In this article you will find the answers to
the following questions:
Bone is a
constantly changing bodily tissue that has several functions. All the
bones together make up the skeleton. The skeleton, muscles, tendons,
ligaments, and other components of joints make up the musculoskeletal
system. The skeleton provides strength, stability, and a frame for
muscles to work against in producing movement. Bones also serve as
shields to protect delicate internal organs.
Bones have two main shapes:
flat bones, such as the plates of the skull and the vertebrae, and long
bones, such as thighbone and arm bones. But their internal structure is
essentially the same. The hard outer part consists largely of proteins,
such as collagen, and a substance called hydroxyapatite. Hydroxyapatite
is composed mainly of calcium and other minerals; in fact it stores much
of the body's calcium and is largely responsible for the strength of
The marrow in the center of
each bone is softer and less dense than the rest of the bone and
contains specialized cells that produce blood cells. Blood vessels run
through a bone, and nerves surround it.
Bones come together to form
joints. The configuration of a joint determines the degree and direction
of possible motion. Some joints, such as those between the plates of the
skull, called sutures, don't move in adults. Others allow a range of
motion. For example, the shoulder joint, which has a ball-and-socket
design, allows inward and outward rotation as well as forward, backward,
and sideways motion of the arm.
Hinge joints in the elbows,
fingers, and toes allow only bending (flexion) and straightening
components provide stability and reduce the risk of damage from constant
use. In a joint, the ends of bones are covered with cartilage, a smooth,
tough, protective tissue that acts as a shock absorber and reduces
Joints also have a lining
(called synovial tissue) enclosing them to form the joint capsule. Cells
in the synovial tissue produce a clear fluid (synovial fluid) that fills
the capsule, which further reduces friction and aids movement.
Muscles are bundles of fibers
that can contract, or tighten. Skeletal muscles, which are responsible
for posture and movement, are attached to bones and arranged in opposing
groups around joints. For example, muscles that straighten the elbows
(triceps muscles) counter muscles that bend them (the biceps muscles).
Tendons are tough bands of
connective tissue, attaching each end of a muscle to a bone. Ligaments,
which are similar tissues, surround joints and connect one bone to
another. They help strengthen and stabilize joints, permitting movement
only in certain directions.
Bursas are fluid-filled sacs
that provide extra cushioning, usually between adjacent structures that
otherwise might rub against each other and as a result might cause wear
and tear - for instance, between a bone and a ligament.
Body Parts Fit Together
components work together to facilitate balanced movement that causes no
damage. For example, when the knee is bent to take a step, the hamstring
muscles on the back of the thigh contract and shorten, pulling the lower
leg in and bending the knee. At the same time, the quadriceps muscles on
the front of the thigh relax, allowing the knee to bend.
Within the knee joint, the
cartilage and synovial fluid minimize friction. Five ligaments around
the joint help keep the bones properly aligned. Bursas provide
cushioning between structures such as the shinbone (tibia) and the
tendon attached to the kneecap (patellar tendon).
That Can Go Wrong
the musculoskeletal system (muscles, bones, and joints) are major causes
of chronic pain and physical disability. Although the components of the
musculoskeletal system thrive on use, use can lead to wear, injury, or
Injuries to bones, muscles, and
joints are very common, ranging in severity from mild pulled muscles to
strained ligaments, dislocated joints, and broken bones (fractures).
these injuries are generally painful and might lead to long-term
complications, most of them heal completely.
is a natural response to tissue irritation or damage and causes
swelling, redness, heat, and loss of function. Inflammation of a joint
is called arthritis and inflammation of a tendon is tendonitis.
Inflammation may be confined to a small part of the body (i.e.,
localized), such as in a single joint or an injured tendon, or it may be
widespread, as in certain inflammatory diseases such as rheumatoid
can become chronic and persistent, sometimes because of continuous
movement and mechanical stresses, and sometimes because of immune
reactions, infections, or deposits of abnormal materials.
Bone and joint infections can
be crippling. Immediate treatment can prevent permanent joint damage.
Benign tumors and cancers can
originate in bone, and cancers can spread to bone from other locations
in the body.
Metabolic or hormonal
imbalances can also affect bones and joints. An example is osteoporosis,
a thinning of bone resulting from the excessive loss of minerals in
bone. Another example is gout, in which crystals develop in the joints
of susceptible people whose blood has an abnormally high concentration
of uric acid.