Skeleton Axial by MikeJenny

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									06 Skeleton: Axial

   Human Biology
       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
 Gross Anatomy of Bones: Bone
 Every bone has two textures:
 Compact bone (also called cancellous bone)
  – dense outer layer
 Spongy bone - (internal) honeycomb of
  trabeculae filled with red or yellow bone
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
• Long bones –
  longer than
  they are wide
  humerus)                        Ex: All limb bones
                                  except patella and
• Has a shaft
                                  wrist and ankle
  plus two ends                   bones are long bone
                                                        Figure 6.2a
Structure of Long Bone

                         Figure 6.3
        Structure of Long Bone
 Long bones consist of a diaphysis and an
  epiphysis and membranes.
 Diaphysis
   Tubular shaft that forms the axis of long bones

   Composed of compact bone that surrounds the
    medullary cavity

   Yellow bone marrow (fat) is contained in the
    medullary cavity
       Structure of Long Bone
 Epiphyses
   Expanded ends of long bones

   Exterior is compact bone, and the interior is
    spongy bone

   Joint surface is covered with articular (hyaline)

   Epiphyseal line (remnant of the epiphyseal
    plate) separates the diaphysis from the
 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
    alter 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

                              Figure 6.2c
Structure of a Flat Bone

                           Figure 6.4
Classification of Bones: By Shape

• Irregular
  bones –
  bones with
  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
• 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
Organic components:
• 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
 Chemical Composition of Bone:
 The balance of the bone tissue (65% by
  mass) consists of inorganic mineral salts:
 Hydroxyapatites, or mineral salts
   Mainly calcium phosphates

   Responsible for bone hardness and its
    resistance to compression
               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
• The skeleton is divided into Axial and
          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
  – 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
• 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
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
• 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
• 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
Vertebral Column: Ligaments

                         Figure 7.14a
 Vertebral Column: Intervertebral
• Cushionlike pad composed of two parts
  – Nucleus pulposus – inner gelatinous nucleus
    that gives the disc its elasticity and
  – Annulus fibrosus – surrounds the nucleus
    pulposus with a collar composed of collagen and
Vertebral Column: Intervertebral

                             Figure 7.14b
  General Structure of Vertebrae

• Body or centrum – disc-shaped, weight-
  bearing 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
• 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
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
  – 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 (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
Characteristics   Cervical (3-7)           Thoracic                    Lumbar

Body              Small, wide side to      Larger than cervical,       Massive, kidney
                  side                     heart shaped, bears         shaped
                                           two costal demifacets

Spinous           Short bifid, projects    Long, sharp, projects       Short, blunt, projects
process           directly posteriorly     inferiorly                  directly posteriorly

Vertebral         Triangular               Circular                    Triangular

Transverse        Contain foramina         Bear facets for ribs        Thin and tapered
process                                    (except T11-T12)

Sup. and inf. art. Sup facet→ sup-pos      Sup facets→ posterior Sup facet→ posmed
process            Inf facet → inf-ant     Inf. facets → anterior Inf. facet → ant-lat

Movements         Flex and extension,      Rotation, limited           Flex and ext, some
                  lateral flex, rotation   lateral flex (ribs), flex   lat flexion, rotation
                                           & ext prevented             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
• 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
• There are twelve pair of ribs forming the
  flaring sides of the thoracic cage
• All ribs attach posteriorly to the thoracic
• The superior 7 pair (true, or vertebrosternal
  ribs) attach directly to the sternum via costal
• Ribs 8-10 (false, or vertebrocondral ribs)
  attach indirectly to the sternum via costal
• Ribs 11-12 (floating, or vertebral ribs) have
  no anterior attachment

       Figure 7.19a
    Structure of a Typical True Rib

• Bowed, flat bone
  consisting of a
  head, neck,
  tubercle, and shaft

                        Figure 7.20

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