Axial Skeleton: Structure and Function Study Notes

Axial Skeleton

Overview of the Axial Skeleton

The axial skeleton forms the central axis of the human body and provides support and protection for the brain, spinal cord, and vital organs within the thorax. It consists of the skull, vertebral column, and thoracic cage.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral Column: Supports the body and protects the spinal cord.

• Thoracic Cage: Composed of the ribs and sternum, it protects the heart and lungs.

Example: The axial skeleton is essential for posture and movement, as well as for protecting the central nervous system.

Skull

Structure and Function of the Skull

The skull is a complex structure composed of several bones that protect the brain and form the framework of the face. It provides attachment points for facial muscles and forms the orbits for the eyes.

• Cranial Bones: Enclose and protect the brain.

• Facial Bones: Form the structure of the face and provide attachment for muscles.

• Orbits: Cavities that house the eyes.

Example: The mandible is the only movable bone of the skull, allowing for chewing and speech.

Cranium

Sutures and Cranial Bones

The cranium is the part of the skull that encloses the brain. It is formed by several bones joined together by immovable joints called sutures.

• Coronal Suture: Between the frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between the parietal and occipital bones.

• Squamous Suture: Between the parietal and temporal bones.

Key Cranial Bones: Frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones.

Example: The coronal suture is named for its crown-like position across the top of the skull.

Vertebral Column

Structure and Regions of the Vertebral Column

The vertebral column, or spine, is a flexible structure composed of individual vertebrae separated by intervertebral discs. It supports the head and trunk and protects the spinal cord.

• Cervical Vertebrae (7): Located in the neck region; the atlas (C1) and axis (C2) allow for head movement.

• Thoracic Vertebrae (12): Articulate with the ribs.

• Lumbar Vertebrae (5): Largest vertebrae, support the lower back.

• Sacrum: Five fused vertebrae forming the posterior wall of the pelvis.

• Coccyx: Four fused vertebrae forming the tailbone.

Example: The intervertebral discs act as shock absorbers and allow for flexibility in the spine.

Thoracic Cage

Components and Function of the Thoracic Cage

The thoracic cage consists of the ribs, sternum, and thoracic vertebrae. It protects the heart and lungs and provides attachment points for muscles involved in respiration.

• Ribs: 12 pairs; the first 7 are true ribs (attached directly to the sternum), 8-10 are false ribs (attached indirectly), and 11-12 are floating ribs (not attached to the sternum).

• Sternum: Flat bone at the center of the chest.

• Costal Cartilage: Connects ribs to the sternum and allows for expansion during breathing.

Example: The floating ribs (11 and 12) provide protection for the kidneys but do not attach to the sternum.

Table: Classification of Ribs

Type of Rib	Number	Attachment
True Ribs	1-7	Directly to sternum via costal cartilage
False Ribs	8-10	Indirectly to sternum via cartilage of rib 7
Floating Ribs	11-12	No anterior attachment to sternum

Additional info:

• The axial skeleton is distinct from the appendicular skeleton, which includes the limbs and girdles.

• Sutures in the cranium are fibrous joints that allow for growth during childhood.

• Intervertebral discs consist of an outer annulus fibrosus and an inner nucleus pulposus.