UNIT- MUSCULAR SYSTEM
Introduction-
Muscular system is the biological system of humans that produces movement.
There are approximately 640 skeletal muscles in the human body.
Muscle is contractile tissue and is derived from the mesodermal layer of embryonic
germ cells.
Muscle is composed of muscle cells or muscle fibers. cells are composed of
myofibrils that contain sarcomeres which are composed of actin and myosin.
Individual muscle cells are lined with endomysium. Muscle cells are bound together
by perimysium into bundles called fascicles.
There are three basic types of muscles in the body: Skeletal, smooth and cardiac
muscles
Skeletal muscle is voluntary and striated. These are the muscles that attach to bones
and control conscious movement.
Smooth muscle is involuntary and non-striated. It is found in the hollow organs of
the body, such as the stomach, intestines, and around blood vessels.
Cardiac muscle is involuntary and striated. It is found only in the heart and is
specialized to help pump blood throughout the body.
Skeletal Muscle
Skeletal muscle consists of hundreds or even thousands long, string-like skeletal
muscle fibers.
Skeletal muscle fibers are individually wrapped in connective tissue called
endomysium.
The skeletal muscle fibers are bundled together in units called muscle fascicles,
which are surrounded by sheaths of connective tissue called perimysium.
Sequentially, fascicle are bundled together to form individual skeletal muscles, which
are wrapped in connective tissue called epimysium.
The connective tissues in skeletal muscles have a variety of functions.
They support and protect muscle fibers, allowing them to withstand the forces of
contraction by distributing the forces applied to the muscle.
They also provide pathways for nerves and blood vessels to reach the muscles. In
addition, the epimysium anchors the muscles to tendons.
Muscle fiber consists of a bundle of myofibrils, which are themselves bundles of
protein filaments.
These protein filaments consist of thin filaments of the protein actin, which are
anchored to structures called z discs and thick filaments of the protein myosin.
Filaments are arranged together within a myofibril in repeating units called
sarcomeres, which run from one z disc to the next.
The sarcomere is the basic functional unit of skeletal muscles. It contracts as actin
and myosin filaments slide over one another
1
, Skeletal muscle tissue is said to be striated, because it appears striped. It has this
appearance because of the regular, alternating a (dark) and i (light) bands of
filaments arranged in sarcomeres inside the muscle fibers.
Other components of a skeletal muscle fiber include multiple nuclei and
mitochondria.
Smooth muscle
Smooth muscle cell is 3-10 µm thick and 20-200 µm long Cells that make up smooth
muscle are generally called myocytes. Unlike the muscle fibers of striated muscle
tissue, the myocytes of smooth muscle tissue do not have their filaments arranged in
sarcomeres
Cell membrane forms small pouch-like invaginations into the cytoplasm, which are
functionally equivalent to the T-tubules of the skeletal musculature.
Cytoplasm is homogeneously eosinophilic and consists mainly of myofilaments.
Nucleus is located in the center and takes a cigar-like shape during contraction.
Smooth muscle cells are anchored to the surrounding connective tissue by a basal
lamina
Smooth muscle fibers group in branching bundles.
As opposed to skeletal muscle fibers these bundles do not run strictly parallel and
ordered but consist in a complex system. Thus the cells can contract much stronger
than striated musculature.
2
Introduction-
Muscular system is the biological system of humans that produces movement.
There are approximately 640 skeletal muscles in the human body.
Muscle is contractile tissue and is derived from the mesodermal layer of embryonic
germ cells.
Muscle is composed of muscle cells or muscle fibers. cells are composed of
myofibrils that contain sarcomeres which are composed of actin and myosin.
Individual muscle cells are lined with endomysium. Muscle cells are bound together
by perimysium into bundles called fascicles.
There are three basic types of muscles in the body: Skeletal, smooth and cardiac
muscles
Skeletal muscle is voluntary and striated. These are the muscles that attach to bones
and control conscious movement.
Smooth muscle is involuntary and non-striated. It is found in the hollow organs of
the body, such as the stomach, intestines, and around blood vessels.
Cardiac muscle is involuntary and striated. It is found only in the heart and is
specialized to help pump blood throughout the body.
Skeletal Muscle
Skeletal muscle consists of hundreds or even thousands long, string-like skeletal
muscle fibers.
Skeletal muscle fibers are individually wrapped in connective tissue called
endomysium.
The skeletal muscle fibers are bundled together in units called muscle fascicles,
which are surrounded by sheaths of connective tissue called perimysium.
Sequentially, fascicle are bundled together to form individual skeletal muscles, which
are wrapped in connective tissue called epimysium.
The connective tissues in skeletal muscles have a variety of functions.
They support and protect muscle fibers, allowing them to withstand the forces of
contraction by distributing the forces applied to the muscle.
They also provide pathways for nerves and blood vessels to reach the muscles. In
addition, the epimysium anchors the muscles to tendons.
Muscle fiber consists of a bundle of myofibrils, which are themselves bundles of
protein filaments.
These protein filaments consist of thin filaments of the protein actin, which are
anchored to structures called z discs and thick filaments of the protein myosin.
Filaments are arranged together within a myofibril in repeating units called
sarcomeres, which run from one z disc to the next.
The sarcomere is the basic functional unit of skeletal muscles. It contracts as actin
and myosin filaments slide over one another
1
, Skeletal muscle tissue is said to be striated, because it appears striped. It has this
appearance because of the regular, alternating a (dark) and i (light) bands of
filaments arranged in sarcomeres inside the muscle fibers.
Other components of a skeletal muscle fiber include multiple nuclei and
mitochondria.
Smooth muscle
Smooth muscle cell is 3-10 µm thick and 20-200 µm long Cells that make up smooth
muscle are generally called myocytes. Unlike the muscle fibers of striated muscle
tissue, the myocytes of smooth muscle tissue do not have their filaments arranged in
sarcomeres
Cell membrane forms small pouch-like invaginations into the cytoplasm, which are
functionally equivalent to the T-tubules of the skeletal musculature.
Cytoplasm is homogeneously eosinophilic and consists mainly of myofilaments.
Nucleus is located in the center and takes a cigar-like shape during contraction.
Smooth muscle cells are anchored to the surrounding connective tissue by a basal
lamina
Smooth muscle fibers group in branching bundles.
As opposed to skeletal muscle fibers these bundles do not run strictly parallel and
ordered but consist in a complex system. Thus the cells can contract much stronger
than striated musculature.
2
