THE SKELETAL SYSTEM
The Human skeletal system consists of a set of
206 bones that support and protect the body.
They also work with the muscles to provide
The skeleton is divided into 2 parts: the
axial and the appendicular
THE AXIAL SYSTEM
The axial system is made up with the skull
bones, the vertebrae, the ribs and the
The spine is divided into several
sections. The cervical vertebrae
make up the neck. The thoracic
vertebrae comprise the chest
section and have ribs attached. The
lumbar vertebrae are the
remaining vertebrae below the last
thoracic bone and the top of the
sacrum. The sacral vertebrae are
caged within the bones of the
pelvis, and the coccyx represents
the terminal vertebrae or vestigial
THE APPENDICULAR SYSTEM
The appendicular system is formed by the
bones of pectoral girdle, pelvic girdle
and upper and lower limbs.
STRUCTURE OF THE BONES
There are two types of
bone tissue: compact
The names imply that
the two types differ in
density, or how tightly
the tissue is packed
CLASSIFICATION OF BONES
The bones of the body come in a variety of
sizes and shapes. The four principal types of
bones are long, short, flat and irregular
Bones that are longer
than they are wide are
called long bones. They
consist of a long shaft
with two bulky ends or
extremities. They are
bone but may have a
large amount of
spongy bone at the
ends or extremities.
Long bones include
bones of the thigh, leg,
arm, and forearm.
primarily of spongy
bone, which is
covered by a thin
layer of compact
bone. Short bones
include the bones of
the wrist and ankle.
Flat bones are thin, flattened, and usually
curved. Most of the bones of the cranium are
Bones that are not in any
of the above three
categories are classified
as irregular bones. They
are primarily spongy
bone that is covered with
a thin layer of compact
bone. The vertebrae and
some of the bones in the
skull are irregular bones.
BONE DEVELOPMENT & GROWTH
Osteoblasts, osteocytes and osteoclasts are
the three cell types involved in the
development, growth and remodeling of
Osteoblasts are bone-forming cells,
osteocytes are mature bone cells and
osteoclasts break down and reabsorb
A joint is the point where two or more bones
meet. There are three main types:
Cartilagenous (partially moveable) and
Synovial (freely moveable) joint.
This type of joint is held together by
only a ligament.
Cavities between bones in synovial joints are filled
with synovial fluid. This fluid helps lubricate and
protect the bones. Bursa sacks contain the synovial
The bursitis is the inflamation of the bursa.
There are six types of synovial joints: pivot joint,
ball-and-socket join, hinge joint, condyloid joint,
saddle joint and gliding joint.
• pivot joint
Enables rotation around a lengthwise axis: the cylindrical
terminal part of a bone is encased in a hollow cylinder.
Examples include the tibia and the fibula.
• ball-and-socket joint
Allows movement along three axes, such as in the shoulder:
flexion and extension, rotation, and adduction (arm
drawing near the trunk) and abduction (arm drawing away
from the trunk).
• hinge joint
Enables flexion and extension along a single axis. The elbow
is a particularly good example: the round terminal part of
the humerus turns in the hollow of the ulna.
An example is the wrist, which the hand can move on
two axes: flexion and extension; it can also be tilted
sideways (toward the radius and ulna).
• saddle joint
Resembles the condyloid joint but allows a wider range
of motion; this type of joint is rare.
• gliding joint
Surfaces of these joints are relatively flat and not very
mobile; they allow only a narrow gliding range (e.g.,
vertebrae, certain bones of the carpus).
• A tendon is a tough but flexible structure
made of fibrous tissue that joins a bone to a
• When a muscle contracts it pulls on a bone to
cause movement. The tendon transmits the
force from the muscle to the bone.
• The tendonitis is the inflammation of a
• Ligaments are bands of
connective tissues that link two
or more bones.
• Ligaments make joints stable and
prevent from excessive
THE MUSCULAR SYSTEM
• Our skeletal has more than 650 muscles, most
of them disposed in pairs to provide
THE MUSCULAR TISSUE
Muscular cells are called muscle
Every fibers contain thousand of
Inside each myofibril there are
many myofilaments that are made
of two proteins: the actin and the
The myobibrils are divided is
subunits called sarcomeres.
TYPES OF MUSCLES
• There are three types of muscles: cardiac,
smooth and skeletal.
• It is only found in the heart.
• It’s made of striated fibers and its contraction
is directed by the ANS.
• It contracts involuntarily and rhythmically. It’s
also very resistant to fatigue due to the large
number of mitochondria they have.
• Smooth muscle are also known as involuntary
as its contraction is lead by the CNS and the
• It covers the hollow walls of many organs such
as the oesophagus, the broncchi, the uterus or
• It contracts slowly.
• The skeletal muscles are also known as
striated or voluntary.
• They are attached to bones by tendons
• Their contraction is quick and variable from
powerful to precise. It is controlled by the
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