Transcript The Skeletal System

The Skeletal System
Introduction: Functions of the
Skeletal System
• Support. The skeletal system provides structural support
for the entire body.
• Leverage. Bones of the skeleton function as levers that
change the magnitude and direction of the forces
generated by skeletal muscles.
• .
Introduction: Functions of the
Skeletal System
• Protection. Delicate tissues and organs
are often surrounded by skeletal elements.
• Storage. The calcium salts of bone
represent a valuable mineral reserve that
maintains normal concentrations of
calcium and phosphate ions in body fluids.
• Blood cell production. Red blood cells and
other blood elements are produced within
the red marrow, which fills the internal
cavities of many bones
The Structure of Bones
Macroscopic Features
Long bones: longer than
they are wide
Short bones: just as long as
they are wide
Flat bones: thin and
relatively broad
Irregular bones: complex
shapes that do not fit
easily into any other
category
Diaphysis: a long bones
central shaft
• Microscopic Features
• Osteocytes: bone
cells
• Lacunae: small
pockets containing
bone cells
• Lamellae: narrow
sheets of calcified
matrix
• Canaliculi: small
channels that radiate
through the matrix
The Structure of Bones
Epiphyses: Expanded
• Osteon: basic
ends of a long bone
functional unit of
compact bone
Compact bone:
relatively solid
• Central canal:
contains one or more
Spongy bone: a network
blood vessels
of bony rods or struts
separated by spaces
that are normally filled
with bone marrow
The Structure of Bones
Periosteum: a fibrous
outer layer and a
cellular inner layer
Endosteum: lines the
marrow cavity and
other inner surfaces
• Perforating canals:
provide passageways
for linking the blood
vessels of the central
canals wit those of
the periosteum of the
marrow cavity
• Trabeculae: rods or
plates formed by
lamellae
Bone Development and Growth
• Intramembranous Ossification
• Intramembranous ossification:
begins when osteoblasts
differentiate within fibrous
connective tissue
• Ossification center: the place
where ossification first occurs.
• Bone develops within sheets
or membranes of connective
tissue
Bone Development and Growth
Continued
• Endochondral Ossification
• Endochondral ossification: bone replaces
existing cartilage
• Epiphyseal plates: bone of the shaft and
the bone of each epiphysis are separated
by these areas of cartilage
Remodeling and Homesostatic
Mechanisms
• Remodeling and Support
• Regular mineral turnover gives each bone the
ability to adapt to new stresses. Heavily stressed
bones become thicker, stronger, and develop
more pronounced surface ridges; bones not
subjected to ordinary stresses become thin and
brittle. Regular exercise is thus an important
stimulus that maintains normal bone structure.
Remodeling and Homeostatic
Mechanism continued
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4 Steps of the Repair Process
Remodeling and Homeostatic
Mechanism continued
• Step 1: In even a small fracture, many
blood vessels are broken and extensive
bleeding occurs. Pooling and clotting of
the blood forms a swollen area called a
fracture hematona, which closes off the
injured blood vessels
Remodeling and Homeostatic
Mechanism continued
• Step 2: Cells of the periosteum and
endosteum migrate into the fracture zone.
There they form localized thickening-an
external callus and internal callus. At the
center of the external callus, cells
differentiate into chondrocytes and build
blocks of cartilage.
Remodeling and Homeostatic
Mechanism continued
• Step 3: Osteoblasts replace the central
cartilage of the exteral callus with spongy
bone. When this process is complete, the
external and internal calluses form a
continuous brace of spongy bone at the
fracture site.
Remodeling and Homeostatic
Mechanism continued
• Step 4: The remodeling of spongy bone at
the fracture site may continue from a
period of 4 months to well over a year.
When the remodeling is complete, the
fragments of dead bone and spongy bone
of the calluses will be gone, and only living
compact bone will remain. The repair may
be “good as new” with no sign that a
fracture occurred, but the bone may be
slightly thicker than normal at the fracture
Aging and the Skeletal System
• The bones of the skeleton become thinner and
relatively weaker as a normal part of the aging
process. Inadequate ossification is called
osteopenia, and all people become slightly
osteopenic as they age.
Aging and the Skeletal System
• The reduction in bone mass occurs
because between the ages of 30 and 40,
osteoblast activity begins to declining
while osteoclast activity continues at
normal levels. Once the reduction begins,
women lose roughly 8% of their skeletal
mass every decade, whereas men’s
skeletons deteriorate at about 3% per
decade.
Skeletal Terminology
• Each of the bones in the human skeleton not
only has a distinctive shape but also has
characteristic external features.
• Elevations or projections form where tendons
and ligaments attach and where adjacent bones
articulate.
• Depressions and openings indicate sites where
blood vessels and nerves lie alongside or
penetrate the bone.
• These external landmarks are called bone
markings.
Skeletal Divisions
• The skeletal system consists of 206
separate bones and a number of
associated cartilages.
• Axial skeleton: forms the longitudinal axis
of the body
• Skull: has 22 bones plus associated bones
• Vertebral column: has 26 bones
• Thoracic cage: has 24 ribs and a sternum
The Skull
• The bones of the skull protect the brain
and support delicate sense organs
involved with vision, hearing, balance,
smell, and taste
• The skull is made up of the 8 bones of the
cranium and 14 of the face
• The cranium encloses the cranial cavity
which is a fluid-filled chamber that
cushions and supports the brain
The Skull
• Frontal bone: forms the forehead and
superior surface of the orbits
• Orbits: the bony recesses that contain the
eyes
• Parietal bone: is posterior to the frontal
bone
• Sagittal structure: extends along the
midline of the cranium
• Occipital bone: forms the posterior and
inferior portions of the cranium
The Skull
• Foramen magnum: the opening that
connects the cranial cavity with the spinal
cavity
• Temporal bones: bones along the sides
and base of the cranium
• Mandibular fossa: the point of articulation
with the lower jaw
The Skull cont..
• Sphenoid bone: forms part of the floor of the cranium
• Ethmoid bone: consists of two honeycombed masses of
bone
• Maxillary bones: form the floor and medial portion of the
rim of the orbit, the walls of the nasal cavity, and anterior
roof of the mouth
• Palatine bones: form the roof of the mouth
• Zygomatic bones: form the lateral walls of the orbit
• Zygomatic arch: the cheekbones
• Nasal bones: forms the bridge of the nose
• Inferior nasal conchae: form the lateral walls of the nasal
cavity
• Mandible: the lower jaw
The Neck and Trunk
• Cervical region: consists of the 7 cervial
vertebra of the neck
• Thoracic region: consists of the 12
thoracic vertebrae
• Lumbar region: contains the 5 lumbar
vertebrae
• Sacral region: consists of the sacrum
• Coccygeal region: contains the coccyx,
which consists of fused vertebrae
The Neck and Trunk cont…
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Spinal curvature: the vertebrae do not form a straight and rigid structure. A
side view of the spinal column reveals four spinal cures. The thoracic and
sacral curves are called primary curves because they appear late in fetal
development. The cervical and lumbar curves, known as secondary curves,
do not appear until months after birth.
Vertebral Anatomy: body- more massive, weight bearing portion of the
vertebrae, transverse process- projecting laterally or dorsolaterall from the
pidicles serve as sites for muscle attachments, vertebral arch- form the
lateral and posterior walls of the vertebral foramen, intervertebral discfibrocartilage
Cervical vertebrae: The 7 cervical vertebrae extend from the head to the
thorax. Atlas- hold up the head
Thoracic Vertebrae: Distinctive features of a thoracic vertebra include: (1) a
characteristic heart-shaped body that is more massive than that of a
cervical vertebrae, (2) a large, slender spinous process that points inferiorly,
(3) articular surfaces on the body and on the transverse processes for
articulation with one or more pairs of ribs
The Neck and Trunk cont…
• Lumbar Vertebrae: Distinctive features include: (1) a vertebral body
that is thicker and more oval than that of a thoracic vertebra, (2) a
relatively massive, stumpy spinous process that projects posteriorly,
providing surface area for the attachment of the lower back muscles,
(3) bladelike transverse processes that lack articulations for ribs
• Sacrum and Coccyx: The sacrum consists of the fused elements of
5 sacral vertebrae. This structure protects the reproduction gestive,
and excretory organs and attaches the axial skeleton to the
appendicular skeleton by articulation with the pelvic girdle. The
coccyx provides an attachment site for muscles that closes the anal
opening.
• Thorax: Consists of the thoracic vertebrae, the ribs, and the
sternum. The ribs and the sternum form the thoracic cage, or rib
cage, and establish the contours of the thoracic cavity.
The Pectoral Girdle
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The clavicle: The S-shaped clavicle bone articulates with the manubrium
component of the sternum and the acromion of the scapula.
The scapula: Its anterior face forms a broad triangle bounded by the
superior, medial, and lateral borders. The intersection of the lateral and
superior borders thickens into the shallow, cup-shaped glenoid cavity. At the
glenoid cavity, the scapula articulates with the proximal end of the humerus
to form the should joint.
The humerus: The prominent greater tubercle established the contour of the
shoulder. The lesser tubercle lies more anteriorly, separated from the
greater tubercle by a deep groove. Muscles are attached to both tubercles,
and a large tendon runs along the groove. The proximal shaft of the
humerus is round in section. The posterior surface of the shaft flattens and
the humerus expands to either side, forming a broad triangle.
The radius and ulna: The radius and ulna are the bones of the forearm. In
the anatomical position, the radius lies along the lateral side of the forearm.
The ulna forms the medial support of the forearm.
The wrist and hand: There are 27 bones in the hand, supported the wrist,
palm, and fingers. There are 4 carpal bones, 4 distal carpal bones, 5
metacarpal bones, and each hand has 14 phalangeal bones.
The Pelvic Girdle
• The coxa: The ilium is the most superior and
largest coxal bone. The ilium forms broad,
curved surface that provides an extensive area
for the attachment of muscles, tendons, and
ligaments.
• The pelvis: The pelvis consists of the coxae, the
sacrum, and the coccyx. It is thus a composite
structure that includes portions of both the
appendicular and axial skeletons.
The Lower Limb
• The femur: The femur, or thighbone, is the longest,
heaviest, and strongest bone in the body. The femur
articulates with the tibia of the leg at the knee joint.
• The tibia and fibula: The condyles of the femur aticulate
with the lateral and medial condyles of the tibia, or
shinbone, the large medial bone of the leg. A ligament
from the patella attaches to the tibial tuberosity just
below the knee joint.
• The ankle and foot: The ankle includes 7 separate tarsal
bones, only the talus articulates with the tibia and fibula.
The basic organizational pattern of the metatarsals and
phalanges of the foot resembles that of the hand.
Classification of Joints
• Immovable joints (synarthroses): the bony edges
are quite close together and may even interlock
• Slightly movable joints (ampiarthroses): permits
very limited movement, and the bones are
usually father aprat then they are at a
synarthrosis
• Freely movable joints (diarthroses): permit a
wide range of motion, usually found at the ends
of long bones
Articular Form and Function
Types of Movements
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Gliding: two opposing surfaces slide past each other
Flexion: movement in the anterior-posterior plane that reduces the angle
between the articulating elements
Abduction: movement away from the midline of the body in the frontal plane
Rotation: turning around the longitudinal axis of the body or limb
Pronation: moving the wrist and hand from palm-facing front to palm-facing
back
Supination: palm is turned forward
Inversion: twisting motion of the foot that turns the sole forward
Dorsiflexion: flexion of the ankle and elevation of the sole
Plantar flexion: extending the ankle and elevating the heel, as in standing
on tiptoes
Opposition: special movement of the thumb that enables it to grasp and
hold an object
Protraction: moving a part of the body anteriorly in the horizontal plane
A Functional Classification of
Synovial Joints
• Gliding joints: have flattened or slightly curved faces, the relatively
flat articular surfaces slide across one another, ex: clavicles
• Hinge joints: permit angular movement in a single plan, like the
opening and closing of a door, ex: elbow
• Pivot joints: permit only rotation, ex: rotating your head
• Ellipsoidal joint: an oval articular face nestles within a depression on
the opposing surface, ex: connect the fingers and toes with the
metacarpals and metatarsals
• Saddle joints: have articular faces that resemble saddles, each face
is concave on one axis and convex on the other, and the opposing
faces nest together, permits angular motion, but prevents rotation,
ex: twiddling your thumbs
• Ball and socket joints: the round head of one bone rests within a
cup-shaped depression in another, ex: shoulder
Representative Articulation
Intervertebral Articulations
• The vertebrae articulate with one another
in one of two ways: (1) at gliding joints
between the superior and inferior articular
processes, and (2) at symphyseal joints
between the vertebral bodies. Articulations
between the superior and inferior articular
processes of adjacent vertebrae permit
small movements that are associated with
flexion and rotationof the vertebra column.
Representative Articulations
Articulations of the Upper Limb
• The shoulder joints permits the greatest range of motion
of any join in the body. Because it is also the most
frequently dislocated joint, it provides an excellent
demonstration of the principle that strength and stability
must be sacrificed to obtain mobility.
• The elbow joint, which consists of two articulations: the
humerus and ulna, and the humerus and radius. The
elbow joint is extremely stable because (1) the bony
surfaces of the humerus and ulna interlock; (2) the joint
capsule is very thick; (3) the capsule is reinforced by
stout ligaments.
Representative Articulations
Articulations of the Lower Limb
• The hip joint: The articulating surface of the
acetabulum has a fibro cartilage pad along its
edges, a flat pad covered by snyovial membrane
in its central portion, and a stout central
ligament.
• The knee joint: The rounded femoral condyles
roll across the top of the tibia, so the points of
contact are constantly changing. The knee
combines three separate joints-two between the
femur and tibia, and one between the patella
and fumur.
Conclusion
• The skeletal system includes the bones of
the skeleton and the cartilages, ligaments,
and other connective tissues that stabilize
or interconnect bones. Its functions include
the structural support, storage, blood cell
production, protection, and leverage.