1. What is the difference between the appendicular skeleton & the axial skeleton?

The term "appendicular skeleton" refers to the bones of our appendages -- the arms & legs -- & the bones that attach them to the other major division of the skeletal system, the axial skeleton.

The appendicular skeleton's upper portion includes all the bones of the arms and hands plus the pectoral girdle, which is formed by the collar bone (clavicle) and the shoulder blade (scapula).

The appendicular skeleton's lower portion includes all bones of the legs & feet plus the pelvic girdle, which attaches the lower appendages to the axial skeleton at the sacrum.

The axial skeleton is composed of the entire vertebral column including the sacrum & tailbone (coccyx), the skull, the ribs & sternum, and the hyoid bone which is located under the lower jaw.
 
 
 

2. What are the primary & secondary curvatures of the vertebral column?

Primary curvatures are the ones we are born with and that will continue to be present into adulthood. If you think of the position a fetus is in before it's born, you think of the shape of a "C". The slight forward curve of the chest or thoracic area is still seen in the upper back area of a child or adul t-- this is one of the primary curvatures. Another portion of that original "C" shape that persists into adulthood is the curve of the sacrum, so it is also a primary curvature.

Normal secondary curvatures develop after birth, & for that reason are referred to as secondary. As a baby gains enough strength to raise or pick up its head, the cervical curvature begins to develop. Then as the baby learns to stand, a lumbar curvature develops in response to the baby's center of gravity as it is in a standing position.

When viewed from behind (posterior aspect), the vertebral column normally appears straight up & down, from the neck to the hips.
 
 
 

3. Are there some abnormal curvatures of the vertebral column?

Yes, and some of these are extreme curvatures of otherwise normally present curvatures. They can cause problems by putting stress on internal organs &/or bones by causing the person to stand & walk in a certain way to compensate for the shifted body position.

Kyphosis is an exaggerated thoracic (upper back area) curvature.

Lordosis is an exaggerated lumbar (lower back area) curvature.

Scoliosis is a shifting from the normal "straight up & down" posterior view to where it appears to be pulling off to the left or right side.
 
 
 

4. Do all bones of the body form in the same way?

No. There are 2 different processes by which bones may form, depending on the type of bone. The terms "osteogenesis" and "ossification" refer to the process of bone formation.

Most bones form by the endocartilagenous method. A cartilage "model" of the bone forms during fetal development, & then the model begins to ossify, with bone tissue replacing the cartilage model. The bones of the arms, legs, fingers, etc., form by this method.

Intermembranous ossification is the term for the second method of bone formation. In this method of bone formation, a connective tissue membrane forms and is gradually replaced by bony tissue. Skull bones are an example of some bones that form by intramembranous ossification.