A green lacewing Chrysopa sp' in flight

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A green lacewing (Chrysopa sp.) in flight
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Figure 19.1 The organization of skeletal muscles
(Part 1)

• Muscle fiber is a muscle cell sheathed in
  endomysium
• A bundle of muscle fibers is a fascicle sheathed
  in perimysium
• A bundle of fascicles make up a muscle sheathed
  in epimysium.

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Figure 19.1 The organization of skeletal muscles
(Part 2)
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Figure 19.1 The organization of skeletal muscles
(Part 3)
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Figure 19.1 The organization of skeletal muscles
(Part 4)
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Figure 19.2 The arrangement of thick (myosin)
and thin (actin) myofilaments in a sarcomere

• Thick filaments (myosin) make up A band
• Thin filaments (actin) make up I band
• And titin extends from M line to Z disc

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Figure 19.3 Muscle contraction produced by
sliding filaments

• Contraction
• I bands and H zones decrease in length
• A bands remain unchanged
• Strong contractions eliminate the H zone

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Figure 19.4 Myosin molecules form the thick
filament
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Figure 19.5 Molecular interactions that underlie
muscle contraction
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Figure 19.6 The regulation of contraction
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Figure 19.7 Excitationcontraction coupling
(Part 1)
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Figure 19.7 Excitationcontraction coupling
(Part 2)
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Figure 19.7 Excitationcontraction coupling
(Part 3)
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Figure 19.8 Interaction between contractile and
elastic components (Part 1)
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Figure 19.8 Interaction between contractile and
elastic components (Part 2)

• Muscle contractions are a combination of
  isometric and isotonic contractions.
• For experimental purposes the two are separated.

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Figure 17.9 Recording isometric and isotonic
contractions (Part 1)
Figure 19.9 Recording isometric and isotonic
contractions (Part 1)

• A twitch is the response to a single AP
• Latent period is the time it takes for AP to
  reach VG Ca2 channels and for Ca2 to increase
  in the sarcoplasm
• Contraction is the sliding of filaments
• Relaxation is the sequestering of Ca2 in the
  sarcoplasmic reticulum

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Figure 19.9 Recording isometric and isotonic
contractions (Part 2)

• The heavier the load the longer the latent period

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Figure 19.10 The loadvelocity relationship of
skeletal muscle

• Isotonic contractions are used to look at the
  velocity of shortening.
• Greater loads decrease detachment rate between
  actin and myosin.
• The tension produced by a muscle must match the
  force of the load.

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Figure 19.11 Summation and tetanus

• Single twitches
• Summationtwitches can sum because of the time it
  takes for a muscle to relax
• Tetanus is produced by high frequency stimulation
• Fused tetanus is a smooth contraction produced by
  many APs

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Cellular physiology of tetanus and summation

• Tetanus leads to greater amounts of Ca2 released
  into sarcoplasm
• Greater number of crossbridges formed
• The elastic elements (connective fiber sheaths
  and Titin) need time to be pulled taut to
  increase force
• Crossbridges cycle repeatedly until elastic
  elements are taut.
• Tension depends on the the length of the muscle
  when stimulated.
• Muscle tension is greatest when muscle is at its
  ideal length.

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Figure 19.12 The relationship between length and
tension produced by skeletal muscle (Part 1)
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Figure 19.12 The relationship between length and
tension produced by skeletal muscle (Part 2)
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Figure 19.13 Work of contraction
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Box 19.1 The electric eel possesses both strong
and weak electric organs (Part 1)
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Box 19.1 The electric eel possesses both strong
and weak electric organs (Part 2)
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Box 19.1 The electric eel possesses both strong
and weak electric organs (Part 3)
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Figure 19.14 The production and use of ATP
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Figure 7.6 The fueling of intense but sustained
muscular work in humans
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Figure 7.9 The mechanisms of meeting the ATP
costs of world-class competitive running
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Types of Muscles

• Tonic muscle fibers are postural
• Generate no APs
• Slow cross-bridge cycling produces long sustained
  contractions with low energy costs
• Twitch muscle fibers
• Slow oxidative (SO)
• Fast oxidative glycolytic (FOG)
• Fast glycolytic (FG)
• The velocity of a contraction depends on load and
  the type of muscle fiber

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Figure 19.15 Whole muscles typically consist of
mixtures of different types of fibers
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The cat hindlimb and ankle extension

• The soleus muscle consists of SO fibers and
  functions in postural standing
• The medial and lateral gastrocnemius muscles are
  mixed (45 FG, 25 FO and 25 SO)
• The FO contributes fatigue resistance for walking
  and running
• The FG are reserved for short burst fast
  locomotion and for jumping

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Exceptional muscles

• Hummingbird flight muscles contract at 80 Hz
• Tail shaker muscles of rattlesnake contract up to
  90 Hz at the proper temperature
• Factors contributing to speed
• Myosin isoforms capable of rapid crossbridge
  recycling
• Troponin isoforms that have low affinity for Ca2
• Increased density of Ca2 ATPase pumps in SR for
  rapid relaxation
• Cost of speed is limited ability to build up
  tension in muscles
• Shaker muscles require high amounts of ATP,
  glycogen and a large SR

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Box 19.2 Insects exhibit two types of flight
muscles synchronous and asynchronous (Part 1)

• One AP leads to one contraction

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Box 17.2 Insects exhibit two types of flight
muscles synchronous and asynchronous (Part 2)

• One AP leads to many oscillating contractions.
• One contraction one wing beat
• Verticle muscle induces contraction of
  longitudinal muscle and vice versa

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Figure 19.16 Vertebrate skeletal muscles consist
of many different, independent motor units
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Figure 19.17 Innervation patterns of vertebrate
tonic muscle fibers and arthropod muscle fibers
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Figure 19.18 Smooth muscle (Part 1)
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Figure 17.18 Smooth muscle (Part 2)
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Organization of smooth muscle
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Regulation of smooth muscle contractions
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Smooth muscle physiology

• Smooth muscle maintains long term tone
• Provides steady pressure on GI contents
• Provides steady pressure in arterioles
• Smooth muscle fibers contract or relax in
  response to
• Stretching
• Hormones
• Change in pH, O2, CO2
• Temperature
• Ion concentrations

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Smooth muscle contractions

• The bolus distends the gut, stretching its walls.
  
• Stretching stimulates nerves and the muscle
  becomes "more depolarized."
• When a slow wave passes over this area of
  sensitized smooth muscle, spike potentials form
  and contraction results.
• A coordinated contraction moves along the gut
  because the muscle cells are electrically coupled
  through gap junctions.

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Figure 17.19 Cardiac muscle
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