Axial Skeleton
Includes:
80 bones
•Skull (22 bones)
•Hyoid bone
•Auditory ossicles (6)
•Vertebral Column (26 vertebrae in
adults)
•Thorax (12 pair of ribs/sternum)
Skull
• 8 cranial bones which enclose and protect the
brain
– Two parietal, two temporal, frontal, occipital,
sphenoid and ethmoid
• 14 facial bones
– two nasal, two maxillae, two zygomatic, two
palatine, two lacrimal, two inferior nasal conchae,
mandible, vomer
Function
• Besides protection of the brain, cranial bones
function to:
– Stabilize the position of the brain, blood vessels and
nerves (by attachment to inner surfaces of bones)
– Provide large areas of attachment for muscles that
move the head (by attachment to outer surfaces of
bones)
– Facial bones protect and provide support for
entrances to the digestive and respiratory systems;
also provide attachment for some muscles involved in
facial expressions.
Details on Temporal bone markings
• External auditory meatus =
canal in the temporal bone
that leads to the middle ear.
• Mastoid process = rounded
projection on temporal
bone that serves as
attachment site for neck
muscles.
• Styloid process = projects
downward from
undersurface of temporal
bone and serves as
attachment site for muscles
of tongue and neck
• Mandibular fossa = forms a
joint with condylar process
of mandible
• Carotid foramen – hole in temporal bone
through which carotid artery passes.
Details on Occipital bone markings
• Foramen magnum=
largest foramen in
skull; medulla
oblongata of the
brain connects to
spinal cord through
this foramen
• Occipital condyles=
oval processes on
either side of
foramen magnum
that articulate with
the first cervical
vertebra.
Details on Sphenoid bone markings
• Articulates with all the
other cranial bones,
holding them together
• Sella turcica =
depression on superior
surface of sphenoid
bone which surrounds
the pituitary gland
• Foramen ovale =
mandibular nerve
passes through
• Optic foramen= optic
nerve passes through
Details on Ethmoid bone markings
• Ethmoid bone contains 3-18 air spaces that form the
ethmoidal sinuses
• Perpendicular plate= forms upper part of nasal septum
• Cribriform plate = forms roof of nasal cavity
• Olfactory foramina= fibers of the olfactory nerve pass
through
• Crista galli= serves as point of attachment for the
meninges.
• Superior nasal concha and Middle nasal concha = cause
turbulence in inhaled air which cleanses air before it
passes into the rest of the respiratory tract.
Details on Facial bone markings:
• Mandible= largest,
strongest facial bone; only
movable skull bone;
contains the condylar
process which articulates
with the manidibular fossa
of temporal bone to form
the Temporomandibular
Joint (TMJ).
• Mental foramen = holes in
mandible that dentists use
to reach the mental nerve
when injecting anesthetics
Temporomandibular Joint syndrome
• TMJ syndrome is characterized by dull pain
around ear, tenderness of jaw muscles,
clicking or popping noise when opening or
closing mouth.
• Caused by improperly aligned teeth, trauma
to head/neck, or arthritis
• Vomer = triangular bone
on floor of nasal cavity;
one of the components
of nasal septum (divides
the nasal cavity into right
and left sides)
• Nasal Septum = formed
by vomer, septal cartilage
and perpendicular plate
of ethmoid bone
Paranasal Sinuses
• Hollow portions of bones surrounding the nasal cavity
• Named for their locations in bones of the same name
 Functions :
 Lighten the skull
 Give resonance and amplification to voice
The Hyoid Bone
 The only bone that
does not articulate
with another bone
 Serves as a
moveable base for
the tongue
The Fetal Skull
 The fetal skull is large
compared to the
infants total body
length
 Fontanelles – fibrous
membranes connecting
the cranial bones
 Allow the brain
to grow
 Convert to bone
within 24 months
after birth
The Vertebral Column
 Consists of 7 cervical, 12
thoracic, 5 lumbar
vertebrae; sacrum and
coccyx
 Vertebrae separated by
intervertebral discs
 Each vertebrae is given
a name according to its
location
Structure of a Typical Vertebrae
• Body= weight bearing part
• Vertebral arch= formed by
lamina and pedicles
• Vertebral foramen= spaced
between the vertebral arch
and the body; contains the
spinal cord
• Seven processes serve as
points of muscle attachment
or form joints with other
vertebrae
– Know Spinous process and
Transverse process
Characteristics of Cervical Vertebrae
Atlas (C1) – superior articular facets
articulate with occipital condyles of skull and
allow nodding motion of head
Axis (C2) – Dens (odontoid process) extends
superiorly into vertebral foramen of atlas and
allows the atlas to pivot in a “no” type movement.
.
Dens can get shoved into the medulla oblongata
(brain stem) during head trauma.
All cervical vertebrae have 3 foramen:
vertebral and two transverse foramen which
allow passage of arteries, veins and nerves
to and from brain
Characteristics of Thoracic Vertebrae
Thoracic – have a midsized body and a long,
narrow spinous
process which slants
inferiorly at a sharp
angle; facets on
transverse processes
articulate with ribs
Characteristics of Lumbar Vertebrae
Lumbar – have
largest bodies to
support the most
weight;
thick, moose-head
shaped spinous
processes
Abnormal Spinal Curvatures
Thoracic Cage
• Forms a cage to
protect major organs
 Made-up of three
parts
 Sternum
 Ribs
 Thoracic vertebrae
Sternum
• Narrow flat bone consisting of
3 parts:
Manubrium- articulates
with clavicles and 1st and 2nd
ribs
Body – articulates with 2nd
– 10th ribs (directly or
indirectly)
Xiphoid process – doesn’t
ossify until about age 40.
Ribs
• True Ribs – 1st – 7th
pairs; have direct
attachment to sternum
by hyaline cartilage
• False Ribs – 8th – 12th
pairs; attach indirectly
to sternum or not at all
– 11th and 12th pair of ribs
are also called floating
ribs because they do not
attach to sternum at all.