A&P - Skeletal System (Bones)

Axial Skeleton Overview

  • Definition of Axial Skeleton: Comprises the central axis of the body, including the head, neck, and torso.

Vertebral Column

  • Definition: Longitudinal axis of the skeleton, also known as the spinal column.

  • Structure: Contains 24 individual movable vertebrae and the fused sacrum and coccyx at the base.

    • Total vertebrae: 24 movable vertebrae

Views of Vertebral Column

  • Side View: Shows natural curves of the vertebral column.

  • Front/Back Views (Anterior/Posterior): Should appear straight, absence of side-to-side curves helps identify conditions like scoliosis.

Important Features of Vertebrae Curvature

  • Natural Curves:

    • Absorb shock and forces from the head down and legs up.

    • Prevents bone damage during movement.

  • Types of Curvature:

    • Cervical Curve: Called Lordosis (inverted C shape).

    • Lumbar Curve: Also called Lordosis (inverted C shape).

    • Thoracic Curve: Called Kyphosis (C shape).

Number of Vertebrae by Region

  • Cervical Region: 7 vertebrae.

  • Thoracic Region: 12 vertebrae (correspond to pairs of ribs).

  • Lumbar Region: 5 vertebrae.

  • Sacrum: Fused vertebrae at the base.

  • Coccyx: Also known as the tailbone.

Vertebrae Anatomy

  • Each vertebra (except the first two) includes:

    • Body: Anterior flat rounded section.

    • Spinous Process: Posterior protrusion, can be felt on the back.

    • Transverse Processes: Lateral extensions on both sides.

    • Vertebral Foramen: Central opening for the spinal cord.

  • Special Features of Cervical Vertebrae:

    • First Cervical Vertebra (C1): Called Atlas; supports skull and allows head nodding.

    • Second Cervical Vertebra (C2): Called Axis; permits lateral rotation of the head.

    • Odontoid Process (Dens): Projection of the Axis.

Sacrum and Coccyx

  • Sacrum: Composed of 5 fused vertebrae; triangular-shaped bone at the base of the vertebral column.

  • Coccyx: Conical, at the tail end, serves as an attachment point for some ligaments and muscles.

Thoracic Cage

  • Components: Composed of ribs, sternum, and thoracic vertebrae.

  • Rib Arrangement:

    • Total Pairs of Ribs: 12 pairs (24 total).

  • Types of Ribs:

    • True Ribs (1-7): Each connects directly to the sternum via individual costal cartilage.

    • False Ribs (8-10): Connect indirectly by attaching to the cartilage of the rib above.

    • Floating Ribs (11-12): Do not attach to the sternum at all; only attach to their corresponding thoracic vertebrae.

Sternum Structure

  • Parts of the Sternum:

    • Manubrium: Upper part; attachment for collarbone.

    • Body: Main blade portion of the sternum.

    • Xiphoid Process: Cartilaginous tip that ossifies later in life.

Articulation of Vertebral Column

  • Vertebral column articulates (joins) with the skull, ribs, and hip bones (iliac bones).

  • Intervertebral Discs: Made of fibrocartilage, act as shock absorbers between vertebrae.

  • Movement: Most flexibility occurs in the posterior structures through articulation of the articular facets.

Upper Extremity Attachment to Axial Skeleton

  • Key Details:

    • The shoulder girdle is formed by the scapula and clavicle.

    • Sternoclavicular Joint: Connection point between the clavicle and the sternum.

    • Acromioclavicular Joint: Connection between the scapula and the lateral end of the clavicle.

    • Muscle Attachment: Holds scapula against rib cage and supports shoulder movement.