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3 types of vertebrate muscle
- 1.Skeletal:voluntary movement
- 2.Cardiac:beating of the heart
- 3.Smooth:Involuntary, movement of internal organs
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Skeletal muscle cells are...
- 1.Muscle fibers
- -large and multinucleate
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Skeletal muscles form from....
fusion of embryonic myoblasts
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Epimysium
wrap around muscle
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Perimysium
wraps around Fasicles
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Endomysium
wraps the muscle fibers
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How does Muscle get activated?
- 1.Brain sends signals to muscles fiber
- 2.Axon of neuron binds to skeletal muscle fibers
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Fine motor control
one axon to one muscle fiber
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gross motor control
one axon to many muscle fibers
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Myofibrils
Bundles of actin and myosin filament
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How actin filaments surround one myosin filament?
6
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Sarcomeres
1. Repeating units of overlapping actin and myosin filaments
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each sarcomere is bounded by...
Z lines
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what anchors actin?
Z lines
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A band
- 1.Center
- 2.Contains myosin and no actin
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I band
1.Actin, yet no myosin are present
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H zone
- where actin and myosin do not overlap
- -myosin but no actin
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Titin
the largest protein in the body
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M band
holds the myosin together
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What is muscle contraction initiated by?
1.Initiated by action potentials from motor neuron at neuromuscular junction
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Myosin structure
- 1.Two polypeptide chains coiled together
- 2.Globular head
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Actin structure
- Long twisted molecule
- -tropomyosin twists around it
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Motor unit
all the muscle fibers activated by one motor neuron
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To increase strength of muscle contraction....
- 1.Increase rate of firing of motor neuron
- 2.Recruit more motor neurons to fire
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what blocks the binding sites on actin?
at rest, tropomyosin blocks the binding sites on actin
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Steps of muscle contraction
- 1.Neuron action potential arrives at end of motor neuron
- 2. ACH is released
- 3. ACh binds to receptors on motor end plate
- 4.Permeability of sarcolemma changes (Na rushes in)(an action potential is produced)
- 5.Muscle action potential sweeps into the T tubules
- 6. triggering release of Ca from the sarcoplasmic reticulum
- 7.CA binds to troponin
- 8.Troponin changes shape and shifts tropomyosin to expose binding sites of actin
- 9. myosin binds to actin (ADP released from myosin)
- 10. Myosin head pivots (pulling actin)
- 11. Myosin releases from actin
- 12. Myosin re-extends (ATP---ADP)
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what cells initiate and coordinate heart contractions>
Pacemaker and conducting cells
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Myogenic
Heartbeat is myogenic, generated by the heart muscle itself
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Smooth muscles have electrical contact by...
gap junctions
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Smooth muscle contraction
- 1.Ca2+ influx tp sarcoplasm, stimulated by stretching
- 2.Ca2+ binds with calmodulin
- 3.Activates myosin kinases, which phosphorylates myosin heads
- 4.Bind and release actin
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Twitch
minimum unit of contraction
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Tension generated by entire muscle depends on:
- • Number of motor units activated
- • Frequency at which motor units are firing
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Tetanus
action potentials arrive so rapidly that the sarcoplasmic reticulum does not have time to reclaim the calcium ions.
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How long muscle fiber can sustain tetanic contraction depends on
ATP supply
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To maintain contraction, actin-myosin bonds have to keep....
cycling
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ATP is needed to break the
actin-myosin bonds, and“re-cock” the myosin heads
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Slow-twitch fibers
- 1.Oxidative or red muslce
- 2.Contain myoglobin:oxygen binding protein
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Slow-twitch fibers
- 1.Have reserves of glycogen and fat
- 2.Can produce ATP if oxygen is available
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muscles with high proportions of ______ are good for aerobic workout (e.g., long distance running, cycling, swimming, etc.).
slow-twitch fibers
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Fast-twitch fibers
- 1.Glycolytic or white muscle
- 2.Fewer mitochondria, few blood vessels
- 3. Good for sprints, fatigue quickly
- 4.Largely genetic
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Muscles have three systems for supplying ATP for contractions:
- 1.immediate system: uses preformed ATP and creatine phosphate
- 2.Glycolytic system: metabolizes carbohydrates to lactic acid and pyruvate
- 3.Oxidative system: metabolizes carbohydrates or fats to H2O and CO2
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