Axial Skeleton and Bone Markings: Structure and Function

Axial Skeleton Overview

Introduction to 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.

• Axial Skeleton Components: Skull, vertebral column, thoracic cage (ribs and sternum), and associated bones.

• Function: Protects the central nervous system and supports the body's posture.

• Number of Bones: 80 bones in the adult axial skeleton.

Skull Structure and Subdivisions

Major Divisions of the Skull

The skull is a complex structure composed of cranial bones, facial bones, and associated bones. It protects the brain and forms the structure of the face.

• Cranium: Encloses and protects the brain.

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

• Associated Bones: Includes the hyoid bone and auditory ossicles.

Skull Bone Classification

Category	Bones	Number
Facial Bones	Nasal (2), Maxillae (2), Zygomatic (2), Palatine (2), Lacrimal (2), Inferior nasal conchae (2), Vomer (1), Mandible (1)	14
Cranium	Occipital (1), Parietal (2), Frontal (1), Temporal (2), Sphenoid (1), Ethmoid (1)	8
Associated Bones	Hyoid (1), Auditory ossicles (6: 3 per ear)	7

Bone Markings and Features

Introduction to Bone Markings

Bones have various markings that serve as sites for muscle attachment, passageways for nerves and blood vessels, and articulation points for joints. Understanding these features is essential for identifying bones and their functions.

Types of Bone Markings

Type	Description	Example
Sinus	Chamber within a bone, normally filled with air	Frontal sinus
Foramen	Rounded passageway for blood vessels and/or nerves	Foramen magnum
Fissure	Deep furrow, cleft, or slit	Superior orbital fissure
Meatus	Passage or channel, especially the opening of a canal	External acoustic meatus
Canal	Duct or channel	Carotid canal
Condyle	Round prominence at the end of a bone, forms an articulation with another bone	Occipital condyle

Processes Formed Where Tendons or Ligaments Attach

• Trochanter: Large, rough projection (e.g., femur).

• Crest: Prominent ridge (e.g., iliac crest).

• Spine: Pointed process (e.g., scapular spine).

• Line: Low ridge (e.g., linea aspera of femur).

• Tubercle: Small, rounded projection (e.g., greater tubercle of humerus).

• Tuberosity: Rough projection (e.g., tibial tuberosity).

Processes Formed Where Joints (Articulations) Occur

• Head: Expanded articular end of an epiphysis, separated from the shaft by a neck (e.g., femoral head).

• Neck: Narrow connection between the epiphysis and diaphysis.

• Facet: Small, flat articular surface (e.g., vertebral facet).

• Condyle: Smooth, rounded articular process (e.g., occipital condyle).

• Trochlea: Smooth, grooved articular process shaped like a pulley (e.g., trochlea of humerus).

Auditory Ossicles

Structure and Function

The auditory ossicles are three small bones located in the middle ear. They transmit sound vibrations from the eardrum to the inner ear.

• Malleus: Hammer-shaped bone.

• Incus: Anvil-shaped bone.

• Stapes: Stirrup-shaped bone.

• Function: Essential for hearing by amplifying and transmitting sound waves.

Major Sutures of the Skull

Definition and Location

Sutures are immovable joints found only between the bones of the skull. They play a crucial role in protecting the brain and allowing for growth during development.

• Coronal Suture: Between frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between parietal and occipital bones.

• Squamous Suture: Between parietal and temporal bones.

Summary Table: Axial Skeleton Components

Component	Number of Bones	Main Function
Skull	22 (8 cranium, 14 facial)	Protects brain, forms face
Auditory Ossicles	6	Transmit sound
Hyoid	1	Supports tongue
Vertebral Column	26	Protects spinal cord, supports head and body
Thoracic Cage	25 (24 ribs, 1 sternum)	Protects heart and lungs

Key Terms and Definitions

• Axial Skeleton: The part of the skeleton that includes the skull, vertebral column, and thoracic cage.

• Cranium: The portion of the skull that encloses the brain.

• Foramen: An opening or hole in a bone for passage of nerves and blood vessels.

• Condyle: A rounded articular projection at the end of a bone.

• Suture: An immovable joint between skull bones.

Example Application

When identifying bones in the axial skeleton, students should be able to classify each bone by its location and function, recognize major bone markings, and understand the significance of sutures in cranial protection and development.

Additional info: The study notes have expanded on the brief points and diagrams to provide a comprehensive overview suitable for college-level Anatomy & Physiology students, including definitions, tables, and examples for clarity.