The skeleton is a rigid structure formed by a set of bones that support the
human body. At birth the human skeleton has about 270 bones that in the adults
the bones are reduced to 206 because, during the development, some bones are
joined together and go to form one only.
This number is subjected to a variety of anatomical differences; for example, a
small part of the human population has an extra rib, or a lumbar vertebra. In a
medium adult being, the skeleton accounts for about 20% of body weight.
The skeleton can be subdivided:
-axial skeleton, that is the head and the trunk
-appendicular skeleton, ie limbs, of the scapula and pelvic girdle
The functions of the skeleton are multiple:
support and protection of delicate parts such as the brain and the organs of the
thorax (heart and lung with the respective vessels)
balance and movement, thanks to the fact that the joints and muscles, through
the tendons are inserted on segments of the skeleton and allow movement.
Hematopoietic function, that is the production of blood tissue, thanks to the
bone marrow contained in it (cf. bone marrow transplant), as it gives shape to
the body
storage of mineral salts
The cartilage is a modest part of the skeleton, a connective tissue, devoid of vessels, flexible and hard at the same time.
There are three types of cartilage: hyaline cartilage: the most common, it is
very resistant and is present in the joints; elastic cartilage: very elastic and
flexible, it forms the auricle; fibrous cartilage: it is found in the
intervertebral discs.
Cartilage types are also cartilages of the nasal septum, or of the larynx or
epiglottis, or of the trachea and bronchi, of the articular surfaces, of the
intervertebral discs and of the meniscus.
to learn more>> Anatomy and histology of bone
Bones can be distinguished in:
- unequal bones, ie single bones, for example the frontal bone, while the
parietal bones are even; the unequal bones are always located on the midline of
the body
- even bones, placed on the sides, for example the two femurs, the two humers
and so on.
- long, the length over width and thickness, such as the thigh bone, the femur,
or shoulder bone, humerus, arm, radius and ulna, etc., prevail.
- short, the three dimensions are approximately equal (es.astragalo) flat, the
thickness is much lower than the other measures (es.scapola).
The human skeleton constitutes the supporting structure of the body, and is
formed by the whole of the bones, variously joined together by more or less
mobile formations that take the name of articulations.
They are divided into:
Furniture: allow you to perform large movements, such as the hip, the elbow,
knee or shoulder;
Semi-mobiles: they do not have 100% mobility (vertebrae).
Fixed: like those of the skull.
In the long bones, the central part is called the diaphysis and the epiphysis ends.
The fundamental substance of the bones in the fresh state is constituted by inorganic substance (calcium phosphate, calcium carbonate, magnesium phosphate, calcium fluoride) for 55.28%, organic or osssein for 27.72% and water in the remaining 17%.
The skeleton of the head consists of the bones of the skull: frontal, occipital,
parietal, temporal, sphenoid, and of the bones of the face: including the nasal,
ethmoidal, orbital, zygomatic, maxillary, mandible, etc.
The skull, which contains and protects the brain, is made up of 8 flat bones firmly joined together. It has the function of protecting the brain, the
cerebellum and the brainstem, which are contained within it, but also houses many sensory organs, such as eyes and ears, the first part of the digestive
system and the respiratory system.
It is generally divided into the neurocranium, which is found in the cranial
vault, where the nerve structures of the head are contained, and in the
splacnocranium, which is located below the forehead, where many other organs are
found, including the sensory ones.
It is undoubtedly the most complex bone structure of the human body, being
formed by 25-28 bones both equal and unequal, often with a highly irregular
shape and connected to each other with a certain variability.
Most of these bones are flat, formed by two planks, a thicker exterior, and a
less thick interior, and a low-density spongy central layer called diploe.
The thickness of the bones generally varies according to muscle coverage, so
that those parts of the skull covered by a greater number of muscles or muscle
mass than those relatively exposed will be thinner (and subject to fracture).
An example of the first type is the temporal bone, of the second the occipital bone. The bones of the skull are interconnected by fibrous joints called sutures, which tend to close with aging, each within a more or less defined range of time, even if there are no exceptions.
The skeleton of the trunk consists of the vertebral column and the rib cage.
The vertebral column is made up of 33-34 overlapping bones, the vertebrae, each
of which has a hole in the central part; the vertebral column and then crossed
by a kind of canal, the vertebral canal, which contains and protects the spinal
cord about 70 cm long, the vertebral column is divided into five regions: the
cervical, the dorsal or thoracic, the lumbar, the sacral , which is formed by 5
vertebrae welded into a single bone (called sacrum), and the coccygea, which is
formed of 4-5 vertebrae also welded into a single bone (called coccyx).
Each vertebra is connected to the other by an inter-vertebral cartilage disk;
this gives the vertebral column some flexibility and makes it possible to absorb
shocks.
The rib cage consists of 12 pairs of flat and ribbon-like bones, the ribs, and a
flat bone located in the central part of the chest, the sternum.
The ribs are connected posteriorly to the vertebrae and, at the front, are
joined to the sternum by means of cartilaginous extensions; the last two pairs
of ribs anteriorly do not reach the sternum so they are called floating ribs.
The skeleton of the limbs consists of the skeleton of the upper limbs and the
skeleton of the lower limbs.
The skeleton of the upper limbs includes: the bone of the arm, the humerus; the
bones of the forearm, the ulna and the radio; the bones of the hand, consisting
of the carpus, the metacarpus and the phalanges.
The skeleton of the upper limbs attaches itself and is articulated to the
skeleton of the trunk through the shoulder blades and the clavicles, which
together form the scapular girdle.
The skeleton of the lower limbs includes: the thigh bone, the femur (the longest
bone in the body); the bones of the leg, the tibia and the fibula; the bones of
the foot, made up of the heel, the tarsus, the metatarsus and the phalanges.
In the inner part of the knee there is also the patella, bone that allows the
movement of the leg only backwards. The skeleton of the lower limbs attaches
itself and is articulated to the skeleton of the trunk through three bones: the
ileum, the ischio, and the pubis, and together they form the pelvic girdle or pelvis.
The various bones that form the skeleton are connected to each other by the
joints that, according to the movement that the bones themselves must perform,
can be of three types.
The movable joints: allow large movements, such as those of the knee, elbow,
shoulder. In this type of joint on the contact surfaces of the bones are covered
by cartilage, and the joint itself is enclosed in a fibrous joint capsule
containing a liquid, the synovium, which functions as a lubricant; often inside
the capsule there is also a cartilaginous disk that reduces the friction between
the bones during movement.
Semi-mobile joints: allow only limited movements, such as those of the spine and
ribs. They are enclosed by the fibrous joint capsule and consist of only
cartilage.
The fixed joints: they do not allow any movement; they are, for example, those
found in the cranial box. They consist of fibrous ligaments that fit together
perfectly forming rigid structures.