Types of Bones

Bone Classification Based on Shape

Introduction

  • This classification is based on shape, not size.
  • The five main types are long bones, short bones, flat bones, sesamoid bones, and irregular bones.

Long Bones

  • Longer than they are wide.
  • Found in arms, legs, and so forth.
  • Examples:
    • Phalanges (bones of the fingers):
      • These bones, despite different lengths, have a consistent structure of being longer than they are wide.
    • Metacarpals (bones in the palm)
    • Humerus (upper arm bone).
    • Ulna (medial side of the arm).
    • Femur (thigh bone).
  • Main purpose: motility (ability to move).
  • Act as levers:
    • Muscles contract and pull the bone closer to the muscle's origin.
    • For example, a muscle starts at one point and inserts over a joint. When contracted, it pulls the bone closer to where the muscle originated.

Short Bones

  • Equal in length, width, and depth (cube-like).
  • Found mainly in the wrist (carpals) and ankle (tarsals).
    • Located at the base of the palm, where the palm hinges on the wrist.
  • Useful for stability.
  • Especially important in the tarsals (ankle bones) for weight distribution and ground manipulation.

Flat Bones

  • Generally flat in nature.
  • Often curved (e.g., skull bones curved around the brain, ribs curved around the thorax).
  • Useful for protection.
  • Have some movement capacity (e.g., ribs during inhalation and exhalation).
  • Examples:
    • Bones of the skull
    • Sternum (plate between ribs)
    • Ribs
    • Scapula (shoulder blade)

Sesamoid Bones

  • Form within a tendon.
  • Most common example: the patella (kneecap).
  • Quadriceps muscles:
    • The quadriceps muscles of the anterior thigh extend down and attach via a tendon that crosses the joint.
    • When the quad muscle contracts, it pulls on the bone (patella), causing a slingshot motion, like kicking a soccer ball.
  • Development:
    • A bone forms within the muscle tendon to protect the joint.
  • Thumb Example:
    • A small grain of rice sometimes felt at the thumb could also be the same as the patella.
      • The tendon that exists within your thumb enalbes movements, so ossification has occurd to protect from friction.
    • A little bone is formed there to protect and stop that friction on a tendon, which is much weaker in nature.
  • Function: protect tendons and prevent friction and damage

Irregular Bones

  • Irregular in shape; do not fit into other classifications.
  • No obvious characteristics or commonality.
  • Example: Vertebrae of the vertebral column.
    • Each vertebra is unique.
    • Every single vertebrae is considered different.
    • So much so that all vertebraes could be laid out on a take piece by piece because of just how unique they are.