Download - This week…
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This week…
• The functions of the Muscular System• The types of Muscle, where they are found
and what they do• Muscle cells • How muscles contract on the microscopic
level• How muscles use energy
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THE MUSCULAR SYSTEM
Why do we have muscles?
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Functions• Movement– Jump, run, walk–Move eyeballs, swallow, blink, smile– Blood pressure, moving food, releasing
urine, having a baby–Moving blood through the body
• Support– Posture and stabilizing joints
• Generate Heat
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3Types of Muscle • 1. Skeletal Muscle tissue– Attach to and cover the skeletal system– STRIATED and VOLUNTARY muscle– Can contract fast, but gets tired– Adaptable for light touch or strong
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• 2. Cardiac Muscle– Only found in the heart– STRIATED but INVOLUNTARY– Contracts at a steady rate
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• 3. Smooth Muscle– Found in the walls of your organs– NOT STRIATED and INVOLUNTARY– Contracts slow and the contractions can last a while
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Why is each muscle tissue good for where it is found?
- Skeletal- contracts fast, at variable amounts a lot or a little. We can control it for movements. Needs to rest though.- Cardiac- steady contractions. Can’t ever rest. We don’t want to have to think about beating our heart.- Smooth-slow and sustained contractions. Don’t want to have to think about moving our food along. Good for forcing things through our systems
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Characteristics of Muscle• EXCITABILITY/ IRRITABILITY– Can receive and respond to a stimulus
• CONTRACTILITY– Can shorten when stimulated
• EXTENSIBILITY– Can be stretched or extended when relaxed
• ELASTICITY– Can resume length after being stretched
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Microscopic Anatomy of a Muscle Cell
• Cell= Muscle Fiber– Very long- can run the length of the muscle
• Cell Membrane = Sarcolema• Many Nuclei• Glycosomes store large amounts of glycogen (for making
energy) and Myoglobin (stores Oxygen)• Cytoplasm = Sarcoplasm– Hundreds of Mitochondria here making ATP
• ER = Sarcoplasmic Reticulum– Stores Calcium for muscle contractions
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Muscle cell made of MyofibrilsMyofibrils are cords of protein
2 types that alternateThick – made of MYOSINThin – made of ACTIN
A band = where thick and thin overlap (looks like DARK stripe)I band = only thin (looks like LIGHT stripe)SARCOMERE = from z disc to z disc
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Myofibrils make up Muscle Cells
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Muscle cells all held together with connective tissue into a muscle.
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Muscles and Nerves
• Neuromuscular junction = where nerve meets muscle for stimulus
• Motor neurons = the nerve cells that stimulate the muscle fibers
• Motor End Plate/ Synaptic Cleft = the part of the muscle cell that interacts with the motor neurons
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Muscles and Nerves
• Cell membranes have more positive ions on the outside than on the inside= RESTING MEMBRANE POTENTIAL
• Nerve stimulus causes positive ions to rush into cells= ACTION POTENTIAL
• NEUROTRANSMITTER = a chemical that carries the signal from a nerve to a muscle- Acetylcholine
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How Info gets from Nerve to Muscle
• An action potential arrives at the end of the motor neuron – Releases Acetylcholine- Goes across Synaptic Cleft to Motor End Plate.
• Acetylcholine binds to muscle cell membrane causing positive (sodium) ions to rush into cell = Action potential in muscle cell
• Action potential causes muscle to contract
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Neuromuscular Junction
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How Muscles Contract
• Action potential allows CALCIUM into the muscle cells
• Calcium binds to troponin molecules in the thin filaments causing a shape change– it is like the key opening a lock
• Cross bridges form between Actin and Myosin while Calcium causes the breakdown of ATP– produces energy to move cross bridges and heat
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The Sliding Filament Theory
• YouTube - Sarcomere Contraction - Process Of Muscle Contraction With Myosin & Actin.mp4
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• Actin ratchets down the length of Myosin by forming and reforming cross-bridges
• Sarcomeres get shorter causing muscle to become shorter = Muscle contraction
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