A&P - Skeletal System (Bones)

Overview of the Skeletal System

  • The skeletal system consists of bones, which are the organs of this system.

  • Bones form through either a cartilage model or a soft tissue model.

  • Understanding the relationship between different bones and body structures is essential for comprehension of how the skeletal system functions.

  • Functions of the skeletal system include protection of vital organs and providing structural support.

Composition of the Skeleton

  • The mature adult skeleton consists of 206 separate bones.

  • Newborns have approximately 226 bones due to the presence of extra bones that fuse during early development.

  • By the end of the first year, bones begin to fuse, reducing the total count to 206.

  • Variability: Some people may have anatomical anomalies affecting the number of vertebrae, such as extra lumbar vertebrae.

Divisions of the Skeleton

Axial Skeleton

  • Total Bones: 80 Bones

    • Comprises the head, neck, and torso, forming the upright axis of the body.

    • Components include:

      • Cranial Bones: Protect the brain.

      • Vertebrae: Make up the spinal column.

      • Ribs: Protect the thoracic cavity.

      • Middle Ear Bones (3): Essential for hearing (Hammer, Anvil, Stapes).

Appendicular Skeleton

  • Total Bones: 126 Bones

    • Consists of the limbs (arms and legs) and girdles that attach them to the axial skeleton.

    • Major component includes:

      • Upper Extremity: Arms.

      • Lower Extremity: Legs.

      • Significance: Nearly a quarter of these bones come from the feet.

Skeletal Structure Examination

  • Relationship between the two skeleton portions (axial and appendicular) is pivotal for understanding movement and function.

  • Color Coding in Diagrams:

    • Blue: Axial Skeleton

    • Beige: Appendicular Skeleton

  • Examples: The shoulder blade and hip bones belong to the appendicular skeleton despite their proximity to the axial skeleton.

Major Types of Bones

Cranial Bones

  • Total of 8 cranial bones:

    1. Frontal Bone: Forms the forehead.

    2. Parietal Bones: There are two; form the sides and roof of the cranium.

    3. Temporal Bones: Two distinct bones located at the sides of the cranium; contain structures for hearing.

    4. Occipital Bone: Forms the back and base of the skull, connects to the vertebral column.

    5. Sphenoid Bone: Known as the keystone of the cranial bones; supports and connects many structures.

    6. Ethmoid Bone: Located between the eyes; contains the cribriform plate for olfactory nerve fibers.

Facial Bones

  • Comprised of 14 bones:

    1. Maxillae: Upper jaw; keystone bone of the face.

    2. Mandible: Lower jaw; the only movable bone of the skull.

    3. Zygomatic Bones: Cheekbones; shape the face.

    4. Nasal Bones: Form the bridge of the nose.

    5. Lacrimal Bones: Small bones forming part of the eye socket; contain tear ducts.

    6. Palatine Bones: Form the back part of the hard palate.

    7. Inferior Nasal Conchae: Help form the nasal cavity.

    8. Vomer Bone: Forms part of the nasal septum.

Unique Features of Bones

  • Hyoid Bone: A unique bone that does not connect directly with any other bone; situated in the neck for laryngeal support.

  • Sutures: Points where cranial bones connect; further details will be addressed in articulations segments.

  • Fetal Skull Development: Allows for skull molding during childbirth and unimpeded brain growth; features fontanels (soft spots).

Growth Patterns in the Skull

  • At birth, the head is approximately one quarter of the body height.

  • As individuals mature, the proportion of the head to body becomes approximately one eighth.

  • The fetal skull differs from adult form; the facial structure is much smaller relative to the cranial portion.