Overview of the Skeleton, Bone Classification, and Axial Skeleton Study Guide

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Overview of the Skeleton

Axial and Appendicular Skeleton

The human skeleton is divided into two main regions: the axial skeleton and the appendicular skeleton. Each region contains specific bones that serve distinct functions in support, movement, and protection.

Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage. It supports the central axis of the body and protects vital organs such as the brain, spinal cord, and heart.
Appendicular Skeleton: Includes the bones of the limbs and girdles (shoulder and pelvic girdles). It facilitates movement and interaction with the environment.

Classification of Bones

Types of Bones

Bones are classified based on their shape and structure. Understanding these classifications helps in identifying their functions and locations in the body.

Long Bones: Longer than they are wide; found in arms and legs (e.g., femur, humerus).
Short Bones: Nearly equal in length and width; found in wrists and ankles (e.g., carpals, tarsals).
Flat Bones: Thin, flattened, and usually curved; found in the skull, ribs, and sternum.
Irregular Bones: Complex shapes that do not fit other categories; found in vertebrae and some facial bones.
Sesamoid Bones: Small, round bones embedded in tendons (e.g., patella).
Wormian (Sutural) Bones: Small bones found within sutures of the skull.

Bone Markings

Terminology and Functions

Bone markings are features on bones that serve as sites for muscle attachment, passage of nerves and blood vessels, and articulation with other bones. Refer to Table 8.1 for detailed terminology.

Foramen: Opening for blood vessels and nerves.
Process: Projection for muscle attachment.
Condyle: Rounded articular surface.
Fossa: Shallow depression.
Suture: Immovable joint between skull bones.

Effects of Heat and Acid on Bones

Experimental Observations

Bone tissue is composed of both organic and inorganic components. Experiments with heat and acid demonstrate the importance of these components.

Bones treated with acid (e.g., vinegar): Acid dissolves the inorganic mineral matrix (mainly calcium phosphate), leaving behind the organic collagen. The bone becomes soft and flexible.
Bones that have been baked: Heat removes the organic collagen, leaving the inorganic mineral matrix. The bone becomes brittle and easily breaks.

Example: If a bone is soaked in vinegar, it can be bent; if baked, it snaps easily.

Microscopic Structure of Compact Bone

Key Features

Compact bone is organized into structural units called osteons (Haversian systems). These features are essential for bone strength and nutrient delivery.

Haversian (Central) Canal: Contains blood vessels and nerves.
Canaliculi: Tiny channels connecting osteocytes, allowing nutrient and waste exchange.
Osteocytes: Mature bone cells residing in lacunae.

Importance: These structures maintain bone health and facilitate communication between cells.

Cartilage Types and Locations

Cartilage in the Body

Cartilage is a flexible connective tissue found in various locations. It is classified based on its composition and function.

Hyaline Cartilage: Most common; found in nose, trachea, ends of long bones.
Elastic Cartilage: Contains elastic fibers; found in external ear and epiglottis.
Fibrocartilage: Contains collagen fibers; found in intervertebral discs and pubic symphysis.
Chondrocytes: Cartilage cells located in lacunae.

Axial Skeleton: Skull Bones and Markings

Major Bones and Features

The skull is composed of several bones and markings that protect the brain and form the structure of the face.

Frontal Bone: Forehead region; includes glabella, coronal suture, and frontal sinus.
Parietal Bone: Sides and roof of the skull; sagittal suture.
Temporal Bone: Sides of the skull; squamous suture, styloid process, external acoustic meatus, mastoid process, zygomatic process.
Occipital Bone: Back of the skull; foramen magnum, occipital condyles, lambdoid suture, nuchal lines, external occipital protuberance.
Orbital Cavity: Eye socket; includes lacrimal bone, lacrimal fossa, ethmoid bone, sphenoid bone, orbital fissures, optic canal.
Nasal Bone: Bridge of the nose; includes nasal cavity, nasal conchae, perpendicular plate of ethmoid bone.
Maxilla: Upper jaw; infraorbital foramen, alveolar margin.
Mandible: Lower jaw; mandibular process, mental foramen.
Zygomatic Bone: Cheekbone.
Hyoid Bone: Located in the neck; supports the tongue.

Fetal Skull

Fontanels

The fetal skull contains soft spots called fontanels that allow for growth and flexibility during birth.

Anterior Fontanel
Posterior Fontanel
Mastoid Fontanel
Sphenoid Fontanel

Example: The anterior fontanel is the largest and closes by 18-24 months after birth.

Summary Table: Bone Classification

Main Purpose: Classification and Examples

Bone Type	Description	Example
Long Bone	Longer than wide	Femur, Humerus
Short Bone	Nearly equal length and width	Carpals, Tarsals
Flat Bone	Thin, flattened, often curved	Skull, Ribs, Sternum
Irregular Bone	Complex shape	Vertebrae, Facial bones
Sesamoid Bone	Small, round, in tendons	Patella
Wormian (Sutural) Bone	Small bones in skull sutures	Skull sutures

Summary Table: Cartilage Types

Main Purpose: Classification and Locations

Cartilage Type	Key Features	Location
Hyaline	Glossy, smooth, few fibers	Nose, trachea, ends of long bones
Elastic	Flexible, elastic fibers	External ear, epiglottis
Fibrocartilage	Dense collagen fibers	Intervertebral discs, pubic symphysis

Key Equations and Concepts

Bone Composition

Bones are composed of both organic and inorganic materials:

Organic: Collagen fibers (provide flexibility)
Inorganic: Calcium phosphate (provides strength)

Formula for bone mineral content:

Formula for bone flexibility:

Formula for bone strength:

Additional info:

Fontanels in the fetal skull allow for rapid brain growth and passage through the birth canal.
Bone markings are essential for identifying muscle attachment sites and understanding joint movement.
Cartilage types are distinguished by their fiber content and flexibility, which determines their function in the body.