The Skeletal System: The Axial Skeleton

1
The Skeletal System The Axial Skeleton
2
Divisions of the Skeletal System

• 206 bones in the adult human skeleton
• 2 main divisions axial skeleton (80 bones) and
  appendicular skeleton (126 bones)
• The axial skeleton consists of the bones of the
  skull, ribs, backbone, breastbone, hyoid bone,
  and the auditory ossicles, or ear bones
• The appendicular skeleton consists of the bones
  of the upper and lower limbs and the girdles,
  which connect the limbs to the axial skeleton

3
Types of Bones

• Longhave greater length than width slightly
  curved to help prevent fractures examples
  include the bones of the thigh, lower leg, arm,
  forearm, fingers, and toes
• Shortsomewhat cube-shaped ex. bones of the
  wrist and ankles
• Flatthin bones such as those of the skull,
  breastbone, shoulder blades, and ribs
• Sesamoidassociated with tendons protect them
  from wear and tear ex. kneecaps
• Irregularbones that are not in any of the above
  categories variable ex. vertebrae and some
  facial bones
• Suturalsmall bones located within the joints
  between cranial bones their number varies from
  one individual to another

4
Bone Surface Markings

• Structural features adapted for specific
  functions
• 2 main types
• Depressions and openingsform joints or allow for
  the passage of blood vessels, nerves, etc.
• Processesprojections or outgrowths that allow
  for attachment of tissues such as ligaments and
  tendons

5
Bones of the Skull

• The skull consists of 22 bones
• 8 of these are cranial bones, which enclose and
  protect the brain 14 are facial bones

6
Cranial Bones (8)

• Frontal bone (1)forms the forehead, the roofs of
  the orbits, and part of the cranial floor
• Parietal bones (2)form most of the sides and
  roof of the cranial cavity
• Temporal bones (2)form part of the sides and
  floor of the cranial cavity
• Occipital bone (1)forms the rear and most of the
  base of the cranium
• Sphenoid bone (1)forms the middle part of the
  base of the skull keystone of the cranial
  floor because it articulates with all other
  cranial bones
• Ethmoid bone (1)a light, sponge-like bone that
  forms the cranial floor between the orbits of the
  eyes has projections called the superior nasal
  conchae and middle nasal conchae, which extend
  into the nasal cavity these structures help
  filter, warm, and moisten inhaled air before it
  passes into the lungs the superior nasal conchae
  aid in the sense of smell

7
Facial Bones (14)

• Nasal bones (2)form part of the bridge of the
  nose
• Maxilla bones (2)form the upper jawbone
• Zygomatic bones (2)form the cheekbones
• Mandible (1)forms the lower jawbone the
  largest, strongest facial bone and the only
  movable skull bone articulates with the temporal
  bone at the temporomandibular joint (TMJ)
• Lacrimal bones (2)the smallest bones of the face
  (fingernail-sized) form part of the medial walls
  of the orbits
• Palatine bones (2)form the rear part of the hard
  palate, which separates the nasal cavity from the
  oral cavity
• Inferior nasal conchae (2)form part of the
  inferior lateral walls of the nasal cavity help
  swirl and filter inhaled air before it enters the
  lungs
• Vomer (1)found on the floor of the nasal cavity
  and makes up the lower part of the nasal septum,
  which is the partition that divides the nasal
  cavity into right and left sides

8
Nasal Septum

• Nasal cavitythe inside of the nose divided into
  a right and left side by the nasal septum
• 3 components to the nasal septum
• Vomer
• Ethmoid (perpendicular plate)
• Cartilage

9
Orbits of the Eyes

• Orbiteye socket contains the eyeball
• 7 bones of the skull join to form each orbit
• Frontal
• Sphenoid
• Ethmoid
• Palatine
• Zygomatic
• Lacrimal
• Maxilla

10
Sutures

• Suturean immovable joint in an adult that is
  found between the bones of the skull
• 4 main sutures in the skull
• Coronal suturebetween the frontal bone and the
  parietal bones
• Sagittal suturebetween the two parietal bones
• Lambdoid sutureunites the two parietal bones and
  the occipital bone
• Squamous suturesunite the parietal and temporal
  bones on the sides of the skull

11
Paranasal Sinuses

• Paired cavities in some of the bones of the skull
• Lined with mucous membranes that are continuous
  with the lining of the nasal cavity
• Produce mucus and serve as resonating chambers
  for sound
• 4 bones contain paranasal sinuses
• Frontal
• Sphenoid
• Ethmoid
• Maxillary

12
Fontanels

• Membrane-filled spaces between the cranial bones
  at birth soft spots
• Areas of fibrous connective tissue membranes that
  will eventually be replaced by bone and become
  sutures
• Allow for flexibility of the fetal skull
• 6 main fontanels
• Anterior fontanel (1)between the two parietal
  bones and the frontal bone the largest fontanel
  usually closes 18-24 months after birth
• Posterior fontanel (1)between the two parietal
  bones and the occipital bone usually closes
  about 2 months after birth
• Anterolateral fontanels (2)between the frontal,
  parietal, temporal, and sphenoid bones usually
  close about 3 months after birth
• Posterolateral fontanels (2)between the
  parietal, temporal, and occipital bones usually
  close 1-2 months after birth, but not completely
  until about 12 months

13
Hyoid Bone

• Part of the axial skeleton
• Does not articulate with any other bone
• Located in the anterior neck suspended from the
  lower portion of the temporal bone by ligaments
  and muscles
• Supports the tongue provides an attachment site
  for muscles of the tongue, neck, and pharynx
• Frequently fractured during strangulation

14
Vertebral Column

• Also called the spine or backbone a flexible
  rod that can move in various directions
• Composed of a series of bones called vertebrae
  usually 26 vertebrae in an adult
• Length is about 28 inches in an average adult
  male and about 24 inches in an average adult
  female
• Encloses and protects the spinal cord, supports
  the head, and functions as an attachment point
  for the ribs, pelvic girdle, and muscles of the
  back

15
Vertebral Column (continued)

• 7 cervical vertebraein the neck
• 12 thoracic vertebraebehind the chest cavity
• 5 lumbar vertebraein the lower back
• 1 sacrumconsists of 5 fused vertebrae in the
  region of the pelvis
• 1 coccyxconsists of 4 fused vertebrae the
  tailbone

16
Normal Curves of the Vertebral Column

• When viewed from the side, the vertebral column
  shows 4 normal curves
• The curves increase the strength of the spine,
  help maintain balance, absorb shock, and help
  prevent fracture
• Cervical curveconvex
• Thoracic curveconcave
• Lumbar curveconvex
• Sacral curveconcave

17
Parts of a Typical Vertebra

• Bodythe thick, weight-bearing part
• Vertebral archcircular rear portion of a
  vertebra which surrounds the spinal cord formed
  by the laminae and pedicles
• Vertebral foramenan opening in the center of a
  vertebra (between the vertebral arch and body)
  which allows for the passage of the spinal cord
  the vertebral canal is the complete passageway
  formed by vertebrae stacked upon one another to
  form the backbone intervertebral discs of
  cartilage separate the vertebrae from each other
  and absorb shock at each joint in the spine an
  intervertebral foramen allows for passage of a
  spinal nerve from the spinal cord

18
Processes of a Typical Vertebra

• 7 processes arise from the vertebral arch
• Spinous processa spine-like projection from the
  rear of a vertebra
• Transverse processa projection from each side of
  a vertebra
• Superior articular processa projection from each
  side of the top of a vertebra
• Inferior articular processa projection from each
  side of the bottom of a vertebra

19
Regions of the Vertebral Column

• Cervical vertebrae (C1-C7)
• Thoracic vertebrae (T1-T12)
• Lumbar vertebrae (L1-L5)
• Sacrum
• Coccyx

20
Cervical Region

• Each cervical vertebra has 3 foramina the
  vertebral foramen in the center and a transverse
  foramen on each side
• All cervical vertebrae except C1 are generally
  bifid, or forked
• C1 is called the atlas because it supports the
  head this vertebra lacks a body and spinous
  process
• C2 is called the axis this vertebra has a
  process called the dens or odontoid process the
  atlas rotates around this process as the head
  turns from side to side during certain trauma
  situations involving whiplash, the dens may be
  pushed up into the medulla oblongata of the brain
  and cause death
• C3-C7 are typical cervical vertebrae, except C7
  has a large spinous process called the vertebra
  prominens this process can be felt at the base
  of the back of the neck

21
Thoracic Region

• The bodies of the thoracic vertebrae are larger
  than those of the cervical vertebrae, but smaller
  than those of the lumbar vertebrae
• The spinous processes point downward
• The thoracic vertebrae articulate with the ribs
• The articular processes in this region are called
  facets

22
Lumbar Region

• The lumbar vertebrae are the largest and
  strongest in the vertebral column
• They have short, thick processes the spinous
  processes point straight back, instead of
  downward as in the thoracic region
• Herniated (slipped) discs occur most often in the
  lumbar region, since it supports most of the
  weight of the body and is the region of the most
  flexing and bending

23
Sacrum

• A triangular bone formed from the fusion of 5
  vertebrae
• Serves as a foundation for the pelvic girdle
• The median sacral crest is formed by the fusion
  of the spinous processes of the sacral vertebrae
  the lateral sacral crests are formed by the
  fusion of the transverse processes
• The sacral canal is a continuation of the
  vertebral canal it has a lower entrance called
  the sacral hiatus, which is formed because the
  lower sacral vertebrae do not totally meet
• The sacral promotory is the anterior border of
  the body of the first sacral vertebra it is used
  to make measurements of the pelvis
• The anterior and posterior sacral foramina allow
  for the passage of blood vessels and nerves

24
Coccyx

• A triangular bone formed by the fusion of usually
  4 coccygeal vertebrae
• The tailbone

25
Thorax

• The chest region of the body
• The thoracic cage encloses and protects the
  organs in the chest such as the heart and lungs
  it is formed by the ribs, bodies of the thoracic
  vertebrae, the sternum, and the costal cartilages

26
Sternum

• The breastbone
• A narrow, flat bone about 6 inches long located
  in the center of the chest
• Consists of 3 main parts
• Manubriumthe top part
• Bodythe largest, main part
• Xiphoid processthe pointed part at the bottom
  incorrect CPR may fracture this part and push it
  into the internal organs

27
Ribs

• 12 pair
• Articulate posteriorly with thoracic vertebrae
• The first 7 pairs of ribs attach directly to the
  sternum by costal cartilage these ribs are
  called true ribs
• The other 5 pairs of ribs are called false ribs
  because they do not attach directly to the
  sternum pairs 8-10 attach by way of the 7th pair
  of ribs the 11th and 12th pairs are called
  floating ribs because they do not attach to the
  sternum at all