1. Skeletal System
Axial Skeleton

2. The Axial Skeleton Eighty bones segregated into three regions Skull
Vertebral column
Bony thorax

3. Bones of the Axial Skeleton
Figure 7.1

4. The Skull The skull=the cranium and facial bones
Cranium – protects the brain and is the site of attachment for head and neck muscles
Eight cranial bones – two parietal, two temporal, frontal, occipital, sphenoid, and ethmoid
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

5. Frontal Bone & Major Markings
Figure 7.2a

6. Parietal Bones and Major Associated Sutures
Four sutures mark the articulations of the parietal bones
Coronal suture – between parietal and frontal bones
Sagittal suture – where right and left parietal bones meet
Lambdoid suture – between parietal and occipital bones
Squamosal or squamous suture – between parietal and temporal bones

7. Major Sutures
Figure 7.3a

8. Occipital Bone & Major Markings
Figure 7.2b

9. Temporal Bones
Figure 7.5

10. Temporal Bone & Major Markings
Zygomatic process
External acoustic meatus
Mastoid process
Styloid process
(a)
Figure 7.3a

11. Sphenoid Bone
Butterfly-shaped bone that spans the width of the middle cranial fossa (depression)
Forms the central wedge that articulates with all other cranial bones

12. Sphenoid Bone
Figure 7.6a

13. Ethmoid Bone
Most deep of the skull bones; lies between the sphenoid and nasal bones
Forms most of the bony area between the nasal cavity and the orbits

14. Ethmoid Bone
Figure 7.7

15. Facial Bones
Fourteen bones of which only the mandible and vomer are unpaired
The paired bones are
the maxillae,
zygomatics,
nasals,
lacrimals,
palatines,
and inferior conchae

16. Mandible and Its Markings
Figure 7.8a

17. Maxillary Bones
Medially fused bones that make up the upper jaw and the central portion of the facial skeleton

18. Zygomatic Bones
Irregularly shaped bones (cheekbones) that form the prominences of the cheeks and the inferolateral margins of the orbits

19. Anterior Aspects of the Skull
Frontal bone
Parietal bone
Glabella
Nasal bone
Sphenoid bone
(greater wing)
Temporal bone
Ethmoid bone
Lacrimal bone
Zygomatic bone
Middle nasal concha
Perpendicular plate
Ethmoid
bone
Maxilla
Inferior nasal concha
Vomer bone
Mandible
Mental
foramen
(a)
Figure 7.2a

20. Hyoid Bone Not actually part of the skull
lies just inferior to the mandible in the anterior neck
Only bone of the body that does not articulate directly with another bone
Attachment point for neck muscles that raise and lower the larynx during swallowing and speech

21. Thoracic Cage

22. Bony Thorax (Thoracic Cage)
The thoracic cage is composed of
the thoracic vertebrae dorsally,
the ribs laterally,
and the sternum and costal cartilages anteriorly

23. Bony Thorax (Thoracic Cage)
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

24. Bony Thorax (Thoracic Cage)
Figure 7.19a

25. Sternum (Breastbone)
A dagger-shaped, flat bone that lies in the anterior midline of the thorax
Anatomical landmarks include
the jugular (suprasternal) notch,
the manubrium,
the sternal angle,
the xiphoid process
and the xiphisternal joint

26. 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

27. Ribs (continued)
Ribs 8-12 (false, or vertebrocondral ribs) attach indirectly to the sternum via costal cartilage
Ribs (floating, or vertebral ribs) have no anterior attachment

28. Structure of a Typical True Rib
Bowed, flat bone consisting of a head, neck, tubercle, and shaft
Figure 7.20a

29. Structure of a Typical True Rib
Figure 7.20b

30. Vertebral Column

31. 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 – 5 fused bones inferior to the lumbar vertebrae that articulates with the hip bones
Coccyx-4 fused bones that make up the “tailbone”

32. Vertebral Curvature
Spine has an sinusoid (or “s”) shape due to curvature
Concave (posteriorly)=cervical and lumbar
Convex (posteriorly)=thoracic and sacral
Allows it to act like a spring when walking upright
Provides flexibility and resiliency
At birth, spine curved out like 4 legged animals

33. Vertebral Column
Figure 7.13

34. Intervertebral Discs Act as shock absorper
Cushion-like pad composed of two parts
Nucleus pulposus:
inner gelatinous center
gives the disc its elasticity and compressibility
Annulus fibrosus:
surrounds the nucleus pulposus with a collar composed of collagen and fibrocartilage

36. Intervertebral Discs
As one gets older, discs become thinner & more rigid
Causes slight decrease in height
More herniated discs occur
Return to baby curvature of spine (“hump”)
Herniated Disc (slipped disc):
Nucleus pulposus bulges out past annulus fibrosus
Painful if presses on spinal cord or nerve

37. Regional Characteristics of Vertebrae
Table 7.2.1

38. General Structure of Vertebrae
Figure 7.15

39. Regional Characteristics of Vertebrae
Table 7.2.2

41. Cervical “neck” Atlas & Axis (1st 2 vertebra) Modified to rotate
No intervertebral disc between them
Atlas “carries” skull (like Atlas of Greek mythology carries the world)
Articulating surfaces allow head to move up and down (“yes”)
Altas rotates around dens of axis
Rotates head side to side (“no”)

43. Thoracic Vertebrae
Figure 7.17b

44. Thoracic and Lumbar Vertebra
Attach to ribs
Larger spines for muscle attachments
Lumbar:
“lower back”
Thicker and well connected for support & stability

45. Lumbar Vertebrae
Figure 7.17c

46. Sacrum and Coccyx Sacrum: Coccyx: Bones fuse as develop
Makes up posterior of pelvis
Coccyx:
“tailbone”

47. Sacrum and Coccyx: Anterior View
Figure 7.18a