The Axial and Appendicular Skeleton: Structure and Function

The Skeletal System Overview

Introduction to the Axial and Appendicular Skeletons

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. Understanding these divisions is fundamental to the study of human anatomy and physiology.

• Axial Skeleton: Forms the longitudinal axis of the body and consists of bones that support and protect the organs of the head, neck, and trunk.

• Appendicular Skeleton: Composed of bones of the limbs and girdles that attach them to the axial skeleton, enabling movement and manipulation of objects.

The adult human skeleton contains 206 bones. Key anatomical features to study include:

• Articulations: Points where bones contact each other.

• Landmarks: Areas for muscle and ligament attachment.

• Foramina: Openings for blood vessels and nerves.

Axial Skeleton

Structure and Function

The axial skeleton consists of 80 bones, including the skull, vertebral column, and thoracic cage. It provides support and protection for the brain, spinal cord, and organs in the thoracic cavity.

• Functions:

  • Attachment for muscles of the head, neck, and trunk

  • Facilitation of respiratory movements

  • Stabilization of parts of the appendicular skeleton

Major Components of the Axial Skeleton

Region	Number of Bones	Main Structures
Skull and Associated Bones	29	Cranium, face, auditory ossicles, hyoid
Thoracic Cage	25	Sternum, ribs
Vertebral Column	26	Vertebrae, sacrum, coccyx

The Skull

Structure and Protective Functions

The bones of the skull protect the brain and form the entrance to the digestive and respiratory systems. The skull is divided into the cranium and facial bones:

• Cranium: Composed of eight cranial bones that enclose the cranial cavity. These bones provide protection for the brain and serve as attachment points for head and neck muscles.

• Facial Bones: Fourteen bones that form the structure of the face. Superficial facial bones provide areas for muscle attachment, while deeper bones help separate the oral and nasal cavities.

• Associated Bones: Includes the hyoid bone and six auditory ossicles (three in each ear), which are involved in sound transmission and support of the tongue.

Key Anatomical Features

• Sutures: Immovable joints between cranial bones. Major sutures include the lambdoid, coronal, sagittal, and squamous sutures.

• Sinuses: Air-filled chambers within certain skull bones that reduce weight and contribute to voice resonance.

Learning Objectives for the Axial Skeleton

• Identify the function of the bones of the axial skeleton.

• Identify the bones of the cranium and face, and explain the significance of their markings.

• Describe the orbital complex, nasal complex, and paranasal sinuses.

• Describe differences between the skulls of infants and adults.

• Describe the curvatures of the spinal column.

• Identify vertebral regions and describe distinguishing characteristics of vertebrae in each region.

• Explain the significance of articulations between thoracic vertebrae/ribs and between ribs and sternum.

Summary Table: Axial Skeleton Components

Component	Number of Bones	Examples
Cranium	8	Frontal, parietal, occipital, temporal, sphenoid, ethmoid
Face	14	Maxilla, zygomatic, mandible, nasal, lacrimal, palatine, inferior nasal concha, vomer
Auditory Ossicles	6	Malleus, incus, stapes (each ear)
Hyoid	1	Hyoid bone
Sternum	1	Sternum
Ribs	24	12 pairs of ribs
Vertebrae	24	Cervical, thoracic, lumbar vertebrae
Sacrum	1	Sacrum
Coccyx	1	Coccyx

Key Terms and Definitions

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

• Appendicular Skeleton: The part of the skeleton consisting of the limbs and girdles.

• Articulation: A joint or connection between bones.

• Landmark: A prominent anatomical feature on a bone, often serving as an attachment point.

• Foramen (plural: foramina): An opening in a bone for the passage of blood vessels or nerves.

• Suture: An immovable joint between skull bones.

• Sinus: An air-filled cavity within a bone.

Example Application

• Clinical Example: Damage to the foramina in the skull can affect the passage of nerves and blood vessels, leading to neurological deficits or impaired blood flow.

• Functional Example: The articulation between the occipital bone and the first cervical vertebra (atlas) allows for nodding movements of the head.