The Axial Skeletal System

1
The Axial Skeletal System
2
Divisions of the Skeletal System

• Humans are born with approximately 300 bones
  which fuse to 206 bones as adults.
• There are 2 main divisions of the skeletal
  system axial skeleton and appendicular skeleton.

3
Divisions of the Skeletal System

• Axial skeleton forms the vertical axis of the
  body.
• 80 bones skull (22), vertebral column (26),
  ribcage (25), auditory ossicles (6), and hyoid
  (1)
• Appendicular skeleton forms the arms, legs and
  the girdles
• Girdles attach the arms and legs to the axial
  skeleton
• 126 bones pectoral girdle (4), arms (60), legs
  (60) and pelvic girdle (2)

4
(No Transcript)
5
Skull

• Superior end of the vertebral column
• Composed of flat and irregular shaped bones
• Large hollow space within the skull is called the
  cranial vault or cranial cavity.
• Functions to
• Surround and protect the brain
• Be points of attachment for the facial muscles
  (landmarks)

6
Divisions of the Skull

• Cranial division consists of 8 flat bones that
  form a protective box around the brain.
• Help to form the cranial vault (cavity)
• Frontal (1) forms the anterior portion of the
  cranial cavity
• Forms the superior orbits of the eyes and forms
  the forehead

7
Frontal Bone Landmarks

• Supraorbital margin a thickened ridge of bone
  found superior to the orbit of the eye.
• Just deep to the eyebrow and more prominent on
  the lateral portion
• Point for muscle attachment (PFMA)
• Supraorbital foramen a small opening found on
  the medial aspect of the supraorbital margin.
• Can feel it best inferior to the margin
• Allows blood vessels and nerves to enter the
  frontal bone

8
Frontal Bone Landmarks

• Frontal sinus A hollow space found within the
  frontal bone, superior and medial to the
  supraorbital margin.
• Can only be seen with a sagittal cut
• ¼ inch superior to the eyebrows
• House mucus and macrophages for trapping and
  destroying foreign particles.

9
Frontal Bone Landmarks

• Frontal sinus A hollow space found within the
  frontal bone, superior and medial to the
  supraorbital margin.
• Can only be seen with a sagittal cut
• ¼ inch superior to the eyebrows
• House mucus and macrophages for trapping and
  destroying foreign particles.

10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
Parietal Bones (2)

• Form the lateral walls and the superior portion
  of the cranium.
• Landmarks
• Temporal fossa A large, shallow depression that
  begins on the parietal bone and extends to the
  frontal bone.
• PFMA

18
Temporal Bones (2)

• Form the inferior lateral walls and a portion of
  the floor of the cranium.
• Articulate with the mandible (lower jaw) to form
  the temporomandibular joint (TMJ)
• Temporal bone landmarks
• Mastoid process A large, blunt projection found
  posterior to the external auditory meatus.
• Bump behind the ear
• PFMA

19
Temporal Bone Landmarks cont..

• Styloid process A thin, sharp projection found
  inferior and medial to the external auditory
  meatus.
• Covered with muscle so it is more difficult to
  identify
• PFMA
• Zygomatic process A thin, flat projection found
  anterior to the external auditory meatus.
• PFMA
• External auditory meatus The external ear canal
• Opening through which the auditory nerve runs.

20
Temporal Bone Landmarks cont..

• Mandibular fossa A shallow depression found
  inferior and slightly anterior to the external
  auditory meatus
• This forms an articulation with the mandible
• Easy to see inferiorly if the mandible is removed

21
Occipital Bone (1)

• Forms the posterior wall and the floor of the
  cranium.
• The spinal cord passes through this as it exits
  the cranial vault.
• Occipital bone landmarks
• External occipital protuberance A prominent
  midline projection found on the superior surface.
• Where the occipital bone turns to form the
  horizontal part.

22
Occipital Bone Landmarks cont..

• Superior nuchal line Two curved ridges that
  extend laterally from the external occipital
  protuberance.
• PFMA
• Inferior nuchal line Two curved ridges that
  extend laterally from the external occipital
  protuberance, inferior to the superior nuchal
  line.
• PFMA
• Foramen magnum A large opening in the inferior
  surface of the occipital bone that allows the
  spinal cord to exit the cranial cavity.
• Largest foramen in the body.

23
Occipital Bone Landmarks cont..

• Occipital condyles Paired oval-shaped
  projections found lateral to the foramen magnum.
• Form an articulation with the 1st bone of the
  spine (atlas)

24
(No Transcript)
25
Sphenoid Bone (1)

• Forms the anterior floor of the cranial cavity.
• Also forms a portion of the lateral walls of the
  cranial cavity.
• Forms the posterior wall of the orbits of the
  eyes.
• The keystone bone for the cranium because it
  articulates with all other cranial bones.
• Shape resembles a bat with outstretched wings
  when viewed superiorly.

26
Sphenoid Bone Landmarks

• Greater wing The larger, inferior projection of
  the sphenoid that forms a portion of the floor
  and the lateral walls of the cranium.
• Also forms the posterior wall of the orbits of
  the eyes.
• Lesser wing The smaller, superior projection of
  the sphenoid bone located posterior to the
  frontal bone.

27
Sphenoid Bone Landmarks cont..

• Sella turcica A small, saddle-like depression
  found between the greater and lesser wings that
  surrounds and protects the pituitary gland.
• Pituitary is an important endocrine gland
• 3 parts to the sella turcica
• Tuberculum sellae The anterior portion of the
  sella turcica.
• Closest to the lesser wing.

28
Sphenoid Bone Landmarks cont..

• 3 parts to the sella turcica continued
• Hypophyseal fossa The seat of the saddle.
• Where the pituitary gland resides
• Dorsum sellae The posterior portion of the sella
  turcica.
• Closer to the greater wing

29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
Ethmoid Bone (1)

• The small bone located anterior to the sphenoid
  bone in the middle of the frontal bone.
• Forms a small portion of the anterior floor of
  the cranium.
• Also forms a small portion of the medial wall of
  the eye orbits.
• Also forms the superior portion of the nasal
  septum.

35
Ethmoid Bone Landmarks

• Cribriform plate Paired projections found
  lateral to the crista galli.
• Has small openings called the olfactory foramina.
• Olfactory foramina A series of small openings
  found within the cribriform plate that allow
  nerves from the olfactory epithelium to pass
  directly into the brain.
• These nerves give us our sense of smell.

36
Ethmoid Bone Landmarks cont..

• Crista galli A small triangular projection found
  in the center of the ethmoid bone.
• Near the front of the cranial cavity.
• Point of attachment for the meninges (protective
  coverings of the brain).
• Perpendicular plate A small vertical projection
  arising from the inferior surface of the ethmoid
  bone.
• Forms the superior portion of the nasal septum.
• Articulates with the vomer (facial bone).

37
Ethmoid Bone Landmarks cont..

• Superior and middle nasal conchae Two thin,
  scroll-shaped projections found lateral to the
  perpendicular plate
• The middle nasal conchae is inferior to the
  superior nasal conchae.
• These increase surface area of the nasal
  passageways
• Ethmoidal cells Air spaces found within the
  lateral masses of the ethmoid bone.
• Small sinuses

38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
Sutures

• Fibrous joints found between the bones of the
  cranium.
• There are 4 major sutures
• Coronal unites the frontal bone and both
  parietal bones
• Sagittal unites the two parietal bones on the
  superior midline of the skull
• Lambdoid unites the two parietal bones to the
  occipital bone.
• Squamous (2) unite the parietal and temporal
  bones on the lateral sides of the skull

44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
The Facial Division

• A group of 14 irregular bones that serves as
  points of attachment for muscles of the face.
• Nasal (2) form the bridge of the nose.
• Rectangular shaped bones
• PFMA
• Maxillae (2) Form the upper jaw.
• Articulate with every face bone except the lower
  jaw.
• Form part of the floors of the orbits, lateral
  walls and floor of the nasal cavity, and most of
  the hard palate (bony roof of the mouth).

48
Maxillary Landmarks

• Infraorbital foramen Small openings found
  inferior to the orbits of the eyes.
• Allows passage of blood vessels and nerves.
• Palatine process a lateral projection that forms
  one half of the anterior portion of the hard
  palate.
• Typically the 2 processes unite during weeks
  10-12 of embryo development. If not, cleft
  palate will result. This negatively impacts
  speech and swallowing.

49
Maxillary Landmarks cont

• Maxillary sinuses a series of small spaces
  within the maxillae.
• Empty into the nasal cavity.

50
(No Transcript)
51
(No Transcript)
52
(No Transcript)
53
Zygomatic Bone (2)

• Form the prominence of the cheeks.
• Also form part of the lateral wall and floor of
  each orbit.
• Articulate with the frontal, maxilla, sphenoid
  and temporal bones.
• Zygomatic bone landmarks
• Temporal process a thin, flat projection arising
  from the lateral, posterior surface of the
  zygomatic bone.
• Articulates with the zygomatic process of the
  temporal bone.

54
Zygomatic Bone Landmarks cont..

• Zygomatic arch created by the articulation of
  the temporal process of the zygomatic bone and
  the zygomatic process of the temporal bone.

55
(No Transcript)
56
Lacrimal Bones (2)

• The smallest bones of the facial division.
• Resemble the shape and size of a fingernail
• Posterior and lateral to the nasal bones and form
  part of the medial wall of each orbit.
• Lacrimal bone landmark
• Lacrimal fossa a small vertical groove formed
  with the maxilla, that helps drain fluid away
  from the eye.
• Houses a lacrimal sac that gathers tears and
  passes them into the nasal cavity.

57
(No Transcript)
58
(No Transcript)
59

• Palatine Bones (2) L shaped bones that form
  the posterior portion of the hard palate.
• The parts that make-up the hard palate are called
  horizontal plates.
• Inferior Nasal Conchae (2) scroll shaped bones
  that form a portion of the inferior, lateral
  walls of the nasal cavity.
• Increase surface area and help filter air along
  with the superior and middle nasal conchae of the
  ethmoid bone.

60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64

• Vomer (1) a triangular bone that forms a portion
  of the posterior floor of the nasal cavity.
• Articulates with the perpendicular plate of the
  ethmoid bone to form the inferior portion of the
  bony nasal septum.
• Mandible (1) the largest bone of the facial
  division.
• Except for the ossicles, it is the only moveable
  skull bone.

65
Mandibular Landmarks

• Mandibular body a triangular bone that forms a
  portion of the posterior floor of the nasal
  cavity.
• Ramus the short, vertical portion of the
  mandible.
• Angle the area where the ramus and the body of
  the mandible meet.
• Coronoid process a small triangular projection
  found on the superior anterior portion of the
  ramus.

66
Mandibular Landmarks cont

• Condylar process a small rounded projection
  found on the superior posterior portion of the
  ramus.
• Articulates with the mandibular fossa to create
  the temporomandibular joint (TMJ).
• Mental foramen small openings found in the
  anterior surface of the body of the mandible that
  allow blood vessels and nerves to enter the
  mandible.
• Alveoli sockets for teeth

67
(No Transcript)
68
Auditory Ossicles

• The 6 smallest bones in the human body.
• Located medial to the eardrum.
• Connected by synovial joints.
• Function to transfer sound waves from the eardrum
  to the inner ear.
• The bones are as follows
• Malleus- attaches to the eardrum and is commonly
  called the hammer.
• Incus- middle bone that is commonly called the
  anvil.
• Stapes- Smallest bone and is commonly called the
  stirrup.

69
(No Transcript)
70
(No Transcript)
71
Hyoid Bone

• Located superior to the larynx (voice box).
• U shaped
• The only bone that does not articulate with
  another bone.
• Suspends from the styloid processes by ligaments
  and muscles.
• Often fractured during strangulation.
• Functions to support the tongue.

72
(No Transcript)
73
(No Transcript)
74
The Vertebral Column

• Also called the spine, backbone or spinal column.
• Consists of 33 (children) or 26 (adults) bones
  called vertebrae.
• Functions to protect the spinal cord, support the
  head, and serve as attachment points for the
  ribs, pelvis, back muscles and arm muscles.

75
Vertebrae

• Vary in size, shape and detail but have many
  similarities.
• Consist of 3 main parts vertebral body,
  vertebral arch and several processes.
• Vertebral body the thickened anterior portion of
  a vertebra.
• Holds the intervertebral disc and contains
  foramina for the entrance of blood vessels.
• Intervertebral discs pads of fibrocartilage that
  help hold the vertebrae in place.
• Compress throughout the day due to weight and
  water loss. This compression does not change
  height as we age.

76
(No Transcript)
77
Vertebrae continued

• Vertebral arch located posterior to the
  vertebral body.
• Forms the vertebral foramen with the vertebral
  body.
• The vertebral arch consists of the pedicles and
  the laminae.
• Pedicles the shorter anterior portions of the
  vertebral arch.
• Laminae the longer posterior portions of the
  vertebral arch.

78
Vertebrae continued

• Vertebral foramen the opening formed by the
  vertebral body and the vertebral arch.
• Contains the spinal cord, adipose tissue, areolar
  connective tissue and blood vessels.
• Processes bony projections that arise from the
  vertebral arch.
• Transverse processes paired lateral projections
  that arise from the vertebral arch.
• Spinous process the single posterior projection
  that arises from the vertebral arch.
• Both of these are PFMA

79
(No Transcript)
80
(No Transcript)
81
Cervical Vertebrae

• The first 7 vertebrae (C1-C7).
• Smaller bones than other vertebrae but larger
  vertebral foramen.
• Also have 2 transverse foramen through which the
  vertebral artery, vein and nerve fibers pass.
• C2-C6 have a branching spinous process.
• C1 is called the atlas.
• Supports the skull.
• It lacks a body and a spinous process.

82
Cervical Vertebrae cont

• C2 is called the axis.
• Has a body and a peglike process called the dens
  or the odontoid process.
• The dens makes a pivot on which the atlas and
  head rotate.
• C7 is called the vertebra prominens.
• Has a large spinous process that is not branched
  and can be felt at the back of the neck.

83
(No Transcript)
84
Thoracic Vertebrae

• The next 12 vertebrae (T1-T12).
• Have facets (flat surfaces) where they articulate
  with the 12 rib pairs.
• Movement of these vertebrae are most limited
  because the ribs attach to the sternum anteriorly.

85
(No Transcript)
86
Lumbar Vertebrae

• The next 5 vertebrae (L1-L5).
• The largest and strongest of the bones of the
  spine.
• Spinous processes are thick and broad.

87
(No Transcript)
88
Sacrum

• The next vertebra in the adult vertebral column.
• A triangular shaped bone formed from the fusion
  of 5 bones. This starts around age 16 and is
  usually completed by age 30.
• Auricular surfaces large, ear-shaped roughened
  surfaces found on the lateral aspect of the
  sacrum.
• This articulates with the hip bones of the pelvis.

89
(No Transcript)
90
Coccyx

• The last vertebra in the adult vertebral column.
• The tailbone that is formed by the fusion of 4
  vertebrae that occurs between the age of 20-30.
• In males, it points anteriorly and in females it
  points inferiorly.

91
ACT-UP
92
ACT-UP

1. What region of the vertebral column might be most
   affected by osteoporosis?
2. Why?
3. What would we expect to see (on the outside) when
   looking at a person suffering from osteoporosis?

93
Thorax

• Includes the sternum, ribs and the bodies of the
  thoracic vertebrae.
• Sternum located along the anterior midline of
  the thorax.
• Also known as the breastbone
• Consists of 3 parts that fuse by age 25 and the
  points of fusion can be seen as transverse
  ridges.
• If thoracic surgery is necessary, the sternum may
  be cut along the midline.

94
Regions of the Sternum

• Manubrium the superior portion of the sternum
• Articulates with the clavicles (collarbones) and
  the costal cartilages of the 1st-2nd rib pairs.
• Sternal body the intermediate portion of the
  sternum.
• Articulates directly or indirectly with the
  costal cartilages of the 2nd-10th rib pairs.
• Xiphoid process the inferior portion of the
  sternum.
• Where some abdominal muscles attach.

95
(No Transcript)
96
Ribs

• 12 pairs of flat bones that form a protective
  cage around the heart and the lungs.
• Increase in length from 1-7 and then decrease
  from 7-12.
• Each rib pair articulates posteriorly with its
  corresponding thoracic vertebra.
• Costal cartilage elongated pads of hyaline
  cartilage used to attach the ribs to the sternum.
• Allows the ribcage to be more elastic and limits
  fracturing from blows to the chest.

97
(No Transcript)
98
(No Transcript)
99
Types of Ribs

• True ribs Rib pairs 1-7
• Their costal cartilages attach directly to the
  sternum.
• False ribs Rib pairs 8-12
• Their costal cartilages do not attach directly to
  the sternum. Rib pairs 8-10 have cartilages that
  attach to the cartilage of 7 (which attaches to
  the sternum.
• Floating ribs Rib pairs 11-12
• The costal cartilages do not attach to the
  sternum at all.

100
(No Transcript)
101
(No Transcript)
102
(No Transcript)
103
(No Transcript)
104
(No Transcript)
105
(No Transcript)
106
(No Transcript)