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MUSCULAR SYSTEM ANATOMY
There are three types of muscle tissue: Visceral, cardiac, and skeletal.
o Visceral Muscle
Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. The
weakest of all muscle tissues, visceral muscle makes organs contract to move substances
through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it
is known as involuntary muscle—it cannot be directly controlled by the conscious mind. The
term “smooth muscle” is often used to describe visceral muscle because it has a very smooth,
uniform appearance when viewed under a microscope. This smooth appearance starkly
contrasts with the banded appearance of cardiac and skeletal muscles.
o Cardiac Muscle
Found only in the heart, cardiac muscle is responsible for pumping blood throughout the body.
Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While
hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates
itself to contract. The natural pacemaker of the heart is made of cardiac muscle tissue that
stimulates other cardiac muscle cells to contract. Because of its self-stimulation, cardiac muscle
is considered to be autorhythmic or intrinsically controlled. The cells of cardiac muscle tissue
are striated—that is, they appear to have light and dark stripes when viewed under a light
microscope. The arrangement of protein fibers inside of the cells causes these light and dark
bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles. The cells of
cardiac muscle are branched X or Y shaped cells tightly connected together by special junctions
called intercalated disks. Intercalated disks are made up of fingerlike projections from two
neighboring cells that interlock and provide a strong bond between the cells. The branched
structure and intercalated disks allow the muscle cells to resist high blood pressures and the
strain of pumping blood throughout a lifetime. These features also help to spread
electrochemical signals quickly from cell to cell so that the heart can beat as a unit.
o Skeletal Muscle
Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled
consciously. Every physical action that a person consciously performs (e.g. speaking, walking,
or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts
of the body closer to the bone that the muscle is attached to. Most skeletal muscles are
attached to two bones across a joint, so the muscle serves to move parts of those bones closer
to each other. Skeletal muscle cells form when many smaller progenitor cells lump themselves
together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these
skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these
muscles always connect to the skeleton in at least one place.
MUSCULAR SYSTEM ANATOMY
There are three types of muscle tissue: Visceral, cardiac, and skeletal.
o Visceral Muscle
Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. The
weakest of all muscle tissues, visceral muscle makes organs contract to move substances
through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it
is known as involuntary muscle—it cannot be directly controlled by the conscious mind. The
term “smooth muscle” is often used to describe visceral muscle because it has a very smooth,
uniform appearance when viewed under a microscope. This smooth appearance starkly
contrasts with the banded appearance of cardiac and skeletal muscles.
o Cardiac Muscle
Found only in the heart, cardiac muscle is responsible for pumping blood throughout the body.
Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While
hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates
itself to contract. The natural pacemaker of the heart is made of cardiac muscle tissue that
stimulates other cardiac muscle cells to contract. Because of its self-stimulation, cardiac muscle
is considered to be autorhythmic or intrinsically controlled. The cells of cardiac muscle tissue
are striated—that is, they appear to have light and dark stripes when viewed under a light
microscope. The arrangement of protein fibers inside of the cells causes these light and dark
bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles. The cells of
cardiac muscle are branched X or Y shaped cells tightly connected together by special junctions
called intercalated disks. Intercalated disks are made up of fingerlike projections from two
neighboring cells that interlock and provide a strong bond between the cells. The branched
structure and intercalated disks allow the muscle cells to resist high blood pressures and the
strain of pumping blood throughout a lifetime. These features also help to spread
electrochemical signals quickly from cell to cell so that the heart can beat as a unit.
o Skeletal Muscle
Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled
consciously. Every physical action that a person consciously performs (e.g. speaking, walking,
or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts
of the body closer to the bone that the muscle is attached to. Most skeletal muscles are
attached to two bones across a joint, so the muscle serves to move parts of those bones closer
to each other. Skeletal muscle cells form when many smaller progenitor cells lump themselves
together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these
skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these
muscles always connect to the skeleton in at least one place.
