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Muscular System
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Intro to Muscles Nearly half our weight comes from muscle tissue
There are 650 different muscles in the human body
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Three Main Functions Responsible for body movement
Responsible for body form and shape (posture) Responsible for body heat and maintaining body temperature
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4 Characteristics of a Muscle
CONTRACTILITY – the capability or quality of shrinking or contracting EXCITEABILITY– the ability to respond to certain stimuli by producing impulses EXTENSIBILITY – the ability to be stretched. ELASTICITY – ability of muscle to return to its original length when relaxing.
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Types of Muscle Skeletal – striated, voluntary, multinucleated, long and run parallel to eachother, found on bones Smooth – non-striated, involuntary, single nucleus, tapered, found in many organs, contract using peristalsis Cardiac – striated, involuntary, 1-2 nuclei, long and branched, found in heart, contain intercalated discs, rhythmic contractions The word “striated” means striped. Skeletal muscle appears striped under a microscope.
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Muscles and Muscle Fiber Structure
Individual muscles are separated by FASCIA, which also forms tendons **Tendonitis – inflammation of the tendons Muscle fibers (cells) are arranged in bundles called FASCICLES
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EPIMYSIUM = outermost layer, surrounds entire muscle.
PERIMYSIUM = separates and surrounds fascicles (bundles of muscle fibers) ENDOMYSIUM = surrounds each individual muscle fiber This model of the muscles uses straws to represent fibers. Green = endomysium Yellow = perimysium Blue = epimysium
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Muscle Layers
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Epimysium Perimysium Endomysium
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It is important to remember the hierarchy
ACTIN (light) FASCICLES MUSCLE FIBERS MYOFIBRILS FILAMENTS MUSCLE MYOSIN (dark) Wrapped in EPIMYSIUM Wrapped in PERIMYSIUM Wrapped in ENDOMYSIUM
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Muscles / Cells Sarcolemma = muscle fiber membrane
Sarcoplasm = inner material surrounding fibrils (like cytoplasm) Myofibrils = individual threads within muscle fiber made of myofilaments
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Nucleus Sarcolemma Mitochondrion Sarcoplasm Myofibril
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Myofibrils are made of MYOSIN = thick filaments ACTIN = thin filaments
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Myofilaments ACTIN (thin) and MYOSIN (thick)
form dark and light bands A band = dArk • thick (myosin) I band = lIght • thIn (actin)
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Z-line – the borders that separate and link adjacent sarcomeres
H-zone – region where only myosin is found and actin does not overlap A-band – the dark striations I – band – light striations
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SLIDING FILAMENT THEORY (MODEL) - theory of how muscle contracts
This occurs as the thin filament (actin) slides past the thick filaments (myosin)
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Explanation of Skeletal Muscle and Sliding Filament Theory
Start at 1:40
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How Muscles Work with the Nervous System
NEUROMUSCULAR JUNCTION - where a nerve and muscle fiber come together
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Neuromuscular Junction
Synaptic cleft – the gap between the motor neuron and the muscle fiber Synaptic vesicles – where NEUROTRANSMITTERS are stored before being released into the synaptic cleft
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Motor neurons stimulate muscle fibers to contract
Motor neuron secretes neurotransmitter known as ACETYLCHOLINE One motor neuron connected to muscle fibers make up a motor unit
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Energy Source -ATP is produced by CELLULAR RESPIRATION; occurs in the MITOCHONDRIA
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Other Terms 1. All-or-None Response 2. Motor Unit 3. Recruitment
4. Muscular Hypertrophy 5. Muscular Atrophy 6. Muscle Cramp 7. Origin & Insertion 8. Hernia 9. Ligaments vs. Tendons 10. Strain vs. Sprain
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2. Motor Unit The muscle fiber + the motor neuron
1. All-or-None Response Fibers do not contract partially, they either do or don't 2. Motor Unit The muscle fiber + the motor neuron
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4. Hypertrophy - muscles enlarge (working out or certain disorders)
3. Recruitment More fibers contract as the intensity of stimulus increases 4. Hypertrophy - muscles enlarge (working out or certain disorders) 5. Atrophy - muscles become small and weak due to disuse Cardiomyopathy
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6. Muscle Cramp - a sustained involuntary contraction
7. Origin and Insertion Origin = the immovable end of the muscle Insertion = the movable end of the muscle
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9. Hernia – protrusion of an organ or tissue through a weak muscle or opening 11. Ligaments vs. Tendons Ligaments – bone to bone Tendons – muscle to bone
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10. Strain vs. Sprain Strain – tear in muscles/tendons from excessive use Sprain – tear in ligaments
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Treatments (R.I.C.E.) Rest Ice Compression Elevation
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