Axial Skeleton: Structure and Function

Axial Skeleton

Overview of the Axial Skeleton

The axial skeleton forms the central axis of the human body and is essential for supporting and protecting the organs of the head, neck, and trunk. It consists of 80 bones, including the skull, hyoid bone, vertebral column, sternum, and ribs.

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

• Hyoid Bone: Supports the tongue and is associated with swallowing.

• Vertebral Column: Protects the spinal cord and supports the head and body.

• Sternum: Also known as the breastbone, it connects the ribs via cartilage.

• Ribs: Protect the thoracic organs and assist in respiration.

Key Point: The axial skeleton is distinct from the appendicular skeleton, which includes the bones of the limbs and girdles.

The Skeleton

General Structure and Function

Understanding the names, shapes, and positions of individual bones is crucial for locating other organs and comprehending how muscles produce movement through their attachments and leverage at joints. The bones and joints together form the skeletal system, which provides support, protection, and movement.

• Total Bones: 206 in the adult human skeleton (86 paired, 34 single).

• Divisions: Axial skeleton (central axis) and appendicular skeleton (limbs and girdles).

Skull

Structure of the Skull

The skull is composed of several bones joined together by immovable joints called sutures. It is divided into cranial bones and facial bones.

• Cranial Bones: Protect the brain and provide attachment for head and neck muscles.

• Facial Bones: Form the framework of the face, house the sense organs, provide openings for air and food, and anchor facial muscles.

Openings in the skull allow for the passage of nerves and blood vessels.

Sutures

Sutures are immovable joints that connect most of the bones of the skull. Major sutures include:

• Coronal Suture: Between frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between parietal and occipital bones.

Fontanels

Fontanels are membrane-filled spaces between the cranial bones of infants. They allow for overlapping of the skull bones during birth and rapid brain growth during infancy. The main fontanels are:

• Anterior Fontanel: Between frontal and parietal bones at the meeting of coronal and sagittal sutures.

• Posterior Fontanel: Between parietal and occipital bones at the meeting of lambdoid and sagittal sutures.

Fontanels gradually ossify and become sutures as the child grows.

Chapter Objectives

• Describe and locate the cranial and facial bones of the skull.

• Locate the four paranasal sinuses.

• Describe the hyoid bone.

• Differentiate between the types of vertebrae.

• Describe the sternum.

• Describe the structure of a rib, list the types of ribs, and explain how the rib articulates with the thoracic vertebrae.

Summary Table: Major Components of the Axial Skeleton

Component	Main Function	Key Features
Skull	Protects brain, forms face	Cranial and facial bones, sutures, fontanels (in infants)
Hyoid Bone	Supports tongue	Does not articulate with other bones
Vertebral Column	Protects spinal cord, supports body	Cervical, thoracic, lumbar vertebrae, sacrum, coccyx
Sternum	Protects thoracic organs	Manubrium, body, xiphoid process
Ribs	Protect thoracic cavity	True, false, and floating ribs

Key Terms

• Axial Skeleton: The part of the skeleton forming the central axis, including the skull, vertebral column, ribs, and sternum.

• Sutures: Immovable joints connecting the bones of the skull.

• Fontanels: Soft spots on an infant's skull that allow for growth and flexibility during birth.

• Cranial Bones: Bones that encase and protect the brain.

• Facial Bones: Bones that form the structure of the face.