Here you will find a small summary on a sheet about the skeletal muscle cell, which is, how the skeletal muscle, the sarcomere and the most important proteins that make it up are formed.
MUSCLE CELL
THE MUSCLE CELL: The skeletal striated muscle cell
them at the same level. They are also related to the
is known as a muscle fiber. It has a variable length,
SKELETAL STRIATED MUSCLE sarcolemma. They generate a distribution of forces within the
ranging from a few millimeters to as much as 30 cm in
It presents striations, is voluntary (meaning the human body connective tissue.
very large muscles. Its diameter varies between 10 and
controls it). It is known as muscle fiber, with a cylindrical/oval IMPORTANT PROTEINS
100 microns.
and multinucleated cellular shape (with a peripheral ● DESMIN is a protein corresponding to intermediate
arrangement), located close to the sarcolemma. filaments that provides stability and is important for
LEVELS OF MUSCLE STRUCTURAL ORGANIZATION
➢ THE SARCOPLASMIC RETICULUM aligning the Z-disks.
A muscle is composed of bundles or fascicles of muscle
The most developed cellular structure of the striated muscle ● DYSTROPHIN is visualized in actin filaments and its
fibers. Within the fascicles are muscle fibers (grouped muscle
cell is the sarcoplasmic reticulum (it surrounds the myofibrils), function is to link Laminin with the matrix (i.e., linking
cells), and within the muscle fiber are myofibrils. Myofibrils
where large amounts of calcium are stored and will be used the sarcomere to the matrix).
are composed of sarcomeres, which are structures formed by
in muscle contraction. The T-tubules are invaginations of the ● PLECTIN is found in intermediate filaments and binds
a regular sequence of actin and myosin filaments.
sarcolemma that allow rapid synaptic impulse action in the them to Actin Filaments or Microtubules.
CONNECTIVE TISSUE AND ITS RELATION TO MUSCLE
muscle cell. The triad is a combination of a T-tubule with two
Muscle is surrounded by connective tissue, with fasciae being
terminal cisterns of the sarcoplasmic reticulum. BANDS OF MUSCLE FIBER
the term for the connective tissue that delimits a region of the
muscle, allowing the muscle to contract and stretch. There The Z-line (Z-disc) delimits the sarcomere.
SARCOMERE PROTEINS
are different types of connective tissue that can surround the
Actin is unstable, but in a muscle, it must be stable. To The H band is formed by the overlap of thick filaments and is
muscle:
achieve this, the ends of the filament are blocked. At the (-) located in the middle of the A band.
● Epimysium: Surrounds the muscle.
end, blocking is done with tropomodulin, and at the (+) ends,
● Perimysium: Surrounds the fascicle.
it is blocked with alpha-actinin, Cap Z, and Titin. MYOMESIN The I band is formed by the overlap of thin filaments
● Endomysium: Surrounds the individual muscle fiber.
is a protein found in the M-line of the sarcomere, on a protein
lattice (composed of Protein C, Myosin, etc.) and stabilizes The M band is located in the middle of the sarcomere.
this lattice.
● NEBULIN is known as the molecular ruler, which
The A band is between the overlapping thin and thick
positions and gives a determined length to the actin
filaments.
filament.
● TROPONIN is a protein complex formed by 3 units.
● TROPOMYOSIN stabilizes the actin filament laterally.
COSTAMERES Fundamental for muscle contraction.
Costameres are multiprotein complexes located at the Z-line,
whose function is to align the Z-disks of all myofibrils, placing
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