Chapter 7: The Skeletal System – Structure, Classification, and Bone Markings

Chapter 7: The Skeletal System

Overview of the Skeleton

The human skeleton is a framework of bones that supports the body, protects internal organs, and enables movement. It is divided into two main parts: the axial skeleton and the appendicular skeleton.

• Axial Skeleton

  • Components: Skull, vertebral column, and thoracic cage (ribs and sternum).

  • Function: Supports and protects the brain, spinal cord, and thoracic organs.

• Appendicular Skeleton

  • Components: Limbs (arms and legs), pectoral girdle (shoulder), and pelvic girdle (hip).

  • Function: Facilitates movement and interaction with the environment.

Classification of Bones by Shape

Bones are classified according to their shapes, which relate to their functions and locations in the body.

• Flat Bones: Thin, flattened, and usually curved. Example: Frontal bone of the skull.

• Sutural Bones: Small, irregular bones found between the flat bones of the skull.

• Short Bones: Cube-shaped and mostly spongy bone. Example: Carpal bones of the wrist.

• Irregular Bones: Complex shapes that do not fit other categories. Example: Vertebrae.

• Long Bones: Longer than they are wide, with a shaft and two ends. Example: Femur.

• Sesamoid Bones: Small, round bones embedded in tendons. Example: Patella (kneecap).

Bone Markings

Bones have various markings that serve as sites for muscle, ligament, and tendon attachment, as well as passages for nerves and blood vessels.

Depressions

• Facet: Smooth, flat surface for articulation.

• Fossa: Shallow depression or hollow.

• Fovea: Small pit or depression.

• Groove: Furrow for a tendon, nerve, or blood vessel.

Openings

• Canal: Tubular passage or tunnel in a bone.

• Fissure: Narrow, slit-like opening.

• Foramen: Round or oval opening through a bone.

Projections

• Condyle: Rounded articular projection.

• Crest: Prominent ridge or elongated projection.

• Head: Expanded articular end, often rounded.

• Tubercle/Tuberosity: Small/large rounded projection.

• Epicondyle: Raised area above a condyle.

• Process: Any bony prominence.

• Spine: Sharp, slender, often pointed projection.

• Trochanter: Large, blunt, irregularly shaped process (found only on the femur).

• Line: Narrow ridge of bone.

Skull: Cranial and Facial Bones

The skull is composed of cranial bones that protect the brain and facial bones that form the structure of the face.

• Cranial Bones (8):

  • Frontal bone

  • Parietal bones (2)

  • Sphenoid bone

  • Ethmoid bone

  • Temporal bones (2)

  • Occipital bone

• Facial Bones (14):

  • Nasal bones (2)

  • Lacrimal bones (2)

  • Palatine bones (2)

  • Zygomatic bones (2)

  • Inferior nasal conchae (2)

  • Vomer bone

  • Maxilla (2)

  • Mandible

Example: The frontal bone forms the forehead and part of the eye sockets, while the mandible is the only movable bone of the skull.

Additional info:

• Bone markings are essential for understanding muscle attachment and joint movement.

• Classification by shape helps in identifying bone function and location.