Axial Skeleton Overview

Definition and Components

The axial skeleton forms the central framework of the human body, supporting and protecting vital organs and providing attachment points for muscles. It consists of the skull, vertebral column, and thoracic cage.

• Skull: 8 cranial bones and 14 facial bones

• Associated bones: 6 auditory ossicles and 1 hyoid bone

• Thoracic cage: Sternum and 24 ribs

• Vertebral column: 24 vertebrae, sacrum, and coccyx

Primary functions:

• Support and protection for the brain, spinal cord, and organs in the thoracic and abdominopelvic cavities

• Surface area for muscle attachment

• Facilitation of breathing movements

• Positioning of the head, neck, and trunk

• Support or positioning of parts of the appendicular skeleton

Skull Structure

Cranial and Facial Bones

The skull is divided into cranial bones, which protect the brain, and facial bones, which support the entrances to the digestive and respiratory tracts.

Additional info: The auditory ossicles are the smallest bones in the body and are located in the middle ear, essential for sound transmission.

Major Sutures of the Skull

Sutures are immovable joints that connect the bones of the skull.

• Lambdoid suture: Connects the occipital bone with the parietal bones

• Coronal suture: Attaches the frontal bone to the parietal bones

• Sagittal suture: Extends from the lambdoid suture to the coronal suture between the parietal bones

• Squamous suture: Joins the temporal bone to the parietal bone

Example: The sagittal suture runs along the midline of the skull, dividing the parietal bones.

Functions of the Axial Skeleton

Support and Protection

The axial skeleton provides a rigid framework that supports the body and protects the brain, spinal cord, and thoracic and abdominal organs.

• Maintains posture and balance

• Protects vital organs

• Serves as an anchor for muscle attachment

Facilitation of Movement

Muscles attached to the axial skeleton enable movements such as breathing and positioning of the head and trunk.

• Respiratory movements (e.g., expansion and contraction of the thoracic cage)

• Movement of the head, neck, and trunk

Associated Bones of the Skull

Hyoid Bone and Auditory Ossicles

The hyoid bone is a U-shaped bone in the neck that supports the tongue and is associated with swallowing. The auditory ossicles (malleus, incus, stapes) are located in the middle ear and transmit sound vibrations.

• Hyoid bone: Does not articulate directly with other bones; supports the larynx and tongue

• Auditory ossicles: Three small bones in each ear (malleus, incus, stapes)

Example: The auditory ossicles are so small that they would fit on the surface of a dime.

Summary Table: Axial Skeleton Components

Key Terms and Definitions

• Axial skeleton: The central part of the skeleton, including the skull, vertebral column, and thoracic cage

• Suture: An immovable joint between skull bones

• Foramen: An opening in a bone for nerves and blood vessels

• Process: A projection or outgrowth of bone for muscle attachment

Applications and Clinical Relevance

• Understanding the axial skeleton is essential for diagnosing fractures, congenital abnormalities, and diseases affecting bone structure.

• Knowledge of sutures and foramina is important in neurosurgery and dentistry.

Additional info: The axial skeleton is distinct from the appendicular skeleton, which includes the limbs and girdles.