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CLIL SCIENCE
Muscle tissue and muscle
contraction
Rosalie Crawford - Veronica Revel
Fondazione Liceo Linguistico Courmayeur
How does it happen?? How do our
muscles work??
Skeletal, cardiac and smooth muscle
Skeletal muscle fibre
The structure of skeletal muscle
• A group of myofibrils (from
myo, the prefix for muscle),
each of which is surrounded
by the specialized endoplasmic
reticulum of muscle cells, the
sarcoplasmic reticulum.
• The sacs of the sarcoplasmic
reticulum contain calcium ions
(Ca2+) , which, when released,
trigger muscle contraction.
• Myofibrils are composed of
units called sarcomeres, which
have two types of filaments
running parallel.
• The sarcomere is composed
of two types of filaments
running parallel to one
another. The thicker
filaments are composed of
the protein myosin while the
thinner ones are primarily
actin.
What causes a muscle contraction?
• Muscle contractions occur as the sarcomeres present in
muscle fibers shorten. When muscle fibres are triggered by
neuromuscular junctions, a process begins in which thick and
thin filaments overlap causing the sarcomeres to shorten over
a brief period of time. The thick filaments are composed of
about 200 mysosin fibres that look similar to golf clubs.
Along the long filament, the myosin proteins line up in
opposite directions with their “heads” protruding out from
the filament. The thin filaments, composed of actin,
tropomyosin, and troponin, form a spiral helix with myosin
binding sites on the actin.
The cycle of muscle contraction
Muscle contraction
• When a muscle contraction is triggered,
• 1) calcium ions and energy-supplying ADP cause
rearrangement of the thin filaments,
• 2) the myosin heads bind to the actin,
• 3) the myosin heads pull the thin filaments towards the
center of the sarcomere.
• Once contraction is complete, ATP binds to myosin, the
myosin-actin bond is broken, and the myosin head “re-cocks”
to the starting position until the cycle repeats. This cycle
occurs simultaneously in many muscle fibers present in the
entire muscle tissue causing contractions in the muscles of
your eye, to the movement of your arms and legs.
Molecular mechanism of muscular contraction
Isometric & isotonic contractions
• Skeletal muscles undergo two
types of contractions:
isometric and isotonic. Because
isometric contractions occur
when the muscle does not
shorten, as when pushing
against a wall, no work is done
and no power is produced. In
isometric contractions,
myofibrils slide over each
other causing the sarcomeres
to shorten and external work
is performed.