Muscular Contraction
Characteristics of Muscles
• Muscle fibres are elongated
• Contraction of muscles is due to the
movement of microfilaments
• All muscles share some terminology:
– Prefix myo refers to muscle
– Prefix mys refers to muscle
– Prefix sarco refers to flesh
Skeletal Muscle Characteristics
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•
•
•
•
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by
connective tissue
Connective Tissue Wrappings of
Skeletal Muscle
• Endomysium =
around single muscle
fibre
• Perimysium = around
a fascicle (bundle) of
fibres
Connective Tissue Wrappings of
Skeletal Muscle
• Epimysium = covers
the entire skeletal
muscle
• Fascia = on the
outside of the
epimysium
Gross Structure of Skeletal Muscle
• Skeletal muscles are encased by epimysium:
fascia of fibrous connective tissue.
• A bundle of cylindrical muscle fibres is
surrounded by the perimysium.
• Endomysium surrounds each muscle fibre.
• Sarcolemma beneath endomysium is a thin,
elastic membrane.
Microscopic Anatomy of Skeletal
Muscle
• Cells are multinucleate
• Nuclei are just beneath the sarcolemma
Microscopic Anatomy of Skeletal Muscle
• Sarcolemma – specialized plasma membrane
• Sarcoplasmic reticulum – specialized smooth
endoplasmic reticulum (network of
membranous tubules within the cytoplasm )
• Sarcoplasm (cytosol)
is the fluid portion in
muscle fibres.
• Contains contractile
proteins, nuclei,
mitochondria,
sarcoplasmic
reticulum.
Microscopic Anatomy of Skeletal
Muscle
• Myofibril
– Bundles of myofilaments
– Myofibrils are aligned to give distinct bands
• I band =
light band
• A band =
dark band
Muscle Structure
• Each myofibril is made up of parallel filaments.
• There are 2 kinds of filament called thick & thin
filaments.
• These 2 filaments are linked at intervals called cross
bridges, which stick out from the thick filaments
Thick
filament
Thin
filament
Cross
bridges
Microscopic Anatomy of Skeletal
Muscle
• Sarcomere
– Contractile unit of a muscle fibre
Microscopic Anatomy of Skeletal
Muscle
• Organization of the sarcomere:
– Thick filaments = myosin filaments
• Composed of the protein myosin
• Has ATPase enzymes
Microscopic Anatomy of Skeletal
Muscle
• Organization of the sarcomere
– Thin filaments = actin filaments
• Composed of the protein actin
• Distinguished area between Z lines.
• Thicker filaments confined to A band, a lighter
middle region called the H zone.
• Thinner filaments arise in middle region of I band,
at the Z line.
• During contraction, neither thick nor thin
filaments change in length. They slide.
Microscopic Anatomy of Skeletal
Muscle
• Myosin filaments have heads (extensions, or
cross bridges)
• Myosin and actin overlap
Microscopic Anatomy of Skeletal
Muscle
• At rest, there is a bare zone that lacks actin
filaments
• Sarcoplasmic reticulum (SR) – for storage of
calcium
Sarcome
re
H
zone
A
band
I band