Skeleton: Axial
Lab 4
Classification of Bones
Human body consists in 206 bones. They are
divided in two groups:
• Axial skeleton (form the long axis of the
body) includes – bones of the skull, vertebral
column, and rib cage. Functions: protecting,
supporting or carry other body parts.
• Appendicular skeleton – bones of the upper
and lower limbs, shoulder, and hip. Function:
locomotion and manipulation of our
enviroment
Classification of Bones: By Shape
Bones come in many sizes
and shapes. For most part ,
bones are classified by their
shape as: long, short flat and
irregular
• Long bones –
longer than
they are wide
(e.g.,
humerus)
• Has a shaft
plus two ends
Ex: All limb bones
except patella and
wrist and ankle
bones are long bone
Figure 6.2a
Classification of Bones: By Shape
• Short bones
– Cube-shaped bones of
the wrist and ankle
– Sesamoid bones
“shaped like a sesame
seed” that form within
tendons (e.g., patella).
They vary in size and
number in different
individual. Some
sesamoid bones act to
atter the direction of pull
of a tendon
Figure 6.2b
Classification of Bones: By Shape
• Flat bones –
thin, flattened,
and a bit
curved (e.g.,
sternum, and
most skull
bones)
Figure 6.2c
Classification of Bones: By Shape
• Irregular
bones –
bones with
complicated
shapes (e.g.,
vertebrae and
hip bones)
Figure 6.2d
Function of Bones
• Support – form the framework that supports
the body and cradles soft organs. Ex: Lower
limb
• Protection – provide a protective case for:
the brain (bones of skull), spinal cord
(vertebrae), and vital organs (rib cage)
• Movement – provide levers for muscles
• Mineral storage – bone is a reservoir for
minerals, especially calcium and phosphorus
• Blood cell formation – hematopoiesis occurs
within the marrow cavities of bones
Bone Markings: Projections –
Sites of Muscle and Ligament Attachment
•
•
•
•
Tuberosity – rounded projection
Crest – narrow, prominent ridge of bone
Trochanter – large, blunt, irregular surface
Line – narrow ridge of bone
Bone Markings: Projections –
Sites of Muscle and Ligament Attachment
•
•
•
•
Tubercle – small rounded projection
Epicondyle – raised area above a condyle
Spine – sharp, slender projection
Process – any bony prominence
Chemical Composition of Bone: Organic
• Bone has both organic and inorganic
components.
Organic components:
1.-Cells:
• Osteoblasts – bone-forming cells
• Osteocytes – mature bone cells
• Osteoclasts – large cells that resorb or break
down bone matrix
2.- Osteoid – unmineralized bone matrix
composed of proteoglycans, glycoproteins,
and collagen
The Skeleton
• The skeleton (“dried up body” or mummy)
• It is strong, yet light, and almost perfectly
adapted for the protective, locomotor and
manipulative functions it perform
• Composed of bones, cartilages, joints and
ligaments, accounts for about 20% of body
mass.
• The skeleton is divided into Axial and
Appendicular
The Axial Skeleton
• This part of skeleton supports the head,
neck and trunk and it protects the brain,
spinal cord and the organs in the thorax
• Eighty bones segregated into three regions
– 1.- Skull
– 2.- Vertebral column
– 3.- Bony thorax
The Skull
• The skull, the body’s most complex bony
structure, is formed by the cranium and
facial bones
• Cranium – protects the brain and is the site
of attachment for head and neck muscles
• Facial bones
– Supply the framework of the face, the sense
organs, and the teeth
– Provide openings for the passage of air and
food
– Anchor the facial muscles of expression
Anatomy of the Cranium
• The cranium can be divided in :
1.- cranial vault (calvaria)
2.- cranial base (floor)
• Eight cranial bones – two parietal, two
temporal, frontal, occipital, sphenoid, and
ethmoid
• Cranial bones are thin and remarkably
strong for their weight
Frontal Bone
• Forms the anterior portion of the cranium
• Articulates posteriorly with the parietal bones
via the coronal suture
• The most anterior part of the frontal bone is
the vertical frontal squama, commonly called
the forehead
• Major markings include the supraorbital
margins, the anterior cranial fossa, and the
frontal sinuses (internal and lateral to the
glabella)
Skull: Anterior View
Figure 7.2a
Skull: Posterior View
Figure 7.2b
Parietal Bones and Major Associated Sutures
• They are curved, rectangular bones. Form most of
the superior and lateral aspects of the skull
Figure 7.3a
Occipital Bone and Its Major Markings
• It articulates anteriorly
with the paired parietal
and temporal bones via
the lambdoid and
occipitomastoid sutures.
• It also joins with the
sphenoid bone in the
cranial floor via a plate
called the pharingeal
tubercule.
• Forms most of skull’s
posterior wall and base
• Major markings include
the posterior cranial fossa,
foramen magnum,
occipital condyles, and the
hypoglossal canal
Figure 7.2b
Temporal Bones
• Between the styloid and
mastoid processes exist the
stylomastoid foramen that
allow cranial nerve VII to
leave the skull.
• The mastoid region of the
temporal bone exhibits the
conspicuous mastoid
process, an anchoring site
for some neck muscles
Figure 7.5
Sphenoid Bone
Figure 7.6a, b
Ethmoid Bone
Allow the olfatory nerves to
pass from the smell receptors
in the nasal cavites to the brain
Figure 7.7
Mandible and Its Markings
Figure 7.8a
Maxillary Bone
The anterior nasal spine allows the infraorbital
nerve and artery to reach the face
Figure 7.8b
Vertebral Column & Ribs
Vertebral Column
• Formed from 26 irregular bones (vertebrae)
connected in such a way that a flexible
curved structure results
– Cervical vertebrae – 7 bones of the neck
– Thoracic vertebrae – 12 bones of the torso
– Lumbar vertebrae – 5 bones of the lower back
– Sacrum – bone inferior to the lumbar vertebrae
that articulates with the hip bones
Vertebral Column
Figure 7.13
Vertebral Column: Curvatures
• Posteriorly concave curvatures – cervical
and lumbar
• Posteriorly convex curvatures – thoracic and
sacral
• Abnormal spine curvatures include scoliosis
(abnormal lateral curve), kyphosis
(hunchback), and lordosis (swayback)
Vertebral Column: Ligaments
• Anterior and posterior longitudinal ligaments
– continuous bands down the front and back
of the spine from the neck to the sacrum
• Short ligaments connect adjoining vertebrae
together
Vertebral Column: Ligaments
Figure 7.14a
Vertebral Column: Intervertebral
Discs
• Cushionlike pad composed of two parts
– Nucleus pulposus – inner gelatinous nucleus
that gives the disc its elasticity and
compressibility
– Annulus fibrosus – surrounds the nucleus
pulposus with a collar composed of collagen and
fibrocartilage
Vertebral Column: Intervertebral
Discs
Figure 7.14b
General Structure of Vertebrae
• Body or centrum – disc-shaped, weightbearing region
• Vertebral arch – composed of pedicles and
laminae that, along with the centrum,
enclose the vertebral foramen
• Vertebral foramina – make up the vertebral
canal through which the spinal cord passes
General Structure of Vertebrae
• Spinous processes project posteriorly, and
transverse processes project laterally
• Superior and inferior articular processes –
protrude superiorly and inferiorly from the
pedicle-lamina junctions
• Intervertebral foramina – lateral openings
formed from notched areas on the superior
and inferior borders of adjacent pedicles
General Structure of Vertebrae
Figure 7.15
Cervical Vertebrae
• Seven vertebrae (C1-C7) are the smallest,
lightest vertebrae
• C3-C7 are distinguished with an oval body,
short spinous processes, and large,
triangular vertebral foramina
• Each transverse process contains a
transverse foramen
Cervical Vertebrae
Table 7.2
Cervical Vertebrae: The Atlas (C1)
• The atlas has no body and no spinous
process
• It consists of anterior and posterior arches,
and two lateral masses
• The superior surfaces of lateral masses
articulate with the occipital condyles
Cervical Vertebrae: The Atlas (C1)
Figure 7.16a, b
Cervical Vertebrae: The Axis (C2)
• The axis has a body, spine, and vertebral
arches as do other cervical vertebrae
• Unique to the axis is the dens, or odontoid
process, which projects superiorly from the
body and is cradled in the anterior arch of
the atlas
• The dens is a pivot for the rotation of the
atlas
Cervical Vertebrae: The Axis (C2)
Figure 7.16c
Cervical Vertebrae: The Atlas (C2)
Figure 7.17a
Thoracic Vertebrae
• There are twelve vertebrae (T1-T12) all of
which articulate with ribs
• Major markings include two facets and two
demifacets on the heart-shaped body, the
circular vertebral foramen, transverse
processes, and a long spinous process
• The location of the articulate facets prevents
flexion and extension, but allows rotation of
this area of the spine
Thoracic Vertebrae
Figure 7.17b
Lumbar Vertebrae
• The five lumbar vertebrae (L1-L5) are located
in the small of the back and have an
enhanced weight-bearing function
• They have short, thick pedicles and laminae,
flat hatchet-shaped spinous processes, and
a triangular-shaped vertebral foramen
• Orientation of articular facets locks the
lumbar vertebrae together to provide stability
Lumbar Vertebrae
Figure 7.17c
Sacrum
• Sacrum
– Consists of five fused vertebrae (S1-S5), which
shape the posterior wall of the pelvis
– It articulates with L5 superiorly, and with the
auricular surfaces of the hip bones
– Major markings include the sacral promontory,
transverse lines, alae, dorsal sacral foramina,
sacral canal, and sacral hiatus
Coccyx
• Coccyx (Tailbone)
– The coccyx is made up of four (in some cases
three to five) fused vertebrae that articulate
superiorly with the sacrum
Sacrum and Coccyx: Anterior View
Figure 7.18a
Characteristics of Cervical,Thoracic and Lumbar
Vertebrae
Characteristics
Cervical (3-7)
Thoracic
Lumbar
Body
Small, wide side to
side
Larger than cervical,
heart shaped, bears
two costal demifacets
Massive, kidney
shaped
Spinous
process
Short bifid, projects
directly posteriorly
Long, sharp, projects
inferiorly
Short, blunt, projects
directly posteriorly
Vertebral
foramen
Triangular
Circular
Triangular
Transverse
process
Contain foramina
Bear facets for ribs
(except T11-T12)
Thin and tapered
Sup. and inf. art. Sup facet→ sup-pos
process
Inf facet → inf-ant
Sup facets→ posterior Sup facet→ posmed
Inf. facets → anterior
Inf. facet → ant-lat
Movements
Rotation, limited
lateral flex (ribs), flex
& ext prevented
Flex and extension,
lateral flex, rotation
Flex and ext, some
lat flexion, rotation
prevented
Homeostatic Imbalance
• Herniated (prolapsed) disc.
Severe or sudden physical trauma to the
spine, may result in hernation of one or more
discs. A herniated disc (slipped disc) usually
involves rupture of the annulus fibrosus
followed by protrusion of the spongy nucleus
pulposus through the annulus (Fig 7.14). If
the protrusion presses on the spinal cord or
on spinal nerves exiting from the cord,
numbness or excruciating pay result.
Treatments: moderated exercise, massage,
heat ther. and painkillers if this fail→ surgery
Bony Thorax (Thoracic Cage)
• The thoracic cage is composed of the
thoracic vertebrae dorsally, the ribs laterally,
and the sternum and costal cartilages
anteriorly
• Functions
– Forms a protective cage around the heart, lungs,
and great blood vessels
– Supports the shoulder girdles and upper limbs
– Provides attachment for many neck, back, chest,
and shoulder muscles
– Uses intercostal muscles to lift and depress the
thorax during breathing
Bony Thorax (Thoracic Cage)
Figure 7.19b
Sternum (Breastbone)
• A dagger-shaped, flat bone that lies in the
anterior midline of the thorax
• Results from the fusion of three bones – the
superior manubrium, the body, and the
inferior xiphoid process
• Anatomical landmarks include the jugular
(suprasternal) notch, the sternal angle, and
the xiphisternal joint
Ribs
• There are twelve pair of ribs forming the
flaring sides of the thoracic cage
• All ribs attach posteriorly to the thoracic
vertebrae
• The superior 7 pair (true, or vertebrosternal
ribs) attach directly to the sternum via costal
cartilages
• Ribs 8-10 (false, or vertebrocondral ribs)
attach indirectly to the sternum via costal
cartilage
• Ribs 11-12 (floating, or vertebral ribs) have
no anterior attachment
Ribs
Figure 7.19a
Structure of a Typical True Rib
• Bowed, flat bone
consisting of a
head, neck,
tubercle, and shaft
Figure 7.20