CHAPTER 7
“The Axial Skeleton”
Course objectives:
Define and identify the bones of the axial
skeleton
Axial Skelton
– 80 total bones
– consists of the bones that form the long axis
of the body including the:
• Skull (total 28 with ear bones)
• Vertebral column [(total 26) C7;T12; L5; S1; Co1]
• Bony thorax [ribs and sternum (total 25)]
• Hyoid bone (1)
Skull Bones
– the skull has two major divisions:
Cranium and Facial bones
Cranium – the 8 bones that enclose the brain.
-1 occipital, 1 frontal, 2 parietal, 2 temporal,
1 sphenoid and 1 ethmoid.
•
These typical flat bones of the cranium are
connected by a special kind of joint called a
suture (Synarthroses).
Cranial bones
Cranial Bones
Cranium
•
Made up of 2 major divisions:
1. Calvarium (skull cap)
2. Base
•
Base contains three large depressions (fossa):
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Anterior cranial fossa where the frontal lobes sit
Middle cranial fossa where the temporal lobes sit
Posterior cranial fossa where the cerebellum sits
Cranial Bones
Sutures/Sutural Bones
• Sutures (synarthrotic) are immovable fibrous
joints; except for the jaw.
-all bones in the skull are united by sutures.
-Coronal
-Sagittal
-Squamous
-Lamboid
Sutural bones- small bones that occur within
the sutures, especially the lamboid suture.
They are not present in all people.
Facial bones
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•
There are 14 bones that can be thought of as
creating the face.
As part of this function they provide:
- protection for many sense organs,
-provide anchors for many muscles
-create the openings for air and food to
pass.
Facial Bones
2-maxilla; 2-palatine; 2-nasal; 2- zygomatic;
2-lacrimal; 2-inf nasal concha; 1- vomer; and
1-mandible
Sphenoid bone
Looks like a Bat in flight. Greater and lesser
wings; optic foramen; sella turcica, superior
orbital fissure.
Ethmoid bone
• Anterior to
sphenoid bone
forms anterior
base of skull
and nasal cavity.
• Cribriform plate.
• Crista gali
• Perpendicular
plate
Foramen/ Orbits
• Foramen: Special openings in bones where
nerves, blood vessels enter into the bone
cavity.
- Ex.: Foramen magnum, Supraorbital
Infraorbital, Mental, Jugular, Olfactory,
Mandibular
• Orbits: Cone shaped bony cavities that hold the
eyes, fat, occular muscles and tear glands.
Meatus/ Sinuses
• Meatus: a canal or opening into bone
- Ex.: external auditory, internal acoustic
• Sinus: cavities within bones filled with air.
-Ex.: frontal, ethmoid, sphenoid and
maxillary sinuses
Cranial sinuses
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Frontal
Ethmoid
Sphenoid
Maxillary
The Fetal Skull
• Sutures are called fontanels in fetus.
• Fontanels
-Frontal (anterior)
-Occipital (posterior)
-Sphenoidal (anterior lateral)
-Mastoid (posterior lateral)
Vertebral column
• composed of 26 irregular bones.
• These bones provide a solid support
structure, but are also remarkably flexible.
Regions of the Vertebral Column
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Cervical − neck region 7 vertebrae
Thoracic – thorax region 12 vertebrae
Lumbar – lower back 5 vertebrae
Sacral – low, low back 1 vertebrae (5
fused)
– COccygeal – tail bone 1 vertebrae (4
fused)
Spinal Curvature
• Thoracic and sacral are concave (i.e.
backward)
• Primary curves since they developed first.
• Cervical and lumbar curves are convex (i.e.
forward) and secondary curves.
Vertebrae
• Individual vertebrae are found in the
cervical, thoracic and lumbar regions of
the vertebral column.
• There are significant differences between
the vertebrae in each of these regions that
you should know.
Cervical vertebrae – C1- C7
• Body is oval; spinous process is short (except C-7)
and sometimes split;
• Large vertebral foramen
• Transverse foramen for vertebral artery to brainstem.
• C1 is Atlas articulates (atlanto-occipital joint) with
occipital bone of skull
-allows “yes” motion of head
• C2 is Axis characterized by peg-like process called
“dens” or odontoid process which interlocks with atlas
(atlanto-axial joint)
-allows sideward rotation or “no” motion of head.
Cervical Vertebrae
Cervical Vertebrae
Atlanto/axial joint
Thoracic vertebrae T1- T12
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•
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Body is roughly heart shaped
Demifacets for rib articulation
Vertebral foramen are circular
Spinous process long and points inferiorly
• These vertebra look like a giraffe’s head!
Lumbar Vertebrae L1-L5
• Pedicles and laminae are short and thicker
• Spinous processes are short, flat and hatchet
shaped
• Vertebral foramen is triangular
• Inferior and superior processes lock the
adlacent vertebrae together for strength and
stability.
• These vertebra look like a Moose’s head!
Sacral Vertebrae S1-S5
• Sacral vertebrae consists of 5 fused vertebrae
fully fused by 30 years of age
• Women sacrum is shorter, wider and more
curved
• Joins the spine to the pelvic girdle via
sacroiliac joint.
• Sacral canal is continuation of vertebral canal.
Sacrum and Coccyx
Coccyx Vertebrae Co1-Co4
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Coccyx is Greek for “cuckoo”
Consists of 4 fused vertebrae
Fuse between 20 and 30 years
Tailbone is vestige of tail
- Men it points anteriorly
- Women it points inferiorly
Additional structures of the vertebral column
Intervertebral discs
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•
•
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Present between all vertebrae C2- L5/S1;
Composed of fibro cartilage
Two regions of disc:
- nucleus pulposis – central core of disc
- annulus fibrosis - outer covering of fibro
cartilage
Function: -discs permit various movements
-provide shock absorbing functions for
vertebral column
Vertebra and vertebral disc
Slipped Intervertebral discs
Vertebral Ligaments
(1). Anterior and posterior longitudinal ligaments
hold vertebral column together along with trunk
skeletal muscles
-prevent hyper-extension and hyper-flexion of
the vertebral column.
(2). Shorter ligaments connect adjoining
vertebrae together.
-There are 3 of these ligaments the ligamentum
flavum, the supraspinous ligaments and the
interspinous ligaments.
Vertebral Ligaments
Bony Thorax
• Consists of ribs attached to the vertebral
column and sternum
• True ribs R1-R7 attach directly to sternum
• False ribs R8-R10 attach indirectly
• Two floating ribs R11 & R12
• The Sternum consisting of:
- manubrium
- body
- Xiphoid process
Bony Thorax
Ribs
1. true ribs – the first (superior) seven pairs of ribs R1R7 are directly connected to the sternum via costal
cartilage.
- are called vertebrosternal ribs.
2. false ribs – the remaining five pairs of ribs.
There are two types of false ribs.
» vertebrochondral ribs -- rib pairs #8, #9, and #10
are connected by a single band of costal cartilage
to the inferior portion of the sternum. Unlike the
first seven pairs of ribs they do not have their
own individual attachments.
» floating or vertebral ribs – rib pairs #11 and #12
are connected only to the vertebral column, they
have no anterior connection to the skeleton.
Sternum “breast plate”
• Anterior central portion of thorax
• Only bony attachment of axial skeleton to
appendicular skeleton via clavicle.
• Consists of Manubrium, Body and Xiphoid
process
• Key landmarks: calvicular notches, jugular
notch “suprasternal notch”, sternal angle.
Sternum
Hyoid bone
• Lies inferior to the mandible
• Is not attached to skeleton by bony means
• Helps movement of base of tongue
Hyoid bone