Physiology of Muscles The Sliding Filament Theory

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Physiology of MusclesThe Sliding Filament Theory
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The Neuromuscular System
Linkage between the _______________system and the
_______________ system (nerve impulses from the
brain or spinal cord).

• Motor Unit
• Motor Unit
• Motor Units range from small (eye movements) to
  large (quadriceps of leg).
• Muscle Twitch
• A single nervous impulse and the resulting
  contraction.
• Nerves transmit impulses in waves that ensure
  smooth movements.

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Neuromuscular Joint

• Junction point between the nervous and muscular
  systems.
• A chemical neurotransmitter is released (Ach -
  acetylcholine)
• Detected by receptors on surface of muscle
  fibre.
• Results in muscle contraction

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The All-or-None Principle

• When a motor unit is stimulated to contract, it
  will do so to its fullest potential (maximum)
• Whether a motor unit consists of 10 muscle fibres
  or 800, either ___________________________________
  _______________________________________

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Outside Anatomy of Skeletal Muscle

• Skeletal muscle makes up a substantial portion of
  human body weight
• The _________________ (outer connective tissue)
  binds groups of muscle fibres called
  __________________ together which are then bound
  by the larger/stronger ______________
• The ___________________ envelopes the entire
  muscle, it changes its properties as it becomes
  one with the tendon
• Remember the ______________________ of the long
  bone?
• This is where the tendon of the muscle attaches
  to the bone
• Muscle is attached to bone at two locations
• Origin
• Insertion

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Perimysium
Endomysium
Epimysium
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Inside Anatomy of Skeletal Muscle

• The endomysium (sheath of connective tissue)
  surrounds each individual muscle fibre
• Beneath the endomysium is the sarcolemma a plasma
  membrane containing the muscle cells cytoplasm
  (sarcoplasm)
• The endomysium is surrounded by a rich blood
  supply and, therefore, a good system for O2 and
  CO2 removal
• Nerves also supply the muscle
• Thread like structures, myofibrils, run the
  length of the muscle
• Within the myofibril are thin (Actin) and thick
  (Myosin) filaments
• Actin and Myosin are contained within Sarcomeres
  (compartments)

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• Myofibril
• Myosin thick filaments
• Actin thin filaments, contains the proteins
• Troponin
• Tropomyosin
• Together, actin and myosin, have a swivel-locking
  mechanism
• This is the Sliding Filament Theory

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Myofibril
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Sliding Filament Theory

• Myosin head will not attach to actin unless
  ____________ is released by the sarcoplasmic
  reticulum (SR)
• _______ (acetylcholine) initiates this
• _______________ swivels, allowing the binding
  sites on ___________ filament (_____________) to
  be exposed
• During contraction, protein filaments interact at
  molecular level causing them to slide across each
  other (the sarcomere shortens)
• REST
• the cross-bridges extend toward _____________
• The _____________and ______________ are now in a
  coupled position.
• The level of _______________ concentration is low

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Sliding Filament Theory

• STIMULATION
• myosin ___________________ form a type of bond
  with selected sites on the actin filament
• Acto-myosin formation takes place
• There is an immediate increase of intracellular
  _______
• This is brought about by the arrival of the
  action potential at the transverse tubules, which
  causes Ca2 to be released by the SR
• The inhibitory action of _______________ that
  prevents actin-mysoin interaction is released
  when Ca2 ions bind rapidly with troponin in the
  actin filament.
• Now the muscle is turned on

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Sliding Filament Theory

• CONTRACTION
• Cross-bridges _________________________
• The muscle shortens and the __________ slides
  over the _______________
• Tension develops
• The _________ is broken down to ______ plus
  _____plus energy
• Contraction will continue as long as
  ___________ions remain at a level that inhibits
  the troponin-tropomyosin system

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Sliding Filament Theory

• RELAXATION
• nerve stimulus to the muscle is removed,
  _________ions move back into the SR
• The retrieval of __________from the
  troponin-tropomyosin proteins ____________ the
  active sites on the actin filaments
• This deactivation accomplishes two things
• It prevents any mechanical link between the
  myosin cross-bridges and the actin filaments
• It reduces the activity of myosin ATPase so there
  is no more splitting. Muscle now returns to
  resting state.

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THE ROLE OF ADENOSINE TRI-PHOSPHATE (ATP)

• ATP is a chemical compound stored in muscles,
  which contains three phosphates attached by
  high-energy bonds to adenosine.
• When the myosin heads on the myosin filaments
  attach themselves to binding sites on the actin,
  ATP is broken down and the energy released causes
  the myosin to pull on the actin.
• As the work of the muscle increases, more and
  more ATP is used up.
• ATP ? ___________________________

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For more help on the sliding filament theory

• http//www.blackwellpublishing.com/matthews/myosin
  .html