosin head: forms cross bridges with thin filaments to contract muscle cell Thin Filaments  Tropomyosin: protein strand stabilizes actin  Troponin: bound to actin, affected by Ca 2+ 6/13/2016 12 Muscular System

13.  Sarcoplasmic Reticulum (SR): specialized smooth ER, surrounds each myofibril  Stores and releases calcium  T Tubule : part of sarcolemma, conduct nerve impulses to every sarcomere  Triggers release of calcium from SR 6/13/2016 13 Muscular System

14. Sliding Filament Model  During contractions : thin filaments slide past thick ones so they overlap more 6/13/2016 14 Muscular System

15. Sliding Filament Model cross-bridge  Myosin heads latch onto active sites on actin to form a cross-bridge  Attachments made to propel thin filaments to center of sarcomere 6/13/2016 15 Muscular System

16. Basic Muscle Contraction 1.Stimulation by nerve impulse action potential 2.Generate and send electrical current (action potential) along sarcolemma 3.Rise in calcium ion levels to trigger contraction 6/13/2016 16 Muscular System

17. Nerve Impulse motor neuron  1 nerve cell (motor neuron) stimulates a few or hundreds of muscle cells  Motor unit = 1 neuron + muscle cells stimulated  Axon: extension of neuron  Axon terminal: end of axon  Neuromuscular junction (NMJ): where axon terminal meets muscle fiber  Synpatic cleft: space between neuron & muscle fiber  Acetylcholine (ACh): neurotransmitter 6/13/2016 17 Muscular System

18. Excitation of Muscle Cell 1.Action potential travels down axon and arrives at neuromuscular junction acetylcholine (ACh) 2.Release of acetylcholine (ACh) into synaptic cleft 3.ACh diffuses across cleft & attaches to ACh receptors on sarcolemma of muscle fiber sodium (Na + ) 4.Rush of sodium (Na + ) into sarcoplasm produces action potential in sarcolemma 5.ACh broken down 6/13/2016 18 Muscular System

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25. Contraction of Muscle Cell 1.Action potential travels down sarcolemma along T- Tubules 2.Calcium is released from SR 3.Calcium binds to troponin  changes shape  myosin binding sites exposed on actin 4.Myosin cross-bridge forms with actin 5.Myosin head pivots and pulls actin filament toward M line 6.ATP attaches to myosin and cross-bridge detaches 7.Myosin can be reactivated 6/13/2016 25 Muscular System

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27. Homeostatic Imbalances  Myasthenia gravis  Myasthenia gravis: loss of ACh receptors in sarcolemma by immune system attack  progressive muscular paralysis  Botulism  Botulism: from bacterial toxin; prevents release of ACh at synaptic terminals  muscular paralysis  Rigor mortis  Rigor mortis: “death stiffness” = no ATP production, myosin cross-bridges “stuck” until proteins break down (peak: 12 hrs, fades: 48-60 hrs later) 6/13/2016 27 Muscular System

28. Muscle Responses  Twitches  Twitches (single, brief, jerky contractions) = problem, Healthy muscle shows smooth contraction  Graded muscle responses  Graded muscle responses: different degrees of muscle shortening Greater force by : frequency 1.Increase frequency of muscle stimulation complete tetanus  Contractions are summed (max tension = complete tetanus) number of muscle cells 2.Increase number of muscle cells being stimulated 6/13/2016 28 Muscular System

29. Muscle response to changes in stimulation frequency 6/13/2016 29 Muscular System

30. Increasing stimulus  Increasing muscle tension 6/13/2016 30 Muscular System

31. Energy  ATP  ATP = only energy source for muscles  Regenerated by: 1.Creatine phosphate (CP) 1.Creatine phosphate (CP): transfers energy to ATP 2.Aerobic respiration 2.Aerobic respiration: complete glucose breakdown with O 2 present 3.Lactic acid fermentation 3.Lactic acid fermentation: glucose breakdown without O 2  Muscle fatigue  Muscle fatigue: lack of O 2, ATP supply low, lactic acid accumulates, soreness  muscle contracts more weakly until it stops 6/13/2016 31 Muscular System

32. Types of Contractions Isotonic  “same tension”  Muscle length changes  Concentric: shortens  Eccentric: lengthens  Eg. bicep curl, bend knee, smiling Isometric  “same length”  Muscle length stays same  Tension increases  Moving against heavy load or immovable object  Eg. lifting heavy weights 6/13/2016 32 Muscular System

33. Isotonic Contractions 6/13/2016 33 Muscular System

34. Sequence the events for Muscle Contraction: Put the following events in order: A.Calcium binds to troponin  changes shape  myosin binding sites exposed on actin B.Myosin head pivots and pulls actin filament toward M line C.ATP attaches to myosin and cross-bridge detaches D.Action potential travels down sarcolemma along T- Tubules E.Myosin cross-bridge forms with actin F.Calcium is released from sarcoplasmic reticulum (SR) 6/13/2016 34 Muscular System