INTERNAL HUMAN ANATOMY

What is so special about hair to the criminalists? In this article, I will discuss the anatomy of human hair and what part of hair is the focus of a forensic investigation.

Hair grows out of the skin from a hole containing highly specialized cells called the follicle. There are three things that make up the shaft of human hair. The forensic scientist can use any of these three things to find a match between hair taken from the victim and unknown hair taken from the back seat of a car. The makeup of hair resembles that of a yellow No. 2 pencil that you used in school. From inside out, the medulla would be the lead, the cortex would be the wood, and the cuticle would be the yellow paint on the outside of the pencil.

• Medulla: The central part of the hair is called the medulla which contains a slew of cells but looks as though it is an empty or mud-filled central tube. The internal diameter of the "tube" with regard to the overall diameter of the hair is referred to as the medullary index. In human beings, the medullary index is measured out to be 0.3. What this means is that the medulla makes up 30% of the total diameter of the hair. In animals the medullary index is a bit larger than 0.5. If forensic scientists determine that hair found in the back seat of a car has a medullary index greater than 0.5, they can conclude that the hair is not human in origin. Another thing in the medulla that forensic scientists look for is whether the medulla looks solid and continuous, or fragmented. Such characteristics can help the scientist determine the species of origin. There are databases of hair types from various animals that help criminalists arrive at a match.
• Cortex: External to the medulla is the cortex. It is the largest part of the shaft and is the part that contains pigment, the substance that gives hair its color. Pigment particles display a wide range of colors, shapes, and distribution patterns. All of these characteristics help forensic scientists determine race, match unknown to known hair, and identify origin of hair. On the microscopic scale, forensic scientists take advantage of the pattern of air pockets and structures within the cortex to arrive at a match.
• Cuticle: The cuticle refers to the layer of cells that cover the external surface of the shaft and resemble scales on a fish or maybe tiles on a roof. Forensic scientists take advantage of the patterns found in the cuticle to determine if hair is human and whether or not there is a match between this hair to another.

Small hairs can not escape the prying eyes of an expert forensic scientist. Finding a consistent pattern between unknown and known hair can bring crime scene investigators one step closer to solving a crime.

The next time you watch your favorite CSI TV show, you will have a better understanding of why hair is important in a criminal investigation.