Unit Study: "I Can't Hair You!"
- Wednesday, October 12, 2005
"Hair helps me hear? What did you say? I can't hair you!"
I said, "Hair helps you hear." It is the hair inside your ears that relays sounds to your brain. Don't believe it? Well, let's find out. Let's start from the beginning. For this study you will need a project notebook, drawing paper and pencils, and books about the ear. So start with a trip to the library. Find books about ears and hearing. Look particularly for one on the subject of deafness.
Your ears have three main parts: the outer ear, the middle ear and the inner ear. We will study each of these parts and their role in the marvelous process of hearing. Divide your study and notebook into three sections.
Part I. The Outer Ear
The outer ear part called the auricle is the part we all see, the fleshy curved part of the ear outside of the head. It has no bones but is supported by cartilage. Define cartilage. Find cartilage in a chicken and examine it.
A study of the three muscles that attach the ear to the head will teach us a difference in the function of the ears of humans as opposed to some animals that use the muscles to turn their ears in the direction of sound. Why is this important? What does it tell us about the human sense of hearing? Why is the human ear shaped as it is?
The ear canal or external auditory canal is the second part of the outer ear and is the opening and passageway that leads to the eardrum. It is about one inch long and has hairs, sweat glands and glands that produce earwax. How does earwax help protect your ears? Is it good or bad? When can it be harmful? Write a short lesson for kindergarten students about how to protect their ears. Use the line; "Never stick anything smaller than your elbow into your ear." How should a child clean his ears? Younger students make an ear safety poster.
Part II. The Middle Ear
The tympanic membrane or eardrum separates the outer ear from the middle ear. It is a thin, round, tightly stretched membrane about 10 mm in diameter. What purpose does the eardrum serve besides this separation? Is it flexible? Does sound bounce off of the eardrum? Is it like a drum in function? What happens when a person's eardrum is punctured? How about if the eardrum ruptures due to infection? Would a rupture cause deafness?
The three smallest bones in the human body, the auditory ossicles, are in the middle ear. Draw sketches of them and label them with the Latin names, (malleus, incus and stapes) and the common names, (hammer, anvil and stirrup). How big is the stapes? Why are the bones so named? The hardest bone in the human body, the temporal bone, is also located in the ear. What is the temporal bone for?
The Eustachian tube connects the ear to the throat. What is the purpose of this tube? How does it help us with air pressure changes? When does it open and close? Draw these ear parts in your notebook and label them using colored pencils to differentiate the parts easily. There are two "windows" in the middle ear. Draw them. What are their functions?
Part III. The Inner Ear
The inner ear is called the labyrinth and has three basic parts, the vestibule, the semicircular canals and the cochlea. Two baglike sacs called the utricle and the saccule are found in the vestibule and each is lined with hair cells. Hair cells are specialized sense cells with tiny hairlike projections. These cells attach to nerve fibers. Remember, I mentioned earlier that hair that helps you hear! A membrane above the hair cells is embedded with mineral grains called otoliths.
The semicircular canals are called lateral, superior and posterior canals. Each duct widens and forms a pouch called the ampulla which has hair cells that are attached to nerve fibers. The canals and the utricle and saccule make up the ear's organs of balance.
The cochlea is the part of the inner ear that is coiled and shaped like a snail shell. It is about the size of a pea, but if it were uncoiled, the cochlea would be a little more than 1 1/2 inches long. Three fluid-filled ducts wind through the cochlea. One of these ducts is the cochlear duct and one wall of it is the basilar membrane which is covered with 15,000 hair cells. The hair cells are the organ of corti, which is the actual organ of hearing. The tectorial membrane is above the cells. The inner ear nerve known as the auditory nerve is made up of two branches--the cochlear nerve and the vestibular nerve.
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