Download Notes on Axial Skeleton STUDENT Version

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THE AXIAL SKELETON
Chapter 7: pages 211-245
The Axial Skeleton – 80 bones segregated into three major regions (the skull, vertebral column, and bony
thorax)
THE SKULL
Cranium is the portion of the skull that protects the brain.
The skull also includes the facial bones.
All bones of the skull (except for the mandible) are connected by sutures, which are saw-toothed
connections (immovable joints) between the bones of the skull.
CRANIUM
The cranium has 8 bones.
Parietal bones (2) – attachment of temporalis muscle

sagittal suture –

coronal suture –
Frontal Bone – attachment of frontalis muscle

supraorbital margin –

supraorbital foramen –

supraorbital notch –

frontal sinus:
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frontal squama –
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lacrimal fossa –
Occipital Bone – attachment of occipitalis muscle

lambdoidal suture -

foramen magnum –

occipital condyles –

external occipital protuberance –

external occipital crest –

hypoglossal canals –
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Temporal bones (2) – attachment of temporalis muscle

squamous sutures -

external acoustic (auditory) meatus –
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zygomatic process (arch)–

styloid process –

mastoid process –

stylomastoid foramen –

jugular foramen –

carotid canal (foramen lacerum) -
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condylar (mandibular) fossa -
Sphenoid Bone – floor of cranium, unites facial & cranial bones

sella turcica -

hypophyseal fossa –

sphenoid sinuses:

foramen ovale –

optic foramen –
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greater wings –

lesser wings –
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Ethmoid Bone

crista galli -

cribiform plates –

olfactory faromina –

superior and middle nasal concha –

perpendicular plate -

ethmoidal sinuses:
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Paranasal sinuses – sinuses that are positioned around the nasal cavity
o
o
o
o
frontal sinus
sphenoid sinuses
ethmoidal sinuses
maxillary sinus
Function – the sinuses lighten the skull, act as resonating chambers
for speech, and produce mucus to moisten and clean inhaled air
Infection – since the paranasal sinuses are so closely related to the
nasal cavity they are commonly infected. A sinus infection can
create discomfort in any of the paranasal sinuses. A build up of
mucus changes the resonating ability of the sinuses and therefore
changes our speech
FACIAL BONES
There are 14 facial bones.
Mandible

body –

rami (ramus)–

alveoli (alveolar process) -

condylar process -

coronoid process –

mandibular foramen –

mental foramen –

mandibular angle –

mandibular notch –

mental protuberance –
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Maxillae (2) – supports teeth of upper jaw as well as forms inferior orbital rim, hard palate, and lateral
margins of nasal cavity

palatine processes –

infraorbital foramen –

maxillary sinus:

alveoli (alveolar process) -

inferior orbital fissure –
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Palatine Bones (2) – forms posterior hard palate
Lacrimal Bones (2) – forms medial optic orbit
Nasal bones (2) – forms bridge of nose
Zygomatic bones (2) – forms orbit rim and lateral wall; zygomatic arch

Zygomaticofacial foramen-

Temoral process –
Vomer Bone (Vomer = plow) – forms midline of nasal cavity with perpendicular plate of ethmoid bone
Inferior Conchae (kong’ke) (2) – increase surface area of the nasal cavity
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OTHER BONES ASSOCIATED WITH THE SKULL
Hyoid Bone – not really part of the skull, but very closely
associated; serves as a movable base for the tongue and an
attachment point for neck muscles that raise and lower the
larynx as we swallow
 Body – main portion
 greater cornua - larger horns
 lesser cornua – smaller horns
Both cornua are sites of muscle attachment
Auditory ossicles – bones in inner ear; Malleus, Incus, and Stapes
Malleus – hammer
Incus – anvil
Stapes - stirrup
Additional Individualized Bones - Sometimes tiny fragments of bone are separated from the major bones
of the skull by sutures. These tiny bones are called Sutural Bones or Wormian Bones. Not all skulls
have these bones, and for those that do, the number may vary between individuals.
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THE FETAL SKULL
Difference in proportions:
 The skull of an adult is 1/8 the length of the body.
 The skull of a fetus or newborn is ¼ the length of the body.
 In addition, an infant’s face is very small compared to the size of its cranium.
When a baby is born, the skull is not completely formed. Fibrous membranes called fontanels connect the
infant’s cranial bones creating “soft spots”. The fontanels allow the skull to be compressed slightly during
childbirth and allow the brain to grow. The fontanels are replaced by bone within 22 to 24 months after birth.
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THE VERTEBRAL COLUMN (SPINE)
Consists of 26 irregular bones
Before birth the spine consists of 33 separate
vertebrae, but 9 of these fuse forming two
composite bones called the sacrum and coccyx.
The central cavity of the vertebral column
contains the spinal cord which it surrounds and
protects. The spinal cord continues into the
sacrum as the sacral canal.
The vertebrae are separated by intervertebral
discs composed of fibrocartilage.
Herniated or slipped discs can cause pressure to
the spinal cord creating pain or numbness.
SPINAL CURVATURES
The vertebrae are connected and reinforced by ligaments in such a way that a flexible curved structure
results. The spinal curvatures in the thoracic and sacral regions are referred to as primary curvatures
because they are present when we are born. They can also be called accommodation curves, as they
accommodate the abdominopelvic and thoracic viscera. The secondary curvatures include the cervical
curvature and the lumbar curvature. These curvatures appear as a baby begins to raise its head and walk
respectively. The secondary curves can also be called the compensation curves as they help shift the
weight to allow for upright posture. All four curves are fully developed by age 10.
Abnormal curvatures include: Kyphosis, Lordosis, and Scoliosis (page 232)
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ANATOMY OF A VERTEBRA

Vertebral Body or Centrum:

Vertebral Arch:
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Vertebral Foramen:

Transverse Processes:

Spinous Process:

Superior and Inferior Articular processes:
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Articular facet –
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Lamina –
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Pedicle –

Intervertebral foramina –
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3 DIVISIONS OF VERTEBRAE
Cervical vertebrae – (C1-C7) Neck region.
C1 is called the atlas and has no body. Articulates with the occipital condyles of the head.
Allows the head to nod “YES”. (Greek mythology – Atlas holds the world on his shoulders).
C2 is called the axis acts as a pivot for the rotation of the atlas. Allows your head to twist from
side to side to indicate “NO”.

Dens or Odontoid process –

Transverse foramina –
Thoracic vertebrae – (T1 – T12) Upper and
middle back regions. Each articulates with one
or more pairs of ribs

Costal Facets –

Transverse costal facets –
Lumbar vertebrae – (L1 – L5) Lower back
region. Bear the most weight. Larger body and
smaller vertebral foramen.
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SACRUM (sacral) AND COCCYX (coccygeal)
Sacrum (5 fused bones, begin fusing after puberty and completely fused by age 25-30).
Provides and extensive area for muscle attachment (thigh).

sacral canal –
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sacral cornua –

sacral hiatus –

sacral foramina –

median sacral crest –
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lateral sacral crests –
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auricular surface (sacroiliac joint) –
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sacral tuberosity –

articular process –

sacral promontory –
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Coccyx (tailbone; 3-5 but typically 4 fused bones, fusing begins by age 26). Attachment site for
number of ligaments and for a muscle that constricts the anal canal

Coccygeal cornua – prominent laminae of the of the first coccygeal vertebrae
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THE BONY THORAX
Composed of the Ribs, Sternum, and Thoracic Vertebrae
Characteristics:
 Provides a protective cage for the vital organs of the thoracic cavity (heart, lungs, thymus, and
great blood vessels)
 Supports the shoulders and upper limbs
 Provides attachment points for major muscles of the neck, back, chest, and shoulders
In addition, the spaces between the ribs are occupied by intercostal muscles, which lift and contract the
thorax during breathing.
STERNUM (breastbone)
Is a typical flat bone and is divided into three parts (based on the fusion of three bones). :
 Manubrium –
i. Jugular notch –

Body of the sternum –

Xiphoid Process-
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RIBS
There are 12 pairs of ribs
True ribs: 7 pairs that are directly attached to the sternum by costal cartilages

Costal Cartilages – connect ribs to sternum
False ribs The remaining 5 pairs of ribs that either do not attach directly to the sternum or do not
attach at all (includes the floating ribs)
Ribs pairs 11 and 12 are called Floating Ribs because they lack sternal attachment
Ribs increase in length from 1-7, then decrease in length from pair 8-12
The intercostal spaces (between ribs) are filled with intercostal muscles that aid in breathing.
Rib Features:
 Vertebral end – the portion that contacts the vertebrae
o Head (capitulum) –

Inferior and superior articular facets –
o Neck –
o Tubercle –
o Angle –

Body –
o Costal groove –

Sternal Extremity (end) -
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angle
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