Download Axial Skeleton

Crafton Hills College
Human Anatomy & Physiology
Axial Skeleton
A. Major Divisions
1. Axial: Part of skeleton lies along long axis of body
2. Appendicular: Bones & features of the appendages
B. AXIAL SKELETON
* Eighty bones segregated into three regions
* Divisions of Axial Skeleton
- Skull
- Vertebral column
- Thoracic cage
1. Skull
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The skull, the body's most complex bony structure, is formed by:
a. Bones
i. Cranium - protects the brain and is the site of attachment for head and neck muscles
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Thin and remarkably strong for weight
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Eight cranial bones - 2 Parietal, 2 Temporal, Frontal, Occipital, Sphenoid, and
Ethmoid
1) Frontal Bone
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Anterior portion; bordered posteriorly by parietal bones via coronal suture
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Major markings: Supraorbital margins, and frontal sinuses
2) Parietal Bones
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Form most of superior and lateral aspects of skull
3) Occipital Bone
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Skull's posterior wall & base
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Major markings: Foramen magnum, Occipital condyles, Hypoglossal canal
4) Temporal Bones
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Forms inferolateral (& some floor) aspects of skull
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Major markings: Zygomatic, Styloid, and mastoid processes, ALSO: Mandibular
fossae
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Major openings: Jugular foramina, External/Internal auditory meatuses, and
Carotid canal
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5) Sphenoid Bone
a. Butterfly-shaped bone (middle cranial fossa)
b. Central; Articulates with all other cranial bones
c. Major parts: Central body, Greater wings, Lesser wings, and pterygoid processes
d. Major markings: Sella turcica and the pterygoid processes
e. Major openings: Foramina rotundum, ovale, and spinosum; Optic canals;
Superior orbital fissure
6) Ethmoid
a. Deepest of the skull bones; Between sphenoid and nasal bones
b. Major markings: Cribriform plate, Crista galli, perpendicular plate, Nasal
conchae, and Ethmoid sinuses
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SUTURES
1) Coronal suture - articulation between parietal bones and frontal bone anteriorly
2) Sagittal suture - where right and left parietal bones meet superiorly
3) Lambdoid suture - where parietal bones meet the occipital bone posteriorly
4) Squamosal or squamous suture - where parietal and temporal bones meet
ii. Facial
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Supply the framework (sense organs, teeth)
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Openings: Passage of air & food while projections anchor facial muscles (expression)
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Fourteen bones of which only the mandible and vomer are unpaired
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The paired bones are the maxillae, zygomatics, nasals, lacrimals, palatines, and
inferior conchae
1) Mandible (lower jawbone)
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Largest, strongest bone of the face: Body, Ramus, Angle
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Major markings: Coronoid process, mandibular condyle, alveolar margin,
mandibular and mental foramina
2) Zygomatic Bones
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Irregular shaped: Form cheekbones and inferolateral margins of the orbits
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Process names for bone it projects TOWARDS!
3) Nasal bones - thin medially fused; bridge of the nose
4) Lacrimal bones - Part of orbit's medial walls; contain a lacrimal fossa (houses
lacrimal sac)
5) Palatine bones - two plates form portion of hard palate
6) Vomer - Rises to meet perpendicular plate; part of nasal septum
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Inferior nasal conchae - paired, curved "lobes" bones in the nasal cavity
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C. Orbits
1. Bony cavities in which the eyes are firmly encased and cushioned by fatty tissue
2. Formed by parts of seven bones - frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and
ethmoid
D. Hyoid Bone
1. Just inferior to mandible in anterior of neck
2. Only bone that does not articulate directly with another bone
3. Attachment point for neck muscles (raise and lower the larynx during swallowing and speech)
E. Vertebral Column
1. Functions
a. Protects spinal cord, anchors muscles of back and supports skull
b. 26 irregular bones (vertebrae) connected in a flexible curved structure
2. Types of Vertebra
a. Cervical vertebrae - 7 bones of the neck
b. Thoracic vertebrae - 12 bones of the torso
c. Lumbar vertebrae - 5 bones of the lower back
d. Sacrum - bone inferior to the lumbar vertebrae that articulates with the hip bones
1. Cervical Vertebrae
a. General Features:
i. Seven vertebrae (C1-C7): smallest/lightest vertebrae
ii. Unique features: Each transverse process contains a transverse foramen
iii. NO facets or demifacets for ribs!!!
b. Atlas (C1)
i. No body; no spinous process
ii. Superior surfaces (lateral masses) articulate with the occipital condyles
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Shake head "Yes"
c. Axis (C2)
i. Unique feature: Dens, or odontoid process
1) Projects superiorly -- cradled in anterior arch of the atlas
2) Dens is a pivot for the rotation of the atlas; Shake head "No"
2. Thoracic Vertebrae
a. 12 vertebrae (T1-T12); All articulate with ribs
b. Major markings: 2 facets and two demifacets on body, circular vertebral foramen, transverse
processes, long spinous process
c. Articulate facets prevents flexion and extension, allows rotation
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3. Lumbar Vertebrae
a. 5 vertebrae (L1-L5); Located in small of back; Enhanced weight-bearing function
b. Short, thick pedicles and laminae, flat hatchet-shaped spinous processes, and a
triangular-shaped vertebral foramen
c. Articular facets (vertebral, NOT ribs) orientated to lock lumbar vertebrae together for
stability
4. Sacrum
a. 5 fused vertebrae (S1-S5); Posterior wall of pelvis
b. Articulates with L5 superiorly and hip bones inferiorly
c. Major markings: Alae, dorsal sacral foramina, sacral canal, and sacral hiatus
5. Coccyx (Tailbone)
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The coccyx is made up of four (in some cases three to five) fused vertebrae that articulate
superiorly with the sacrum
6. General Structure of a Vertebra
a. Body or centrum:
Disc-shaped, weight-bearing region
b. Vertebral arch:
Composed of pedicles and laminae that, along with the centrum,
enclose the vertebral foramen
c. Vertebral foramina:
Make up the vertebral canal through which the spinal cord passes
d. Spinous processes:
Project posteriorly, and transverse processes project laterally
e. Superior & inferior
articular processes:
Protrude superiorly & inferiorly from the pedicle-lamina junctions
f. Intervertebral foramina: Lateral openings formed from notched areas on the superior and
inferior borders of adjacent pedicles
7. Curvatures
a. Posteriorly concave curvatures: Cervical and lumbar
b. Posteriorly convex curvatures:
Thoracic and sacral
c. Abnormal spine curvatures
i. Scoliosis (abnormal lateral curve)
ii. Kyphosis (hunchback)
iii. Lordosis (swayback)
8. Ligaments
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Anterior and posterior longitudinal ligaments - continuous bands down the front and back of
the spine from the neck to the sacrum
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Short ligaments connect adjoining vertebrae together
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9. Intervertebral Disk
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Cushion-like pad composed inner gelatinous nucleus surrounded by collar of fibrocartilage
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Can bear TREMENDOUS and repeated compression-type stress
F. Rib Cage
1. Regional Composition
a. Dorsal = Thoracic vertebrae
b. Lateral = Ribs laterally
c. Anterior = sternum and costal cartilages
2. Functions
a. Protective cage around the heart, lungs, and great blood vessels
b. Supports shoulder girdles and upper limbs
c. Provides attachment for many neck, back, chest, and shoulder muscles
3. Parts of Ribcage
a. Sternum (Breastbone)
i. Flat bone; anterior midline of thorax
ii. Result of 3 fused bones
1) Manubrium (superior)
2) Body (medial)
3) Xiphoid process (inferior)
iii. Landmarks: jugular notch, the sternal angle
b. Ribs
i. 12 pair
1) True (vertebrosternal) Ribs: Directly costal cartilage connect to the sternum
Ribs 1-7; Superior Ribs
2) False (vertebrocondral) Ribs:
Shared costal cartilage connect to the sternum
Ribs 8-12; Inferior Ribs
(Ribs 11-12: Floating Ribs-NO connect to sternum)
ii. Parts of a Rib
1) Head:
Terminal end of rib that articulates with facet/demifacets of
thoracic vertebra
2) Tubercle:
“Lump-like” projection near head of rib
3) Angle:
Sharp “bend” in the rib as it curves around towards sternum
4) Body/Shaft:
Long, relatively straight part of rib
5) Costal Grove:
Groove along the inferior, posterior border of the rib
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