Skeletal System Part I

 

The Skeletal System is a framework consisting of bones and other connective tissues, which protects and supports the body tissues and internal organs.

 

The human skeleton contains 206 bones, six of which are the tiny bones of the middle ear (three in each ear) that function in hearing.

So, what are these 206 bones?

1. Axial Bones of the Skull

    (head)

  • Nasal

  • Maxilla

  • Zygomatic

  • Temporal

  • Parietal

  • Frontal

  • Mandible

  • Occipital

2. Axial Bones of the Torso

    (trunk of body)

  • True Rib 1-7

  • False Rib 8-10

  • Floating Rib 11-12

  • Hyoid

  • Sternum

  • C1 – C7

  • T1 – T12

  • L1 – L5

  • Sacrum

  • Coccyx

 

 

3. Appendiuclar Bones

    of the Upper Extremity (arms)

  • Scapula

  • Clavicle

  • Humerus

  • Radius

  • Ulna

  • Carpals (wrist bones) (there are 8 of these per hand)

  • Metacarpal (palm/hand bones) 1 – 5

  • Proximal Phalange (finger bones) 1 – 5

  • Distal Phalange (finger bones) 1 – 5

  • Intermediate Phalange (finger bones) 2 – 5

 

 

  • Pelvic

  • Femur

  • Patella

  • Tibia

  • Fibula

  • Tarsals (foot bones)  (there are 7 of these per foot)

  • Metatarsal (foot bones) 1 – 5

  • Proximal Phalange (toes) 1 – 5

4. Appendicular Bones

    of the Lower Extremity (Legs)

The underlined bones are single bones; there are two of each of the other bones.

C = “Cervical Vertebrae” (Neck vertebrae)

T = “Thoracic Vertebrae” (chest Vertebrae)

L = “Lumbar Vertebrae” (Back vertebrae)

That's a lot of names.  Am I really expected to remember all of this?

Yes you are.  There are a lot of definitions you need to know in order to be successful in this class.  You can drop the course if you think this is too difficult for you.

Why a Skeleton?

A Skeleton is composed of the body’s bones and associated ligaments, tendons, and cartilages.

•Functions:

1.  Support

  • The bones of the legs, pelvic girdle, and vertebral column support the weight of the erect body.

  • The mandible (jawbone) supports the teeth.

  • Other bones support various organs and tissues.

2. Protection

  • The bones of the skull protect the brain.

  • Ribs and sternum (breastbone) protect the lungs and heart.

  • Vertebrae protect the spinal cord.

3. Movement

  • Skeletal muscles use the bones as levers to move the body.

4. Storage

  • 99% of the body’s calcium is stored in bone.

  • 85% of the body’s phosphorous is  stored in bone.

  • Adipose tissue is found in the marrow of certain bones.

5. Hematopoiesis (Blood Cell Formation)

  • All blood cells are made in the marrow of certain bones.

Bone Classification

Bones comprise 20% of body mass

Bones are classified into two large groupings

1. Axial skeleton – 80 bones

  • Forms long axis of the body.

  • Includes the bones of the skull, vertebral column, and rib cage.

The bones of the Axial Skeleton are involved in protection, support, and carrying other body parts.

2. Appendicular skeleton – 126 bones

  • Bones of upper & lower limbs and the girdles (shoulder bones and hip bones) that attach them to the axial skeleton.

The bones of the Appendicular Skeleton are involved in locomotion and manipulation of the environment.

There are 206 named bones in the human body.

While we are children,, special cells at the end of bones add new calcium to the network of bone. Children have layers of these cells in the shape of plates at the ends of their bones. These “growth plates,” make the bones get longer, and close up when we become adults.

How do bones grow?

Bone remodeling

Two types of cells are responsible for bone growth:

1. Osteoclasts

  • Bone-destroying cells
    For bone to grow, existing bone has to be removed so that new bone matrix can be built.

  • Break down bone matrix for remodeling

  • releases calcium and phosphorus to body

2. Osteoblasts

  • Bone-forming cells

  • Become osteocytes

 

 

Osteocytes are a third type of bone cell that is not involved in bone growth. 

Osteocytes are mature bone cells

 

  • Osteon

  • The fundamental functional unit of much compact bone.
    Osteons are roughly cylindrical structures that are typically
    several millimeters long and around 0.2mm in diameter.


 

Osteon

Osteon

Osteocyte

Bone Remodelling video