The skeletal system consists of the bones. There are
206 bones in adults.
Functions of the Skeleton
1)
The skeleton supports the body. The bones and lower
limbs support the entire body when we are standing, and the pelvic girdle
supports the abdominal cavity.
2)
The skeleton protects soft body parts. The bones of the
skull protect the brain; the rib cage protects the heart and lungs.
3)
The skeleton produces blood cells. All bones in the
fetus have red bone marrow that produces blood cells. In adults only
certain bones produce blood cells.
4)
The skeleton stores minerals and fats. All bones have a
matrix that contains calcium phosphate, a source of calcium ions and phosphate
ions in the blood. Fat is stored in the yellow bone marrow.
5)
The skeleton, along with muscles, permits flexible body
movement. While joints occur between all the bones, we associate body
movement in particular with the bones of the limbs.
Classification of Bones
Long
Bones- Long bones are longer than they are wide.
Short
Bones- Short bones are cubed shaped; their lengths and widths are about
equal.
Flat Bones- Flat bones are platelike and have broad surfaces.
Irregular Bones- Irregular bones have varied shapes with many
places for connections with other bones.
Round Bones- Round bones are circular.
The anatomy of Long Bones
Bones are classified according the their shape. Long bones have
greater length than width and consist of a shaft and a variable number of
endings. They are usually somewhat curved for strength.
Examples include femur, tibia, fibula, humerus, ulna and
radius.
The Growth and Development of Bones
Parts of the skeleton form during the first few weeks after
conception. By the end of the eighth week after conception, the skeletal
pattern is formed in cartilage and connective tissue membranes and ossification
begins.
Bone development continues throughout adulthood. Even after
adult stature is attained, bone development continues for repair of fractures
and for remodeling to meet changing lifestyles. Osteoblasts, osteocytes and
osteoclasts are the three cell types involved in the development, growth and
remodeling of bones. Osteoblasts are bone-forming cells, osteocytes are mature
bone cells and osteoclasts break down and reabsorb bone.
Fractures:
There are 6 types of fractures.
Complete fracture: A complete fracture is if the bone
is broken clear through.
Incomplete fracture: An incomplete fracture is if the
bone is not separated into two parts.
Simple fracture: A simple fracture is if it does not
pierce the skin.
Compound fracture: A compound fracture is if it does
pierce the skin.
Impacted fracture: An impacted fracture means that the
broken ends are wedged into each other.
Spiral fracture: A spiral fracture occurs when the
break is ragged due to twisting of a bone.
Fracture Repair
There are 4 steps in fracture repair.
1) Hematoma: Within six to eight hours
after a fracture, blood escapes from ruptured blood vessels and forms a
hematoma (mass of clotted blood) in the space between the broken bones.
2) Fibrocartilaginous callus: Tissue
repair begins, and fibrocartilage fills the space between the ends of the
broken bone for about three weeks.
3) Bony callus:
Osteoblasts produce trabeculae of spongy bone and convert the
fibrocartilaginous callus to a bony callus that joins the broken bones together
and lasts about three to four months.
4) Remodeling:
Osteoblasts build new compact bone at the periphery, and osteoclasts reabsorb
the spongy bone, creating a new medullary cavity.
Axial Skeleton and Appendicular Skeleton
The skeleton is divided into the axial skeleton and the
appendicular skeleton.
Axial Skeleton- The axial skeleton forms
the central axis of the body. It consists of the skull, the vertebral
column, the ribs and the sternum or breastbone.
Appendicular Skeleton- The appendicular skeleton
consists of the girdles and the skeleton of the limbs. The upper
(anterior) limbs are attached to the pectoral (shoulder) girdle and the lower
(posterior) limbs are attached to the pelvic (hip) girdle.
The skull consists of 28 different bones. The bones of
the skull can be divided into two main groups: the cranium, which encloses and
protects the brain and facial bones. The cranium protects the brain and
is composed of eight bones.
Frontal Bone: One frontal bone forms the
forehead, a portion of the nose, and the superior portions of the orbits (bony
sockets of the eyes).
Parietal Bone: Two parietal bones are just
posterior to the frontal bone. They form the roof of the cranium and also
help form its sides.
Occipital Bone: One occipital bone forms the most
posterior part of the skull and the base of the cranium. The spinal cord
joins the brain and by passing through a large opening in the occipital bone
called the foramen magnum.
Temporal Bones: Two temporal bones are just
inferior to the parietal bones on the sides of the cranium. They also
help form the base of the cranium. Each temporal bone has the following:
External
auditory meatus- A canal that leads to the middle ear.
Mandibular
fossa- Articulates with the mandible.
Mastoid
process- Provides a place of attachment for certain neck muscles.
Styloid
process- Provides a place of attachment for muscles associated with
the tongue and larynx .
Zygomatic
process- Projects anteriorly and helps form the cheekbone.
Skull Bones (Bones of the Face)
Maxillae: The two
maxillae form the upper jaw. Aside from contributing to the floors of the
orbits and to the sides of the floor of the nasal cavity, each maxillae has the
following processes:
Alveolar
process- The alveolar process contain the tooth sockets for teeth:
incisors, canines, premolars, and molars.
Palatine
process- The left and right palatine processes form the anterior
portion of the hard palate (roof of the mouth).
Palatine
Bones: The two palatine bones contribute to the floor and lateral
wall of the nasal cavity. The horizontal plates of the palatine bones
form the posterior portion of the hard palate.
Zygomatic
Bones: The two zygomatic bones form the sides of the orbits. They also contribute to the
ÒcheekbonesÓ.
Lacrimal Bones: The two
small, thin bones are located in the medial walls of the orbits. A small opening between the orbit and
the nasal cavity serves as a pathway for a duct that carries tears from the
eyes to the nose.
Nasal
Bones: The two
nasal bones are small, rectangular bones that form the bridge of the nose.
Inferior Nasal Conchae: The two
inferior nasal conchae are thin, curved bones that form the wall of the
inferior lateral wall of the nasal cavity. They support the nasal cavity.
Mandible: The
mandible, or lower jaw, is the only movable portion of the skull. The body has an alveolar process, which
contains tooth sockets for 16 teeth.
Hyoid Bone
The hyoid bone helps to support the tongue
and serves as an attachment point for several muscles that help to elevate the
larynx during swallowing and speech. The hyoid bone is unique in
that it is the only bone of the body that does not articulate with any
other bone. Instead, it is suspended above the larynx where it is
anchored by ligaments to the styloid processes of the temporal bones of the
skull.
Vertebral Column
*Typical vertebral
*Atlas
*Axis
*Sacrum
*Coccyx
The vertebral column (also
called the backbone, spine, or spinal column) consists of a series of 33
irregularly shaped bones, called vertebrae. These 33 bones are divided into
five categories depending on where they are located in the backbone.
The first seven vertebrae are called the cervical vertebrae. Located at the top of the
spinal column, these bones form a flexible framework for the neck and support
the head. The first cervical vertebrae is called the atlas and the second is
called the axis. The atlas' shape allows the head to nod "yes"
and the axis' shape allows the head to shake "no".
The next twelve vertebrae are called the thoracic vertebrae. These bones move with the
ribs to form the rear anchor of the rib cage. Thoracic vertebrae are larger than
cervical vertebrae and increase in size from top to bottom.
After the thoracic vertebrae, come the lumbar vertebrae. These five bones are the
largest vertebrae in the spinal column. These vertebrae support most of the
body's weight and are attached to many of the back muscles.
The sacrum is a triangular bone located just
below the lumbar vertebrae. It consists of four or five sacral vertebrae in a
child, which become fused into a single bone after age 26. The sacrum forms the
back wall of the pelvic girdle and moves with it.
The bottom of the spinal column is
called the coccyx or tailbone. It consists of 3-5 bones
that are fused together in an adult. Many muscles connect to the coccyx.
These bones compose the
vertebral column, resulting in a total of 26 movable parts in an adult. In
between the vertebrae are intervertebral discs made of fibrous cartilage that act
as shock absorbers and allow the back to move. As a person ages, these discs
compress and shrink, resulting in a distinct loss of height (generally between
0.5 and 2.0cm) between the ages of 50 and 55.
When looked at from the side, the spine forms four curves. These curves are called the cervical,
thoracic, lumbar, and pelvic curves. The cervical curve is located at
the top of the spine and is composed of cervical vertebrae. Next come the
thoracic and lumbar curves composed of thoracic and lumbar vertebrae
respectively. The final curve called the pelvic or sacral curve is formed by
the sacrum and coccyx. These curves allow human beings to stand upright and
help to maintain the balance of the upper body. The cervical and lumbar curves
are not present in an infant. The cervical curves forms around the age of 3
months when an infant begins to hold its head up and the lumbar curve develops
when a child begins to walk.
In addition to allowing humans to
stand upright and maintain their balance, the vertebral column serves several
other important functions. It helps to support the head and arms, while
permitting freedom of movement. It also provides attachment for many muscles,
the ribs, and some of the organs and protects the spinal cord, which controls
most bodily functions.
Thoracic Cage
The upper ten ribs articulate anteriorly
either directly with the sternum through their costal cartilages (true ribs),
or through a fused cartilage (false ribs). The eleventh and twelfth ribs do not
articulate anteriorly (floating ribs). The first rib is flattened above and
below. Its anterior cartilage is fused to the manubrium forming a rigid ring,
the thoracic inlet. During respiration the thoracic inlet is fixed, in part by
muscles such as scalenus anterior anchoring it to the cervical column. The
second to seventh ribs articulate anteriorly with the sternum through synovial
joints. Posteriorly the ribs articulate with the vertebral bodies (the head of
the rib) and the transverse processes (tubercle of the rib). These
articulations allow the ribs to move upwards and outwards during inspiration,
so increasing both the anterior - posterior and right - left diameters of the
thorax. These movements, referred to as pump-handle and bucket-handle
movements, increase the thoracic diameters due to the downward course of the
rib and to its curvature.
Three types of Ribs and three types of
Sternum
*True Ribs
*False Ribs
*Floating
Ribs
*The ribs
are thin, flat, curved bones that form a protective cage around the organs in
the upper body. They are comprised 24 bones arranged in 12 pairs.
These bones are divided into three categories:
The first seven bones are called the true ribs. These bones are connected
to the spine (the backbone) in back. In the front, the true ribs are connected
directly to the breastbone or sternum by a strips of cartilage called the
costal cartilage.
The next three pairs of bones are called false ribs. These bones are slightly
shorter than the true ribs and are connected to the spine in back. However,
instead of being attached directly to the sternum in front, the false ribs are
attached to the lowest true rib.
The last two sets of rib bones are called floating ribs. Floating ribs are smaller
than both the true ribs and the false ribs. They are attached to the spine at
the back, but are not connected to anything in the front.
The ribs form a kind of cage the encloses the upper body.
They give the chest its familiar shape.
The ribs serve several important purposes. They protect the
heart and lungs from injuries and shocks that might damage them. Ribs also
protect parts of the stomach, spleen, and kidneys. The ribs help you to
breathe. As you inhale, the muscles in between the ribs lift the rib cage up,
allowing the lungs to expand. When you exhale, the rib cage moves down again,
squeezing the air out of your lungs.
Sternum
The sternum is a flat, dagger shaped bone located in the
middle of the chest. Along with the ribs, the sternum forms the rib cage that
protects the heart, lungs, and major blood vessels from damage.
The sternum is composed of three parts:
The manubrim, also called the "handle",
is located at the top of the sternum and moves slightly. It is connected to the
first two ribs.
The body, also called the "blade" or the
"gladiolus", is located in the middle of the sternum and connects the
third to seventh ribs directly and the eighth through tenth ribs indirectly.
The xiphoid process, also called the
"tip", is located on the bottom of the sternum. It is often
cartilaginous (cartilage), but does become bony in later years.
Appendicular
Skeleton
The appendicular skeleton consists of
the girdles and the skeleton of
the limbs. The upper (anterior) limbs are attached to the pectoral
(shoulder) girdle and the lower (posterior) limbs are attached to the pelvic (hip)
girdle.
The Pectoral (Shoulder) Girdle: The Pectoral
girdle consists of two shoulder blades (scapulae) and two collar bones
(clavicles). These bones articulate with one another, allowing some degree of
movement.
Shoulder
Blades (Scapulae)-The shoulder blade is a flat triangular bone which
stretches from the shoulder to the vertebral column at the back. On the back
side it has a bony ridge for the attachment of the muscles. The bony ridge
forms a prominent projection, the acromion, above the shoulder joint. Beneath
the collar bone and just on the inside of the shoulder joint, is another bony
projection of the shoulder blade, the coracoid process, which also serves for
the attachment of muscles. The upper outer corner of the shoulder blade ends in
the glenoid cavity into which fits the head of the upper arm bone, forming a
ball and socket joint.
Collar Bones (Clavicles)-Each collar bone is rod-shaped
and roughly S-shaped. It lies horizontally and articulates with the upper end
of the breastbone, right in the middle and front, just above the first rib. The
lateral end articulates with the acromium. Collar bones serve as a support for
the shoulder blades in front and keep the shoulder blades back so that the arms
can hang freely at the sides of the body. They prevent the pectoral girdles
from getting out of joint easily and ample movement of the shoulders.
The Pelvic (Hip) Girdle
The pelvic girdle consists of two large, sturdy hip bones.
Each hip bone consists of three fused bones namely the ilium, ischium and the
pubis. The ilium is the largest of the three and forms the upper part of the
hip bones. The sacrum fits like a wedge posteriorly between the two hip bones.
The sacrum has a large, flat articular surface on each side for articulation
with the ilia. The ischium forms the inferior part of the hip bone and the
pubis the central in front. The two pubic bones are attached in the middle, on
the front side by a symphysis which consists of fibrocartilage and ligaments,
the pubic symphysis. The two hip bones and the sacrum form a complete bony
ring, the pelvis . On the outer side of the point where the fused bones meet,
there is a deep hip socket into which the head of the femur fits.
The pelvic girdle forms a strong support for the attachment
of the limbs. Strong muscles of the back, the legs and the buttocks are
attached to it. It protects some of the internal organs. In females it forms a
strong basin-like structure for supporting and protecting the developing foetus
during child-bearing.
The Upper
Limbs: The skeleton of the upper limbs or arm may be divided into
five main regions: an upper arm bone, the forearm (radius and ulna), the wrist,
the palm of the hand and the fingers.
*The Upper Arm (Humerus)- The upper arm
is a single long bone. The upper end consists of a hemi-spherical ball which
fits into the socket of the shoulder blade to form the shoulder joint. The
lower end of the humerus forms a shallow ball and socket joint with the radius
and a hinge joint with the ulna in the elbow.
*The Forearm (Radius and Ulna)-The two long
bones of the forearm are known as the radius and the ulna. The ulna is the
larger of the two bones and is situated on the inner side (i.e. the little
finger side) of the forearm. The upper end of the ulna articulates with the
lower end of the humerus forming a strong hinge joint in the elbow region. The
lower end of the ulna is slender and plays a minor role in the formation of the
wrist joint. The radius is situated on the thumb side of the forearm. Its upper
end articulates with both the humerus and the ulna. The broad, lower end of the
radius forms a major part of the wrist joint, where it articulates with the
wrist bones (carpals). The radius also allows the forearm to be rotated. The
radio-ulnar joints are pivot joints in which the moving bone is the radius. As
the head of the radius pivots at these joints, the lower end of the radius
moves round the lower head of the ulna.
Lower Limbs:
The Upper Leg or Thigh-The upper leg
has a single long bone, the femur and is the longest bone in the body. The head
of the femur is turned slightly inwards and has a large, rounded portionwhich
articulates in the acetubulum, forming a ball-and-socket joint. At its distal
end, the femur widens to form two large knobs (condyles) which form the hinged
knee joint with the main long bone (tibia) of the lower leg. On the anterior
side of these two condyles, there is an articular surface against which the
kneecap (patella) slides. The patella is a small, triangular, flat bone which
develops on the tendon of the thigh muscle and is attached by ligaments to the
tibia. This enables movement in the knee joint.
The Lower Leg-The two bones
of the lower leg are the tibia (shinbone) in front and the fibula behind. The
tibia is the larger of the two and extends from the knee to the ankle. The
upper end of the tibia has two articulating facets into which the condyles of
the femur fit to form the knee joint. The lower end of the tibia articulates
with one of the tarsals to form the ankle joint. The fibula is smaller than the
tibia and is situated on the outside and slightly behind it. The upper end
articulates with the tibia but does not form part of the knee joint. The lower
end forms part of the ankle joint.
Differences between the Male and
Female Pelvises
1. Female iliac bones
are more flared than those of the male
2.The female pelvis is wider
3.The female inlet and outlet of the true
pelvis are wider
4.The female pelvic cavity is more
shallow, while the male is more funnel shapped
5.Female bones are lighter and thinner
6.The female pubic arch is wider
Joints
A joint, or articulation,
is the place where two bones come together. There are three types of joints
classified by the amount of movement they allow: immovable, slightly movable,
and freely movable.
Immovable joints are synarthroses. In this type of joint, the
bones are in very close contact and are separated only by a thin layer of
fibrous connective tissue. An example of a synarthrosis is the suture in the
skull between skull bones.
Slightly movable joints are called amphiarthroses. This type
of joint is characterized by bones that are connected by hyaline cartilage
(fibro cartilage). The ribs that connect to the sternum are an example of an
amphiarthrosis joint.
Most of the joints in the adult human body are freely movable
joints. This type of joint is called a diarthrosis joint. There are six types
of diarthroses joints.
There
are six types synovial joints
Ball-and-Socket: The ball-shaped end of one bone
fits into a cup shaped socket on the other bone allowing the widest range of
motion including rotation. Examples include the shoulder and hip.
Condyloid: Oval shaped condyle fits into elliptical
cavity of another allowing angular motion but not rotation. This occurs between
the metacarpals (bones in the palm of the hand) and phalanges (fingers) and
between the metatarsals (foot bones excluding heel) and phalanges (toes).
Saddle: This type of joint occurs when the touching surfaces of two
bones have both concave and convex regions with the shapes of the two bones
complementing one other and allowing a wide range of movement. The only saddle
joint in the body is in the thumb.
Pivot: Rounded or conical surfaces of one bone fit into a ring of
one or tendon allowing rotation. An example is the joint between the axis and
atlas in the neck.
Hinge: A convex projection on one bone fits into a concave
depression in another permitting only flexion and extension as in the elbow and
knee joints.
Gliding: Flat or slightly flat surfaces move against
each other allowing sliding or twisting without any circular movement. This
happens in the carpals in the wrist and the tarsals in the ankle.
Movements of Synovial joints
Flexion-Bending at a joint so that the angle decreases and the parts
become closer together
Extension-Straitening a joint so that the angle increases and
the parts move farther apart
Hyperextension-Excess extension at a joint, beyond the
anatomical position
Dorsiflexion-Bending the foot at the ankle toward the shin
Planter Flexion-Bending the foot at the ankle toward the
sole
Abduction-Moving a part away from the midline
Adduction-Moving a part toward the midline
Rotation-Moving a part around an axis
Circumduction-Moving a part so that its end follows a circular path
Supination-Turning the hand so that the palm faces anteriorly
Pronation-Turning the hand so that the palm faces
posteriorly
Eversion-Turning the foot so that the sole faces laterally
Inversion-Turning the foot so that the sole faces medially
Protraction-Moving a part forward
Retraction-Moving a part backward
Elevation-Raising a part
Depression-Lowering a part
Effects of Aging
Aging Muscles:
As muscles age, they begin to shrink and lose mass. This is a
natural process, but a sedentary lifestyle can accelerate it.
The number and size of muscle fibers also decrease. Thus, it
takes muscles longer to respond in our 50s than they did in our 20s.
The water content of tendons, the cord-like tissues that
attach muscles to bones, decreases as we age. This makes the tissues stiffer
and less able to tolerate stress.
Handgrip strength decreases, making it more difficult to
accomplish routine activities such as opening a jar or turning a key.
The heart muscle becomes less able to propel large quantities
of blood quickly to the body. We tire more quickly and take longer to recover.
The body's metabolic rate (how quickly the body converts food
into energy) slows. This can lead to obesity and an increase in "bad"
cholesterol levels.
Aging bones
The mineral content of bones decreases, so that bones become
less dense and more fragile.
As bones lose mass, osteoporosis develops,
affecting both women and men. In the spine, osteoporosis can lead to crush
fractures of the vertebrae, resulting in a "dowager's hump."
Osteoporosis is also responsible for almost all hip fractures in older men and
women.
The chemistry of cartilage, which provides cushioning between
bones, changes. With less water content, the cartilage becomes more susceptible
to stress. As cartilage degenerates, arthritis can develop.
Ligaments, connective tissues between bones, become less
elastic, reducing flexibility.
Homeostasis
Homeostasis is one of the fundamental characteristics of
living things. It refers to the maintenance of the internal environment within
tolerable limits. All sorts of factors affect the suitability of our body
fluids to sustain life; these include properties like temperature, salinity,
acidity, and the concentrations of nutrients and wastes.
Other systems assist the skeletal system. The bones protect the internal
organs. As the rib cage protects
the heart and lungs. The bones
assist all phases of respiration.
The rib cage assist the breathing process. The bones store and release calcium. The storage of calcium on the bones are
under hormonal control. The bones assist the lymphatic system and
immunity. Red bone marrow produces
not only red blood cells but also white blood cells. The bones assist digestion. The jaws contain sockets for the teeth which chew food. The skeleton is necessary to the
locomotion.