Skeletal Unit

Axial Skeleton

Part of the skeleton that consists of 80 bones along the central axis of the body.

Appendicular Skeleton

Part of the skeleton that consists of 126 bones and includes the limbs and girdles.

Long Bones

Bones that are greater in length than width; examples include the humerus and femur.

Short Bones

Typically cubish in shape; examples include carpals.

Flat Bones

Bones consisting of two flat compact layers with spongy bone in between; examples include the sternum and scapula.

Irregular Bones

Bones with unique or complex shapes; examples include the mandible and vertebrae.

Cranium

The part of the skull that protects the brain, composed of 8 bones.

Frontal Bone

Bone that makes up the forehead and roof of the eye socket; one of the strongest bones of the body.

Occipital Bone

Bone located at the back of the head, containing the foramen magnum where the spinal cord passes through.

Sphenoid Bone

Known as the keystone of the cranium, this bone touches every other bone in the cranium.

Mandible

The only movable bone of the skull and the strongest of the facial bones.

Vertebral Column

Made up of vertebrae, it accounts for about 40% of a person's height and protects the spinal cord.

Cervical Vertebrae

The first 7 vertebrae of the spine, includes the atlas and axis.

Thoracic Vertebrae

The 12 vertebrae in the upper back, each connected to a pair of ribs.

Lumbar Vertebrae

The 5 vertebrae in the lower back.

Pelvic Girdle

Attaches the lower limbs to the body and includes the ilium, ischium, and pubis.

Femur

The largest and heaviest bone in the body, located in the thigh.

Osteoblasts

Bone-forming cells that secrete collagen and mineral salts.

Osteocytes

Mature bone cells derived from osteoblasts.

Osteoclasts

Cells that break down bone tissue, involved in the resorption process.

Calcification

The process wherein minerals in the bone harden to form solid bone.

Wolff's Law

The principle stating that a bone grows or remodels in response to the forces or demands placed upon it.

Fracture

A break in a bone classified based on the position of the bone ends, completeness of the break, orientation, and whether the ends penetrate the skin.