Download Skeletal System

Unit Four
The Skeletal
System
There are 206 named
bones in the adult
human.
The skeletal system is
divided into 2 sections.
Axial Skeleton
Bones that lie along or
near the vertical axis
Bones of the:
Skull
Vertebral column
Thoracic cage
Appendicular Skeleton
Bones that are lateral to the
vertical axis.
Bones of the:
Shoulder or pectoral girdle
Upper limbs
Hip or pelvic girdle
Lower limbs
Joints – also called
articulations:
Junctions between bones
Ligaments support and
strengthen joints…
They attach one bone to
another.
Tendons are tough
bands of connective
tissue…
They also support and
strengthen joints
and attach muscles to
bone.
I. Functions of the skeletal
system
Support soft body tissues
and organ
Surround and protect organs
(ex: brain & spinal cord)
Store mineral salts (Ca & P)
Site of blood cell formation
(called hemopoiesis)
this occurs in the red
marrow of spongy bone
tissue.
Provides attachment sites
for muscles –
making body movement
possible.
Triglyceride storage
occurs in yellow bone marrow
where adipose cells are stored
At birth, all bone marrow is
red…
as individuals age, red bone
marrow changes into yellow
bone marrow
II. Types of bones
Long bones:
Are greater in length than
width
Are designed to absorb
stress from body weight.
Examples: bones of arms,
legs, hands, feet
Short bones:
Equal in length and
width
Their shape is similar
to a cube.
Examples: bones of
the wrists and ankles
Flat bones:
Are thin and flat.
Examples: bones of the
cranium, ribs and sternum.
Irregular bones:
Have complex shapes unlike
any other
Examples: vertebral bones
and bones of the face.
III. Parts of a long bone
Diaphysis:
The long, central shaft.
Epiphyses:
The extreme
ends…proximal and
distal.
Articular cartilage:
Located along the outer
surface of the articulation.
Made of hyaline cartilage.
Periosteum:
The layer of connective
tissue surrounding the bone.
Medullary cavity:
The chamber within
the diaphysis that
contains bone marrow.
The endosteum is a thin
membrane that lines the
medullary cavity
It contains a single layer of
bone-forming cells and a small
amount of connective tissue
Within bones are a series
of interconnecting canals
that allow for the
transportation of nutrients
and for the flow of blood.
They are called osteonic
or haversian canals.
IV. Ossification
The process of bone
formation.
This process begins during the
first two months of prenatal
life.
After birth, bones grow in
length and width until the end
of the growth period.
There are two types of bone
formation:
 Intramembranous and
endochondral
A. Intramembranous Ossification
Bone forms directly within
mesenchyme
I.O. is a much simpler method
Flat bones of the skull and the
mandible are formed through
I.O. The soft spot hardens
through I.O.
B. Endochondral ossification
Bone forms within hyaline
cartilage that develops from
mesenchyme
Most bones of the body are
formed through E.O.
V. Bone Growth and Remodeling
A. Bones grow in length
by
the addition of bone
material on the diaphyseal
side of the epiphyseal plate
At about 18 in females and 21
in males, the epiphyseal plate
closes…the cartilage cells stop
dividing and bone replaces all
cartilage.
The epiphyseal line (a bony
structure) replaces the
epiphyseal plate signifying the
cessation of growth.
If a fracture damages the
epiphyseal plate (aka: the
growth plate), the fractured
bone may be shorter than
the normal bone.
B. Bones grow in thickness by
appositional growth…growth due
to surface deposition of bone
material
Periosteal cells differentiate into
osteoblasts that secrete collagen
fibers and organic molecules
that form the extracellular
matrix
C. Bone remodeling is the
ongoing replacement of old
bone tissue by new bone
tissue
It involves bone resorption
(the removal of minerals and
collagen) by osteoclasts
and the deposition of new
minerals and collagen by
osteoblasts
Throughout adulthood (after
the cessation of growth)
bone remodeling continues
providing a recycling of bone
material.
Every gram of bone tissue in
your body will be recycled at
least twice by the time you
are 60 years old!
The benefits of remodeling:
 removal of injured bone
 increase in strength (when
newly formed bone is
subjected to heavy loads it
forms stronger)
 alteration of shape (stress
patterns result in altered
shape for better support)
VI. Axial Skeleton
A. Skull
Sutures:
Jagged lines between
adjacent bones of the skull
Sinuses:
Chambers within the skull
lined with mucous
membranes
These chambers are
normally filled with air.
There are 22 bones in
the skull:
8 bones of the cranium
13 bones of the face
1 mandible
1. The Cranium
Encloses and protects the
brain.
Provides an attachment site
for muscles of the scalp,
lower jaw, neck and back.
Frontal bone:
the large bone forming
the anterior portion of
the skull above the
eyes…your forehead.
Parietal bones:
Two bones forming much of
the lateral portion of the
cranium.
These two bones are
separated by:
Sagittal suture: between the
two parietal bones
Coronal suture: between the
frontal and parietal bones.
Occipital bone:
The thick bone that forms
the posterior wall and
floor of the cranium
Lambdoidal suture:
between the occipital and
parietal bones
Foramen magnum
The large opening
through which the
spinal cord passes as it
extends between the
cranial cavity and the
vertebral canal
Temporal bones:
The two bones on either
side of the cranium below
the parietal bones
The squamosal suture
separates the temporal
and parietal bones
Along the inferior margin of
the temporal bone is:
External auditory meatus:
the opening that leads to the
inner ear
Mandibular fossa: a
groove/depression that
provides the articular surface
for the mandible
Zygomatic process: an
extension that joins the
zygomatic bone to form the
cheekbone.
Styloid process: a narrow
projection that serves as an
anchor for the muscles of
the tongue and pharynx.
Mastoid process: a
projection that provides
an attachment site for
the muscles of the
neck.
Sphenoid bone
Wedged between the
zygomatic, temporal, parietal
and frontal bones
Contains the optic foramen
which is the opening through
which the optic nerve passes
from the eyes to the brain.
Ethmoid bone:
A small bone anterior to
the sphenoid
It is mostly internal
Portions form the cranial
floor, orbital walls and
nasal cavity walls.
2. Facial Bones
Includes:
13 immovable bones
1 movable jaw
Supports the face
Provides attachment
sites for muscles that
control facial
expressions and move
the jaw
Maxillary bones:
Two bones on each side of
the face: form the upper jaw
A few facial bones:
Zygomatic bones: two bones
on each side of the face:
form part of the cheekbones
and occular orbits
Zygomatic arch: cheekbone
Nasal bones:
Two small bones that meet
at the midline to form the
bridge of the nose
Vomer:
A single bone located along
the midline within the nasal
cavity.
Joins with the ethmoid
bone to form the nasal
septum which divides
the nasal cavity into
two nares
3. Mandible:
The single lower jaw
It articulates with the
temporal bones at the
mandibular fossa
Is the only movable
bone of the skull
B. Hyoid Bone
Is located in the neck below
the mandible
Does not articulate with any
other bone
Is suspended from the
styloid process of the
temporal bone by ligaments
and muscles
Supports the tongue
and provides
attachment for some
of its muscles.
C. Vertebral Column
Strong and flexible
Supports the trunk
Permits anterior,
posterior, rotational
and lateral movements
Composed of a series of
vertebrae
Extends from the base of
the skull to the pelvis
Intervertebral discs are a
compressible mass of
fibrocartilage located
between adjacent vertebrae
Provides protection to the
spinal cord.
Contains 33 vertebrae:
7 cervical vertebrae
12 thoracic vertebrae
5 lumbar vertebrae
5 fused sacral vertebrae
~4 fused coccygeal
vertebrae
Vertebral regions correspond
to curves of the vertebral
column
Cervical curvature
Bends anteriorly
Concave curve
Thoracic curvature
Bends posteriorly
Convex curve
Lumbar curvature
Bends the back anteriorly
Concave curve
Sacral curvature
Bends the back posteriorly
Convex curve
Coccygeal curvature
Concave curve
Immovable in males,
movable in females.
Curves in vertebral column
provide:
Added strength
Maintenance of balance
while upright
Shock absorption while
running, jumping and/or
walking
At birth, a newborn has a
single, convex curvature
When the cervical curvature
develops, the infant is able
to hold up their head
When the lumbar curvature
develops, the infant is able
to stand and walk
D. Thoracic Cage
Composed of the thoracic
vertebrae, the sternum and
the ribs
It creates a partial enclosure
around the organs of the
thoracic region
It supports the shoulder
girdle and the upper limbs
The sternum
Is also called the breastbone
It is a thin, flat bone
located along the vertical
midline of the chest
The superior aspect of the
sternum is called the
manubrium
and is the region of
articulation to the clavicles
The main portion of the
sternum is called the body
The inferior portion of the
sternum is a cartilaginous
projection called the
Xiphoid process
The lateral borders of
the sternum articulate
with the ribs through
costal cartilage.
The Ribs
There are usually 12 pairs
They are attached to the
vertebral column posteriorly,
and curve around anteriorly
to articulate with the
sternum
Ribs articulate to the
sternum through costal
cartilage
The first 7 pairs are true ribs
They are called this because
the cartilage attaches the
ribs directly to the sternum
The next 5 pairs are false
ribs
They are called this because
the ribs are indirectly
attached to the sternum…
Cartilage from the false ribs
connects to cartilage from
the bottom true rib
The bottom 2 pairs of false
ribs are floating ribs
They are called this because
they are only attached to the
vertebral column
and do not attach to the
sternum at all.
VII. The Appendicular Skeleton
A. Pectoral Girdles
Provide a connection
between the axial skeleton
and the upper limbs
Each pectoral girdle contains
2 bones which support the
arms and attach to the
muscles that move the arms:
Clavicle:
AKA: collarbone
Helps to hold the shoulder in
place during movement of
the arm
Scapulae:
AKA: shoulder blade
Provides an important
attachment site for muscles
that move the shoulder and
upper arm
B. Upper Limbs
Consist of 60 bones
They support the arms,
wrists, hands and fingers of
each side of the body
Humerus
The long bone of the arm
Extends from the shoulder
to the elbow
Radius
The lateral bone of the
forearm (when in supination)
It is always in line with the
thumb
The styloid process is the
pointed lateral projection of
the wrist
Ulna
Located medially to the
radius (when in supination)
The proximal projection is
called the olecranon process
The distal, medial projection
is the styloid process
Carpals
8 short bones that
support/comprise the wrist
Metacarpals
5 long bones that comprise
the palm of the hand
The distal ends form the
knuckles
Phalanges
14 long bones
2 in the thumb
3 in each finger
Comprise the digits
C. Pelvic Girdle
Provides a strong, durable
frame for the support of the
lower limbs
Consists of 2 large coxal
bones which are
Also called the pelvic or hip
bones
The Coxal Bones
unite with one another
anteriorly
and with the sacrum
posteriorly
to form the pelvis
Consists of the:
Ilium:
The largest of the 3 bones
Forms the superior portion
of the hip bone
Ischium:
Forms the posterior portion
of the hip bone
Pubis
The thin, anterior bone of
the hip
As the bones develop, they
fuse together into a single
bone
Structural differences
according to gender:
The pelvic girdle in males
is tilted posteriorly
has a narrow and heartshaped inlet
has a narrow and pointed
pubic arch
has a narrow and long
sacrum
has an immovable coccyx
has thicker and heavier
bones
The pelvic girdle in females
is tilted anteriorly
has a wide and oval shaped
inlet
has a wider and rounder
pubic arch
has a wider, shorter and
more curved sacrum
has a movable coccyx
has thinner and lighter
bones
D. Lower Limbs
Consists of 60 bones
that support the thigh, leg,
ankle and foot
1. Femur
The longest and heaviest
bone in the body
It extends from the union
with the coxal bone at the
hip joint to the knee
The patellar surface is
located at the distal end on
the anterior side of the
femur
2. Tibia
The larger of the 2 bones
that support the leg
Located medially
Extends between the knee
and the ankle
The distal end contains a
pointed process called the
medial malleolus
Which forms the bony ridge
on the medial side of the
ankle
Articulates with the large
bone in the foot called the
talus
3. Fibula
The thin, twisted bone
Lateral to the tibia
The distal end contains the
lateral malleolus
Articulates with the talus
4. Foot
7 tarsal bones
that make up the ankle
two prominent tarsals:
Talus
Calcaneus (heel bone)
5 metatarsal bones
The heads form the ball of
the foot
14 phalanges:
2 in the big toe and 3 in the
others
skeletal overview