Hair Structure and Characteristics

Cortex

• Function:
  • Gives hair its shape.
  • Provides hair with its color.
• Melanin:
  • Pigment granules that give hair its color.
  • Types of Melanin:
    • Eumelanin: Dark, smooth granules, egg-like shape.
    • Pheomelanin: Light, irregular granules, jagged puzzle-like shape.
  • Combination of eumelanin and pheomelanin results in natural hair shades.
  • Artificial hair color affects cortex but doesn't chemically change melanin.

Cortical Fuci

• Little air spaces within the cortex of hair.
• Found denser near the root but can be throughout the hair shaft.

Medulla

• Structure:
  • Core of the hair, a hollow airspace.
  • Provides insulation by trapping air, similar to double-pane windows.
• Types of Medulla:
  • Intermittent/Interrupted: Large spaces with no medulla.
  • Fragmented: More medulla than not, but still gaps.
  • Continuous: No breaks in the medullary structure.
  • Stacked: Looks like packets of medulla stacked on top of each other.
  • Absent: No medulla present.
• Patterns of Medulla:
  • Uniserial: Ladder-like with breaks between boxes.
  • Multiserial: Multiple ladder types.
  • Vacuolated: Irregular shape with round and square spots.
  • Lattice: Looks like round bubbles packed together.
  • Amorphous: Irregular, patternless, or solid structure.

Medullary Index

• Definition:
  • A measurement determining the medulla's proportion in the hair's diameter.
  • Formula: Medullary Index = Diameter of Medulla / Diameter of Hair
  • Index is a fraction, not a decimal.
• Values:
  • Human hair: Medullary index < 1/3.
  • Animal hair: Medullary index > 1/2.
• Example Calculation:
  • Hair width = 200 micrometers, Medulla = 50 micrometers.
  • Medullary Index = 50/200 = 1/4.
  • Likely to be from a human due to lower index.

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This lesson focused on the structure and properties of the cortex and medulla in hair. Next lesson will cover hair shape determination and forensic applications.