1. The Skeletal System
Chapter 5

2. The Skeletal System
The skeleton is divided into two divisions: axial and appendicular
Axial Skeleton: bones that form the longitudinal axis of the body
Appendicular Skeleton: bones of the limbs and girdles
The Skeletal System includes:
Bones
Joints
Cartilage
Ligaments

3. Bones: An Overview
Besides contributing to body shape and form, our bones perform several important body functions:
Support – Bones form the internal framework that supports and anchors all soft organs
Ex: Bones of the legs act as pillars to support the body trunk when we stand
Protection – Bones protect soft body organs.
Ex: fused bones of the skull provide a snug enclosure for the brain that provides protection against injury

4. Bones: An Overview
Movement – Skeletal muscles use the bones as levers to move the body and its parts
As a result, we can walk, swim, throw a ball, and breathe
Storage – Bones act as a storage device for many things:
Fat is stored in the internal cavities of bones
Bones serve as a storehouse for minerals such as calcium and phosphorus
Blood Cell Formation – Hematopoiesis (blood cell formation) occurs within the marrow cavities of certain bones

5. Bones: An Overview Classification of Bones
The adult skeleton is composed of 206 bones
There are two basic types of bones:
Compact Bone: dense and looks smooth and homogenous
Spongy Bone: composed of small needlelike pieces of bone and lots of open space

6. Bones: An Overview
There are many different shapes and sizes of bones that depend on the function of the particular bone.
There are 4 classifications of shape for bones:
Long
Short
Flat
Irregular

7. Bones: An Overview Classification of Bone:
Long Bones: typically longer than they are wide
As a rule, they have a shaft with heads at both ends
Mostly compact bone
Include all of the bones of the limbs, except the wrist and ankle bones

8. Bones: An Overview Classification of Bone:
Short Bones: generally cube-shaped and contain mostly spongy bone
Includes the bones of the wrist and ankle
Includes Sesamoid Bones
Sesamoid Bones: specialized short bone that forms within tendons
Best known example = patella (kneecap)

9. Bones: An Overview Classification of Bone:
Flat Bones: thin, flattened, and usually curved bones
Have two thin layers of compact bone sandwiching a layer of spongy bone
Includes most bones of the skull, ribs, and sternum (breast bone)

10. Bones: An Overview Classification of Bone:
Irregular Bones: Any bones that do not fit one of the other categories are called irregular bones
This includes the vertebrae, which make up the spinal column, and the hip bones

11. Bones: An Overview Structure of a Long Bone:
Most of the bone’s length is made up of a diaphysis, or shaft.
The diaphysis is covered and protected by a fibrous connective tissue membrane called the periosteum
Hundreds of connective tissue fibers attach the periosteum to the underlying bone. These fibers are called Perforating Fibers
At the ends of the bones are the epiphyses, which consist of a thin layer of compact bone enclosing an area filled with spongy bone
Articular Cartilage covers the outside of epiphyses instead of periosteum

12. Bones: An Overview Bone Structure Continued…
In adult bones, there is a thin line of bony tissue spanning the epiphysis that looks different from the rest of the bone in the area
This is known as the Epiphyseal Line, which is a remnant of epiphyseal plate used for bone growth in young, growing bones
In adults, the cavity of the shaft is primarily a storage area for adipose tissue and is known as the Medullary Cavity
In infants, this area forms red blood cells. Red blood cells only form in specific long bones in adults

13. Bones: An Overview

14. Bones: An Overview Bone Markings:
When looking at a bone, it is easy to see bumps, holes, ridges, etc.
These characteristics are known as Bone Markings
These bone markings reveal where muscles, tendons, and ligaments were attached as well as where blood vessels and nerves passed
There are 2 categories of Bone Markings
Projections (or Processes): grow out from bone surfaces
Depressions (or Cavities): indentations in the bones