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The Axial Skeleton

Forms longitudinal axis of the body 80 bones 40% of the bones in the human body. The Axial Skeleton. Three Regions: 1. Skull (8 cranial & 14 facial) ** bones associated with skull (6 auditory ossicles and hyoid) 2. Vertebral column (24 vertebrae, sacrum & coccyx)

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The Axial Skeleton

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  1. Forms longitudinal axis of the body • 80 bones • 40% of the bones in the human body The Axial Skeleton

  2. Three Regions: 1. Skull (8 cranial & 14 facial) ** bones associated with skull (6 auditory ossicles and hyoid) 2. Vertebral column (24 vertebrae, sacrum & coccyx) 3. Thoracic cage (sternum & 24 ribs) Axial Skeleton

  3. Eight cranial bones: • 2 parietal • 2 temporal • Frontal • Occipital • Sphenoid • Ethmoid • The cranial bones enclose the cranial cavity, a fluid-filled chamber that cushions and supports the brain • Cranial bones are thin and remarkably strong for their weight Anatomy of the Cranium

  4. Skull – Anterior View Figure 7.2a

  5. Forms the anterior portion of the cranium & the roof of the orbits (eye sockets) Frontal Bone

  6. Forms most of the superior and lateral aspects of the skull Parietal Bones Figure 7.3a

  7. Located at the back and lower part of the cranium Occipital Bone

  8. Form part of both the lateral walls of the cranium & zygomatic arches Temporal Bones Figure 7.5

  9. Four sutures mark the articulations of the parietal bones 1. Coronal suture – articulation between parietal bones and frontal bone anteriorly 2.Sagittal suture – where right and left parietal bones meet superiorly Parietal Bones & Major Associated Sutures

  10. 3. Lambdoid suture – where parietal bones meet the occipital bone (posterior) • 4. Squamosal or squamous suture – where parietal and temporal bones meet Parietal Bones & Major Associated Sutures

  11. Butterfly-shaped bone that forms part of the floor of the cranium, unites the cranial and facial bones, and acts as a cross brace that strengthens the sides of the skull • Forms the central wedge that articulates with all other cranial bones Sphenoid Bone

  12. Most deep of the skull bones; lies between the sphenoid and nasal bones Ethmoid Bone Figure 7.7

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

  14. The mandible (lower jawbone) is the strongest bone of the face Mandible Figure 7.8a

  15. Medially fused bones that make up the upper jaw and the central portion of the facial skeleton (largest facial bones) Maxillary Bones Figure 7.8b

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

  17. Nasal bones – thin medially fused bones that form the bridge of the nose • Lacrimal bones – contribute to the medial walls of the orbit and contain a deep groove that house the tear ducts • Palatine bones– two bone plates that form portions of the hard palate and contribute to the floor of each orbit Other Facial Bones

  18. Vomer – forms part of the nasal septum • Inferior nasal conchae – paired, curved bones in the nasal cavity that form part of the lateral walls of the nasal cavity Other Facial Bones continued…

  19. 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 Hyoid Bone Figure 7.12

  20. 26 irregular bones (vertebrae) • Provide a column of support, bearing the weight of the head, neck, and trunk. • Transfers weight to the appendicular skeleton of the lower limbs • Protects spinal cord • Helps maintain an upright body position • Approx. length of an adult column is 71cm Vertebral Column

  21. Cervical vertebrae 7 bones of the neck Thoracic vertebrae 12 bones of the torso Lumbar vertebrae 5 bones of the lower back Vertebral Column Figure 7.13

  22. Sacrum - 5 fused vertebrae • bone inferior to the lumbar • vertebrae that articulates with the hip bones Coccyx – 4 fused vertebrae Vertebral Column Figure 7.13

  23. Disks are small shock absorbers between the vertebrae (gel-like interior)

  24. Vertebral body (centrum) – disc-shaped, weight-bearing region 2. Vertebral arch – composed of pedicles (walls) and flat layers called laminae (roof) ** forms the posterior margin of each vertebral foramen (together they form the vertebral canal which encloses the spinal cord) 3. Articular processes– projections on each vertebra General Structure of Vertebrae:

  25. Table 7.2

  26. Most mammals have 7 cervical vertebrae (giraffes, whales, mice & humans) • Seven vertebrae (C1-C7) are the smallest and lightest vertebrae Cervical Vertebrae

  27. Holds up the head • Has no body and no spinous process Cervical Vertebrae: The Atlas (C1)

  28. The axis has a body, spine, and vertebral arches as do other cervical vertebrae • Articulates with the atlas to permit rotation Cervical Vertebrae: The Axis (C2) Figure 7.16c

  29. There are twelve vertebrae (T1-T12) • Distinctive heart-shaped body (more massive than that of a cervical vertebra) • Each thoracic vertebra articulate with ribs Thoracic Vertebrae

  30. The five lumbar vertebrae (L1-L5) are located in the small of the back and have an enhanced weight-bearing function • Largest vertebrae Lumbar Vertebrae

  31. Breakfast: 7 a.m. (7 cervical) Lunch: 12 p.m. (12 thoracic) Dinner: 5 p.m. (5 lumbar) Tip: Mealtimes

  32. Consists of five fused vertebrae (S1-S5), which shape the posterior wall of the pelvis • Begin fusing after puberty and are completely fused at age 25-30 • Protects reproductive, digestive, and urinary organs • It articulates with L5 superiorly, and with the auricular surfaces of the hip bones Sacrum

  33. Coccyx (Tailbone) • The coccyx is made up of four (in some cases three to five) fused vertebrae that articulate superiorly with the sacrum • Generally begun fusing by age 26 Coccyx

  34. Sacrum and Coccyx Figure 7.18b

  35. The thoracic cage is composed of the thoracic vertebrae, the ribs, and the sternum • 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 Bony Thorax (Thoracic Cage)

  36. Figure 7.19a

  37. A dagger-shaped, flat bone that lies in the anterior midline of the thorax • Fusion is not complete until at least age 25 (until this age the sternal body consist of four separate bones) Sternum (Breastbone)

  38. There are twelve pair of ribs • 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

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