AXIAL BONE

• Axial skeleton


  Bones that lie around the axis of the human body, an imaginary longitudinal line that runs through the body's center of gravity from the head to the space between the feet

  
• Bones of the axial skeleton

  • Skull bones
  • Auditory ossicles (ear bones)
  • Hyoid bone
  • Ribs
  • Sternum (breastbone)
  • Bones of the vertebral column

  
• Appendicular skeleton


  Bones of the upper and lower limbs (extremities or appendages), plus the bones forming the girdles that connect the limbs to the axial skeleton

  
• The adult human skeleton consists of 206 named bones, most of which are paired, with one member of each pair on the right and left sides of the body

  
• The skeletons of infants and children have more than 206 bones because some of their bones fuse later in life

  
• Types of bones based on shape

  • Long
  • Short
  • Flat
  • Irregular
  • Sesamoid

  
• Long bones


  Have greater length than width, consist of a diaphysis (body) and a variable number of extremities or epiphyses (ends), and are slightly curved for strength

  
• Short bones


  Somewhat cube-shaped and are nearly equal in length and width
• Flat bones


  Generally thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue

  
• Irregular bones


  Have complex shapes and cannot be grouped into any of the previous categories

  
• Sesamoid bones


  Develop in certain tendons where there is considerable friction, tension, and physical strain, and protect tendons from excessive wear and tear
• Sutural bones


  Small flat bones located in sutures (joints) between certain cranial cavity bones

  
• Bone surface markings


  Structural features adapted for specific functions, including depressions/openings and processes/projections

  
• Types of bone surface markings

  • Fissure
  • Foramen
  • Fossa
  • Sulcus
  • Meatus
  • Condyle
  • Facet
  • Head
  • Crest
  • Epicondyle
  • Line

  
• Bones of the skull

  • Cranial cavity bones: Frontal, Parietal (2), Temporal (2), Occipital, Sphenoid, Ethmoid
  • Facial bones: Bones surrounding the mouth (upper and lower jaw), nasal cavity, and orbits

  
• Meatus


  Tubelike opening
• External acoustic meatus


  Tubelike opening in the temporal bone that directs sound waves into the ear
• Processes


  • Projections or outgrowths on bone that form joints or attachment points for connective tissue, such as ligaments and tendons
• Condyle


  Large, round protuberance with a smooth articular surface at end of bone

  
• Facet


  Smooth, flat, slightly concave or convex articular surface
• Head


  Usually rounded articular projection supported on neck (constricted portion) of bone

  
• Crest


  Prominent ridge or elongated projection
• Epicondyle


  Typically roughened projection above condyle
• Line (linea)


  Long, narrow ridge or border (less prominent than crest)
• Spinous process


  Sharp, slender projection
• Trochanter


  Very large projection
• Tubercle


  Variably-sized rounded projection
• Tuberosity


  Variably-sized projection that has a rough, bumpy surface
• Occipital bone


  Forms the posterior part of the cranial cavity and most of the cranial base

  
• Occipital bone


  • Foramen magnum is in the inferior part of the bone
  • Medulla oblongata connects with the spinal cord within this foramen
  • Vertebral and spinal arteries also pass through foramen magnum
• Temporal bone


  Articulates with the occipital bone
• Sphenoid bone


  • Lies at the middle part of the cranial base
  • Called the keystone of the cranial base because it articulates with all the other cranial cavity bones of the cranial base, holding them together

  
• Sphenoid bone


  • Body is the hollowed cubelike medial portion between the ethmoid and occipital bones
  • Space inside the body is the sphenoidal sinus, which drains into the nasal cavity
  • Sella turcica is a bony saddle-shaped structure on the superior surface of the body
  • Anterior part of the sella turcica is a ridge called the tuberculum sellae
  • Posterior part of the sella turcica is another ridge called the dorsum sellae
  • Greater wings project laterally from the body and form the anterolateral cranial base
  • Lesser wings form a ridge of bone anterior and superior to the greater wings

  
• Optic canal (foramen)


  Through which the optic (II) nerve and ophthalmic blood vessels pass into the orbit
• Superior orbital fissure


  • Triangular slit lateral to the body between the greater and lesser wings
  • Blood vessels and cranial nerves pass through this fissure
• Foramen ovale


  • Located at the junction of the anterior and medial parts of the sphenoid bone
  • Maxillary division of the trigeminal (V) nerve passes through

  
• Foramen lacerum


  • Bounded anteriorly by the sphenoid bone and medially by the sphenoid and occipital bones
  • Transmits a branch of the ascending pharyngeal artery
• Pterygoid processes


  • Project inferiorly from the points where the body and greater wings of the sphenoid bone unite
  • Form the lateral posterior region of the nasal cavity
  • Some muscles that move the mandible attach to
• Ethmoid bone


  • Located in the anterior part of the cranial base medial to the orbits
  • Spongelike in appearance
  • Forms part of the anterior portion of the cranial base, the medial wall of the orbits, the superior portion of the nasal septum, and most of the superior sidewalls of the nasal cavity

  
• Ethmoid bone


  • Cribriform plate forms part of the cranial base and contains cribriform foramina through which the olfactory (I) nerves pass
  • Perpendicular plate forms the superior portion of the nasal septum
  • Ethmoidal labyrinths contain 3-18 air sinus spaces called ethmoidal cells
  • Orbital plates of the ethmoidal labyrinths help form the medial walls of the orbits
  • Contains the superior and middle nasal conchae