Axial skeleton

Axial skeleton

CT of a normal abdomen and pelvis, axial plane

The axial skeleton is an integral part of the human skeletal system, encompassing the bones central to the body's axis. Comprising bones that support and protect the brain, spinal cord, and vital organs, it serves as the foundational framework of the body.

Structure and Components

The axial skeleton, primarily associated with humans, is comprised of 80 distinct bones. It serves as the body's medial core, linking the pelvis, where the appendicular skeleton connects. As individuals age, most bones of the skeleton tend to weaken, but the skull remains robust, shielding the brain from potential harm.

Skull

The human skull, divided into the cranium and facial bones, serves as a protective casing for the brain within the cranial vault. It's made up of:

• Eight plate-like bones that form the cranium, merging at joints termed sutures.
• Fourteen facial bones constructing the lower frontal section of the skull.

Crucial facial bones encompass the mandible (jaw), maxilla (upper jaw), zygomatic (cheek bone), and nasal bone. At birth, these plates are distinct, but over time, they fuse, leaving the mandible separate.

Rib Cage

Consisting of 25 bones, the rib cage offers protection to vital organs, such as the heart and lungs. The ribs, crescent-shaped, are divided into:

• True ribs (1st to 7th) - Directly attached to the sternum via costal cartilage.
• False ribs (8th to 10th) - Linked to the above ribs without direct sternum connection.
• Free ribs (11th & 12th) - Lacking attachment to the sternum or adjacent ribs.

The rib lengths vary, with the first rib being the shortest and most curved.

Vertebral Column

Comprising varying numbers of vertebrae, from 32 to 34 in total, the vertebral column's structure includes:

• Cervical (7) - Connecting the vertebral column to the cranium.
• Thoracic (12)
• Lumbar (5)
• Sacral (4-5) - Often referred to as the "sacral bone."
• Coccygeal (3-4) - Fused vertebrae known as the "coccygeal bone."

The sacral bone establishes the link between the vertebral column and pelvic bones.

Evolution and Lineage

While the primary focus is on human axial skeletons, understanding its evolutionary lineage is essential. Throughout evolution, the axial skeleton's design has transformed to house and protect vital organs and the nervous system.

History

The term "Axial" originates from "axis", signifying the bones' position near or along the central "axis" of the body.

See Also

• Appendicular Skeleton
• Vertebrae
• Cranium
• Rib Cage

Axial skeleton Resources
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