Intro to Human Skeleton - Lecture 2

Intro to the Human Skeleton

Overview

  • The lecture delves into the human skeleton, progressing from gross anatomy (visible physical features) to the microscopic level (cells involved in bone remodeling).
  • The skeletal system is relatively uncommon in nature, with only about 10% of species having an internal skeleton.
  • The human skeleton is a living system covered with muscle and tissue, essential for life, with a variety of functions.

Skeletal Structure

  • Axial Skeleton: Includes the skull, vertebral column (spine), ribs, sternum (chest plate), and sacrum (bony plate at the back of the bum).
    • Contains approximately 80 bones in the adult human.
  • Appendicular Skeleton: Includes bones in the arms and legs.
    • Comprises the girdles (shoulder and pelvic) that attach the limbs to the axial body, along with the bones within the limbs.
    • Shoulder girdle: clavicle (collarbone) and scapula (shoulder blade).
    • Pelvic girdle: hip bones.
    • Includes the femur, tibia, fibula, and bones of the foot.
    • Contains approximately 126 bones in the adult human.

Regional Terms

  • Axial Body: Head, neck, torso, and abdominal region down to the sacrum.
  • Appendicular Body: Upper limbs (arms) and lower limbs (legs) that extend from the trunk.
  • Examples of regional terms:
    • Cephalic: Head
    • Axillary: Armpit
    • Cervical: Neck
    • Pelvic: Pelvis
    • Brachial: Arm

Bone Count

  • At birth, humans have around 270 bones.
  • In adulthood, the number reduces to 206 (80 in the axial skeleton and 126 in the appendicular skeleton).

Ossification Centers

  • Primary Ossification Centers: The first area where bone formation (ossification) occurs during development.
  • Secondary Ossification Centers: The second area where bone formation occurs, contributing to the final bone structure.
  • The higher number of bones in babies occurs because some bones are not yet fused.
  • Bones grow via primary and secondary ossification centers and eventually fuse together.
  • For example, a child's pelvis has spaces between bones that fuse in adulthood.
  • The femur in a young child may appear as three separate bones due to ossification centers, but these fuse into one bone in adults.