Introduction to the Skeletal
System
Structure, function, and
classification of bones
Skeletal System
 Interconnected
system of bones
ligaments and
tendons
 Provide support and
protection for body
 Composed of 206
bones
Functions of Skeletal System
 1)Support – provides
solid axis for muscles
to act against,
creating motion.
 2)Protection- bones
such as skull provide
barrier of protection
from external forces
 3)Hematopoiesisproduction of red
blood cells
Types of Bones
 Bones are divisible
into 5 class.
Long
Short
Flat
Irregular
Sesamoid
Long Bones
 Found in the limbs
 Each bone is made of
a body (diaphysis)
and two extremities
(epiphyses)
 Wall consists of
dense tissue
 Central canal called
medullary canal is
filled with marrow
Short Bones
 Found in skeleton
where strength,
compactness, and
limited movement are
desired
 2 main examples
Tarsus
Carpus
Flat Bones
 Used in spots where
protection or
muscular attachment
is desired
 Main locations are
skull and scapula
Irregular Bones
 Bones which don’t fit
into other categories
due to irregular
shapes
 Examples:
vertebrae;sphenoid;
hyoid
Sesamoid (Round)
Bones
 Usually small and
round.
 Embedded within
tendons adjacent to
joints.
 Example: patella
(knee cap)
Bone Formation and Fractures
Fetal Skeleton
Begins as mainly
cartilage
Calcifies in utero
At birth, fontanels
remain
Ossification
Bone production process gives bone
extreme tensile and compressional
strength
Several things contribute to strength
Factors which contribute to bone growth
Nutrition
Exposure to sunlight
Hormonal Secretion
Physical Exercise
Nutrition
Mainly calcium
consumption
Increased blood
calcium triggers
release of calcitonin
Causes uptake of
calcium by
osteoblasts (bone
builders)
Nutrition (contd)
Decrease in calcium
triggers release of
Parathyroid hormone
Triggers osteoclasts
to break down bone,
releasing calcium
into blood
Exposure to Sunlight
UV light on the skin causes Vitamin D
production
Promotes proper absorption of calcium in
the SI
Hormonal Secretion
Human growth
hormone
Somatotropin
Both hormones
stimulate activity in
the epiphyseal plate
Physical Activity
Increase in physical
exertion on bone
tissue actually
increases bone
density and strength
Bone maintenance
 Osteoblastsconstantly producing
new bone tissue
 Osteoclasts – clean
out old bone tissue
Causes holes or
tunnels in bone which
osteoblasts then fill in
with calcium and
phosphate compounds
Fractures
Simple Fracture
 Also called closed
fracture
 Bone breaks cleanly,
and does not
penetrate skin.
 Little chance of
infection
Compound Fracture
 Bone breaks
completely
 Bone ends protrude
through skin
 Major chance of
serious bone infection
Comminuted Fracture
 Bone breaks into
many fragments
 Common in elderly
Compression Fracture
 Bone is crushed
 Common in porous
bones
 Especially common in
vertebrae of
osteoporosis patients
Depression fracture
 Broken bones are
forced inward
 Common in skull
fractures
Impacted Fracture
 Broken bone ends are
forced into each other
 Common in falls (ie.
From ladder) where
person attempts to
break their fall
Spiral Fracture
 Occurs from
excessive twisting
force on bone
 Common in sports
injuries
Greenstick Fracture
 Bone breaks
incompletely
 Common in children
due to more collagen
in bones
Repairing Fractures
Closed reduction = bones
are eased back into
alignment and “reset”
Open reduction = bones are
surgically reset using
screws or wires
After either, a cast is
usually applied to
immobilize the bone;
healing begins
Internal Bone Repair
 1)Hematoma forms from
ruptured blood vessels.
 2)After new capillaries
form, fibrocartillage callus
“splints” broken bone
using cartilage and bony
matrix.
 3)Osteoblasts migrate to
area, forming bone
“patch” over break.
Fibrocartilage is replaced
by bony callus.
The Axial Skeleton
Divisions of the Skeletal System
 Skeletal system is
divided into two main
division
Axial – central skeleton
that protects and
supports vital organs
Appendicular – skeleton
of the extremities
Axial Skeleton
 Composed of skull and
vertabrae
 Mainly flat and irregular
bones
 Serve to protect organs
such as brain, heart,
and lungs
 Also helps to support
body along central axis
(backbone)
Parts of the axial skeleton
 Skull – protects brain
 Vertebrae – protect
spinal chord ;also serves
to keep skeleton upright
 Ribs – protect lungs and
heart ; gives intercostal
muscles a hard surface
to move against for
breathing
Divisions of the skull
 Skull is divided into 2
sets of bones
Cranium – collection of
8 bones which hold and
protect brain
Facial bones – 14
bones that make up the
face; all but 2 are
paired
Cranium
 Frontal Bone – makes up
forehead, eyebrows, and
superior section of eye orbital
 Parietal Bone – form most of
the superior and lateral walls
of cranium
 Temporal bones – lie inferior
to parietal bones
 Occipital bone – forms back
and floor of cranium; foramen
magnum (large hole) allows
spinal chord to meet brain
Facial Bones
 Mandible- lower jaw
bone
 Maxillary bones
(maxillae) fuse
together to form
upper jaw
 Palatine processes –
directly posterior to
maxillae; forms rear
of hard palate
Facial Bones Contd.
 Zygomatic bones – cheekbones
 Lacrimal bones – inferior section of orbital
bones; provides passageway for tears
 Ethmoid bone- forms roof of nasal cavity
More Facial Bones
 Nasal bones- form
bridge of nose
 Vomer – divides nasal
cavity in half
 Inferior conchae- thin
curved bones which
project from interior of
nasal cavity
Axial Skeleton
Intervertebral Discs
Spinal curvatures
Bony Thorax
Intervertebral Discs
 Pads of cartilage
between each vertebrae
 Provide cushioning;
reduce shock
 High water content
 As you age, water
content lowers, drying
discs
 Can cause herniated
(slipped) disc; where
disc protrudes from
spine
Bony Thorax
 Made of bones which
connect and protect
heart and lungs
 Ribs, Costal
Cartilage, and
Sternum
Ribs
 12 pairs of ribs, each
connects to a thoracic
vertebrae
 First 7 pairs = true ribs;
attach directly to
sternum
 Last 5 pairs = false ribs;
indirect or no
attachment; last two are
floating (no sternal
Sternum
 Fusion of three bones
 1) Manubrium (top)
 2) Body (middle)
 3) Xiphoid Process
(bottom)
 Location for rib
attachment
 Surrounded by costal
cartilage
Sternal Puncture
 Process by which
marrow is removed
from sternum
 Good location
because of proximity
to body surface
The Spinal Column
Intro
 Supports body
 Connects skull to
pelvis
 Sends weight down to
pelvis, where it is
transmitted through
the legs
 Surrounds and
protects spinal cord
 26 total bones
Divisions of the Spinal Column
 4 main divisions
1) Cervical curvature
2)Thoracic curvature
3)Lumbar curvature
4)Pelvic
 Sacrum
 Thorax
Cervical curvature
 Begins where skull
meets spine
 Composed of 7
vertebrae
 Labeled C1-C7,
starting at skull
 First two vertebrae
(C1 and C2)are
different
C1 and C2
 Perform different jobs
than other vertebrae
 C1 (atlas) has
depressions that
accept the occipital
codyles (“yes nod”)
 C2 (axis) acts as pivot
point for skull (“no”
head shake)
Thoracic Curvature
 12 bones
 T1-T12
 Costal demifacet –
point of attachment of
ribs
Lumbar Vertebrae
 5 vertebrae
 (L1-L5)
 Sturdiest because
under the most stress
Sacrum
 1 bone composed of
5 fused vertebrae
 “wing-like” alae
connect laterally with
hip bones (forms
sacroiliac joints)
 Makes up posterior
wall of pelvis
Coccyx
 1 bone formed by
fusion of 3 vertebrae
 Tailbone
 Thought to be left
over from when our
ancestors had tails
Spinal Curvatures
Scoliosis- lateral
curvature
Lordosis- Apex
towards anterior (ie.
Lumbar curvature)
Kyphosis- Apex
towards posterior
(Osteoporosis
patients)
Appendicular Skeleton
Pelvic Girdle
Pelvis
 Juncture point for axial
skeleton and lower
body
 Holds internal organs
 Distributes weight
down legs
 3 fused bones
 Obturator foramenlarge hole through
which nerves and
muscles pass
Bones of the Pelvis
Ilium
Ischium
Pubis
Become fused
into “pelvis” at
puberty
Ilium
Makes up top of hip
(iliac crest)
Lateral portions of
the pelvis
Contains hip socket
Features of the Ilium
 Iliac crest – rounded
projection on superior
surface; makes up “hip”
 Acetabulum- joint
between femure and
pelvis
 Width from crest to crest
= false pelvis
 Width of actual inlet =
true pelvis
Ischium
Inferior portion of pelvis
Ischial Tuberosity –
point of muscle
attachment; “sit bones”
Pubis
Anterior portion of pelvis
Joined medially by pubic symphysis
Leg bones
Hands and Feet
Appendicular Skeleton
Superior Extremities
Shoulder Girdle
 Also called pectoral
girdle
 Composed of only
two bones
Clavicle
Scapula
Clavicle
 Collar bone
 Double-curved
 Attaches medially to manubrium
of sternum
 Attaches laterally to scapula
 Acts as a brace, keeping arm
away from thorax
 Also prevents shoulder
dislocation
Scapula
 Shoulder Blade
 Main function is
attachment of shoulder
 Major point of muscle
attachment for movement
of arms
 Weakly attached to
thorax, so moves easily
Major Processes of the Scapulae
 1)Acromion – extends
from spine of
scapulae
Point of attachment of
clavicle
 2)Coracoid- main site
of arm muscle
attachment
Glenoid Cavity
 Socket of arm joint
 Shallow
 Allows for great range
of motion
 Also dislocates easily
Movement in the Shoulder Girdle
 Very free moving because
1)Only attaches at one point to axial
skeleton
2)Loose attachment of scapula allows it to
slide
3)Glenoid cavity very shallow
Arm Bones
 Arms composed of
long bones
 Humerus (upper arm)
 Radius and Ulna
(forearm)
Humerus
 Simple long bone
 Greater and lesser
tubercle allow for
muscle attachment
 Deltoid tuberosityplace of attachment
for deltoid muscle
Attachment to the forearm
 Trochlea articulates
against bones of
forearm
 Olecranon fossa
shaped like spoon
Forearm bones
 Ulna – pinkie-side of
forearm
 Radius – Thumb side
of forearm
Processes of the ulna
 Olecranon process
attaches to humerus
at olecranon fossa
 Allows for articulation
between upper and
lower arm
Hands and Feet
Joints
Intro
 Any point where bones
meet
 Also called
articulations
 Every bone (except
hyoid) articulates with
at least 1 other bone
Classifications of Joints
 Can be classified by
mobility, or by the
type of tissue which
connects the bones
Joint classification by Mobility
 Can be one of three
types.
1) Synarthroses –
immovable joint
2)amphiarthroses- slightly
moveable joint
3)diarthroses- freely
movable
Classification by connective tissue
type
 Joints are connected by
either fibrous, cartilage,
or synovial connective
tissue.
 Fibrous is usually
synarthroses,
 Synovial – diarthroses
Fibrous Joints
 Fibrous tissue
 Example= sutures of
the skull
 Tight fibrous tissue
allows for essentially no
movement
Cartilaginous Joints
 Cartilage
 Example=
intervertebral joints
 Can express either
type of movement
Synovial Joints
 Bones separated by
synovial cavity
 Empty pocket serves to
reduce friction between
moving bones
 Usually located in
extremities, where
movement is necessary
So… What does it mean to be
double-jointed?
 Usually not actually
two joint cavities
 Ligaments are simply
less taut than
normal, allowing for
more flexibility
 Can be indicative of
serious genetic
defects
Joint Problems
 Osteoarthritis –
general break-down
of joints, leading to
ossification, and
then pain.
 Rheumatoid Arthritis
– autoimmune
disease where body
attacks its own
tissues; cause
unknown
Features of the Skull
Sutures of the cranium
 Suture – location
where flat bones of
the cranium meet and
fuse
 Squamous- fuses
temporal and parietal
 Coronal – fuses frontal
to parietal
 Saggital – fuses plates
of parietal bones
 Lambdoid – fuses
occipital to parietal
Bone markings of the Temporal Bones
 1) external auditory
meatus – canal which
leads to inner ear
 2) styloid process – sharp,
needlelike projections
inferior to the
e.a.m.;location of muscle
attachment
 3) zygomatic processforms cheek bones;forms
large hole which allows
jaw muscles to pass
through to mandible
Temporal bone markings (contd.)
 4) mastoid process –
posterior and inferior to
e.a.m.;location of muscle
attachment for muscles of
the neck
 5) jugular foramen- at
junction of occipital and
temporal bones; allows
jugular vein to pass
through from brain
 6) carotid canal – anterior
to j.f. Allows carotid
artery to pass to brain
Occipital Condyles
 Lie lateral to the
foramen magnum
 Rest upon the spinal
column
 Provides point of
attachment for skull to
spinal column
Cribriform Bones
 Cribriform bones –
“holey” bone plates
which make up roof of
nasal cavity;allow for
olfactory sensors to
pass from nose to brain
Sinuses
 Empty pocket inside
bones which are lines
with mucous
membranes
 Paranasal sinussurrounds nasal
cavity
 Lighten skull, and
thought to amplify
sounds when
speaking
Deformations
 Cleft palate = when
palatine bones fail to
properly or completely
fuse.
 Leads to inability to
nurse, due to failure
to form a vacuum.
Male vs. Female Skeleton
In general
Male skeleton is larger, with thicker bones
Female bones maintain many
characteristics of prepubescent skeleton
Male features change at puberty (usually
at points of muscular attachment)
Skull
 Male mastoid process
more pronounced
 Superior portion of
female orbital (brow
ridge) less pronounced
 Female mandible is
pointed, while male is
squared
Facial Differences
 Female face wider than
male
 Females have more
pointed nose, while
males are more blunt
 Female forehead less
sloping
 Eyebrows positioned
higher in females
Pelvis
 Female Pelvis wider
and more shallow
 Male iliac crests more
pointed
 Male pelvis more
narrow
Sacrum
Female sacrum wider and flatter
Usually more rounded than male
Forensic anthropology
Most will say that there is no exact way to
determine sex from skeleton (not exact
science)
Pelvis is probably most reliable feature to
analyze, followed by mandible