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MUSCULAR SYSTEM
MUSCULAR SYSTEM IS A SYSTEM OF MUSCLES THAT WORK TOGETHER
WITH BONES TO HELP MOVE THE BODY.
A MUSCLE TISSUE IS TISSUE THAT CAN CONTRACT IN A COORDINATED FASHION
AND INCLUDES MUSCLES TISSUE, BLOOD VESSELS, NERVES, AND CONNECTIVE
TISSUE.
Approximately 40 to 50 percent of the MASS of the Human Body is composed of Muscle Tissue.
THE MUSCULAR SYSTEM IS COMPOSED OF MUSCLE TISSUE (MUSCLE FIBER) THAT IS
HIGHLY SPECIALIZED TO CONTRACT, OR SHORTEN, TO PRODUCE MOVEMENT WHEN
STIMULATED.
TYPES OF MUSCLE TISSUE (THREE TYPES)
There are Three Types of Muscle Tissue, or
Muscles: SKELETAL, SMOOTH, AND
CARDIAC.
SKELETAL MUSCLE
Skeletal Muscle are attached to bones and are responsible for
moving body parts.
When viewed under a microscope, Skeletal Muscles appear to
have STRIATIONS (BANDS Or STRIPES).
Skeletal muscles are VOLUNTARY (you CAN control)
MUSCLES.
SMOOTH MUSCLES
SMOOTH MUSCLES ARE INVOLUNTARY
SMOOTH MUSCLE CELLS ARE
SPINDLE-SHAPED
SMOOTH MUSCLES ARE FOUND IN MANY INTERNAL
ORGANS, STOMACH, INTESTINES, AND IN THE WALLS OF
BLOOD VESSELS.
Most Smooth Muscle Cells can CONTRACT WITHOUT Nervous
Stimulation. Because most of its movements cannot be
consciously controlled, Smooth Muscle is referred to as
Involuntary Muscle.
The contractions in Smooth Muscles move food through our
digestive tract control the way blood flows through the circulatory
system, and increase the size of the pupils of our eyes in bright
light.
CARDIAC MUSCLE
THE ONLY PLACE IN THE BODY WHERE CARDIAC
MUSCLE IS FOUND IS IN THE HEART.
Cardiac Cells are striated and are involuntary.
Cardiac Muscle contract without Direct stimulation by the
Nervous System. A bundle of specialized muscle cells in the
upper part of the heart sends electrical signals through cardiac
muscle tissue, causing the heart to rhythmically contract and
pump blood through the body.
MUSCLE STRUCTURE
A Muscle Fiber is a single cell, made be made up of hundreds or even thousands of Muscle Fibers,
depending on the muscles Size.
Although Muscle Fiber makes up most of the Muscle Tissue, a large amount of Connective Tissue,
Blood Vessels, and Nerves are also present to feed the muscle of important nutrients for the cell to use
to live.
Active Muscles use a lot of energy and require a continuous supply of oxygen and nutrients, which are
supplied by arteries.
Muscle Fibers consist of Bundles of threadlike structures called
MYOFIBRILS.
Each Myofibril is made up of TWO Types of Protein Filaments- Thick
ones and Thin ones. The THICK FILAMENTS are made up of a
PROTEIN called MYOSIN. The THIN FILAMENTS are made of a
PROTEIN called ACTIN.
Myosin and Actin Filaments are arranged to form overlapping patterns,
which are responsible for the Light and Dark Bands that can be seen in
Skeletal (Striated Appearance) Muscle.
Thin Actin Filaments are Anchored at their Midpoints to a structure
called the Z-LINE.
The Region From one Z-line to the next is called a SARCOMERE the
Functional Unit of Muscle Contractions.
MUSCLE CONTRACTION
SLIDING FILAMENT THEORY
The Sarcomere is the functional
unit of Muscle contractions.
When Muscle Cells Contract, the
light and dark bands contained in
Muscle Cells get closer together.
This happens because when a
Muscle Contracts, Myosin
Filaments and Actin filaments
interact to shorten the length of a
Sarcomere.
When Myosin Filaments and Actin
Filaments come near each other,
many knob (heads) like projections
in each Myosin Filament form
CROSS-BRIDGES with an Actin
Filament.
When the Muscle is stimulated to Contract, the Cross-bridges move, PULLING the two filaments past each
other.
After each Cross-bridge has moved as far as it can, it releases the Actin Filament and returns to its original
position. The Cross-bridge then attaches to the Actin Filament at another place and the cycle is repeated.
This action shortens the Length of the Sarcomere
WHEN THOUSANDS OF ACTIN AND MYOSIN FILAMENTS INTERACT IN THIS WAY, THE
ENTIRE MUSCLE CELL SHORTENS.
Muscle Contractions require Energy, which is supplied by ATP. This Energy is used to detach the Myosin
Heads from the Actin Filaments.
Because Myosin Heads must attach and detach a number of times during a Single Muscle Contraction,
Muscle Cells must have a Continuous Supply of ATP. Without ATP the Myosin heads would stay attached
to the Actin Filaments, keeping muscles permanently contracted.
A muscle contraction, like a nerve impulse, is an All-or-None response- either fibers contract or they remain
relaxed. The force of a muscle contraction is determined by the number of muscle fibers that are stimulated.
As more fibers are activated, the force of the contraction increases.