Skeletal System: Structure and Function of Bones and the Axial Skeleton

Skeletal System Overview

Introduction to the Skeletal System

The skeletal system is a complex organ system that provides structural support, protection, and movement for the human body. It comprises approximately 20% of total body mass and is divided into two major parts: the axial and appendicular skeletons.

• Organs: Bones are considered organs due to their multiple tissue types (bone, cartilage, blood vessels, nerves).

• Body Mass: The skeletal system accounts for about 20% of body mass.

• Divisions: Two major divisions: axial skeleton and appendicular skeleton.

Axial Skeleton

Main Components of the Axial Skeleton

The axial skeleton forms the central axis of the body and includes 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: Includes ribs and sternum, protecting vital organs such as the heart and lungs.

Skull Anatomy

Major Bones of the Skull

The skull consists of cranial and facial bones, which protect the brain and form the structure of the face.

• Cranial Bones: Enclose and protect the brain.

• Facial Bones: Form the framework of the face and support sensory organs.

Eight Cranial Bones

The cranium is composed of eight bones that are fused together by sutures.

• Frontal bone

• Parietal bones (2)

• Occipital bone

• Temporal bones (2)

• Sphenoid bone

• Ethmoid bone

Fourteen Facial Bones

The facial skeleton consists of fourteen bones, some paired and some single.

• Mandible

• Maxillary bones (2)

• Zygomatic bones (2)

• Nasal bones (2)

• Lacrimal bones (2)

• Palatine bones (2)

• Vomer

• Inferior nasal conchae (2)

Sutures of the Skull

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

• Coronal suture: Between frontal and parietal bones.

• Squamous suture: Between parietal and temporal bones.

• Lambdoid suture: Between parietal and occipital bones.

Cranial Fossae

The cranial floor is divided into three fossae that accommodate different parts of the brain.

• Anterior cranial fossa

• Middle cranial fossa

• Posterior cranial fossa

Special Bones and Features

Hyoid Bone

The hyoid bone is a unique U-shaped bone in the neck that does not articulate directly with any other bone.

• Greater horn

• Lesser horn

• Body

• Function: Supports the tongue and is associated with swallowing.

Vertebral Column

Structure and Regions of the Vertebral Column

The vertebral column is composed of 26 vertebrae divided into five regions.

• Cervical (7)

• Thoracic (12)

• Lumbar (5)

• Sacrum (1)

• Coccyx (1)

Curvatures of the Spine

The spine has four main curvatures that help maintain balance and absorb shock.

• Cervical curvature

• Thoracic curvature

• Lumbar curvature

• Sacral curvature

Abnormal Curvatures:

• Scoliosis: Lateral curvature of the spine.

• Kyphosis: Exaggerated thoracic curvature.

• Lordosis: Exaggerated lumbar curvature.

Vertebrae Structure

Each vertebra has several processes and features for articulation and muscle attachment.

• Body

• Spinous process

• Transverse processes

• Articular processes

• Lamina

• Pedicle

Cervical Vertebrae Special Features

The first two cervical vertebrae, atlas (C1) and axis (C2), have unique structures that allow for head movement.

• Atlas (C1): Supports the skull and allows nodding motion.

• Axis (C2): Has the odontoid process (dens) for rotation of the head.

Summary Table: Major Bones of the Skull

Bone	Type	Number	Main Function
Frontal	Cranial	1	Forehead, roof of orbits
Parietal	Cranial	2	Superior and lateral skull walls
Occipital	Cranial	1	Posterior skull, foramen magnum
Temporal	Cranial	2	Inferolateral skull, houses ear structures
Sphenoid	Cranial	1	Base of cranium, unites cranial bones
Ethmoid	Cranial	1	Roof of nasal cavity, part of orbit
Mandible	Facial	1	Lower jaw, only movable skull bone
Maxilla	Facial	2	Upper jaw, forms part of orbit and nasal cavity
Zygomatic	Facial	2	Cheekbones
Nasal	Facial	2	Bridge of nose
Lacrimal	Facial	2	Medial wall of orbit
Palatine	Facial	2	Posterior part of hard palate
Vomer	Facial	1	Inferior part of nasal septum
Inferior nasal conchae	Facial	2	Lateral walls of nasal cavity

Additional info:

• Some slides referenced clinical conditions (e.g., craniosynostosis, abnormal spinal curvatures) and anatomical variations, which are important for understanding pathology and development.

• Images depicted anatomical landmarks and bone features, which are essential for identification in laboratory and clinical settings.