2. Hair Hair grows from a hair follicle The parts of a hair include the bulb, root, and shaft The bulb is an expansion at the end of the hair from which the rest of the hair grows The root of the hair is the part of the hair that is embedded in the skin The shaft of the hair is the part that can be seen

3. Hair (cont.) The shaft of the hair is made up of keratin and has 3 layers: Cuticle Cortex Medulla

4. The Cuticle Transparent, outermost layer that helps hold the medulla and cortex together Scale-like in appearance, the scales point away from the scalp

5. The Cortex Surrounds the medulla and consists of flattened cells It is the largest part of the hair shaft This layer contains the pigment (melanin) that gives hair its color

6. The Medulla The medulla is the central part of the hair and is made up of large cells separated by air spaces; it can be:

7. Medullary Index A ratio of the size of the medulla compared with the size of the entire hair MI = x/y where x is the medullary diameter and y is the total diameter

8. Medullary Index (cont.) In humans, the MI is less than 1/3 In animals, the MI is greater than ½

9. Pigmentation: Human vs. Animal Human hair tends to have more pigment toward the cuticle while animals have more pigment towards the medulla Animal pigments are often found in solid masses called ovoid bodies while human hairs are usually one color along the length Animal hairs can change color abruptly creating a banded pattern; humans do not have banded hair

10. Cuticle: Human vs. Animal Some mammals (i.e. rodents and bats), have scales that give the appearance of a stack of crowns; these are called coronal Some mammals (i.e. cats, seals, and minks), have scales that resemble petals; these are called spinous Humans have scales that are flattened and narrow; these are called imbricate

11. Types of Hair Scalp: has a uniform diameter in cross-section Beard: coarse, curved, and when viewed in cross- section has a distinctive triangular shape Eyebrow, nose, ear, and eyelid: shorter and stubbier than scalp hair and have wide medullas Axillary: have unevenly distributed pigments; end in a fine point when uncut Auxiliary: oval or triangular, depending on whether the body region has been regularly shaved Pubic: oval or triangular

12. Hair Growth Hair proceeds through 3 stages as it develops: Anagen stage: hair actively grows cells around the follicle rapidly divide and deposit materials in the hair 80-90% of hairs are in this stage Catagen stage: hair grows and changes 2% of hairs are in this stage

13. Hair Growth (cont.) Telogen stage: follicle becomes dormant hair easily lost during this stage 8-18% of hairs are in this stage

14. Hair Dyes Cause hair to have less pigment granules Hair dyes will color both the cortex and the cuticle so the cuticle’s inner margin is obscured or dark Because hair grows at a rate of 1.3 cm per month, it is possible to determine the amount of time that has passed since the hair was dyed

15. Forensic Hair Analysis When hair is found at a crime scene, forensic scientists use the medullary index to determine if the hair is human or animal If the hair is human, the part of the body from which it originated can be determined Because hair from one part of the body are not always the same (brown hair with some gray), 50 hairs are usually collected from the suspect’s head

16. Race Determination African: hairs are curly with densely packed, unevenly distributed pigment granules; medulla is discontinuous or absent European: often straight or wavy with pigment that is more evenly distributed; medulla is discontinuous or absent Asian: straight with continuous medulla and thick cuticle