muscle physiology
TRANSCRIPT
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MUSCLE PHYSIOLOGY
BASIC ANATOMY
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FUNCTIONS OF MUSCLE SYSTEM MovementMovement
• Locomotion- bones• Body contents- organs• Stability- postural muscle resist gravity• Communication- facial muscles• Control of body openings- sphincters
Production of heatProduction of heat
ProtectionProtection
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CHARACTERISTICS OF MUSCLE TISSUE Responsiveness (excitability)Responsiveness (excitability)
respond to stimuli with electrical change across membrane
ConductivityConductivity
wave of excitation
ContractilityContractility
shorten when stimulated
Extensibility, ElasticityExtensibility, Elasticity
stretch between contractions & recoil to original resting length after stretch
Cells are long & thin and closely packedCells are long & thin and closely packed
Contain Contain contractile proteinscontractile proteins
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MUSCLE ANATOMY
This is what we will look at under
the microscope.
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ACTION OF MUSCLE = CONTRACTIONMuscle fibers contain many myofibrils
Myofibrils are cylinders of proteins known as:
• Actin- thin, strands of pearls
• Myocin- thick cylinder
During contraction myocin connects with actin and slides the actin past it (power stroke) shortening (contracting) the muscle fiber.
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MYOFIBRILS : ACTIN AND MYOSIN
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MUSCLE TYPES
Skeletal Muscle• striated, voluntary, body movement
Smooth (Visceral) Muscle• no striations, involuntary, organs
Cardiac Muscle• intercalated discs, involuntary, heart
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SKELETAL MUSCLE FIBERSAlso called striated (striped)
Cells are long and thin
Multi-nucleated
Voluntary: you can control it!
Attached to boneStriations
Multiple Nuclei
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SMOOTH MUSCLE FIBERS Also called Visceral
Bipolar, or fusiform shape
Mononucleated –usually in the middle of each cell
No striations
Found in walls of visceral organs
Involuntary- you can NOT control them
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CARDIAC MUSCLE FIBERS Found ONLY in the HEART
Self exciting
Cells are shorter and branched
Mononucleated
Intercalated discs- connect cells, support synchronised contraction of cardiac tissue
Striations
Cells are called myocytes
IntercalateddiscsNuclei
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NEUROMUSCULAR JUNCTIONAction potential travels down the axon of a motor neuron which synapses with a muscle fiber.
Action potential is propagated into muscle fiber which causes influx of Ca++ ions
Motor Unit = one motor nerve fiber and all the muscle fibers innervated by it.
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WHEN CA++ IONS HIT TROPONIN AND TROPOMYCIN, THEY MOVE OUT OF THE WAY AND EXPOSE THE BINDING SITE FOR THE MYOSIN-ACTIN CROSS BRIDGE. THE MYOSIN USES POWER STROKE TO SLIDE ACTIN FILAMENT PAST IT CREATING TENSION IN THE MUSCLE FIBER.
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SLIDING FILAMENT MECHANISM OF CONTRACTION
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THRESHOLD, LATENT PERIOD, TWITCH
• Threshold-minimum voltage necessary to generate action potential & produce contraction. Action potential causes release of Ca++ and activates sliding filament mechanism.
• Twitch- quick cycle of contraction & relaxation
• Latent period- delay between onset of stimulus & onset of twitch ( 2 milli-seconds)
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LATENT PERIOD
• Internal tension: force generated during the time of excitation, excitation-contraction coupling, and tensing of muscle. No shortening of the muscle!
• External tension: muscle components are taut and move a load. This is the contraction phase of the twitch.
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ISOMETRIC VS ISOTONIC
IsometricIsometric: muscle develops tension but does NOT shorten. (lifting heavy objects)
Isotonic concentric contractionIsotonic concentric contraction: Muscle shortens while maintaining a constant degree of tension. Moves a load.
Isotonic eccentric contractionIsotonic eccentric contraction: Muscle maintains tension while it lengthens. Relaxes without going limp.