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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

Muscle Anatomy and Physiology

The Neuromuscular Junction / Motor Unit

anatomy max min
Anatomy: Max=>Min
  • Muscle, fasciculus, fiber, fibrils, filaments
  • Epimysium, perimysium, endomysium
  • “Bundles within bundles”
contractile units sarcomeres
Contractile units:SARCOMERES
  • Thin: actin, troponin, tropomysim
  • Thick: myosin
  • Z-lines, A-band, I-band, H-Zone
motor units
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?
how many units
How Many Units?
  • The number of Motor Units recruited for a task depends on: 1. Demand

2. Duration

excitation contraction coupling
Excitation - Contraction Coupling
  • Pre-Synaptic Terminal (Nerve): Acetylcholine released
  • Post-Synaptic Terminal (Motor Endplate): Ach stimulates by binding =>Muscle fiber depolarization
  • Contraction!
  • Resting Membrane Potential: Membranes separate charges: Polarized
  • Depolarization: Charge reversal across membrane
Action Potential (AP) Depolarization travels along membrane

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

sliding filament theory
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
  • All-or-None “Twitch”
  • Sarcomere units shorten by thin and thick filaments “sliding” past each other

The Physiology of Muscle

Contraction and ATP

take five
Take “Five”:

Draw and Label The Neuromuscular Junction:

Page 158

*What is the chemical


one more visit to that neuromuscular junction
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.
what happens to the acetylcholine
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…
toxins neuromuscular junction
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
death by sarin acetylcholine accumulates in nmj
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
something lighter please
Something Lighter Please
  • Check out this cool site for specific exercises!
where does all that atp come from
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
energetics of contraction continues
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
all three contribute apt at all times
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
the marathon
The Marathon:
  • Hours of exercise possible
  • Uses ATP from aerobic (oxidative) sources
  • Oxygen Delivery!
the half mile or
The Half-Mile…or:
  • More Intense
  • Bursts Lasting 2-5 minutes with rests
  • Using Anaerobic Glycolysis
  • Lactic Acid Buildup
the sprints and jumps
The Sprints and Jumps
  • Less than 10 seconds duration
  • Very Intense
  • Creatine Stores in Muscles contribute to CP-ATP production
creatine phosphate
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…
one last crazy engebretsen simulation
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 
muscle fatigue
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
muscle fiber types fast ii iia vs slow i
II Myosin

Fast, Force, Fatigue

“White”: Glycogen



I Myosin

Slow, Endure

“Red”: Myoglobin, mitochondria,



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