Marisa A. Ferrarese
The Eye and the Sense of Sight
Eye sight is usually considered the most important sense, "according to one estimate, four fifths of everything we know reaches our brain through our eyes."12 In order to understand how the eye functions, it is important to be aware of the structure. Looking at the external eye, students are able to see three parts of a person's eye. The sclera, which is the white part of the eye or the outer layer of the eyeball made of tough, white, fibrous tissue that keeps the shape of the eye. The iris, which is the colored part of the eye made up of strong muscle and the pupil, the black part or hole in the middle of iris. The cornea is also on the external portion of the eye, because it is the transparent covering protecting the eye it cannot be seen. The cornea is a continuation of the sclera, but transparent so light can pass through.
The internal section of the eye contains the lens directly behind the iris. The multilayered lens is also transparent. Inside the sclera is the choroid, which is a thin, dark red layer containing blood vessels that nourishes the eye. Inside the choroids is the retina which contains light detecting cells. When going to the doctors for a physical or check up, the doctor has used an ophthalmoscope, an instrument used to view the retina.
Connecting the eye to the brain is the optic nerve, which transmits electrical impulses from the retina to the brain. Because the beginning of the optic nerve is located on the retina, it creates a blind spot in our vision. Students can view this blind spot through a simple activity.
Blind Spot Activity
http://www.exploratorium.edu/snacks/blind_spot.html
There are two fluid filled transparent sections of the eye that are separated by the lens. The smaller of the two is the aqueous humor which is a water like substance between the cornea and the lens. The vitreous humor, which is larger, is a gel-like material between the lens and the retina that helps the eye retain its shape.
In order to see, light must be reflected off an object (hence we cannot see in the dark) and pass through the cornea. The iris adjusts around the pupil to let in the appropriate amount of light. The light passes through the convex lens bringing the light together at a focal point. This focuses the image on the retina upside down. The image is transmitted to the brain for interpretation in the correct manner by way of the optic nerve.
Before exiting the eye through the optic nerve the image is displayed on the retina. The retina senses light using either rod or cone cells. The 125 million rods are named for their rod like shape. Rods have poor visual acuity but high dark sensitivity, specifically identify shades of gray and working well in dim light. Cones work in bright light identifying color and detail. There are approximately seven million cones in each eye and they are named for their more cone like shape.
There are striking similarities between an eye and a camera. Like the human eye lid a camera's shutter opens to take a picture. While a camera has no cornea, light must also pass through a lens. The diaphragm, like the iris, controls the amount of light entering the camera. Because the lens of a camera is also convex, the image is brought to a focal point and released upside down on the film. In a camera we move the lens to bring the image to focus, but in the eye we change the shape of the lens. Through chemical change the image remains on the film.
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Light
How does light help us see? Light travels as a wave. Imagine a sink filled with water. If a stone is dropped in still water, waves travel across the water from that spot. Unlike the waves in the water, light can travel through a vacuum, that is, it can travel without matter. These waves have four main parts. The crest is the highest point of a wave and the trough is the lowest point of a wave. The wavelength is the distance between the two crests or troughs and the amplitude is the height of the wave from it resting point to either the crest or the trough. Laying a slinky on the floor and waving it is a good way to simulate the movement and identify the parts of a wave. This can also be used when discussing sound waves.13
Light can be reflected, refracted or absorbed and these processes effect the way an image is viewed. Reflection occurs when light is replicated off an object. For example, when light hits the chalkboard some of the light is absorbed and yet some is reflected. The reflected light travels outward being perceived by the eye. The eye processes the image, sends the message to the brain, allowing us to see the chalkboard. The frequency will determine the color of the chalkboard.
Understanding how colored is viewed is an abstract concept for students to understand. Explanation will be necessary, as well as possible comparison to a rainbow. Using a rainbow as a platform to address color will help students understand the fundamentals of color. When light from the sun is passed through water droplets a natural prism is created. The rainbow is created by refracted or bent white light. When light passes from air to water it changes speed, causing the light to refract. Like a rainbow, when light passes through a prism "the different colors are refracted in different amounts, so the colors spread out…".13 When light hits the earth it radiates at different wavelengths. These different wavelengths form the various colors and hues we see. These different light wavelengths activate different combinations of rods and cones in the retina causes an electrical impulse to the brain to interpret the color.
Some objects we see also reflect an image. What items do we often look in to see our reflection? A flat mirror reflects light back to the eye the same size and shape it is received, allowing us to see an opposite image. The shape of a mirror can effect the image we see. For example, a concave mirror makes a mirror look smaller while a convex mirror makes an image look larger.
Scientific Imaging
Clear and accurate labeled and unlabeled schematic diagrams of the eye.
http://www.nei.nih.gov/health/eyediagram/index.asp
An image of a retina as seen through an ophthalmoscope.
http://webvision.med.utah.edu/sretina.html
Color blind tests and optical illusions that can be used for the section on vision
http://www.schools.net.au/edu/lesson_ideas/optics/optics_actsht1_p1.html
Art Connections
"Regular Division of the Plane with Birds", "Relativity", and "Circle Limit IV", MC Escher
http://www.mcescher.com
Student Art Connections
Students will diagram an eye and a camera and compare and contrast their structure and function.
The Ear and the Sense of Hearing
Sound is a pressure wave that is transmitted through the air and is received by the ear. Unlike a light wave, sound waves need matter in which to travel. A sound is produced by a vibration or back and forth motion of molecules. Molecules push together causing compressions. The distance from one compression to the next is what causes a wavelength. A high sound or pitch is produced when there is a high frequency, that is, there are many waves per second, while a low sound or pitch is produced when there are few waves per second. For example, a flute, a high pitched instrument can have up to 2000 hertz or waves per second. A tuba, a low pitched instrument can only have up to 350 hertz or waves per second. Different frequency tuning forks or instruments can also be used to listen and compare frequencies.13
In order to truly comprehend how one hears it is important to understand the ear's structure. There are three parts to the human ear: The outer ear, the middle ear, and the inner ear. The outer ear begins with the pinna, which is the cartilage filled fleshy part that is outside the head. The pinna's shape captures the carrying sound. Next is the ear canal, which is a long passageway to the middle ear. (Students love to learn that this is where ear wax is produced.) This is also where the doctor will use the otoscope to see the first part of the middle ear which is the ear drum or tympanic membrane. The sound will cause the ear drum to vibrate hitting the first of the three smallest bones in the human body, the hammer. The hammer vibrates hitting the anvil, and then the anvil causes a vibration of the stirrup. These three bones connect to the oval window which is the ending point of the middle ear. The inner ear contains the cochlea, which is a snail shaped canals filled with liquid. The sound travels from the cochlea to the auditory nerve which then passes to the brain. The semicircular canals, also filled with fluid, are used for balance. The eustachian tube, which connects the throat to the middle ear is used for transferring air.
What we hear can be effected by transmission, absorption, and the reflection of sound waves. Imagine a student yelling from outside the classroom door. Some of the sound will be transmitted through the door, some sound will be absorbed by the door, and some sound will be reflected off the door. The material of which the door is made from can and will effect how the sound is heard.
As stated above in order for sound waves to be perceived they need material to transmit through. The object or material that sound waves travel through can greatly effect how the sound is heard. Cold air slows the frequency of sound waves, while hot air speeds it up. Sound travels slower through wood and copper, than in glass and brick. Students can compare how sound changes depending on the material by taping their finger on their desk and listening to the sound, then tapping their finger on their desk with their ear on their desk. Again, students can use a glass or a plastic cup and put their ear on the cup to observe and compare the differences in sound based upon the material.13
As sound waves transmit through materials they are also absorbed by the molecules within the material. Sound is absorbed by all materials, even air. For example, thunder is heard louder the closer it is because the farther it is away, the more of the sound that is absorbed by the air. Sound absorption may seem as an abstract concept to students but have them consider the sound differences between a crowded restaurant and a crowded cafeteria. A restaurant is generally quieter because it is made with or filled with sound absorbing materials. Soft cloth materials, plants, specific types of plaster, and banners or flags all absorb sound. Generally these are absent from a school cafeteria.
Sound is reflected by hard, non-porous materials such as metal, wood, and concrete, such as a mirror reflects light. In a small room reflected sound may cause reverberation. As the sound reflects off the hard material, a garbled repeat sound is emitted. This can be damaging in an auditorium for a theatrical performance. However, engineers often us it to their advantage to trap noises from a highway to eliminate sound from traveling to neighboring houses. In a large area, reflected sound can cause one to hear an echo.
Art Connections
"Hearing", Jan Bruegel the Elder, 1617
"Cochlea Surrounded by Waves II", Julie Newdoll
"Self Portrait with Bandaged Ear", Vincent Van Gogh, 1889
The Tongue and the Sense of Taste
Students will begin this sense by observing their tongue in the mirror and identifying the tiny little bumps called papillae. While papillae look virtually identical, the round collection of receptor cells actually differs. Most, but not all papillae contain taste buds. It is possible that papillae can contain up to 200 taste buds, with the largest on the rear of the tongue. While there are approximately 9000 taste buds on your tongue, in order for a person to actually interpret taste, food must mix with saliva. Food breaks down and mixes with saliva allowing the taste buds to determine the flavor.
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Located on different parts of the tongue there are four main taste sensations which can actually be tasted without the assistance of the sense of smell. The sweet region is mainly located on the tip of the tongue and two salty regions on either side. Two sour regions are located in the rear sides of the tongue with one bitter region on the rear of the tongue. Few solitary taste buds are located in the middle region of the tongue.
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If taste buds are looked at under a microscope they look like bulbs with tiny hair like extensions reaching above the surface of the tongue. These hair-like extensions, called microvilli, receive the information that passes to the nerve that connects to the brain stem leading to the cerebral cortex on each side of the brain.
Art Connection
"Allegory of Taste" by Jan Bruegel the Elder (1618)
"Allegory of Taste" also by Jan Bruegel the Elder
"Taste", by Theresa Lucero
Student Art Connection
Students will create a taste bud collage. Using red construction paper students will cut out a tongue and label the four main taste sensations in the proper locations. The four taste sensations will be listed on the board and students will create a list of foods corresponding to each taste sensation. Using a combination of magazine pictures, newspaper clippings, and personal drawings students can cover the parts of the tongue with the correct corresponding foods creating a collage.
The Nose and the Sense of Smell
While the sense of smell is a primitive system, it is a valuable method of obtaining information from outside the body. Odor flows first into the nasal cavity with air that is breathed in.14 While the air flows into the lungs, the odor is received by the 20 million sensory olfactory cells that cover an area the size of a thumb nail or postage stamp that is located in the upper back part of the nasal cavity. The information travels to the olfactory bulb where the olfactory nerves carry the information to both sides of the brain in the cerebral cortex.15
Smell has many uses and can cause a number of reactions. Smells can alert of us of danger by identifying hazards such as smoke or chemicals. Smells also cause physical reactions. A pleasant smell of food can cause a person to salivate or stimulate gastric juices, while unpleasant odors can cause gagging .15 Our nose can also become accustom to the odors around us. After about 30 seconds exposed to a smell habituation occurs in which repeated exposure to the smell or stimulus produces a small response.
Our sense of smell faces other challenges. Long term complications also occur with in the nose as our age increases. Each year of our life we lose 1% of the olfactory cells in our nose. For example at the age of 20, approximately 80% of the cells function and at age 50, approximately 50% of cells function. This break down of olfactory cells not only effects our sense of smell, but also our sense of taste.
While it is our taste buds that decipher bitter, sour, sweet, and salty tastes, it is the odor molecules that travel from our through the passage way between the mouth and nose that gives us 70% - 75% of our taste sensation.
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As a result, the common cold can causes difficulty for our sense of smell. Excess mucus is produced and increases the thickness of the lining on our nasal cavity making it difficult to interpret different odors.
Scientific Imaging
Students can view a digital image of human olfactory receptor cells processed by an electron microscope to better understand the three dimensional structure of cells. http://darwin.iz.uj.edu.pl/iz/anatomy/jakub/grafika/o1b.html
Art Connection
"Sense of Smell One; Olfactory Garden", Julie Newdoll, (2002), is a mixed media representation of the olfactory receptor cells and the sense of smell. This painting also depicts the array of receptor cells located in the olfactory epithelium and incorporates it into a floral motif that represents a floral scent.
http://www.brushwithscience.com/Winter2002work/WinterSenses2002.html#Anchor-Garden-49575
Student Art Connection
Due to the strong sense memory connection students will create a picture of a memory they have associated to a smell. Through modeling I will begin by having students smell items in unlabeled bags that will possible evoke a memory, such as cinnamon, pine needles, chocolate, or flowers. Rather than guess what the item is, students will attempt to recreate a memory from that smell. Students will draw a picture entirely in black pen, only using color on the object that releases the smell and memory. A written description can be attached describing how the sense of smell works and the memory the smell elicits.
The Skin and the Sense of Touch
Our sense of touch is controlled by the body's largest organ. The skin, which on an adult can weight 8 to 10 pounds grows faster and renews itself faster than any other organ in the human body.14 We rely on our skin to protect us, keeps our body at a certain temperature, and provide us with the sense of touch.
The skin has two main layers, the epidermis and the dermis. The epidermis contains no nerves, but is several layers of cell. New cells form at the base of the epidermis and work their way up to the surface of the skin pushing off dead skin cells. In the epidermis melanin is formed, which is the pigment that provides us with skin color. Skin covers the entire body, the thickest is found on the palms of hands and the soles of feet, while the thinnest is the eyelids.14
The dermis rests below the epidermis and is much thicker. The dermis contains blood vessels, hair follicles, sweat glands, muscle, and an array of nerves. The nerves in the dermis are all for touch, but each plays a different role in sensory perception. There are nerves to detect temperature, light and heavy pressure, pain, vibration, two-point discrimination, texture, and joint position. Touch also includes sensations from inside the body, such as muscle pain, cramps, headaches, etc. Touch information is conveyed up the spinal cord to the brain stem and finally to the cerebrum.
Art Connections
"Sense of Touch", Damon Winter, Photograph
http://www.poyi.org/59/02/
"Sense of Touch", Mohamed Hagelamin,mixed media http://www.mogallery.net/senseoftouch.html
Student Art Connection
Through observation students will search the building for 4 different textures. With a crayon students will create a rubbing of the texture and below it a description of how the object felt and how the information was passed through the nervous system. Students will repeat this process three addition times. Students can be challenged to locate objects addressing different types of nerves, i.e. temperature, pain, light touch, etc…