Axial skeleton

Axial Skeleton Topics

A. Cranial & Facial Bones

1. List of Cranial Bones
  • The skull consists of eight cranial bones:
    • Frontal
    • Parietal (2)
    • Temporal (2)
    • Occipital
    • Sphenoid
    • Ethmoid
2. Articulations of Skull Bones
  • All skull bones are joined by sutures, which are immovable joints.
  • Fontanel: An unossified area in an infant's skull where the bones have not yet fused, allowing for growth and development. Fontanels close as the child matures.
3. Base of the Skull
  • The cranial bones that form the base of the skull include:
    • Occipital
    • Sphenoid
    • Temporal
4. Skull and Vertebral Column
  • The skull fits onto the vertebral column via the occipital condyles, which articulate with the first vertebra (C1).
  • The two bones forming the joint between the skull and the vertebral column are:
    • Occipital
    • Atlas (C1)
5. List of Facial Bones
  • The skull has fourteen facial bones:
    • Nasal (2)
    • Maxilla (2)
    • Zygomatic (2)
    • Palatine (2)
    • Lacrimal (2)
    • Inferior nasal concha (2)
    • Vomer (1)
    • Mandible (1)
6. Eye Socket Composition
  • The bones making up the eye socket include at least five:
    • Frontal
    • Zygomatic
    • Maxilla
    • Sphenoid
    • Ethmoid
7. Hard Palate Formation
  • The hard palate is formed by:
    • Maxilla (2)
    • Palatine (2)

B. Hyoid Bone

Unique Features of the Hyoid Bone
  • The hyoid bone is unique because it does not articulate with any other bone in the body, being isolated.
  • Purpose: It supports the tongue and aids in swallowing.
  • Attachment: It is anchored by ligaments and muscles rather than a joint.

C. Vertebral Column

1. Types of Vertebrae
  • The vertebral column consists of:
    • Cervical Vertebrae: 7
    • Thoracic Vertebrae: 12
    • Lumbar Vertebrae: 5
  • The two bones at the caudal end of the vertebral column are:
    • Sacrum
    • Coccyx
2. Structure of Intervertebral Discs
  • Intervertebral discs consist of two major parts:
    • Fibrocartilage Ring: Annulus fibrosis
    • Nucleus Pulposus: Gel-like center
  • Blood Vessels in Discs: There are typically no blood vessels in the intervertebral disc, relying on diffusion for nutrition.
  • Herniated Disc: A condition where the nucleus pulposus protrudes through a tear in the annulus fibrosis, often causing pain.
3. Curves of the Vertebral Column
  • Primary Curves: Present at birth, shaped like a C and concave anteriorly.
    • Thoracic Curve
    • Sacral Curve
  • Secondary Curves: Develop after birth, convex anteriorly.
    • Cervical Curve: Develops when the infant begins to hold their head up (approximately 3-4 months).
    • Lumbar Curve: Develops when the child starts to walk (approximately 12-18 months).
4. Abnormal Curves of the Vertebral Column
  • Lordosis: An exaggerated inward curvature of the spine (often in the lumbar region).
  • Kyphosis: An exaggerated outward curvature of the spine (often in the thoracic region).
  • Scoliosis: Lateral curvature of the spine.
5. Anatomical Features of Vertebrae
  • Each vertebra has a large hole called the vertebral foramen, which allows the spinal cord to pass through.
  • When two vertebrae articulate, they create lateral holes known as intervertebral foramina, essential for the passage of spinal nerves.
  • Differentiating Vertebrae: Cervical vertebrae can be identified by the presence of transverse foramina, which thoracic and lumbar vertebrae lack.
  • Names of Key Vertebrae:
    • C1 is referred to as the Atlas.
    • C2 is referred to as the Axis.
  • Articulations with C1:
    • Occipital bone
    • C2 (Axis)
  • Articulations with C2:
    • C1 (Atlas)
    • The body of the C3 vertebra
6. Ribs and Their Connections
  • The superior surface of L5 forms a joint with T12, and the inferior surface of T12 articulates with L1.
  • The os coxae (coxal bones) connect to the vertebral column via the sacrum.
  • Articulation of Ribs: 12 thoracic vertebrae articulate with the ribs:
    • True Ribs: 1-7 - attach directly to the sternum via costal cartilage.
    • False Ribs: 8-10 - attach indirectly to the sternum.
    • Floating Ribs: 11-12 - do not attach to the sternum at all.
  • Type of Cartilage: Costal cartilage is made of hyaline cartilage.
7. Components of the Sternum
  • The sternum has three parts:
    • Manubrium
    • Body
    • Xiphoid process
  • Connection to Appendicular Skeleton: The sternum attaches to the clavicles and the first pair of ribs, serving as a midline structure that connects to the appendicular skeleton.