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Date Name Study Guide 8-2 Class The For use with textbook pages 214-222 Key Terms pupil the opening in the iris that regulates the amount of light entering the eye (page 215) lens a flexible, elastic, transparent structure in the eye that changes its shape to focus light on the retina (page 215) retina the innermost coating of the back of the eye, containing the light-sensitive receptor cells (page 215) optic nerve the nerve that carries impulses from the retina to the brain (page 215) binocular fusion the process of combining the images received from the two eyes into a single, fused image (page 216) retinal disparity the differences between the images stimulating each eye (page 216) auditory nerve the nerve that carries impulses from the inner ear to the brain, resulting in the sensation of sound (page 218) vestibular system three semicircular canals that provide the sense of balance located in the inner ear and connected to the brain by a nerve (page 220) olfactory nerve the nerve that carries smell impulses from the nose to the brain (page 220) kinesthesis the sense of movement and body position (page 222) Drawing From Experience Have you ever tried to do something with one eye closed? Was the activity more difficult to do this way? Have you ever felt dizzy after riding on a roller coaster or a boat? In the last section, you learned about the nature of sensations and their thresholds. This section discusses how your body receives and processes sensations from your environment. Organizing Your Thoughts n o © Use the diagram below to help you take notes as you read the summaries that follow. Think about the path that light takes from the time it hits your eye until it becomes vision. Trace the steps in the process in the flowchart below. H s 2 a 1 n o •c 3 o Brain 76 Reading Essentials and Study Guide Name Date Class Read to Learn Introduction (page 214) You probably think that you have just five senses: vision, hearing, taste, smell, and touch. Actually, you have more. The skin has several senses. Plus, you have two "internal" senses: vestibular and kinesthetic. Each sense organ receives some sort of external stimulus, such as light, sound waves, or pressure. It then changes the sensation into a chemical-electrical message transmitted by the nervous system and interpreted by the brain. 6. What are the sense organs for the five familiar senses? Vision (page 215) ""| t 2 43 .3 £• ® § §• The vision process begins when light enters the eye through the pupil and reaches the lens. This is a flexible structure that changes its shape to focus light on the retina. The retina is a coating at the back of the eye. It contains two types of light-sensitive cells: rods and cones. These cells change light into impulses that the neurons carry over the optic nerve to the brain. Cones require more light than rods before they begin to respond, so cones work best in daylight. Since rods can work in much lower light, they are the basis for night vision. There are many more rods than cones, but only cones are sensitive to color. The colors we see are actually different wavelengths of light. We see color only after light waves hit objects and bounce back to us. For example, a pea looks green because green light bounces off of it and all other colors do not. We can sense differences in texture and solidity of objects by the speed at which the waves bounce back. When the cones are not working well, the person can not see color very well. This condition is called color deficiency. For example, some people can not tell the difference between red and green. A few can't tell yellow from blue. A very few can't see any colors at all. They see the world in blacks, whites, and shades of gray. Because we have two eyes, our visual system receives two images. But instead of seeing double, we see a combination of the two images. This is called binocular fusion. Each eye projects a slightly different image on the retina. This difference is called retinal disparity. For example, bring an object such as an eraser close to your eyes. Without moving it, look at the eraser first with one eye and then with the other. You will see a difference in the two images because of Reading Essentials and Study Guide 77 Name Date Class the different viewpoint each eye has. When you open both eyes, you will see no difference. You will see one eraser. Retinal disparity is important to your sense of depth. Your brain knows that a large difference between the images each eye brings in (retinal disparity) means the object is near. A small difference means the object is far away. 7. Bring a small object very close to your face. Look at it with one eye and then the other. Notice the differences in the two images. Then do the same with a distant object. Which object creates the greatest difference in what each eye sees? Hearing (page 218) Hearing depends on sound waves. These are vibrations of the air. Sound waves from the air pass through several bones and fluids until they reach the inner ear. The inner ear contains tiny hairs that move back and forth, like a field of wheat in the wind. These hairs change the sound vibrations into signals that the neurons carry through the auditory nerve to the brain. The amplitude, or height, of sound waves determines the loudness. The higher the amplitude, the louder the sound. Loudness is measured in decibels. The sound's pitch depends on the wave's frequency, or rate of vibration. Low frequencies produce deep bass sounds. High frequencies produce squeaks. You can hear more than one pitch at a time. For example, if you strike two piano keys at the same time, you can pick out two different pitches. Your ears work together to tell you where the sound is coming from. For example, a noise on your right will reach your right ear first and then your left. It is also slightly louder in your right ear because it is closer to it. These differences tell you the direction of the sound. Your outer ear directs sound waves down a short tube called the auditory canal. The vibration (sound wave) causes air in the auditory canal to vibrate, which in turn causes the eardrum to vibrate. The middle ear is filled with air and contains three bones: the hammer, anvil, and stirrup. These bones link to the eardrum on one end and the cochlea at the other. When the eardrum vibrates, the three bones in the middle ear vibrate and push against the cochlea. The cochlea is the inner ear. It is a tube that contains fluids and neurons. The pressure against the cochlea makes the liquid in it move. Tiny hairs inside the cochlea pick up the motion. The hairs are attached to sensory cells. These cells turn the sound vibrations into impulses that the neurons in the auditory nerve carry to the brain. 78 Reading Essentials and Study Guide n § © 'H ™ o I | 1 5| Name 8. Date Class When you hear sounds from a bass guitar, are you hearing waves with high frequency or low frequency? Balance (page 22O) Your body's sense of balance comes from the vestibular system inside your inner ear. It has three semicircular canals filled with fluid. When you turn your head, this fluid moves, which bends hair cells in the fluid. The stimuli that your vestibular sense responds to are movements such as spinning, falling, and tilting your head. Too much stimulation of this sense can cause dizziness and "motion sickness." Without your sense of balance, you would be unable to walk without falling. 9. Give an example of an activity that might overstimulate your vestibular system. Smell and Taste (page 22O) Smell and taste are chemical senses. Their sense organs respond to chemical molecules rather than to light energy or sound waves. To smell something, the right molecules must hit the smell receivers in your nose. These molecules enter your nose in vapors, which reach smell receivers in the nasal passages. These receivers send messages about smells through the olfactory nerve to the brain. To taste something, molecules must stimulate the taste buds on your tongue. The taste buds relay information about taste as well as texture and temperature of the substance to the brain. Four sensory experiences make up taste: sour, salty, bitter, and sweet. The combination of taste, smell, and touch sensations create flavor. Much of what you taste is actually produced by your sense of smell. For example, when your nose is blocked by a cold, your food probably tastes bland. Sensations of warmth, cold, and pressure also affect taste. Try drinking hot soda to see how temperature affects taste. Now think about the differences in texture between pudding and a crunchy chocolate bar. These textures influence taste as well. Reading Essentials and Study Guide 79 Name Date Class 10. Is the sense of smell better in dogs or humans? Give an example. The Skin Senses (page 221) Your skin provides at least four kinds of information to your brain: pressure, warmth, cold, and pain. Some spots on your skin are more sensitive to pressure than others because they contain more receivers. For example, your fingertips contain many receivers and are highly sensitive to pressure. Your calves have few receivers. Some skin receivers are sensitive to hot or cold. To create a hot or cold sensation, the temperature of the stimulus must be greater or less than the skin's temperature. Stimuli such as scratches, punctures, and very high heat can produce pain. Pain is your body's emergency system. It warns you of possible damage to your body from such stimuli. Pain motivates you to stop the harmful activities and take care of injuries. There are two kinds of pain. Pain can be sharp and in a specific spot, or pain can be a dull ache over larger portions of your body. According to the gate control theory of pain, we can reduce some pain by shifting our attention away from it, or we can send other signals to compete with the pain signals. Only so many impulses can get through the bottleneck, or gate. So by increasing nonpain impulses (like rubbing your stubbed toe), you decrease the pain impulses that get through. 11. Use the gate control theory of pain to explain why an injured athlete may be able to continue playing in the game. The Body Senses (page 222) Kinesthesis is the sense of movement and body position. It works with the vestibular system to control posture and balance. The receivers for kinesthesis are located near the muscles, tendons, and joints. These receivers send messages to the brain when movement occurs. Without kinesthetic sensations, your movements would be uncoordinated. You would not know what your hand was doing if it went behind your back. You could not walk without looking at your feet. Complex activities like surgery would be impossible. 12. Give an example of a kinesthetic sensation needed to play tennis. 80 Reading Essentials and Study Guide