Hair Structure & Characteristics

Focus on characteristics that differentiate human hair from non-human hair, and how these features assist in forensic analysis.
Easy distinction between human and non-human hair due to specific morphological structures.

Hair consists of three main parts: - Cuticle: Outermost layer, translucent, contains scales that cover the hair shaft. - Cortex: Middle layer, contains keratin and melanin, responsible for pigmentation. - Medulla: Innermost layer, may vary in presence and structure among species.
Hair is primarily made up of cornified dead cells that solidify and keratinize as they grow out of hair follicles.

Color Banding: - Non-human hair, such as raccoon hair, shows distinct color bands (e.g., four color bands on a raccoon tail). - Human hair generally displays consistent pigmentation or specific transitions when dyed.
Medulla Structure: - Human hair often has an amorphous medulla that lacks a defined structure. - Animal hair typically features a well-defined, regular medulla.
Root Shape: - Human hair roots are generally club-shaped. - Non-human hair roots can be classified into various shapes, including: - Club shaped - Wine glass shaped - Spade shaped - Not distinct

Three regions of hair shaft: - Proximal Region: Near the root. - Distal Region: Towards the tip. - Medial Region: Mid-section of the hair.
Significance of examining scale and medullary structures in forensic evaluations.

Cuticle Definition: - The cuticle is the outer layer featuring scales that help identify hair direction (scales point from proximal to distal).
Scale Patterns: - Important for species identification; three types of cuticular scales: - Coronal: Crown-shaped, encircles the shaft, found in small mammals (not in humans). - Spinous: Triangular, petal-like, found in animals like mink (not in humans). - Imbricate: Flattened, overlapping scales, commonly found in human hair and various animals.
Variability in Scale Patterns: - May change along the hair shaft and differ amongst hair samples from different body regions or species. - Examples include: - Diamond petal: Overlapping pattern with a diamond shape. - Double Chevrons: V-shaped patterns with crests and troughs. - Irregular Mosaic: Non-uniform sizes and shapes of scales.

Cortex Composition: - Main body of hair consisting of spindle-shaped cells. - Contains various structures: - Cortical Fusi: Irregular air spaces primarily near the root. - Pigment Granules: Dark structures varying in size and color; found more towards the cuticle in humans. - Ovoid Bodies: Larger structures, consistent in size with regular margins; abundant in certain animals.

Medulla Structure: - Central core, can be absent or vary in appearance. - Under transmitted light, can appear black/opaque; under reflected light, can be white.
Human vs. Animal Medulla: - Human medulla is usually amorphous; animal medullas tend to be regular and clearly defined.
Observation of Medulla: - Composition may include discrete cells or an amorphous spongy mass. - Medullae in mammal hairs are typically continuous and occupy over one-third of hair diameter.

Human Hair Roots: Commonly club-shaped (bulbous).
Animal Hair Roots: Can vary widely; examples include: - Wine Glass Shaped: Broad at the top, narrowing at the bottom. - Spade Shaped: Curved on one side. - Not Distinct: Indeterminate shapes.
Root Characteristics: - Medulla may extend into the root area; frayed fibrils may be present. - Examples of species with distinctive root shapes: - Cats: Frayed fibrils present. - Cows: Medulla extends into the root area. - Horses: Features elongated or indistinct roots.

Unique Traits: - Cervid hair is distinct in that it bends and retains a teepee shape upon compression. - Raccoon and red fox hair typically bend into loops, not retaining shapes as seen in cervid hair.

The variations in hair morphology are critical for forensic identification and species determination. Understanding these characteristics enables forensic scientists to utilize hair samples effectively in investigations.