The Axial Skeleton
THE SKELETAL SYSTEM
The Axial Skeleton
• The skeleton consists of
– Bones (206)
– Cartilages
– Joints – also called articulations, are the junctions
between skeletal elements
– Ligaments – connect bones
• Divided into axial and appendicular
• Axial skeleton - forms long axis of body
– Skull
– Vertebral column
– Thoracic cage
• Appendicular skeleton – appendages and
what they attach to
– Upper limbs (arms)
– Pectoral girdle (shoulder)
– Lower limbs (legs)
– Pelvic girdle
Axial skeleton
Skull
Vertebral column
Thoracic cage
Axial skeleton is shown in green
The Skull
• Cranial bones (or cranium)
– Enclose the cranial cavity, which supports and protects the
brain
– Attachment sites for some head and neck muscles
• Facial bones (anterior aspect of skull)
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–
–
–
–
Form framework of face
Form cavities for sense organs of sight, taste and smell
Provides openings for passage of air and food
Hold the teeth
Anchor the muscles of the face
Cranium
• Vault – “calvaria” = skullcap
– Forms superior, lateral and
posterior aspects of skull, and
forehead
Anterior cranial
fossa
• Base or floor: inferior part
– Prominent bony ridges divide
cranial base into 3 “fossae”
(steps) – anterior, middle and
posterior
Middle cranial
fossa
Posterior cranial
fossa
(looking down on the floor of the skull)
Cranial bones
•
•
•
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•
Frontal bone
Parietal bones (paired)
Occipital bone
Temporal bones (paired)
Sphenoid bone
Ethmoid bone
Cranial bones
frontal
parietal
temporal
occipital
parietal
parietal
_______sphenoid
_____ethmoid
occipital
Temporal bones
this is the right temporal bone
looking at it from the right side
Small cranial bones…
Sphenoid
Ethmoid
Sutures
• Immovable, interlocking joints of flat bones of skull
• Irregular, saw-toothed appearance
• Largest 4 skull sutures: where bones articulate with
parietal bones
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–
–
–
Coronal
Sagittal
Squamous
Lambdoid
Find: coronal, squamous and lamboid sutures
Find: sagittal and lambdoid sutures
• Cranial “cavity” – houses brain
• Smaller cavities
– Housing middle and inner ear
– Nasal cavity
– Orbits
– Sinuses
• Openings (foramina, canals, fissures) for:
– Spinal cord
– Blood vessels
– Twelve cranial nerves: I-XII
Remember, the skull is composed of:
1. Cranial bones (or cranium)
and
2. Facial bones (anterior aspect of skull)
– Form framework of face
– Form cavities for sense organs of sight, taste and
smell
– Provides openings for passage of air and food
– Hold the teeth
– Anchor the muscles of the face
Facial bones
•
•
•
•
•
•
•
•
Mandible
Vomer
Maxillae (paired)
Zygomatics (paired)
Nasal (paired)
Lacrimal (paired)
Palatines (paired)
Inferior nasal conchae (paired)
Facial bones:
Mandible
Vomer
Maxillae (paired)
Zygomatics (paired)
Nasal (paired)
Lacrimal (paired)
Palatines (paired)
Inferior nasal conchae
(paired)
Maxilla (there are 2 which fuse,
forming the upper jaw)
Mandible (lower jaw)
Nasal cavity
• Of bone and cartilage
nasal bone
maxilla___________
Orbit
Cone-shaped bony cavities holding the eyes, muscles
that move the eyes, some fat and tear-producing glands
optic nerve passes out through it
Paranasal sinuses
• Air-filled sacs in the bones
• “Paranasal” because they cluster around and
connect to the nasal cavity
Hyoid bone
• Only bone which does not
articulate with any other
bone
• Moveable base for the
tongue
• Points of attachment for
neck muscles that raise and
lower the larynx during
swallowing
Skull
Vertebral column
Thoracic cage
Axial skeleton is shown in green
The Vertebral Column
• Fetus and infant: 33 separate
bones or vertebrae
• Adult: 24 vertebrae
– Inferior 9 have fused forming
• The sacrum (5) and
• The coccyx (4)
Vertebrae
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•
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Cervical – 7
Thoracic - 12
Lumbar - 5
Sacrum (5 fused)
Coccyx (4 fused)
Spinal curvatures
• Cervical and lumbar are concave
posteriorly* (lordosis)
• Thoracic and sacral are convex
posteriorly* (kyphosis)
• Abnormal:
– Too much of either
– Scoliosis (more than 10 degrees of
lateral curvature)
*when viewed from the side
Abnormal curvatures
Disorders of the axial skeleton
• Scoliosis (over 10% curvature)
• Kyphosis
• Lordosis
• Vertebral compression fractures
• Spinal stenosis
Non-bony parts
• Intervertebral
discs
– anulus fibrosis
and nucleus
pulposus)
• Anterior
longitudinal
ligament
• Posterior
longitudinal
ligament
• Ligamentum
flavum
Anterior longitudinal ligament: wide, strong and attaches to
vertebrae as well as discs (prevents hyperextension)
Posterior longitudinal ligament: narrow and relatively weak,
attaching only to discs
*
Structure of a typical vertebra
Cervical vertebrae (C1-C7)
C1 (atlas)
C2 (axis)
Cervical Vertebrae
•
•
•
•
Smallest
Lightest
Most flexible
Triangular vertebral
foramen
• Transverse processes
have foramina
(transverse foramen)
• Spinous process bifid
(forked) except for C7
Thoracic Vertebrae T1-T12
• Heart shaped body
• Additional small
costal facets
(costal=ribs)
• Round or oval
vertebral foramen
• Form posterior
part of rib cage
Lumbar Vertebrae L1-L5
• Massive
blocklike bodies
• Short, thick
hatchet-shaped
spinous
processes
• Limited mobility
Shapes posterior wall of pelvis
The Sacrum
Composite bone of 5 fused vertebrae
Sacral foramina allow passage of vessels & nerves
Coccyx
(the tailbone)
Remember that the Axial
skeleton includes:
Skull
Vertebral column
Thoracic cage
Axial skeleton is shown in green
The Thoracic Cage
Sternum
Ribs
• Manubrium
• True ribs 1-7
• Body
• False ribs 8-12
• Xiphoid process
• Floating ribs 11,12