microscopic anatomy of the skeletal muscle · 2019-09-06 · muscle cell microscopic structure of...
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Microscopic Anatomy of the Skeletal Muscle
SKELETAL MUSCLE
Microscopic structure of Skeletal MusclesStructure
Description
Consists of hundreds of
thousands of muscle cells,
plus fascia, blood vessels
and nerve fibers
FASCICLE
Microscopic structure of Skeletal MusclesStructure
Description
FASCICLEDiscrete bundle of
muscle cells,
segregated from the
rest of the muscle by
the perimysiumFascicle
(wrapped by
perimysium)
Sarcolemma
Nucleus
(a) Segment of a muscle fiber (cell)
Muscle Cell
Microscopic structure of Skeletal MusclesStructure
Description
Long multinucleated
cells with a banded
(striated)
appearance.
Cell membrane =
sarcolemma
Cytoplasm =
sarcoplasm.
Myofibril
Microscopic structure of Skeletal MusclesStructure
Description
Specialized organelle
that contracts.
Occupy most of the
muscle cell volume.
Composed of
sarcomeres arranged
end to end.
Sarcomere
Microscopic structure of Skeletal MusclesStructure
Description
The contractile unit,
composed of
myofilaments called
actin and myosin.
Sarcomeres line up
end to end inside a
myofibril. Create
the striations.
Myofilaments: Actin and Myosin
Microscopic structure of Skeletal MusclesStructure
Description
Two types:
Actin: Thin contractile
filament. Contains
regulatory proteins that
controls myosin’s ability to
bind
Myosin: Thick contractile
filament.
Contains myosin heads
where the thin filament
attaches during
contraction.
Thick filament Thin filament
(d) Myofilament structure
(within one sarcomere)
Properties of Skeletal Muscle
Irritability – ability to receive and respond to a stimulus
Contractility – ability to shorten when an adequate stimulus is received
• Which Sarcomere is relaxed and which one is contracted?
• What is happening during contraction to the following?– Z line (disc)– I band– A band– Myosin (thick) filament– Actin (thin) filament– H - zone
Sliding Filament Theory When contraction occurs….
the thin filaments slide toward each other
the light-colored H-zone and I-bands (seen in the relaxed sarcomere) disappear
because the actin and myosin are completely overlapped
This happens because the myosin pulls the actintoward the middle. The z-lines become closer together.