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MUSCLE II - PowerPoint PPT Presentation

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Muscle Anatomy and Physiology The Neuromuscular Junction / Motor Unit Anatomy: Max=>Min Muscle, fasciculus, fiber, fibrils, filaments Epimysium, perimysium, endomysium “Bundles within bundles” Contractile units: SARCOMERES Thin: actin, troponin, tropomysim Thick : myosin

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Muscle anatomy and physiology l.jpg

Muscle Anatomy and Physiology

The Neuromuscular Junction / Motor Unit

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Anatomy: Max=>Min

  • Muscle, fasciculus, fiber, fibrils, filaments

  • Epimysium, perimysium, endomysium

  • “Bundles within bundles”

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Contractile units:SARCOMERES

  • Thin: actin, troponin, tropomysim

  • Thick: myosin

  • Z-lines, A-band, I-band, H-Zone

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Motor Units

  • Motor Neuron + Muscle fiber(s)

  • TERMS:

    • Twitch: Single contraction & relaxation of a motor unit

    • Tetanus: Sustained contraction by summing “twitches”

    • Recruitment: Smooth moves – How many units needed?

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How Many Units?

  • The number of Motor Units recruited for a task depends on: 1. Demand

    2. Duration

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Excitation - Contraction Coupling

  • Pre-Synaptic Terminal (Nerve): Acetylcholine released

  • Post-Synaptic Terminal (Motor Endplate): Ach stimulates by binding =>Muscle fiber depolarization

  • Contraction!

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  • Resting Membrane Potential: Membranes separate charges: Polarized

  • Depolarization: Charge reversal across membrane

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Action Potential (AP) Depolarization travels along membrane

AP travels along sarcolemma=> T-tubules => sarcoplasmic reticulum => Terminal Cisternae => Calcium released

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Sliding Filament Theory

  • The Action Potential reaches the Terminal Cisternae

  • Calcium released binds to Troponin

  • Tropomysin “moves” out of the way

  • Myosin-Actin Crossbridges formed

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  • All-or-None “Twitch”

  • Sarcomere units shorten by thin and thick filaments “sliding” past each other

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The Physiology of Muscle

Contraction and ATP

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Take “Five”:

Draw and Label The Neuromuscular Junction:

Page 158

*What is the chemical


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One More Visit to that Neuromuscular Junction:

  • Acetylcholine released

  • Binds with Ach-Receptors – linked to Na+ Channels

  • Na+ influx – DEPOLARIZES Motor endplate


  • Etc. Etc. Etc.

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What Happens to the Acetylcholine?

  • Good Question Sherlock:

  • Homework:

    • Describe the fate of Acetylcholine

    • Think diabolically of poisons that could interfere with the normal function of the neuromuscular junction…

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Toxins: Neuromuscular Junction

  • Affecting Production, Release, Binding or degradation of Acetylcholine

    • Nerve Gas: Inhibit degradation

    • Black Widow Toxin: Massive release of Acetylcholine

    • Botulism: Inhibits Acetylcholine Release

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Death by Sarin: Acetylcholine accumulates in NMJ

  • Runny nose, eyes, drooling, sweating,

  • Difficulty breathing, tight chest

  • Nausea, vomiting, loss of “control”

  • Twitching, jerking, staggering

  • Headache, confusion, coma and convulsions

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Something Lighter Please

  • Check out this cool site for specific exercises!


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Where Does All That ATP Come From?

  • Energy for work is supplied by the breakdown of “FUELS”


  • Glucose is preferred for intense work

  • Fats are the “slow burners” and use lots of Oxygen

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Energetics of Contraction - Continues

  • ATP-PC: fast, limited

  • Anaerobic Glycolysis: Cytosolic breakdown of Glucose without O2 – Forms Lactic Acid

  • Aerobic Oxidation: slow,but plentiful supply of ATP

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All Three Contribute APT at All times…

  • Supply Rate and Demand Rates

    • ATP-PC: Fastest Rate – 10 seconds max

    • Anaerobic Glycolysis: 2-5 minutes max

    • Aerobic (Oxidative Phosphorylation): Slowest rate, almost endless capacity

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The Marathon:

  • Hours of exercise possible

  • Uses ATP from aerobic (oxidative) sources

  • Oxygen Delivery!

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The Half-Mile…or:

  • More Intense

  • Bursts Lasting 2-5 minutes with rests

  • Using Anaerobic Glycolysis

  • Lactic Acid Buildup

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The Sprints and Jumps

  • Less than 10 seconds duration

  • Very Intense

  • Creatine Stores in Muscles contribute to CP-ATP production

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Creatine Phosphate:

  • Increase ATP-PC contribution of energy

  • Used in Maximum intensity-short term work

  • May extend work effort a few seconds…or repititions

  • Useless without training…

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One Last Crazy “Engebretsen Simulation”

  • 5 Volunteers to be the “Motor Neuron”

  • 1 Volunteer to be “Post-Synaptic Membrane”

  • 6 Sarcolemma-Triad volunteers

  • 2 Terminal Cisternae volunteers

  • The rest are sarcolemmas joining hands 

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Muscle Fatigue:

  • More Complicated than you think:

    • ATP depletion very rare: usually seen with max efforts - cramps

    • Lactic ACIDOSIS slows all functions

    • Psychological fatigue…Central perception of exhaustion

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II Myosin

Fast, Force, Fatigue

“White”: Glycogen



I Myosin

Slow, Endure

“Red”: Myoglobin, mitochondria,



Muscle Fiber Types: Fast (II, IIa) vs Slow (I)