The Axial SkeletonForms longitudinal axis of the
body80 bones 40% of the bones in the
human body
Axial SkeletonThree 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)
Anatomy of the CraniumEight cranial bones:
1. 2 parietal2. 2 temporal3. Frontal4. Occipital5. Sphenoid6. 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
Skull – Anterior View
Figure 7.2a
Frontal Bone
Forms the anterior portion of the cranium & the roof of the orbits (eye sockets)
Parietal Bones
Forms most of the superior and lateral aspects of the skull
Figure 7.3a
Occipital BoneLocated at the
back and lower part of the cranium
Temporal Bones
Form part of both the lateral walls of the cranium & zygomatic arches
Figure 7.5
Parietal Bones & Major Associated SuturesFour 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 Sutures3. Lambdoid suture – where parietal bones meet
the occipital bone (posterior)
4. Squamosal or squamous suture – where parietal and temporal bones meet
Sphenoid BoneButterfly-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
Ethmoid BoneMost deep of the skull bones; lies between
the sphenoid and nasal bones
Figure 7.7
Facial BonesFourteen bones of which only the
mandible and vomer are unpaired
The paired bones are the maxillae, zygomatics, nasals, lacrimals, palatines, and inferior conchae
Mandible The mandible
(lower jawbone) is the strongest bone of the face
Figure 7.8a
Maxillary BonesMedially fused bones that make up the upper jaw and the
central portion of the facial skeleton (largest facial bones)
Figure 7.8b
Zygomatic BonesIrregularly shaped bones (cheekbones)
that form the prominences of the cheeks and the inferolateral margins of the orbits
Other Facial BonesNasal 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 continued…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
Hyoid BoneLies 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
Figure 7.12
Vertebral Column26 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 limbsProtects spinal cordHelps maintain an upright body positionApprox. length of an adult column is 71cm
Vertebral ColumnCervical vertebrae7 bones of the neck
Thoracic vertebrae 12 bones of the torso
Lumbar vertebrae 5 bones of the
lower back
Figure 7.13
Vertebral Column
Sacrum - 5 fused vertebrae
◦bone inferior to the lumbar
◦vertebrae that articulates with the hip bones
Coccyx – 4 fused vertebrae
Figure 7.13
Disks are small shock absorbers between the vertebrae (gel-like interior)
General Structure of Vertebrae:
1. 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
Table 7.2
Cervical VertebraeMost mammals have 7
cervical vertebrae (giraffes, whales, mice & humans)
Seven vertebrae (C1-C7) are the smallest and lightest vertebrae
Cervical Vertebrae: The Atlas (C1)
◦Holds up the head◦Has no body and no spinous process
Cervical Vertebrae: The Axis (C2)The axis has a body, spine, and vertebral
arches as do other cervical vertebraeArticulates with the atlas to permit rotation
Figure 7.16c
Thoracic VertebraeThere are twelve vertebrae (T1-T12)
Distinctive heart-shaped body (more massive than that of a cervical vertebra)
Each thoracic vertebra articulate with ribs
Lumbar VertebraeThe five lumbar vertebrae (L1-L5) are
located in the small of the back and have an enhanced weight-bearing function
Largest vertebrae
Tip: Mealtimes
Breakfast: 7 a.m. (7 cervical)
Lunch: 12 p.m. (12 thoracic)
Dinner: 5 p.m. (5 lumbar)
Sacrum◦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
CoccyxCoccyx (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
Sacrum and Coccyx
Figure 7.18b
Bony Thorax (Thoracic Cage)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
Figure 7.19a
Sternum (Breastbone)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)
RibsThere are twelve pair of ribsAll ribs attach posteriorly to the thoracic vertebraeThe superior 7 pair (true, or vertebrosternal ribs)
attach directly to the sternum via costal cartilagesRibs 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