It functions as a highly dynamic system, undergoing changes throughout development.
A fetus has approximately 300 bones, which fuse during development. In adults, there are about 206 bones.
Note on individual variability:
Some individuals may not possess all ribs, digits, or vertebrae.
Functions of the Skeleton
Support: Provides structural support for the body, protecting vital organs and tissues.
Movement: Acts as levers for skeletal muscles, facilitating movement.
Storage:
Stores lipids for energy.
Stores calcium and other minerals.
Hematopoiesis: Houses stem cells responsible for blood cell production.
Divisions of the Skeleton
The skeleton is divided into two main parts:
Axial Skeleton:
Contains bones that encircle the body's center, including:
Skull (comprised of cranial and facial bones)
Vertebral column
Thoracic cage
Appendicular Skeleton:
Consists of bones of the limbs.
Major Cartilages of the Skeleton
Initially, a fetus’s skeleton is made up of hyaline cartilage which undergoes ossification during development.
Locations where cartilage remains in an adult skeleton include:
Hyaline Cartilage:
Bridge of the nose
Costal cartilages (attach ribs to sternum)
Articular surfaces (ends of bones forming joints)
Fibrocartilage:
Intervertebral discs
Pubic symphysis (joint between pubic bones)
Elastic Cartilage:
External ear
Composition of Bones
Bones, as a type of connective tissue, possess an extensive extracellular matrix composed of:
Ground substance
Fibers, specifically collagen
Hardness of bone is attributed to inorganic calcium salts present in the ground substance.
Flexibility of bones is derived from collagen fibers.
Bone Markings
Bone surfaces are not smooth but exhibit various features due to functionalities such as forming joints, muscle and ligament attachments, and providing passageways for blood vessels and nerves.
These features are collectively referred to as bone markings:
Types of Bone Markings
Projections
Process: A projection or bump.
Ramus: A part of a bone that forms an angle with the rest of the structure.
Head: Expanded articular projection at the end of an epiphysis, often separated from the shaft by a narrower neck.
Trochanter: A large, rough projection.
Crest: A prominent ridge.
Spine: A pointed process.
Neck: A narrow connection between the epiphysis and diaphysis.
Line: A low ridge.
Tubercle: A small, rounded projection.
Tuberosity: A rough projection.
Facet: A small, flat articular surface.
Depressions
Sulcus: A narrow groove.
Sinus: A chamber within a bone, normally filled with air.
Foramen: A rounded passageway for blood vessels and/or nerves.
Fissure: A deep furrow, cleft, or slit.
Meatus: A passage or channel, specifically the opening of a canal.
Canal: A duct or channel.
The Adult Skeleton
At birth, humans possess approximately 300 bones; by adulthood, this number decreases to about 206 bones.
Many bones come in pairs and have specific bone markings based on their functions.