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Because the generation of force depends on the cross-bridge cycle, it makes sense that a maximum number of potential interactions between _______ heads and _____ filaments would lead to an ________ in force.
myosin; actin; increase
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The amount of tension that muscles generate _______ as a function of their length.
varies
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Relaxed muscles ________ generate force; Partially contractyed muscles generate ________ force; Fully contracted muscles ________ generate ____ force.
cannot; maximum; cannot; much
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Force depends on overlap between ______ and ____.
myosin; actin
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At maximum stretch or maximum contraction, _____ actin-myosin interactions ----> ____ force generated.
fewer; less
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The motor neuron and all the fibers it innervates are called, collectively, a
motor unit
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Muscle contraction is "all-or-none". That is , once a muscle fiber contracts,
it contracts as much as possible, until its calcium and/or ATP run out
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A single motor neuron sends axon terminals to
many muscle fibers
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While individual muscle fibers contract fully, not
all the muscle fibers in a muscle contract.
*In fact, most of the time, not very many of them contract at all. They take turns working, then loafing for long periods, then working
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Motor Unit:
Precise control of muscles:
small motor unit
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Motor Unit:
More force from a single motor neuron (less finesse):
large motor unit
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To make movements more smooth, something called the size principle operates. Describe the size principle.
the small motor units are recruited first, then larger motor units, and finally the largest motor units are recruited last.
*This makes sense, because the amount of force generated is directly proportional to the number of muscle fibers that contract.
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The Myogram:
Force vs time is a hump-shaped curve.
Describe the Latent period (first)
the time it takes for an action potential to travel along the muscle surface.
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The Myogram:
Force vs time is a hump-shaped curve.
Describe the Contraction period (second)
release of Ca++ and multiple cross-bridge cycles to generate force.
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The Myogram:
Force vs time is a hump-shaped curve.
Describe the Relaxation period (third)
myosin not bound to actin.
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What is a refractory period?
Depending on the muscle type, it may take a few milliseconds up to a third of a second for the muscle to be ready to contract again.
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The "staircase" pattern seen just before fusion of contractions is called
treppe
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When these contractions fuse into one large contraction of maximum force, it is called
tetanus
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If we begin firing multiple action potentials, something interesting happens. The small bumps begin adding together in the process of
wave formation
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Isotonic contractions are
those muscle contractions that use equal tension (or equal force, or equal strength) to move objects.
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What are two subcategories of isotonic contractions?
Concentric contraction: involves moving a muscle against gravity.
Eccentric contraction: such as lowering a dumbbell, occur when gravity is stretching a muscle (increasing length) at the smae time as you are trying to shorten the muscle (to control the descent of the dumbbell).
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Eccentric contractions are great for building muscle bulk, but they also make the muscle prone to ______. For example, running downhill means that the muscle is in a relaxed state when your foot hits the ground. This can produce _______ ____ _____ ________ about 24 to 72 hours after exercise.
injury; delayed onset muscle soreness
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Isometric contractions involve
holding things in place against gravity. No movement takes place.
*Isometric contractions keep the muscle at the same measurement or length.
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Sources of Muscle Energy:
Glucose is the main source of cellular energy
-if oxygen is plentiful, reaction proceeds through glycolysis ---> Krebs cycle ---> electron transport chain (36-38 ATP per glucos)
-if oxygen scarce, reaction stops at pyruvate (only 2 net ATP per glucose)
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Sources of Muscle Energy:
Sources of glucose in muscle
-Blood glucose
-Muscle stores about 1500 Cal of glycogen, which can be easily converted to glucose.
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Sources of Muscle Energy:
Other carbon sources: fatty acids, amino acids
-these are not easily utilized and protein breakdown destroys muscle.
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Sources of Muscle Energy:
Sources of oxygen in muscle:
-Blood oxygen
-myoglobin, an oxygen-binding protein (similar to hemoglobin in blood)
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Sources of Muscle Energy:
Aerobice metabolism is most efficient, but requires enough oxygen
-blood oxygen + myoglobin-bound oxygen
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In the absence of oxygen, when glucose plentiful, metabolism is anaerobic:
Problem 1: anaerobic glycolysis is inefficient
Problem 2: anaerobic glycolysis produces lactic acid, which lowers blood pH
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Sources of Muscle Energy:
Muscle has an additional energy source:
Creatine;
*When energy is plentiful, phosphate groups are stored on muscle creatine.
*When energy needed, these phosphates can be transferred to ADP to make ATP.
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Sources of Muscle Energy:
What is the approximate amount of time until each (ATP, creatine, anaerobic glycolysis) is consumed.
1. Stored ATP (1-2 seconds)
2. Creatine (4-6 seconds)
3. Anaerobic Glycolysis (hours)
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