Muscle Physiology

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Muscle Physiology

• Chapter 11

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Connective Tissue Components

• Muscle cell muscle fiber
• Endomysium covers muscle fiber
• Perimysium binds groups of muscle fibers
  (fasicles)
• Epimysium covers the entire muscle
• Tendon fibrous tissue that connects muscle to
  bone
• Aponeurosis broad, flat sheet of connective
  tissue
• Fascia fibrous CT surrounding muscle and tendon

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General Function of Muscles

• Movement
• Excitability
• Contractility
• extensibility
• Heat Production
• Posture

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Overview of Muscle Cell

• Muscle cell muscle fiber
• Sarcolemma plasma membrane
• Sarcoplasm cytoplasm
• Sarcoplasmic reticulum (SR) network of tubules
  and sacs
• Multi-nucleated, multiple mitochondrion
• Bundles of myofibrils extend lengthwise fill
  sarcoplasm
• Composed of thick and thin myofilaments

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Sarcomere

• Contractile unit of a muscle fiber
• each myofibril consists of many sarcomeres
• Z line
• Anchors thin filaments
• Boundary of sarcomere
• M line anchors thick filaments
• A band segment of thick thin filaments
• I band segment of thin filaments
• H zone where thin and thick filaments will not
  overlap (only thick)

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Sarcomere cont

• Elastic filaments connect thick filaments to Z
  line
• T (transverse) tubules allows impulses
  traveling along sarcolemma to move deeper within
  the cell
• Triad t tubule sandwiched between sacs of the
  SR
• Allows impulses traveling along a t tubule to
  stimulate sacs of the SR

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Myofilaments

• Myofibrils made up of 1000s of thin and thick
  myofilaments
• Thin filaments
• Actin
• Tropomyosin
• Troponin
• Thick filaments
• myosin

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Muscle Excitation

• Nerve impulse reaches the end of a motor neuron ?
  releases acetylcholine (Ach)
• Ach diffuses across the neuromuscular junction
  and binds with the receptors on the motor endplate

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Muscle Contraction

• Impulses travel along the sarcolemma ? t tubules
  ? sacs of SR
• Ca2 is released into the sarcoplasm ? binds with
  troponin on thin myofilaments
• Tropomyosin shift to expose actins active site
• Energized myosin heads bind with actins active
  site and pulls thin filament towards center of
  sarcomere
• Requires ATP

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Muscle Relaxation

• Nerve impulse is complete ? Ca2 is pumped back
  into the sacs of the SR
• Ca2 is stripped from the troponin ? tropomyosin
  covers the actins active site
• Myosin heads can no longer bind with actin ?
  muscle fiber returns to its resting length

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http//www.sci.sdsu.edu/movies/actin_myosin_gif.ht
ml
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Rigor Mortis

• stiffness of death
• SR releases excess Ca2 ? myosin heads bind with
  actins active sites ? contraction of
  myofilaments
• Lack of ATP after death causes cross bridges to
  stick

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http//highered.mcgraw-hill.com/sites/0072507470/s
tudent_view0/chapter9/
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Sliding Filament Theory

• In fully contracted muscle
• H zone disappears
• I band narrows
• A band remains the same

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Energy for Contractions

• Hydrolysis (breakdown) of ATP
• ATP ? ADP (breaking high energy bond btwn 2nd and
  3rd phosphate groups)
• ATP binds ? myosin head moves to resting position
  (11-7A)
• Breakdown of ATP allow myosin head to bind with
  actin and perform power stroke (11-7B-D)
• ATP binds to return myosin head back to resting
  position

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Alternate Source of Energy

• ATP must be continually re-synthesized
• Breakdown of creatine-phosphate (CP) provides
  energy for ATP re-synthesis
• Catabolism of food provides energy for ATP and CP
  synthesis

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Oxygen Glucose

• O2 and glucose are the starting materials for
  cellular respiration (process that makes ATP)
• During rest oxygen is stored in myoglobin
• Supplies muscle fibers with oxygen during period
  of exercise
• High amounts of myoglobin red fibers slow
  twitch fibers
• Low levels of myoglobin white fibers fast
  twitch fibers

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Aerobic vs. Anaerobic Respiration

• Aerobic Respiration
• Oxygen-requiring process
• Produces maximum amount of ATP from one glucose
  molecule
• Anaerobic Respiration
• Does not require oxygen
• Short-term, rapid process to re-synthesize ATP
• Produces lactic acid
• Burning/soreness in muscles

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Heat Production

• Some energy from catabolic processes is lost as
  heat
• Muscle release massive amts of heat
• Thermoreceptors sense decrease in body temp ?
  hypothalamus integrates information ? signal sent
  to skeletal muscle to contract ? shivering ?
  homeostatic balance is maintained

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Motor Unit

• Motor unit motor neuron muscle fibers it
  attaches to
• Motor neurons can innervate few to 100s of muscle
  fibers
• A lower number of muscle fibers within a motor
  unit more precise movement
• Ex hand vs abdomen

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http//natchem.files.wordpress.com/2009/11/motor-u
nit-lg.jpg
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Isotonic vs Isometric Contractions

• Isotonic tension remains the same length of
  the muscle changes
• Concentric contraction muscle shortens
  (contracts)
• Eccentric contraction muscle lengthens
• Isometric tension changes length of the muscle
  remains the same
• Myosin heads unable to move thin filaments
• Static tension

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Smooth Muscle Contractions

• Small tapered cell w/ single nuclei
• No t-tubules loosely organized SR
• No sarcomeres
• Contract to shorter lengths
• Myofilaments crisscross (balled up appearance
  when contracted)
• Calcium binds to calmodulin

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http//www.cytochemistry.net/microanatomy/muscle/s
mooth1.jpg
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Smooth Muscle Tissue Types

• 1. Visceral
• Gap junctions connect smooth muscle fibers into
  sheets
• Forms inner muscular layer of hollow structures
• Exhibits autorhythmicity
• Peristalsis, excretion of urine, childbirth,
  mixing of stomach contents
• 2. Multiunit
• Composed of many single-cell units
• Ex arrector pili muscles, lines blood vessels