Date: January 28, 2000

Grade Level(s): 9

Subject(s):

• Health/Body Systems and senses

Duration: two 45-50 minute class sessions

Description: This lesson gives an overview to the parts of the skin, functions of the skin, characteristics of the skin, and includes some fun activities for better understanding of the skin.

Goals: Students will demonstrate an understanding of:

1. the importance of the sense of touch.
2. the role that the skin plays in enabling us to touch.

• describe the process that actually gives us the sense of touch
• locate where the major sensory receptors are found in the skin
• identify main parts of a cross sectional piece of skin
• describe some of the changes that skin goes through
• explain from our experiment how the senses work together in order to help us function properly

• computer with LCD
• paper bags
• note cards with several different objects glued to each
• cotton balls soaked in rubbing alcohol
• weak dishwashing liquid
• a few droppers

a) Gaining Attention

A touching story: It is a warm day, I can really feel the heat on my face when I turn it up to the sky. As I walk along the soles of my bare feet are feeling something hard, hot and ridged. I turn and go down steps which feel the same, I hold onto the rail which also feels hot, hard and ridged against my palm. At the bottom of the steps my feet land on a soft surface which gives way with each step I take. After walking for a few minutes the ground feels hard and soon my feet are wet, air is gently blowing on all of my body. With each step my legs are getting wetter. I stop walking when I feel my knees getting wet. I turn around, see a friend in the distance and walk towards her. My foot comes down on something squishy and slimy in the water - Yuck! I run back to the beginning, up the steps and don't stop until my feet feel that hard ridged surface again. Where have I been?

This story is filled with many descriptive words, and they all describe things that you feel.
Our sense of touch is very important, and we usually take it for granted. But as you can tell from this story, we use our sense of touch all the time!
Today we are going to talk about skin, the sense organ of touch, the actual sense of touch and how it works, and we will do an experiment to test your sense of touch.

b) Introduction to the skin

A layer of skin, usually only about 5 mm thick, is the only protection that the insides of our body have against the harsh environment all around us.
We rarely even think about our skin until something happens to it, such as a cut or a burn.
The skin really doesn't seem too complicated just to look at it, and for years that's what people thought.
It wasn't until the invention of the microscope in the 17th century that we began to understand just how complex the skin really is.
When we took our first close up look at the skin, we found that it looked something like this (Show computerized image of a cross section of skin).
The outermost layer of the skin is called the epidermis.  It is waterproof.  It is made up of dead cells.
These cells at the surface of the skin are dead because cells in the lower part of the epidermis are constantly multiplying, pushing cells upward as more are made.
As the cells climb to the surface, they are gradually becoming filled with a tough, fibrous substance called keratin.
Keratin is also found in fingernails and hair
By the time cells reach the surface, they are hard, flat, and dead, and they wear away very easily
Does anyone have any idea how many skin cells we lose every minute?
We lose between 30,000 and 40,000 skin cells every minute
Your skin does not wear away because it is constantly renewing itself
Another interesting fact: We lose up to 9 lb. of skin cells every year.
Beneath the epidermis is another layer called the dermis, and this layer is much thicker than the epidermis
In this layer we find blood vessels, nerves, hair roots, oil glands, and sweat glands
Let's stop for a moment and talk about hair roots in the skin. What happens to the hairs on your arms and on the back of your neck when you are watching a scary movie?
Tiny muscles at the roots of your hairs all flex at once, and cause you to feel all prickly.
The lowest layer of the skin is made up mostly of fat.
This helps to keep us warm, and also acts as padding when we bump into something
After all of this we can summarize 4 main functions of the skin:

1) It protects us from harmful aspects of the environment, keeping out things such as bacteria
2) It keeps the water in your body from drying up

-The waterproof epidermis
-The oil glands in the dermis produce oils that help keep the skin moist

3) It regulates the temperature of your body

-Layers of fat help keep you warm
-Sweat glands let the body give off moisture through the skin, which helps to cool you off

4) The last function, which we will talk about next, is that skin is the sense organ of touch

c) Lesson Focus - The Sense of Touch

Your sense of touch allows you to feel light sensations, such as a bug landing on your skin, as well as heavy sensations, like when you drop something on your foot.
The sensation of touch comes from millions of microscopic sensory receptors located all over your skin
These receptors are located at all different levels within your skin, and they are distributed unevenly
In some places, such as your fingertips, these receptors are very close together, making your fingertip very sensitive. In some places, the receptors are very far apart.
When the receptors are stimulated in some way, they generate nerve signals that flash to the brain
Your brain assembles an overall "touch picture" from these nerve signals, and you might describe certain aspects of this "touch picture" with words such as hot or cold, dry or moist, smooth or rough (Computer image: sensory receptors).
You can see where the receptors are located
These receptors fall into 3 main groups:

1. Touch and Pressure receptors both detect movement or pressure
2. Cold and Heat receptors respond to temperature changes
3. Pain receptors detect many kinds of stimuli, and are placed in their own group

d) Lesson Activity - The Experiment

Now that we've talked a little bit about how your sense of touch works, we are going to do a little activity to test your sense of touch
I have with me today several paper bags, each containing some mysterious substance.
None of these things are out of the ordinary, you probably see and feel them every day.
Your job is to identify some of these unknown substances.
It sounds easy, right? The trick is, you cannot peak into the bag, and you cannot smell the bag; that would give it away.
Some of these things may feel somewhat alike, so you have to be careful.
Think about exactly what it is you are feeling.

Is it hot, cold, or neither?
Is it smooth or rough?
Is it made up of many pieces?
How do your fingers feel after you touch it?

Which objects gave you the most trouble?
What characteristics made these more difficult to identify?
Who seemed to have the best sense of touch in your group?

e) Closure: Other Skin Characteristics

Finally we come back to look at some other interesting characteristics of the skin (Transparency of characteristics of skin).
Many parts of the body change and adapt, depending on how much they are used (When you exercise your muscles, they get bigger).
Skin also adapts to the demands made on it
Some patches of skin become tougher and thicker when they are exposed to great wear and tear
These tough patches are called calluses
Many people develop these on their hands when they constantly work with their hands
You may get these on your feet if you aren't too fond of wearing shoes in the summer (Show picture on computer of calluses)
These calluses develop to protect the parts underneath them
The color of the skin also adapts to changing conditions
If you are out in the sun a lot, your skin becomes darker to help filter out the sun's ultraviolet rays
Too much sun causes sunburn, which is harmful
You can see how skin changes in response to changes in light if you've worn a band aid for a few days
Just as skin becomes darker when it is exposed to more light, it becomes lighter when exposed to less light
Whenever you remove the band aid, you are left with a strip of lighter skin
Everyone's skin texture is unique
Some people have smoother or rougher skin than others
As we get older, our skin becomes less supple, and more lined
This is because fibers in the dermis shrink and become less flexible
Everyone pinch a small section of skin on the back of you hand, don't pinch too hard!
Hold for about 30 seconds and let go
What happens?
How do you think your skin would respond to this test as you get older?
The last characteristic of the skin we are going to talk about is the sebum layer
Sebaceous glands are the glands in the skin that produce oil to help keep the skin moist
This oily substance is called sebum
To really understand the role of the sebum layer, let's see what happens when we remove it
Pair students up
Give each pair of students a cotton ball soaked in rubbing alcohol, and a small cup of weak dishwashing liquid in water, and a dropper
Have one student be the tester, and one be the test subject
The tester wipes the palm of one hand of the test subject with the cotton ball soaked in rubbing alcohol
This removes the sebum layer on this hand
Next the tester places a few drops of the weak dishwashing liquid on the palm that was wiped, and then on the palm that was not
What happens?
The palm that was wiped has lost its waterproof characteristic. The liquid is absorbed into the skin
The sebum layer is still present on the unwiped palm, so the drops stay rounded on the palm. They do not soak in
What happens after you soak in the bathtub or swimming pool for a long time?
What causes this?

Assessment:

f) Conclusion- Review

Lets wrap up with a quick review -What is the uppermost layer of skin called?
Bring up cross section of skin on computer

What is significant about this layer?
What will you find in the dermis?
What is the substance called that makes cells hard, and causes them to wear away easily?
What is the lowest layer of the skin called?
What is the purpose of this layer?
What are the 4 main functions of the skin?
Where does the sensation of touch come from?
What are the 3 main groups of sensory receptors?

What are the tough patches of skin called that form when skin is exposed to great wear and tear?
Why does your skin become darker when it is exposed to a lot of sunlight?
What happens to your skin as you get older?
What is the name of the gland that produces the oil to help keep your skin moist?
What happened to your skin when it was wiped with the rubbing alcohol?