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The Axial Skeleton
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Axial Skeleton
 Forms the longitudinal part of the body
 Divided into three parts
 Skull
 Vertebral column
 Bony thorax
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The Axial Skeleton
Figure 5.6
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The Skull
 Two sets of bones
 Cranium – encloses & protects brain.
 Facial bones – holds eyes in anterior
position & allows the facial muscles to
show emotions.
 All but 1 of the bones are joined by sutures
(interlocking, immovable joints)
 Only the mandible is attached by a freely
movable joint
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The Cranium
 Frontal – forms forehead, brow bone,
superior eye orbit
 Parietal (2) – form most of the superior
& lateral walls of the cranium
 Meet in midline = sagittal suture
 Meet frontal = coronal suture
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The Cranium
 Temporal (2) – inferior to parietals & join to them at
the squamous sutures
 Important bone markings found here
 External acoustic (auditory) meatus – canal
leading to eardrum
 Styloid process – sharp needle-like
projection inferior to external auditory
meatus (attachment point for many neck
muscles and the hyoid bone)
 Zygomatic process – thin bridge of bone that
joins w/ the zygomatic (cheek) bone
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The Cranium
 Important bone markings found in temporal bone
 Mastoid process – rough projection posterior
& inferior to the external auditory meatus
 Full of air cavities (sinuses)
 Attachment for some neck muscles
 Close to middle ear & leads to ear infections
 Jugular foramen – junction of occipital &
temporal
 Allows for passage of jugular vein
 Largest vein of the head – drains the brain
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The Cranium
 Important bone markings found in
temporal bone
 Internal auditory meatus – anterior to
jugular foramen
 Transmits cranial nerves 7 & 8
(facial & vestibulocochlear)
 Carotid canal - anterior to jugular
foramen
 Carotid artery runs through it to
brain
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The Cranium
 Occipital – most posterior bone of cranium
forming back wall & floor of the skull
 Joins parietals anteriorly at lambdoid
suture
 Foramen magnum = large opening in base
of the occipitals (spinal cord connects with
the brain)
 Lateral to the foramen magnum are
rockerlike occipital condyles which
rest on the 1st vertebra
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The Cranium

Sphenoid – butterfly-shaped – spans the width of the skull
and forms part of cranial cavity floor

Sella turcica “Turk’s saddle” = small depression on the
midline of the sphenoid, holds the pituitary gland

Foramen ovale = large oval opening in line w/ the
posterior end of the sella turcica (allows cranial nerve
5 (trigeminal) to pass to chewing muscles of mandible

Parts of the sphenoid form part of the eye orbits


2 important openings:
1.
Optic canal (optic nerve)
2.
Superior orbital fissure (cranial nerves 3, 4 & 6 – eye
movements)
Central part of the sphenoid riddled w/ air cavities =
sphenoid sinuses
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The Cranium

Ethmoid – irregularly shaped, anterior to sphenoid
– forms roof of nasal cavity and medial walls of
the orbits.

Crista galli “cock’s comb” = superior ethmoid
surface projection – outermost brain covering
attaches

Cribriform plates – holey areas on sides of
crista galli= nerve fibers for smell pass through
from nose

Superior & middle nasal conchae – extensions
of the ethmoid – form part of lateral walls of
nasal cavity & increase turbulence of air
flowing
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The Facial Bones
 14 bones
 12 paired, only the mandible and vomer are
single
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The Facial Bones
 Maxillae (2) / maxillary bones – fused to
form upper jaw
 Upper teeth carried in the alveolar
margin
 Palatine processes- extensions that form
the anterior part of the hard palate
 Paranasal Sinuses – drain the nasal
passages, lighten the skull bones, amplify
sounds as we speak
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The Facial Bones

Paranasal Sinuses

Hollow portions of bones surrounding the nasal
cavity

Sinusitis (infection of sinuses) – can result in
headache or upper jaw pain
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The Facial Bones
 Palatine(2) – posterior to palatine processes
of maxillae – form posterior part of hard
palate
 cleft palate= failure of these to fuse
 Zygomatic (2) – cheek bones – form portion
of lateral walls of orbits
 Lacrimal (2) – fingernail sized bones
forming part of medial walls of orbits
 Groove serves as passageway for tears
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The Facial Bones
 Nasal (2)– small rectangular bones – form
bridge of nose – lower part of nose made of
cartilage
 Vomer “plow”(1) – median line of nasal
cavity – forms most of the nasal septum
 Inferior nasal conchae (2) – thin, curve
bones projecting from lateral walls of the
nasal cavity
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The Facial Bones
 Mandible (lower jaw) – largest, strongest
bone of the face – joins temporal bones on
each side of face, forming the only freely
movable joints in the skull (find them!)
 Horizontal part (body) forms the chin
 2 upright bars of bone (rami) extend
from the body to connect the mandible
with the temporal bone.
 Lower teeth lie in alveolar margin
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The Hyoid Bone
 Not really part of the skull
 Horseshoe shaped w/ a body and 2 pair
of horns (cornua)
 Closely related to mandible and
temporal bones
 Unique b/c it’s the only bone that does
not articulate w/ any other bone
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The Hyoid Bone

Suspended in mid–neck
region 2 cm above the
larynx, anchored by
ligaments to the styloid
processes of the temporal
bones

Serves as a movable base
for the tongue &
attachment point for neck
muscles (lower and raise
larynx when we swallow
& speak)
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The Fetal Skull
 Face small
compared to
size of cranium
(skull is large
compared to
body length)
 Adult skull is
1/8 total body
length; newborn
is 1/4
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The Fetal Skull

Fontanels – fibrous membranes connecting the
cranial bones

Baby’s pulse can be felt in these soft spots
(explains their name “little fountain”)

Allow fetal skull to be compressed in birth
process

Allow infants brain to grow

Largest fontanels are diamond shaped anterior
shaped fontanel and smaller triangular shaped
posterior

Convert to bone within 24 months after birth
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The Skull
Figure 5.7
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Bones of the Skull
Figure 5.11
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Human Skull, Superior View
Figure 5.8
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Human Skull, Inferior View
Figure 5.9
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The Vertebral Column
 Serves as axial support
of the body
 Extends from the skull,
which it supports, to the
pelvis, where it transmits
the weight of the body to
the legs.
 26 irregular bones
connected & reinforced
by ligaments creating a
flexible, curved
structure.
Figure 5.14
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The Vertebral Column
 Spinal cord runs
through central
cavity, protected by
vertebrae
 Before birth = 33
separate vertebrae but
9 later fuse to form 2
composite bones – the
sacrum (5 fused) &
the coccyx (4 fused).
Figure 5.14
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The Vertebral Column
 Each vertebrae is given a
name according to its
location
 24 single vertebrae
 7 cervical vertebrae
 12 thoracic vertebrae
 5 lumbar vertebrae
Figure 5.14
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The Vertebral Column
 Vertebrae separated by pads of flexible fibrocartilage
– intervertebral discs –cushion & absorb shocks
while allowing flexibility.
 Young person – discs = 90% water content –
spongy & compressible.
 As you age – water content decreases – harder &
less compressible.
 Can lead to herniated (“slipped”) discs.
 Can also occur from exceptional twisting forces.
 If disc presses on spinal cord or nerves = numbness
& excruciating pain.
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The Vertebral Column
 Disks & S-shaped curvature of spine prevent shock
to head when we walk or run.
 Primary curvatures
 Thoracic & sacral regions
 Present at birth
 Secondary curvatures
 Cervical curvature appears when baby begins to raise
its head.
 Lumbar curvature when baby begins to walk.
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The Vertebral Column
 Abnormal spinal curvatures
 Scoliosis - abnormal lateral curvature of
the spine.
 Kyphosis - Abnormal rearward curvature
of the spine, resulting in hunchback.
 Lordosis - Abnormal forward curvature of
the spine in the lumbar region.
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Vertebrae
 All vertebrae have a similar structural pattern.
 Body: disclike, weight bearing part facing
anteriorly.
 Vertebral arch: formed from the joining of all
posterior extensions, the laminae & pedicles.
 Vertebral foramen: canal through which the spinal
cord passes.
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Vertebrae
 Transverse processes: 2 lateral projections from
the vertebral arch.
 Spinous process: single projection arising from the
posterior aspect of the vertebral arch (fused
laminae).
 Superior & inferior articular processes: paired
projections lateral to the vertebral foramen allowing
a vertebra to form joints w/ adjacent vertebrae.
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Structure of a Typical Vertebrae
Figure 5.16
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Vertebrae
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Cervical Vertebrae
 7 (C1 to C7) – form the neck region.
 First 2 – atlas & axis – are different because
they perform functions not shared by any
other cervical vertebrae.
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Cervical Vertebrae
 Atlas (C1) has no body; the
superior surfaces of its
transverse processes contain
large depressions that
receive the occipital
condyles of the skull; allows
you to nod “yes.”
 Axis (C2) has a large upright
process (dens or odontoid
process), which acts as a
pivot point; allows you to
indicate “no.”
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Cervical Vertebrae
 C3 through C7 are the smallest, lightest
vertebrae
 All transverse processes of cervical vertebrae
only contain foramina through which
vertebral arteries pass to the brain.
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Thoracic Vertebrae
 12 with body somewhat heart shaped w/ 2
costal facets on each side, which receive the
heads of the ribs.
 Spinous process is long & hooks sharply
downward (from the side looks like a giraffe’s
head).
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Lumbar Vertebrae
 5 w/ massive blocklike bodies & short
hatchet-shaped spinous processes (looks like
moose head from side).
 Sturdiest vertebrae – most stress here.
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Sacrum
 Formed by the fusion of 5 vertebrae.
 Winglike alae articulate laterally w/ the
hipbones forming the sacroiliac joints.
 Forms the posterior wall of the pelvis.
 Median sacral crest roughens the posterior
midline & are flanked by sacral foramina.
 Vertebral canal continues inside the sacrum
as the sacral canal – terminates in large
inferior opening called the sacral hiatus.
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Coccyx
 Formed by fusion of 3 to 5 tiny, irregularly
shaped vertebrae
 This is the human “tailbone” – a remnant of
the tail other vertebrate animals have.
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Regional Characteristics of Vertebrae
Figure 5.17a–b
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Regional Characteristics of Vertebrae
Figure 5.17c–d
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The Bony Thorax
 Made-up of
three parts
 Sternum
 Ribs
 Thoracic
vertebrae
Figure 5.19a
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Bony Thorax
 Often called the “thoracic cage” b/c it forms a
cone-shaped cage of slender bones around the
organs of the thoracic cavity.
 Sternum – “breastbone”
 Flat bone that is a result of the fusion
of 3 bones – the manubrium, body and
xiphoid process
 Attached to the first 7 pairs of ribs
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Sternum

Three important bony landmarks:
1. jugular notch (concave upper border of
the manubrium) – can be felt easily –
generally at level of T3
2. sternal angle - where manubrium &
body meet - formed at level of 2nd ribs
(reference to locate 2nd intercostal
space for listening to heart valves)
3. xiphisternal joint – body and xiphoid
process fuse (level of T9)

Sternal puncture used to get bone marrow
tissue to diagnose certain blood diseases
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Bony Thorax
 Ribs – 12 pair – form walls of bony thorax
 Articulate w/ vertebral column posteriorly &
curve downward toward anterior body
surface.
 True ribs = first 7 pair – attach directly to
sternum by costal cartilage
 False ribs = next 5 pair – attach indirectly to
sternum or not at all (last 2 pair are called
“floating ribs” b/c they are the ones not
attached at all)
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Bony Thorax
 Contrary to
popular myth –
men & women
have the same
number of ribs!!

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