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Muscular System
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Muscular System Over 600 muscles 45% of body weight is muscles
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Characteristics a. Excitability – respond to stimuli
Usually the stimulus is electrical or chemical
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Characteristics b. Contractility - shorten
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Characteristics c. Extensibility – be stretched or extended
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Characteristics d. Elasticity – recoil and resume length
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Functions a. Provides movement
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Functions b. Maintains posture
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Functions c. Stabilizes joints
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Functions d. Generates heat
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3 main types of muscle tissue
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a. Skeletal muscle – move your skeleton
Voluntary muscle – we consciously control them Striated – has narrow bands Each cell has many nuclei
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b. Smooth muscle – found in internal organs
Involuntary muscle – don’t consciously control them Not striated – no narrow bands Each cell only has one nucleus
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C. Cardiac Muscle – found only in the heart
Involuntary muscle Striated and branched Each cell has only one nucleus
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35. Skeletal muscle anatomy
A. Muscle – organ made of several tissues a. Surrounded by epimysium sheath
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Skeletal muscle anatomy
B. Fascicle – portion of the muscle a. Surrounded by perimysium sheath
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Skeletal muscle anatomy
C. Muscle fiber – single, multinucleated cell a. Surrounded by endomysium sheath
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Cross section of muscle fibers
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Muscle fibers
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Muscle fibers b. Sarcolemma – cell membrane c. Sarcoplasm – muscle cytoplasm d. Nucleus - many
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Muscle fibers e. Myoglobin – red pigment that stores oxygen f. Mitochondria – lots for energy g. Myofibrils – organelle made of bundles of myofilaments
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Myofibrils a. Responsible for contraction b. 2 myofilaments
Actin – thin one Myosin – thick one
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10,000 or more along each myofibril
c. Sarcomeres – functional unit of contraction, area between 2 z-lines 10,000 or more along each myofibril
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Myofibril d. I-band – light region, actin only e. A-band – dark region, myosin only f. H-zone – center of A-band, both actin and myosin g. Z-line – dark zigzag line in center of I-band
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Sliding Filament Theory
a. Actin filaments slide past myosin b. Z lines get closer together c. Sarcomere shortens-neither actin or myosin get shorter.
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Movement A. Tendons – attach muscle to bone
a. Tendons pull on bones and make them work like levers
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Puppet on a String
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Movement B. Contracting – shortening and fattening of muscle cells
C. Relaxing – returning back to beginning length D. Muscles can only pull; they cannot push
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Movement E. Most muscles work in pairs
This provides movement in two directions When one muscle contracts, the other relaxes
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Movement F. Flexor – the muscle that bends a joint
G. Extensor – the muscle that straightens a joint
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Movement H. triggered by electrical impulses through nerve cells
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Movement I. A sodium solution is released which causes the filaments to lock (contract) J. To unlock, calcium solution is released to relax the fibers as you propel forwards. Nerve cell attaches to the sarcomere of each muscle fiber
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Muscle Size Who has more muscles?
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Muscle Size A. The number of muscle fibers (cells) doesn’t change
they just get larger because more myofibrils are added to the cells
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B. Hypertrophy - increase in number and size of myofibrils
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C. Atrophy - decrease in size due to lack of use
If you don’t use it, it will shut down!
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Muscle fibers and Exercise
A. Two types of fibers: a. Slow-twitch - endurance b. Fast-twitch - explosive Those that want to build up fast-twitch or slow twitch fibers need to look at the exercise that will help them
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Anaerobic Exercise a. Use fast-twitch fibers
b. Requires brief, high energy expenditure Weightlifting – high weight, low reps Sprinting c. Depletes oxygen quickly d. Excess lactic acid, turn to glucose
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e. Builds the big muscles
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Aerobic Exercise a. Use slow-twitch fibers
b. Prolonged and constant energy Weightlifting – low weight, high reps Long distance running, cycling c. Uses same oxygen that is received d. No lactic acid
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e. Leans and tones the muscles
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Body building D. a form of body modification involving intense muscle hypertrophy Eugen Sandow, the "Father of Modern Bodybuilding"
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a. Testosterone – hormone that stimulates hypertrophy
Do girls have it? Yes, boys produce times more than girls
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b. Steroid - synthetic testosterone hormone to artificially build muscle
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