Alrighty, so we're going to be talking about the other parts of the hair. We discussed the cuticle in some detail in our last video and now we're going to be talking about the cortex. So the cortex of a hair is what gives hair its shape.
And you'll understand what I mean by that just a little bit more in a moment. The major other thing that the cortex does is it also provides hair with its color. So There's two major characteristics to that.
The first is melanin. Melanin are little pigment granules that give hair its color, and they come in two types. There's eumelanin, and the E is silent at the beginning, that are dark granules of melanin, and they're very smooth.
If you look at them under a microscope, they look kind of like little eggs, and those are the dark melanin. Then there is pheomelanin, and And pheomelanin is very light colored and the granules themselves are kind of irregularly shaped, sort of like jagged puzzle pieces. Those are the type of melanin that you would have more of in someone who is lighter haired or blonde. A combination of those two types of melanin are what allows us to arrive at all the different shades of hair that exist naturally in the world. Now, obviously, one is not limited to those colors that exist naturally.
in the world. Lots of people have hair color that is artificially enhanced. That affects the cortex, but it doesn't chemically change the melanin.
You can bleach it. You can essentially break it down, but as that hair regrows, it's always going to come back with that natural combination that that person was genetically coded for. Alrighty. Now, the other thing we have is is something called cortical fuci.
Cortical fuci are little air spaces that are in the cortex of the hair. They're usually found closer to the root, much more dense there, but they can be found throughout the hair shaft. And different people, different species, can have different densities of cortical fuci. Now let's take another look at that pigment.
So we already said the eumelanin are the smooth, dark granules, and the pheomelanin are the lighter, more irregular granules. So we have our dark and smooth eumelanin. Remember the E is silent.
And our light and irregular pheomelanin. And combinations of those are what give us black hair, brown hair, red hair, blonde hair, and all the colors in between. Now, the medulla is our next part of the hair.
Oh, going back. One other thing I wanted to say about the cortex. The cortex itself. is made of lots of parallel strands of keratin that come together almost like cables in a giant like cable wire that allow hair to have its strands The cortex is what makes up the bulk of the hair structure itself and I'm going to show you some images of that. The medulla is the center most structure of the hair.
and we sometimes refer to it as the core of the hair. It is a hollow airspace. It's completely hollow and you can't always see it. Oftentimes underneath the microscope it looks like a black line or a broken black line and that's because light refracts differently through an empty space than it does through something solid like the cortex or the cuticle of a hair. And the reason why light refracts differently is because it's not always the same.
that the medulla exists, evolutionarily speaking, is it provides insulation. If you have a tiny little animal that's covered in hair, it's more beneficial to them if there's a little bit of air trapped under that hair. And what's a better way to trap that air than to trap it inside the hair?
I liken this to double pane insulated windows. Most of our houses have windows that are made out of two panes of glass. and those two panes of glass have an air space between them.
Sometimes that space is filled with something like radon or argon. And that space limits the amount of heat that can translate from one side of the window to the other side, because there's that gap in between. Having a medulla in a hair essentially It serves the same purpose. It traps heat in that airspace and makes it harder for the cold to get into the center area of the body underneath that hair or for the heat to escape.
little animal on a cold day a lot of times they'll kind of puff themselves up this goes for little birds little smaller mammals even some animals do that to make themselves seem scarier or more imposing that helps to also try trap heat underneath the hair. In the case of birds, it's to trap heat underneath their feathers, and the central cores of their feathers are also hollow to help retain that heat. Now, the medulla comes in some different types, and you can tell this by looking. And I've given you some diagrams here of the different types of medullas, and now we're going to go through their names, and I'd like you to fill those into your notes as we're working through. So the first type is intermittent.
interrupted medulla. And that's what we see here. And you can see there the black areas here stand for the medulla.
There's these large spaces where there's no medulla. Next we have fragmented. In fragmented there's more medulla than not but there's still gaps.
Then we have something like this. This would be a continuous medulla. There are no large breaks in that medullary structure. And the next one we have here is something called stacked. It's where it almost looks like little packets of medulla packed on top of one another.
And our last one is absent. Sometimes we don't have a medulla at all and in that case our medulla isn't present. It's an absent medulla. Now, the medulla also has some patterns that can be seen within the medulla.
So we just did medulla types. Now we're going to look at medulla patterns. The first pattern is uniserial. It basically looks like a ladder.
where each of these little boxes would be the medulla, and you would see a break in between each little box. So it's uniserial, sometimes referred to as ladder. Our next one is multiserial. It's another ladder type, but in it, you see we have multiple ladders. Our next one is vacuolated.
Vacuolated is a very irregular looking shape to the medulla. Okay, this might have some round spots, some kind of squarish spots. Vacuolated.
Our next one is lateral. And in lattice, it looks like lots of round bubbles, kind of packed in with one another. Now sometimes people confuse multiserial with lattice.
Multiserial looks distinctly squared. those spaces lattice looks distinctly round and then we have a fifth type and this is amorphous and amorphous basically means that it's so irregular that the pattern cannot be described or there's it's a solid structure which means there's no pattern discernible within it already let's look at a couple of medullas and see if we can come up with the types and or the patterns. So here's the human medulla.
First let's think about the type. Now human medullas can be continuous, fragmented, or absent. What does this look like to you?
This one would be continuous. There are no breaks in it. It's not fragmented and it's definitely there, so it's not absent. Now, we're going to look at some hairs from some non-humanoid species.
This is from a rabbit. This is the medulla in a rabbit. And if you look, it takes up most of the space within the hair.
Now, medullas in the rabbit can look different depending on the type of hair. Rabbits have two colors. coats they have an outer coat and an inner coat the inner hairs are usually much finer much more fluffy and then you also have these guard hairs so on this top hair what type of medulla does this look like to you or what pattern what pattern does this look like to you Well, this one would be multiserial.
This would be a ladder type. The bottom would be uniserial. Looks like a single ladder. Here, this looks like multiple ladders.
Now, let's look at another one. These are hair. from a deer. What types of medullas or patterns of medullas do we see here?
Well, in both of these hairs, we have the same pattern type. They're both lattice. The medulla on the top is just thinner compared to the overall width of the hair than the one on the bottom. Okay, now that width of the medulla is going to be important to us.
And in light of that, we're going to discuss something called medullary index. So medullary index is a mathematical way that we can measure the medulla as a function of the width of the rest of the hair to determine what species that hair might have come from. So medullary index has a few rules. It's determined by measuring the diameter of the medulla within the hair and dividing it by the diameter of the hair itself. So if we were to look at medullary index and think of it as a mathematical formula, It would look something like this.
Medullary index equals diameter of the medulla divided by diameter of the hair. And you should jot that formula down in your notes pack in the box in the lower left. This is always given as a fraction. We generally don't write the medullary index as a decimal.
Now the medullary index for most human hairs is generally less than one third. which means the medulla is significantly smaller than the remainder of the hair, the rest of the hair. When you look at a hair from a human, the medulla looks quite thin. For animal hairs, it's generally considered that the medullary index is is greater than 1 half. So if you looked at an animal hair, such as this one, the medulla generally looks like it takes up more than half of the diameter of that hair.
This is one of the major measurements one uses to determine if a hair came from a human or if it came from some other species. The medullary index is a great indicator. So let's try a practice problem. If a hair is 200 micrometers wide, and the medulla is 50 micrometers wide, what is the medullary index? So we have a hair that's 200 micrometers wide and a medulla that is 50 micrometers wide.
What is the medullary index? So we would essentially have a situation where our medulla is 50 micrometers Our hair is 200 micrometers, which means that our medullary index would be one quarter. That means that this hair is what? Is it more likely to be from a human or is it more likely to be from an animal?
Well, if you said more likely to be from a human, you are absolutely correct. That's where we're going to leave off this lesson today. In our last lesson on hairs, we're going to talk about how hair shape is determined and some of the more functional uses of hair in forensic science. See you next time.