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MUSCLES

CHAPTER 6A. MUSCLES. VOCABULARY 6. acetylcholine muscle fatigue sarcoplasm actin muscle fibers sarcoplasmic reticulum action potential muscle tone skeletal muscle cardiac muscle muscle twitch smooth muscle

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MUSCLES

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  1. CHAPTER 6A MUSCLES

  2. VOCABULARY 6 acetylcholine muscle fatigue sarcoplasm actin muscle fibers sarcoplasmic reticulum action potential muscle tone skeletal muscle cardiac muscle muscle twitch smooth muscle cross bridges myosin striated muscle endomysium neurotransmitter synaptic cleft isometric contractions oxygen debt thick filaments isotonic contractions sarcomeres thin filaments motor unit

  3. COLOR CODE – PLATE 7 Smooth muscle cells – light blue Nucleus – red Connective tissue – brown Cells with striations – yellow Intercalated discs – purple Capillaries – blue Sarcolemma – light green Myofibrils - gray

  4. COLOR CODE – PLATE 24 Tendon – tan Epimysium – orange Muscle belly – peach/flesh Perimysium/fascicle – yellow Endomysium/muscle fiber – red Myofibril – gray I Band – pink ABand – dark brown H Band – brown Sarcomere – dark green Z line – green Actin – light green Myosin – aqua Cross bridges – light blue

  5. COLOR CODE – PAGE 36 Skeletal muscle - ---------peach/flesh Muscle cell – ---------------orange Motor nerve - --------------dark brown Axon – -----------------------brown Axon branch – -------------aqua Axon terminal – ------------yellow Neuromuscular junction – red Motor end plate - -----------blue

  6. I. Muscles A. All muscles →contract (essential function) B. Makes up approx. ½ body’s mass C. similarities: 1. contractions depend u/p 2 types of myofilaments 2. muscle fibers *elongated cells wh/ contract *skeletal & smooth muscle cells 3. myo-, mys-, sarco- prefixes used when muscle is being referred to ex: sarcoplasma – muscle cells’ cytoplasm

  7. D. Muscle Functions 1. maintains posture 2. movement 3. helps maintain constant body T (contractions → ATP to break ↓ → generates heat) 4. stabilizes joints (tendons hold bones t/g)

  8. E. Muscle Coverings 1. layered w/ conn. tiss. coverings 2. endomysium a. delicate conn. tiss. sheath surrounding each individual muscle fiber b. allows capillaries & nerves to reach muscle fibers 3. perimysium – surrounds fascicles (bundles of muscle fibers) 4. epimysium a. covers an entire muscle b. separates muscles from ea. other

  9. II. Muscle Types A. Smooth Muscle 1. in walls of hollow organs 2. involuntary 3. cells: a. uninucleated b. non-striated c. spindle-shaped (tapered)\ 4. very slow to contract

  10. B. Cardiac Muscle 1. in heart walls 2. involuntary 3. cells: a. uninucleated b. striated c. branching chains of cells 4. cells interlock @ intercalated disks 5. slow to contract 6. fibers completely relax b/t rhythmic contractions → prevents fatigue

  11. C. Skeletal Muscle 1. attach to skeleton (bones) by tendons 2. voluntary (only muscle type subject to conscious control) 3. cells: a. multinucleated b. striated c. cylindrical (tubular) 4. variable speed of contractions (slow-fast) 5. fibers contract arhythmically NOTE: page 179 for muscle types

  12. III. Microscopic Anatomy (skeletal) A. Muscle fiber components 1. sarcolemma – cell membrane 2. sarcoplasm – cytoplasm 3. sarcoplasmic reticulum a. specialized smooth ER b. stores Ca & releases it on demand when muscle is stimulated to contract 4. myofibrils a. encased in SR b. have striations c. contractile portion of muscle fibers

  13. 5. sarcomeres a. chains of tiny contractile units of myofibrils b. contractile unit b/t 2 Z-lines c. aligned end-to-end 6. myofilaments a. smaller structures of threadlike proteins w/I sarcomeres b. arrangement gives banding pattern c. 2 types

  14. 1) thick filaments *contains bundles of protein molecules → myosin *also contain enzyme to split ATP → power for muscle contraction 2)thin filaments *contains contractile protein→ actin *only filament found in the light “I” bands

  15. B. bands 1. precise arrangement of myofilaments →banding pattern/striations 2. A Bands – dark bands, contain both actin/thin & myosin/thick filaments 3. I Bands – light bands, contain ONLY actin/thin filaments 4. H Zone – contains no actin/thin filaments when @ rest 5. Bare Zone – disappears during a contraction Note: page 183

  16. Note: In order from smallest to largest Myofilament→myofibril(s) → muscle fiber(s) → fascicle → muscle

  17. IV. Skeletal Muscle Activity A. contractions 1. sarcoplasmic reticulum (SR) a. spec. smooth ER b. stores Ca & releases on demand when muscle fiber is stimulated to contract 2. muscle fibers are stimulated to contract by motor neurons (nerves); muscle fibers are innervated 3. axon of a motor neuron has several branches & can stimulate from a few to several muscle fibers in a particular muscle (pg. 184) 4. motor unit 1 motor neuron + all mus. fibers it stimulates (pg. 184)

  18. 5. neuromuscular junction (pg. 185) a. entire region where a neuron and muscle fiber meet b. synaptic cleft gap b/t nerve endings and muscle cells’ membranes

  19. 6. neurotransmitters a. chemical released when nerve impulse reaches the axon terminals (end of nerve fiber branches) b. acetylcholine is neurotransmitter that diffuses a/c synaptic cleft

  20. B. sliding filament theory (pg. 187) 1. myosin/thick filaments attach to binding sites on the thin/actin filaments (cross bridges) 2. during contraction the actin/thin filaments slide past the myosin/thick filaments (thin filaments are pulled t/w center of sarcomere) 3. causes sarcomere to shorten 4. Ca required for cross-bridges to occur 5. Ca triggers the binding of filaments wh/ initiates the sliding; serves as signal for mus. contraction to b/g 6. when action potential ends, Ca is reabsorbed i/t SR 7. E is supplied by ATP

  21. C. E sources Three ways ATP is acquired (ATP is ONLY E source that can be used directly to power muscle activity) 1. Creatine phosphate (CP) interacting w/ADP a. CP is a ↑ E cmpd. made when a muscle is resting b. when CP transfers a ↑E phosphate group to ADP →regenerates ATP in fraction of a sec.

  22. 2. aerobic respiration a. supplies some 95% of ATP for mus. activity b. uses O2 c. glucose is broken ↓to CO2 and H2O & some of E released is captured in bonds of ATP d. provides a rich supply of ATP 3. anaerobic respiration a. does not use O2 b. produces only 5% as much ATP as aerobic resp., but is about 2.5x faster c. produces lactic acid →promotes mus. fatigue & soreness

  23. D. how forcefully a muscle contracts depends u/p how many of its cells are stimulated E. Oxygen debt 1. occurs when there is insufficient O2 to generate ATP aerobically & anaerobic respiration begins 2. insufficient ATP supply due to > consumption 3. when muscles lack O2 lactic acid b/g to accumulate as well as ATP supply starts to run low 4. causes muscles to contract less effectively, finally stopping contractions alt/g (fatigue)

  24. 5. believed to result in muscle fatigue F. muscle fatigue 1. may occur when muscles have been worked strenuously for a long period of time 2. muscle is unable to contract even though it is being stimulated

  25. G. types of contractions Muscles do not a/w shorten when they contract 1. isometric a. means “same msmt.” b. muscles do not shorten c. mmt. does not occur d. muscle tension keeps increasing, but muscle is working a/g an object that is immovable e. ex: pushing a/g a door jamb 2. isotonic a. means “same tone” b. muscle shortens; mmt. does occur

  26. H. muscle twitches 1. single, brief, jerky contractions 2. usu. contractions are smooth and sustained (tetanic contraction) I. muscle tone 1. state of continuous partial contractions 2. results in muscles remaining firm, healthy, and constantly ready for action 3. even relaxed muscles have some fibers that are contracting (not visible) 4. ex: curved fingers when arm is hanging relaxed

  27. J. Exercise 1. increases muscle size, strength, &/ endurance 2. diff. exercises give diff. results 3. inactivity →muscle weakness & wasting → atrophy

  28. About.com – ALS video clip • Medclip.com – neuromuscular junction

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