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Muscles, Tendons, Ligaments and Cartilage2

Muscles, Tendons,
Ligaments and Cartilage
Muscles pull on the joints, allowing us to move. They also help the body do such things as
chewing food and then moving it through the digestive system.
Even when we sit perfectly still, muscles throughout the body are constantly moving. Muscles
help the heart beat, the chest rise and fall during breathing, and blood vessels regulate the
pressure and flow of blood. When we smile and talk, muscles help us communicate, and when
we exercise, they help us stay physically fit and healthy.
Muscle: Muscle is the tissue of the body which primarily
functions as a source of power. There are three types of
muscle in the body. Muscle which is responsible for
moving extremities and external areas of the body is
called "skeletal muscle." Heart muscle is called "cardiac
muscle." Muscle that is in the walls of arteries and bowel
is called "smooth muscle."
There are three types of muscles in the body. Cardiac
muscle makes up the heart. Smooth muscle cells line the
blood vessels, gastrointestinal tract, and certain organs.
Skeletal muscles attach to the bones and are used for
voluntarily movements of the body.
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.
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.
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.
Most skeletal muscles are attached to two bones through tendons. Tendons are tough bands of
dense regular connective tissue whose strong collagen fibers firmly attach muscles to bones.
Tendons are under extreme stress when muscles pull on them, so they are very strong and are
woven into the coverings of both muscles and bones.
Muscles move by shortening their length, pulling on tendons, and moving bones closer to each
other. One of the bones is pulled towards the other bone, which remains stationary. The place on
the stationary bone that is connected via tendons to the muscle is called the origin. The place on
the moving bone that is connected to the muscle via tendons is called the insertion. The belly of
the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction.
A tendon is a fibrous connective tissue
which attaches muscle to bone.
Tendons may also attach muscles to
structures such as the eyeball. A tendon
serves to move the bone or structure. A
ligament is a fibrous connective tissue
which attaches bone to bone, and
usually serves to hold structures
together and keep them stable.
What is Cartilage?
Cartilage is a tough but flexible tissue that is the main type
of connective tissue in the body. Around 65–80% of
cartilage is water, although that decreases in older people,
and the rest is a gel-like substance called the ‘matrix’ that
gives it its form and function.
There are three main types of cartilage:
• Hyaline, or articular cartilage, is found in the joints, septum of the nose (which
separates the nostrils), and the trachea (air tube).
• Elastic cartilage, which has elastic fibres that make the cartilage more flexible, is
found in the ear, part of the nose and the trachea.
• Fibrous cartilage occurs in special cartilage pads called menisci that help to disperse
body weight and reduce friction, such as in the knee.
In the joints, hyaline cartilage forms a very low friction, 2-4 mm thick layer that coats the
bony surfaces. This allows the bones of the joint to glide over one another during
movement and, ideally, last a lifetime. It also serves as a cushion and shock absorber in
the joint.
How Do Muscles Work?
The movements your muscles make are coordinated and
controlled by the brain and nervous system. The
involuntary muscles are controlled by structures deep
within the brain and the upper part of the spinal cord
called the brain stem. The voluntary muscles are
regulated by the parts of the brain known as the cerebral
motor cortex and the cerebellum (pronounced: ser-uhBEL-um).
When you decide to move, the motor cortex sends an
electrical signal through the spinal cord and peripheral
nerves to the muscles, causing them to contract. The
motor cortex on the right side of the brain controls the
muscles on the left side of the body and vice versa.
The cerebellum coordinates the muscle movements ordered by the motor cortex. Sensors in the muscles and
joints send messages back through peripheral nerves to tell the cerebellum and other parts of the brain where
and how the arm or leg is moving and what position it's in. This feedback results in smooth, coordinated
motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it.
When you run, the messages to the brain are more involved, because many muscles have to work in rhythm.
Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can't push them
back to the original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a
limb at a joint. Then, when the movement is completed, the flexor relaxes and the extensor contracts to
extend or straighten the limb at the same joint. For example, the biceps muscle, in the front of the upper arm,
is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the
biceps contracts. Then the biceps relaxes and the triceps contracts to straighten the elbow.
Muscle spasms occur when a skeletal muscle contracts
and does not relax. Muscle spasms are forceful and
involuntary. A sustained muscle spasm is called a muscle
cramp. Leg muscles, especially the quadriceps (thigh),
hamstrings (back of thigh), and gastrocnemius (calves),
are most likely to cramp, but any skeletal muscle in the
body can cramp.
There are many potential causes of muscle cramps
including physical exertion in hot weather, overexertion,
dehydration, electrolyte imbalance, and physical
Muscle cramps can range from being a mild nuisance to
incapacitating and extremely painful. The cramped muscle
may be visibly distorted or look knotted. Twitching may be
evident. The area of a muscle cramp may be firm to the
touch. Some muscle cramps last just a few seconds, while
others can last 15 minutes or more.