Lec 4- Axial Division of the Human Skeletal System: Structure and Function

The Skeletal System: Axial Division

Introduction

The axial division of the human skeletal system forms the central framework of the body, providing support, protection, and structural integrity. It includes the skull, vertebral column, and thoracic cage (ribs and sternum).

Learning Outcomes

• Identify the names and locations of the bones that constitute the axial skeleton.

• Describe the structure and function of the skull, vertebral column, and thoracic cage.

• Compare and contrast vertebral groups and describe their functional differences.

Human Skeleton Overview

Main Divisions

• Axial skeleton: Consists of 80 bones, including the skull, vertebral column, and thoracic cage.

• Appendicular skeleton: Includes the limbs and girdles that connect them to the axial skeleton.

Axial Skeleton Components

• 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 ribs and sternum, protects the heart and lungs.

Function of the Axial Skeleton

Key Functions

1. Support and protection: Provides a framework for the body and shields vital organs (brain, spinal cord, heart, lungs).

2. Attachment for muscles: Facilitates movement and posture.

3. Houses sensory organs: Protects and supports structures for sight, hearing, taste, and smell.

4. Blood cell formation: Contains red bone marrow for hematopoiesis.

The Skull

Divisions of the Skull

• Cranial division: 8 bones that encase and protect the brain.

• Facial division: 14 bones that form the structure of the face.

Major Cranial Bones

• Frontal bone

• Parietal bones

• Occipital bone

• Temporal bones

• Sphenoid bone

• Ethmoid bone

Major Facial Bones

• Maxillae

• Palatine bones

• Nasal bones

• Lacrimal bones

• Zygomatic bones

• Vomer

• Mandible

Views and Landmarks of the Skull

Anterior, Superior, Posterior, and Sagittal Views

• Each view highlights different bones and sutures (e.g., coronal, sagittal, lambdoid, squamous).

• Landmarks include the orbital complex, nasal cavity, and mandible.

The Orbital Complex

Structure and Function

• Composed of 7 bones: frontal, sphenoid, ethmoid, lacrimal, maxillary, palatine, and zygomatic.

• Protects the eyes and supports associated muscles.

• Contains openings for nerves and blood vessels (e.g., optic canal, superior/inferior orbital fissures).

Sphenoid and Temporal Bones

Sphenoid Bone

• Forms the base of the cranium and part of the orbit.

• Contains the sella turcica, which houses the pituitary gland.

Temporal Bones

• Located at the sides and base of the skull.

• Contains structures for hearing and balance (e.g., internal and external acoustic meatus).

The Mandible

Structure and Function

• Forms the lower jaw and is the only movable bone of the skull.

• Articulates with the temporal bone at the temporomandibular joint (TMJ).

The Paranasal Sinuses

Function and Location

• Air-filled chambers within the bones of the nasal complex.

• Lighten the skull, produce mucus, and contribute to voice resonance.

Cranial Fossae

Major Fossae

• Anterior cranial fossa: Supports the frontal lobes of the brain.

• Middle cranial fossa: Houses the temporal lobes and pituitary gland.

• Posterior cranial fossa: Contains the cerebellum and brainstem.

The Skulls of Infants

Features

• Fontanelles (soft spots) allow for flexibility during birth and brain growth.

• Major fontanelles: anterior, posterior, sphenoidal, mastoid.

Sutures of the Skull

Definition and Types

• Suture: Immovable joint made of dense fibrous connective tissue.

• Major sutures: lambdoid, coronal, sagittal, squamous.

Bones of the Cranium and Face

Summary Table

Bone	Location	Function
Frontal	Forehead, roof of orbit	Protects brain, forms face
Parietal	Top and sides of skull	Protects brain
Occipital	Back and base of skull	Protects brain, contains foramen magnum
Temporal	Sides and base of skull	Hearing, muscle attachment
Sphenoid	Base of cranium	Supports brain, houses pituitary
Ethmoid	Roof of nasal cavity	Supports nasal cavity, forms part of orbit
Maxillae	Upper jaw	Holds upper teeth, forms part of orbit and nasal cavity
Mandible	Lower jaw	Holds lower teeth, only movable skull bone
Zygomatic	Cheekbones	Forms cheek, part of orbit
Nasal	Bridge of nose	Supports nose
Lacrimal	Medial wall of orbit	Supports tear duct
Palatine	Posterior part of hard palate	Forms part of nasal cavity and orbit
Vomer	Inferior part of nasal septum	Divides nasal cavity

Additional info:

• Fontanelles in infants ossify over time to form sutures.

• The axial skeleton is essential for posture, movement, and protection of vital organs.