The Skeleton

Overview of the Skeleton

• Two main parts of the skeleton:
  • Axial Skeleton: 80 bones
  • Comprised of:
    • Skull
    • Rib cage
    • Vertebral column
  • Appendicular Skeleton: 126 bones
  • Comprised of:
    • Pectoral girdles: Clavicle (2), Scapula (2)
    • Upper limbs: Humerus (2), Radius (2), Ulna (2), Carpal bones (16), Metacarpals (10), Phalanges (28)
    • Pelvic girdle: Hip bone (2)
    • Lower limbs: Femur (2), Patella (2), Tibia (2), Fibula (2), Tarsal bones (14), Metatarsals (10), Phalanges (28)

Total Bone Count

• Total number of bones in the human skeleton: 206 bones
  • Axial Skeleton: 80 bones
  • Appendicular Skeleton: 126 bones

Functions of the Skeletal System

• Five Primary Functions:
  1. Support: Provides structure and shape to the body
  2. Storage:
  • Minerals (calcium)
  • Lipids (yellow marrow)
  1. Blood Cell Production:
  • Occurs in red marrow
  1. Protection:
  • Protects vital organs
  1. Leverage:
  • Aids in force of motion

Components of the Skeletal System

• Composed of:
  • Bones
  • Cartilages
  • Ligaments
• Types of Cartilage Found in the Body:
  • Cartilage in the External Ear
  • Intervertebral Discs
  • Pubic Symphysis
  • Meniscus: Padlike cartilage in knee joint
  • Articular Cartilage of Joints: Found at joints
  • Costal Cartilage: Connects ribs to the sternum
  • Cartilages in the Nose
  • Thyroid Cartilage
  • Cricoid Cartilage
  • Trachea
  • Lungs

Types of Cartilage

• Three Main Types:
  1. Hyaline Cartilage:
  • Most common type
  • Provides stiff but somewhat flexible support
  • Reduces friction between bones
  • Locations: Ends of bones at joints, trachea, costal cartilages
  1. Fibrous Cartilage:
  • Resists compression and provides padding between bones
  • Limits movement
  • Locations: Intervertebral discs, pubic symphysis (looses during childbirth), menisci of knees
  1. Elastic Cartilage:
  • Provides support while tolerating distortion
  • Locations: Ear, epiglottis

Categories of Bones

• Six Shape Categories:
  1. Sutural (Wormian) Bones:
  • Small, flat, oddly shaped
  • Found between flat bones of the skull
  1. Flat Bones:
  • Thin, parallel surfaces
  • Provide protection and a large surface area for muscle attachment
  • Examples: Roof of the skull, sternum, ribs, scapula
  1. Irregular Bones:
  • Complex shapes
  • Examples: Vertebrae, hip bones, mandible, maxilla, other skull bones
  1. Long Bones:
  • Relatively long and slender
  • Act as levers for skeletal muscles
  • Examples: Humerus, radius, femur, tibia
  1. Short Bones:
  • Boxlike in appearance
  • Examples: Tarsals, carpals
  1. Sesamoid Bones:
  • Usually small, round, and flat
  • Example: Patella (kneecap)
  • Sometimes found in joints of the hands and feet

Bone Structure

• Two Types of Bone:
  • Compact Bone:
  • Dense and forms the outer layer of bones
  • Provides strength and support
  • Spongy Bone:
  • Lighter and made up of trabeculae
  • Contains red marrow

Bone Anatomy

• Regions of Bone:
  • Epiphysis: Ends of the bone
  • Diaphysis (Shaft): Long central part of the bone
  • Metaphysis: Region between the epiphysis and diaphysis
  • Medullary Cavity: Contains yellow marrow
• Histological Features:
  • Osteons: Structural units of compact bone
  • Lacunae: Spaces containing osteocytes
  • Canaliculi: Tiny canals connecting lacunae
  • Central Canal: Contains blood vessels and nerves

Cellular Composition of Bone

• Four Types of Bone Cells:
  1. Osteogenic Cells:
  • Stem cells that differentiate into osteoblasts
  • Important for bone growth and repair
  1. Osteoblasts:
  • Secrete osteoid matrix around themselves
  • Do not divide
  • When matrix calcifies, become osteocytes
  1. Osteocytes:
  • Mature bone cells
  • Maintain bone tissue and respond to mechanical stresses
  1. Osteoclasts:
  • Derived from macrophages
  • Function: Resorb bone tissue by dissolving calcium matrix and digesting collagen
  • Important in bone remodeling and increasing blood calcium levels

Bone Markings

• Elevations and Projections:

  • Process: Projection or bump
  • Ramus: Extension forming an angle with the rest

• Openings:

  • Sinus: Chamber filled with air
  • Foramen: Rounded passageway for blood vessels/nerves
  • Fissure: Deep furrow, cleft, or slit
  • Meatus: Opening of a canal
  • Canal: Duct or channel

• Depressions:

  • Sulcus: Narrow groove
  • Fossa: Shallow depression

• Processes for Joints:

  • Head: Expanded end of an epiphysis
  • Neck: Connection between epiphysis and diaphysis
  • Facet: Small flat articular surface
  • Condyle: Smooth rounded articular process
  • Trochlea: Smooth, grooved articular process

• Processes for Muscle Attachments:

  • Trochanter: Large rough projection
  • Crest: Prominent ridge
  • Spine: Pointed process
  • Line: Low ridge
  • Tubercle: Small, rounded projection
  • Tuberosity: Rough projection

Practice and Key to Bones

• Practice Component:

  • Suggestion to print bone names for practice
  • Utilization of plastic protector and Expo marker for interaction

• Key to Major Bones:

  • Cranium
  • Cervical Vertebrae
  • Mandible
  • Vertebrae: Thoracic, Lumbar
  • Sacrum, Coccyx
  • Clavicle, Scapula
  • Sternum, Ribs
  • Humerus, Ulna, Radius
  • Hip Bone/Coxal Bone
  • Carpals, Metacarpals, Phalanges
  • Femur, Patella, Tibia, Fibula
  • Tarsals, Metatarsals, Phalanges