Introduction

A skeleton is the bones of a human or animal body that form the framework of the body, support the muscles and organs, and protect the inner organs.

About 206 bones

At birth, there are over 270 bones in an infant human's body

2 Main Divisions – Axial & Appendicular

Bones do not make up most of a body’s mass

There are five types of bones in the human body: long, short, flat, irregular, and sesamoid.

Long Bones

1. Epiphysis

2. Diaphysis

3. Articular Cartilage

4. Periosteum

Long Bone Structure

Characterized by a shaft, the diaphysis, that is much longer than it is wide.

A long bone’s surface is covered by a tough membrane called the periosteum.

Periosteum is a white, double layered membrane that covers the entire surface of bone except for the joint surfaces and is richly supplied with nerve fibers and blood vessels.

Under the periosteum is a hard material called compact bone, and this part of the bone gives all bones their strength and rigidity.

Compact bone is composed of cylinders made of mineral crystals and protein fibers called lamellae.

Each lamellae is made up of a narrow channel

called a Haversian canal, which contains the blood vessels in compact bone.

Surrounding each Haversian canal are

protein fibers and osteocytes.

Osteocytes are a specific type of bone

cell.

Beneath some compact bone is a network of connective tissue called spongy bone.

Spongy bone is less dense bone tissue that has many open spaces.

Bone Marrow

Bone marrow is a soft tissue inside some bones that can be either red or yellow.

The type of bone marrow present determines both its composition and function.

Medullary Cavity – hollow chamber filled with bone marrow

Red Marrow (blood)

Yellow Marrow (fat)

Endosteum - lining of the medullary

Other types of bones

Short bones are cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. Examples: wrist and ankle, as are the sesamoid bones.

Flat bones are thin and generally curved, with two parallel layers of compact bones sandwiching a layer of spongy bone. Example: Most of the bones of the skull, sternum.

Sesamoid bones are bones embedded in tendons. Since they act to hold the tendon further away from the joint, the angle of the tendon is increased and thus the leverage of the muscle is increased. Examples: patella and the pisiform.

Irregular bones do not fit into other bone categories.

Consist of thin layers of compact bone surrounding a spongy interior.

Irregular shape is due to their many centers of ossification or because they contain bony sinuses. The bones of the spine, pelvis, and some bones of the skull.

Bone Development

During fetal development, all bones starts as cartilage

Cartilage will slowly be replaced by actual bone. This process is called ossification.

Epiphyseal disk (growth plate) is a band of cartilage between the epiphysis and diaphysis

These areas increase bone length as the cells ossify

Cartilage becomes osteoblasts, then become osteocytes

The epiphyseal disk/plate is found at the joint ends of long bones and is composed of cartilage. This area of bone will eventually become mature bone.

Joints

The place where two bones meet is known as a joint.

Three major kinds of joints are found in the human body

1. Fixed – no movement

2. Semi-movable – limited movement

3. Movable – wide range of movement

Moveable joints Hinge, ball-and-socket, pivot, saddle, and gliding

Moveable joints Hinge joint - allows limited movement in only one

plane.

Ball-and-socket joint - allows 360 degree movement in 2 planes.

Pivot joint - allows 180 degree movement in only one plane.

Saddle joint - allows 360 degree movement in only one plane.

Gliding joint - allows bones to slide over one another.

Joint Structure

Helps movable joints deal with the pressure and stress of everyday life.

Covered with cartilage and secrete synovial fluid to reduce friction.

Joints are connected with ligaments to aid in joint movement.

Even with all this protection a joint can still be injured.

Arthritis Rheumatoid

arthritis develops when the immune system begins to attack body tissues, & joints become stiff & deformed.

Osteoarthritis is a degenerative joint disease in which the cartilage covering the surface of bone becomes thinner and rougher.