MUSCULAR SYSTEM - Norwell High School€¦ · MUSCULAR SYSTEM • Produces movement ... • Motor...
Transcript of MUSCULAR SYSTEM - Norwell High School€¦ · MUSCULAR SYSTEM • Produces movement ... • Motor...
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MUSCULAR SYSTEM
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• Produces movement
• Maintains posture
• Stabilizes joints
• Generates heat
• Vital for maintaining body temperature.
ROLES OF MUSCLES IN BODY
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TYPES OF MUSCLE
•Skeletal – striated & voluntary
•Smooth – involuntary
•Cardiac - heart
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• Muscle attached to the skeleton.
• Striated muscle.
• Contains more than one nuclei per cell
• Contraction is under voluntary control.
SKELETAL MUSCLE
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• Muscle is made up of thousands of cylindrical muscle fibers.
• Run from origin to insertion.
• Bound together by connective tissue.
• Each fiber contains:
• Array of myofibrils that are stacked lengthwise.
• Run the entire length of the fiber
SKELETAL FIBER STRUCTURE
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•Many mitochondria for energy.
•Extensive smooth endoplasmic reticulum
•Many nuclei: each muscle fiber develops from the fusion of many cells
SKELETAL FIBER STRUCTURE
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CARDIAC MUSCLE• Striated
• Each cell contains sarcomeres with sliding filaments of actin and myosin.
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• The myofibrils of each cell are branched.
• The branches interlock with adjacent fibers by adherens junctions.
•Enable heart to contract forcefully without ripping the fibers apart.
• The action potential that triggers the heartbeat is generated within the heart itself.
CARDIAC MUSCLE
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• Action potential that drives contraction of the heart passes from fiber to fiber through gap junctions.
• All fibers contract in a synchronous wave
• Sweeps from atria down through ventricles and pumps blood out of the heart.
• Refractory period is longer than the period it takes for the muscle to contract (systole) and relax (diastole).
• Has richer supply of mitochondria than skeletal muscle.
CARDIAC MUSCLE
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• Made of single, spindle-shaped cells.
• No visible striations
SMOOTH MUSCLE
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• Cells contain thick (myosin) and thin (actin) filaments.
• Slide against each other to produce contraction of the cell.
• Does not depend on somatic motor neurons to be stimulated.
• Motor neurons (of the autonomic system) reach smooth muscle and can stimulate it — involuntary action based on stimulus response.
SMOOTH MUSCLE
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Muscles are composed of many fibers that are arranged in bundles called FASCICLES
Individual muscles are separated by FASCIA, which also forms tendons (connects muscles to bones).
MUSCLE STRUCTURE
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Myofibrils = individual muscle fibers --> made of myofilaments
MUSCLE FIBER MADE OF MYOFIBRILS
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• Contains protein filaments
• ACTIN (thin) and MYOSIN (thick)
• These filaments overlap to form dark and light bands on the muscle fiber.
• A band = dark • thick (myosin)
• I band = light • thin (actin)
• In the middle of each I band are Z lines.
• Sarcomere is section of myofibril from one Z line to the other
MYOFIBRIL
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MYOFIBRILS ARE A SERIES OF CONNECTED SARCOMERES
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SARCOMERE
•Basic contracting unit of muscle.
• The entire array of thick and thin filaments between the Z disks is called a sarcomere.
• Z lines on either end.
• Contains one A-band and 21/2 I-bands
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SARCOMERE STRUCTURE
• The striations are caused by alignment of bands.
• Most prominent: A and I bands and Z line.
• A band: 2 proteins overlap.
• I band: only the actin protein.
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SARCOMERE STRUCTURE
• The H zone: Part of the A band where thick and thin filaments do not overlap.
• M line runs through center of the sarcomere.
• Provides a scaffold for the assembly of myosin molecules in the thick filament
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SARCOMERE STRUCTURE
• When muscle contracts the actin filaments slide into the A band, overlapping with myosin.
• Z lines move closer together
• I band becomes shorter
• A band stays at the same length
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IT IS IMPORTANT TO REMEMBER THE MUSCLE HIERARCHY
fascicles
myofibrils
myofilaments
actin
myosin
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muscle
myofibrilsmyofilament
sarcomere
muscle fiber
epimysium