The Muscular System
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Transcript of The Muscular System
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The Muscular System
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Four Functions
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Four Functions
• Irritability
• Contractibility
• Elasticity
• Conductivity
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Types of Muscle Tissue
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Types of Muscle Tissues
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Types of Muscle Tissue• All highly vascular for transport of oxygen,
CO2, waste and sugars• Human body has three types:
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Skeletal Muscle
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Skeletal Muscle• Made of elongated cells called muscle
fibers• Each fiber has many nuclei and striations
– Striations:
• Skeletal muscles are voluntary muscles and work in pairs– Antagonistic:
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Function of Skeletal Muscles• Five major functions:
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Smooth Muscle
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Smooth Muscle• Forms the walls of the stomach, intestines,
blood vessels, and internal organs• Individual cells are spindle shaped with
one nucleus• No striations
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Cardiac Muscle
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Cardiac Muscle• Location:• Cells are cigar shaped• Intercalated disc:
• Shares three characteristics with other types of muscle:
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Moving Muscles• Muscles are attached to the outer layer of bone
with a tough fibrous cord called a tendon– Origin:
– Insertion:
– Action:
• Most muscles work in pairs; one contracts while one relaxes for smooth movement– Flexor:
– Extensor:
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Muscle Structure
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Muscle Structure• From the outside in…
– Epimysium:
– Fascicle:
• Perimysium:
• Muscle fiber: muscle cell, large, long, cylindrical, multinucleated and made mostly of microfilaments
– Sarcolema– Sarcoplasma– Sarcosomes– Sarcoplasmic reticulum– Endomysium
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The Sarcomere Each muscle fiber is made up of threadlike
structures called myofibrils– Myofibrils –
• Actin:
• Myosin:
• These overlap, giving the striated appearance
– Thin actin filaments are anchored to a structure called the Z line
• Region from one Z line to the next is called…
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The Sarcomere
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The Sarcomere• Unit of muscle contraction is called the sarcomere
– Z disc: boundary found on either end of the sarcomere
• I, A, H bands: in-between Z discs, alternating light and dark bands
• I band – first band moving in from Z disc, composed of actin, light in color
• A band – second band, composed of actin and myosin, dark in color
• H Zone – middle of sarcomere, only myosin present, relatively light in color but darker than the I band
• H Zone – middle of the sarcomere• M line – dark line in the middle of H Zone
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Sliding Filament Theory• In May 1954, Hugh Huxley and Allan
Huxley published their findings of the sliding filament theory
• The theory stated that skeletal muscle contracted when two types of filaments, consisting of the proteins myosin and actin, “slid” past each other without either filament’s length actually changing
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Muscular Contraction
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Steps of Muscular Contraction1. The Central Nervous System initiates a sequence to begin the
sequence of events leading to contraction 2. Action potential from the motor neuron moves down to terminal
end and then calcium ions (Ca++) diffuse into the terminal3. Ca++ trigger the synaptic vesicles to release acetylcholine (ACh)4. ACh diffuses across synaptic clef to a receptor site on the
sarcolemma5. ACh cause new action potential to spread from nerve to muscle6. Action potential spreads over the sarcolemma until it finds an
opening7. It enters the opening to the sarcoplasmic reticulum, where it
triggers the release of Ca++ into the sarcoplasm8. Ca++ cause active sites on actin to be exposed9. Myosin crossbridges link up with the active sites on actin10. Actin moves inward, sarcomere shortens, muscle fibers contract
and use ATP
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Stopping Muscular Contraction
1. Acetylcholinesterase (AChE - enzyme) is released as muscle contracts and neutralizes the ACh
2. No more action potential is traveling to muscle3. Calcium does not tighten so the crossbridges on
mysoin release4. Muscles relax