Download fast-twitch.

MUSCLE
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Slow Twitch
Muscles that are used for extended periods of activity, such as standing or
walking, they need a consistent energy source. The protein myoglobin stores
oxygen in muscle cells, which use oxygen to extract the energy needed for
constant activity.
Fast Twitch
Muscles that are used for situations where quick bursts of activity are needed
are made up of fibers called fast-twitch. These muscles get energy from
glycogen.
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Most skeletal muscles contain some mixture of Type I and Type II fibers, but
a single motor unit always contains one type or the other, never both
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Fish
float in water and don't need constant muscle energy to support their skeletons
most fish meat is white, with some red meat around the fins and tail, which are used for swimming
the red color of some fish, such as salmon and trout, is due to astaxanthin, a naturally occurring
pigment in the crustaceans they eat
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Cattle
spend a lot of time standing, and so their muscles are constantly being used
therefore, beef has a fairly high concentration of myoglobin and is dark red
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Pigs
spend quite a bit of time standing and roaming around
the pink color of pork is due to myoglobin, but because the animals used for pork are young and
small, their muscles are less developed and do less work
so pigs have a lower concentration of myoglobin in their muscles than do cows
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Chickens
spend a lot of time roaming around or standing
their thigh and leg muscles are used constantly, and so the meat from these parts is dark
since they rarely fly, and then only for very short distances, the meat that comes from the breast
and wings is white
in contrast, wild birds such as ducks fly a lot; the meat from their breasts and wings is dark
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Humans
have both types of fibers as well, however, unlike animals and fish, humans' fast- and slow-twitch
fibers can't be delineated quite so neatly
both types are interspersed throughout the body; the average human has about 50% slow-twitch
and 50% fast-twitch fibers
Professional athletes can have a higher percentage of one or the other type
Olympic sprinters may have as much as 80% fast-twitch fibers and long-distance runners may
have as much as 80% slow-twitch; weight-lifters need fast-twitch fibers for quick bursts of strength
while long-distance swimmers need the constant movement provided by slow-twitch fibers
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Type I
loaded with mitochondria and
depend on cellular respiration for ATP production
resistant to fatigue
rich in myoglobin and hence red in color
activated by small-diameter, thus slow-conducting, motor neurons
also known as "slow-twitch" fibers
dominant in muscles that depend on tonus, e.g., those responsible for posture
ATPase staining
type II fibers (dark); type I fibers (light).
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Type II
few mitochondria
rich in glycogen and
depend on glycolysis for ATP production
fatigue easily because of the buildup of lactic acid during glycolysis
low in myoglobin hence whitish in color
activated by large-diameter, thus fast-conducting, motor neurons
also known as "fast-twitch" fibers
dominant in muscles used for rapid movement
reacted for enzyme NADH-TR;
type I fibers (dark); type II fibers (light)
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Muscular Dystrophies
Together myosin, actin, tropomyosin, and troponin make up over three-quarters of the protein in
muscle fibers. Some two dozen other proteins make up the rest. These serve such functions as
attaching and organizing the filaments in the sarcomere and connecting the sarcomeres to the
plasma membrane and the extracellular matrix. Mutations in the genes encoding these proteins
may produce defective proteins and resulting defects in the muscles.
Among the most common of the muscular dystrophies are those caused by mutations in the gene
for dystrophin.
The gene for dystrophin is huge, containing 79 exons spread out over 2.3 million base pairs of
DNA.
The gene for dystrophin is on the X chromosome, so these two diseases strike males in a typical Xlinked pattern of inheritance
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Duchenne muscular dystrophy (DMD)
frame shift mutation  no dystrophin is synthesized and DMD, a very severe form of the disease,
results
Becker muscular dystrophy (BMD)
If the deletion simply removes certain exons, a shortened protein results that produces BMD, a
milder form of the disease
Western blot of dystrophin from dystrophinopathies
Dystrophin staining
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Normal Muscle
Duchenne Muscular
Dystrophy
1:
2:
3:
4:
Becker dystrophy
Becker dystrophy
Normal
Duchenne dystrophy
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