Chapter 29 The Senses.

Chapter 29 The Senses

Introduction Bats use echolocation to detect their environment.
Bats use echolocation to detect their environment. High-pitched sounds are produced in their larynges (singular, larynx) and emitted from their mouths and noses. Their brains process the time delay and spatial arrangement of the echoes to determine the size, shape, location, speed, and direction of objects in their environment. © 2012 Pearson Education, Inc. 2

Introduction Marine mammals
Marine mammals include dolphins, killer whales, and sperm whales, produce ultrasonic clicking sounds in their nasal passages, focus the sound by bouncing it off of skull bones and an oil-filled structure in their forehead, and receive the echo in a narrow window of bone behind the jaw. Echolocation has also been observed in some species of cave-dwelling birds and forest-dwelling shrews. © 2012 Pearson Education, Inc. 3

Chapter 29: Big Ideas Sensory Reception Hearing and Balance Vision
Figure 29.0_1 Chapter 29: Big Ideas Sensory Reception Hearing and Balance Figure 29.0_1 Chapter 29: Big Ideas Vision Taste and Smell 4

Figure 29.0_2 Figure 29.0_2 A bat (Plecotus auritus) navigating by echolocation 5

29.1 Sensory organs share a common cellular basis
All animal senses originate in sensory receptors, specialized cells or neurons that are tuned to the conditions of the external world and the internal organs. All sensory receptors trigger an action potential and send information to the central nervous system. Sensation depends on the part of the brain that receives the action potential. Teaching Tips You might want to ask your students to consider the uneven distribution of sensory receptors in the human body. Sensory receptors may be concentrated in regions where environmental inputs are focused, such as the eyes and ears, or spread more generally, such as skin or the walls of the digestive tract. © 2012 Pearson Education, Inc. 7

Figure 29.1 Figure 29.1 A hammerhead shark hunting by electroreception 8

29.2 Sensory receptors convert stimulus energy to action potentials
Sensory receptors detect stimuli. All stimuli represent forms of energy. In a process called sensory transduction, receptors detect one type of signal (the stimulus) and convert the signal to another type, an electrical signal. Student Misconceptions and Concerns The concept of sensory transduction, as applied to any particular sense organ, is typically new to most students. Students’ familiarity with numerous forms of digital technology may help them make a connection. CD players, DVD recordings, and MP3 players rely upon electricity and signal conversions to store and generate sounds and images. Teaching Tips Students can better understand sensory adaptation by thinking about events in their lives. Perhaps they notice a distinct smell in the hallways and laboratories of the science facilities at your school. However, after a few minutes, we tend not to notice the smells as much. These experiences illustrate sensory adaptation. © 2012 Pearson Education, Inc. 9

When a sensory receptor cell in a taste bud detects sugar molecules, sugar molecules enter the taste bud, sugar molecules bind to sweet receptors, specific protein molecules embedded in a taste receptor cell membrane, and the binding triggers a signal transduction pathway that causes some ion channels in the membrane to close and others to open. These changes in the flow of ions create a graded change in membrane potential called a receptor potential. Student Misconceptions and Concerns The concept of sensory transduction, as applied to any particular sense organ, is typically new to most students. Students’ familiarity with numerous forms of digital technology may help them make a connection. CD players, DVD recordings, and MP3 players rely upon electricity and signal conversions to store and generate sounds and images. Teaching Tips Students can better understand sensory adaptation by thinking about events in their lives. Perhaps they notice a distinct smell in the hallways and laboratories of the science facilities at your school. However, after a few minutes, we tend not to notice the smells as much. These experiences illustrate sensory adaptation. © 2012 Pearson Education, Inc. 10

Figure 29.2A Sensory transduction at a taste bud
pore Sugar molecule Taste bud 1 Sensory receptor cells Sensory neuron Sweet receptor Sugar molecule (stimulus) 2 Membrane of a sensory receptor cell Signal transduction pathway 3 Ion channels Sensory receptor cell 4 Figure 29.2A Sensory transduction at a taste bud Ion Receptor potential 5 Neurotransmitter Sensory neuron Action potential to the brain mV No sugar Sugar present 6 Rates of action potentials 11

Sugar Taste molecule pore Taste bud Sensory receptor cells Sensory
Figure 29.2A_1 Sugar molecule Taste pore 1 Taste bud Sensory receptor cells Figure 29.2A_1 Sensory transduction at a taste bud (part 1) Sensory neuron 12

Sweet receptor Sugar molecule (stimulus) Membrane of a sensory
Figure 29.2A_2 Sweet receptor Sugar molecule (stimulus) 2 Membrane of a sensory receptor cell Signal transduction pathway 3 Figure 29.2A_2 Sensory transduction at a taste bud (part 2) Ion channels 4 Sensory receptor cell Ion 13

Rates of action potentials
Figure 29.2A_3 Ion channels 4 Sensory receptor cell Ion Receptor potential 5 Neurotransmitter Sensory neuron Action potential to the brain Figure 29.2A_3 Sensory transduction at a taste bud (part 3) mV No sugar Sugar present 6 Rates of action potentials 14

The stronger the stimulus, the more neurotransmitter released by the receptor cell and the more frequently the sensory neuron transmits action potentials to the brain. Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly. Student Misconceptions and Concerns The concept of sensory transduction, as applied to any particular sense organ, is typically new to most students. Students’ familiarity with numerous forms of digital technology may help them make a connection. CD players, DVD recordings, and MP3 players rely upon electricity and signal conversions to store and generate sounds and images. Teaching Tips Students can better understand sensory adaptation by thinking about events in their lives. Perhaps they notice a distinct smell in the hallways and laboratories of the science facilities at your school. However, after a few minutes, we tend not to notice the smells as much. These experiences illustrate sensory adaptation. © 2012 Pearson Education, Inc. 15

“Sugar” interneuron “Salt” interneuron Sugar receptor cell Salt
Figure 29.2B “Sugar” interneuron “Salt” interneuron Sugar receptor cell Salt receptor cell Brain Sensory neurons Taste bud Taste bud Figure 29.2B Action potentials transmitting different taste sensations No sugar No salt Increasing sweetness Increasing saltiness 16

29.3 Specialized sensory receptors detect five categories of stimuli
There are five categories of sensory receptors. 1. Pain receptors detect dangerous stimuli including high heat and pressure. 2. Thermoreceptors detect heat or cold. 3. Mechanoreceptors respond to mechanical energy, touch, pressure, and sound. Teaching Tips In elementary school, students often learn that there are five senses (taste, smell, touch, sight, and hearing). Consider matching these five senses to the types of specialized sensory receptor described in Module 29.3. © 2012 Pearson Education, Inc. 17

29.3 Specialized sensory receptors detect five categories of stimuli
4. Chemoreceptors include sensory receptors in our nose and taste buds and respond to chemicals. 5. Electromagnetic receptors respond to electricity, magnetism, and light (sensed by photoreceptors). Teaching Tips In elementary school, students often learn that there are five senses (taste, smell, touch, sight, and hearing). Consider matching these five senses to the types of specialized sensory receptor described in Module 29.3. © 2012 Pearson Education, Inc. 18

Connective tissue Hair movement
Figure 29.3A Heat Light touch Pain Cold Hair Epidermis Figure 29.3A Sensory receptors in the human skin Dermis Nerve to brain Connective tissue Hair movement Strong pressure 19

Figure 29.3B Mechanoreception by a hair cell
“Hairs” of a receptor cell Fluid movement Fluid movement Neurotransmitter at a synapse More neurotransmitter molecules Fewer neurotransmitter molecules Sensory neuron Action potentials Action potentials Figure 29.3B Mechanoreception by a hair cell 1 Receptor cell at rest 2 Fluid moving in one direction 3 Fluid moving in the other direction 20

“Hairs” of a receptor cell Neurotransmitter at a synapse Sensory
Figure 29.3B_1 “Hairs” of a receptor cell Neurotransmitter at a synapse Sensory neuron Action potentials Action potentials Figure 29.3B_1 Mechanoreception by a hair cell (part 1) 1 Receptor cell at rest 21

Fluid moving in one direction
Figure 29.3B_2 Fluid movement More neurotransmitter molecules Figure 29.3B_2 Mechanoreception by a hair cell (part 2) 2 Fluid moving in one direction 22

Fluid moving in the other direction
Figure 29.3B_3 Fluid movement Fewer neurotransmitter molecules Figure 29.3B_3 Mechanoreception by a hair cell (part 3) 3 Fluid moving in the other direction 23

Figure 29.3C Figure 29.3C Chemoreceptors on the antennae of a moth 24

Figure 29.3C_1 Figure 29.3C_1 Chemoreceptors on the antennae of a moth (part 1) 25

Figure 29.3C_2 Figure 29.3C_2 Chemoreceptors on the antennae of a moth (part 2) 26

Infrared receptor Figure 29.3D
Figure 29.3D Electromagnetic receptor organs in a snake Infrared receptor 27

29.4 The ear converts air pressure waves to action potentials that are perceived as sound
The human ear channels sound waves from the outer ear with a flap-like pinna, down the auditory canal, to the eardrum, which separates the outer ear from the middle ear, to a chain of bones in the middle ear (malleus, incus, and stapes), and to the fluid in the coiled cochlea in the inner ear. The Eustachian tube connects the pharynx to the middle ear, permitting pressure equalization. Student Misconceptions and Concerns 1. Lectures on the sensory systems of humans present numerous opportunities to relate new information to familiar student experiences. For example, the functions of the pinna of the ear can be demonstrated by cupping one hand around the pinna, boosting its ability to detect sound. Consider other simple demonstrations and explanations relating common experiences to the structure and function of the senses. 2. The natural tendency to wonder about our world seems to fade with increasing education. Discussions of the human sensory systems can rekindle that curiosity in your students, if time is available to field their questions. Perhaps you might have your class ask questions about their sensory experiences on 3  5 cards, which you can later answer selectively as time permits. Teaching Tips 1. The range of human hearing and the effect of age can be demonstrated by a popular high-pitched ring tone. Searching “high-pitched ringtone” through Google will reveal multiple sites where the pitch can be heard and downloaded. (It is sometimes also called a “mosquito” ring tone.) This can also offer the opportunity to discuss the potentially damaging effect of loud noises on the delicate structures of the ear. 2. MP3 players and similar devices have increased our opportunities to damage our hearing. In addition, listening to loud music while actively exercising outdoors can interfere with the detection of danger or vital communication. Consider discussing these important safety concerns with your class. 3. Consider asking your students why they each have two ears. In general, they help us locate the source of a sound. If a sound is louder in one ear, then that ear is probably closer to the source. In general, when sound is of equal volume in both ears, we are either facing directly towards or away from the source. Of course, there are exceptions. 4. Students might wonder why their voice played back on a recording sounds different from what they hear when they speak. When we hear our own voice, many of the vibrations are transferred from our throat to our ear via bones and cartilage. These materials transfer the sound differently and thus do not sound the same as our voice transmitted through air. © 2012 Pearson Education, Inc. 29

Outer ear Inner ear Eardrum Pinna Auditory canal Middle ear Eustachian
Figure 29.4A Outer ear Inner ear Figure 29.4A An overview of the human ear Eardrum Pinna Auditory canal Middle ear Eustachian tube 30

Pressure waves transmitted to the fluid of the cochlea bend hair cells in the organ of Corti against the basilar membrane and trigger nerve signals to the brain. Louder sounds generate more action potentials. Various pitches stimulate different regions of the organ of Corti. Student Misconceptions and Concerns 1. Lectures on the sensory systems of humans present numerous opportunities to relate new information to familiar student experiences. For example, the functions of the pinna of the ear can be demonstrated by cupping one hand around the pinna, boosting its ability to detect sound. Consider other simple demonstrations and explanations relating common experiences to the structure and function of the senses. 2. The natural tendency to wonder about our world seems to fade with increasing education. Discussions of the human sensory systems can rekindle that curiosity in your students, if time is available to field their questions. Perhaps you might have your class ask questions about their sensory experiences on 3  5 cards, which you can later answer selectively as time permits. Teaching Tips 1. The range of human hearing and the effect of age can be demonstrated by a popular high-pitched ring tone. Searching “high-pitched ringtone” through Google will reveal multiple sites where the pitch can be heard and downloaded. (It is sometimes also called a “mosquito” ring tone.) This can also offer the opportunity to discuss the potentially damaging effect of loud noises on the delicate structures of the ear. 2. MP3 players and similar devices have increased our opportunities to damage our hearing. In addition, listening to loud music while actively exercising outdoors can interfere with the detection of danger or vital communication. Consider discussing these important safety concerns with your class. 3. Consider asking your students why they each have two ears. In general, they help us locate the source of a sound. If a sound is louder in one ear, then that ear is probably closer to the source. In general, when sound is of equal volume in both ears, we are either facing directly towards or away from the source. Of course, there are exceptions. 4. Students might wonder why their voice played back on a recording sounds different from what they hear when they speak. When we hear our own voice, many of the vibrations are transferred from our throat to our ear via bones and cartilage. These materials transfer the sound differently and thus do not sound the same as our voice transmitted through air. © 2012 Pearson Education, Inc. 31

Semicircular canals (function in balance) Skull bones Oval window
Figure 29.4B Semicircular canals (function in balance) Skull bones Oval window (behind the stirrup) Auditory nerve, to the brain Hammer Anvil Stirrup Eardrum Figure 29.4B The middle ear and the inner ear Cochlea Eustachian tube (connects to the pharynx) 32

Bone Middle canal Auditory nerve Upper canal Lower canal
Figure 29.4C Bone Middle canal Auditory nerve Upper canal Lower canal Figure 29.4C A cross section through the cochlea Organ of Corti 33

To the brain via the auditory nerve
Figure 29.4D Hair cells Tectorial membrane Sensory neurons Figure 29.4D The organ of Corti Basilar membrane To the brain via the auditory nerve 34

Outer Ear Middle Ear Inner Ear Auditory canal Ear- drum Hammer,
Figure 29.4E Outer Ear Middle Ear Inner Ear Auditory canal Ear- drum Hammer, anvil, stirrup Oval window Cochlear canals Pinna Upper and middle Lower Pressure Figure 29.4E The route of sound wave vibrations through the ear Concentration in the middle ear Organ of Corti stimulated Time One vibration Amplitude 35

Outer Ear Middle Ear Inner Ear Auditory canal Ear- drum Hammer,
Figure 29.4E_1 Outer Ear Middle Ear Inner Ear Auditory canal Ear- drum Hammer, anvil, stirrup Oval window Cochlear canals Pinna Upper and middle Lower Pressure Concentration in the middle ear Organ of Corti stimulated Time Figure 29.4E_1 The route of sound wave vibrations through the ear (detail) One vibration Amplitude 36

Deafness is the loss of hearing. Deafness can be caused by the inability to detect sounds resulting from middle-ear infections, a ruptured eardrum, or stiffening of the middle-ear bones. Deafness can also result from damage to sensory receptors or neurons and is often progressive and permanent. Student Misconceptions and Concerns 1. Lectures on the sensory systems of humans present numerous opportunities to relate new information to familiar student experiences. For example, the functions of the pinna of the ear can be demonstrated by cupping one hand around the pinna, boosting its ability to detect sound. Consider other simple demonstrations and explanations relating common experiences to the structure and function of the senses. 2. The natural tendency to wonder about our world seems to fade with increasing education. Discussions of the human sensory systems can rekindle that curiosity in your students, if time is available to field their questions. Perhaps you might have your class ask questions about their sensory experiences on 3  5 cards, which you can later answer selectively as time permits. Teaching Tips 1. The range of human hearing and the effect of age can be demonstrated by a popular high-pitched ring tone. Searching “high-pitched ringtone” through Google will reveal multiple sites where the pitch can be heard and downloaded. (It is sometimes also called a “mosquito” ring tone.) This can also offer the opportunity to discuss the potentially damaging effect of loud noises on the delicate structures of the ear. 2. MP3 players and similar devices have increased our opportunities to damage our hearing. In addition, listening to loud music while actively exercising outdoors can interfere with the detection of danger or vital communication. Consider discussing these important safety concerns with your class. 3. Consider asking your students why they each have two ears. In general, they help us locate the source of a sound. If a sound is louder in one ear, then that ear is probably closer to the source. In general, when sound is of equal volume in both ears, we are either facing directly towards or away from the source. Of course, there are exceptions. 4. Students might wonder why their voice played back on a recording sounds different from what they hear when they speak. When we hear our own voice, many of the vibrations are transferred from our throat to our ear via bones and cartilage. These materials transfer the sound differently and thus do not sound the same as our voice transmitted through air. © 2012 Pearson Education, Inc. 37

29.5 The inner ear houses our organs of balance
Three organs in the inner ear detect body position and movement. These include three semicircular canals and two chambers, the utricle and the saccule. All three of these structures operate on the same principle: the bending of hairs on hair cells. The three semicircular canals detect changes in the head’s rotation or angular movement. The utricle and saccule detect the position of the head with respect to gravity. Student Misconceptions and Concerns 1. Lectures on the sensory systems of humans present numerous opportunities to relate new information to familiar student experiences. For example, the functions of the pinna of the ear can be demonstrated by cupping one hand around the pinna, boosting its ability to detect sound. Consider other simple demonstrations and explanations relating common experiences to the structure and function of the senses. 2. The natural tendency to wonder about our world seems to fade with increasing education. Discussions of the human sensory systems can rekindle that curiosity in your students, if time is available to field their questions. Perhaps you might have your class ask questions about their sensory experiences on 3  5 cards, which you can later answer selectively as time permits. Teaching Tips The lumping together of hearing and balance in the five senses learned in elementary school may result in a decreased appreciation for the sense of balance. Yet, hearing and balance are clearly separate senses. (Hearing-impaired people can still walk!) Consider asking your students to close their eyes and tilt their heads in different directions. How can they tell the position of their heads? In addition to the semicircular canals, stretch receptors in the neck provide positional information. © 2012 Pearson Education, Inc. 38

Direction of body movement
Figure 29.5 Semicircular canals Nerve Cochlea Utricle Saccule Flow of fluid Flow of fluid Figure 29.5 Equilibrium structures in the inner ear Cupula Hairs Hair cell Nerve fibers Cupula Direction of body movement 39

Semicircular canals Nerve Cochlea Utricle Saccule Figure 29.5_1
Figure 29.5_1 Equilibrium structures in the inner ear (part 1) Utricle Saccule 40

Flow of fluid Flow of fluid Cupula Hairs Hair cell Cupula Nerve fibers
Figure 29.5_2 Flow of fluid Flow of fluid Cupula Hairs Hair cell Figure 29.5_2 Equilibrium structures in the inner ear (part 2) Nerve fibers Cupula Direction of body movement 41

29.6 CONNECTION: What causes motion sickness?
Motion sickness may be caused by conflicting signals between the inner ear and eyes. Motion sickness can be a severe problem for astronauts. Student Misconceptions and Concerns 1. Lectures on the sensory systems of humans present numerous opportunities to relate new information to familiar student experiences. For example, the functions of the pinna of the ear can be demonstrated by cupping one hand around the pinna, boosting its ability to detect sound. Consider other simple demonstrations and explanations relating common experiences to the structure and function of the senses. 2. The natural tendency to wonder about our world seems to fade with increasing education. Discussions of the human sensory systems can rekindle that curiosity in your students, if time is available to field their questions. Perhaps you might have your class ask questions about their sensory experiences on 3  5 cards, which you can later answer selectively as time permits. Teaching Tips Ask your class to consider the hypothesis that motion sickness results from mixed sensory inputs from the eyes and balance organs. For example, do students agree that they might be able to read while traveling down a straight highway, but become sick if they read on a winding road? How might standing on the outside of a boat be different from standing deep inside a boat, unable to see the horizon? Considering the causes of motion sickness affords an opportunity to practice informed critical thinking. © 2012 Pearson Education, Inc. 42

29.6 CONNECTION: What causes motion sickness?
Motion sickness may be reduced by closing the eyes, limiting head movements, focusing on a stable horizon, sedatives such as dramamine or bonine, or long-lasting, drug-containing skin patches. Student Misconceptions and Concerns 1. Lectures on the sensory systems of humans present numerous opportunities to relate new information to familiar student experiences. For example, the functions of the pinna of the ear can be demonstrated by cupping one hand around the pinna, boosting its ability to detect sound. Consider other simple demonstrations and explanations relating common experiences to the structure and function of the senses. 2. The natural tendency to wonder about our world seems to fade with increasing education. Discussions of the human sensory systems can rekindle that curiosity in your students, if time is available to field their questions. Perhaps you might have your class ask questions about their sensory experiences on 3  5 cards, which you can later answer selectively as time permits. Teaching Tips Ask your class to consider the hypothesis that motion sickness results from mixed sensory inputs from the eyes and balance organs. For example, do students agree that they might be able to read while traveling down a straight highway, but become sick if they read on a winding road? How might standing on the outside of a boat be different from standing deep inside a boat, unable to see the horizon? Considering the causes of motion sickness affords an opportunity to practice informed critical thinking. © 2012 Pearson Education, Inc. 43

29.7 EVOLUTION CONNECTION: Several types of eyes have evolved independently among animals
The ability to detect light plays a central role in the lives of nearly all animals. All animal light detectors are based on cells called photoreceptors that contain pigment molecules that absorb light. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Optical illusions can reveal the mental gymnastics our mind performs to make sense of our visual world. Consider searching for “optical illusions” on the Internet to identify some examples to share with your class. 2. Cataracts, a clouding of the lens of the eye, are a common vision problem. Extensive exposure to ultraviolet (UV) light is one known cause of cataracts. Using eyeglasses and/or sunglasses with 100% UV coating can reduce exposure to UV light. © 2012 Pearson Education, Inc. 45

Most invertebrate eyes include some kind of light- detecting organ. One of the simplest organs is the eye cup, used by planarians, which senses light intensity and direction. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Optical illusions can reveal the mental gymnastics our mind performs to make sense of our visual world. Consider searching for “optical illusions” on the Internet to identify some examples to share with your class. 2. Cataracts, a clouding of the lens of the eye, are a common vision problem. Extensive exposure to ultraviolet (UV) light is one known cause of cataracts. Using eyeglasses and/or sunglasses with 100% UV coating can reduce exposure to UV light. © 2012 Pearson Education, Inc. 46

Figure 29.7A Figure 29.7A The eyecups of a planarian 47

Two major types of image-forming eyes have evolved in the invertebrates. 1. Compound eyes of insects consist of up to several thousand light detectors called ommatidia, function as acute motion detectors, and usually provide excellent color vision. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Optical illusions can reveal the mental gymnastics our mind performs to make sense of our visual world. Consider searching for “optical illusions” on the Internet to identify some examples to share with your class. 2. Cataracts, a clouding of the lens of the eye, are a common vision problem. Extensive exposure to ultraviolet (UV) light is one known cause of cataracts. Using eyeglasses and/or sunglasses with 100% UV coating can reduce exposure to UV light. © 2012 Pearson Education, Inc. 48

Figure 29.7B Figure 29.7B The two compound eyes of a fly, each made up of thousands of ommatidia 49

In single-lens eyes light enters the front center of the eye through a small opening, the pupil, controlled by an iris, passes through a single disklike lens, and is focused onto the retina, which consists of many photoreceptor cells. The center of focus is the fovea, where photoreceptor cells are highly concentrated. Single-lens eyes evolved independently in the vertebrates but are similar in structure. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Optical illusions can reveal the mental gymnastics our mind performs to make sense of our visual world. Consider searching for “optical illusions” on the Internet to identify some examples to share with your class. 2. Cataracts, a clouding of the lens of the eye, are a common vision problem. Extensive exposure to ultraviolet (UV) light is one known cause of cataracts. Using eyeglasses and/or sunglasses with 100% UV coating can reduce exposure to UV light. © 2012 Pearson Education, Inc. 50

Sclera Choroid Ciliary body Retina Ligament Fovea (center of Cornea
Figure 29.7C Sclera Choroid Ciliary body Retina Ligament Fovea (center of visual field) Cornea Iris Optic nerve Pupil Aqueous humor Figure 29.7C The single-lens eye of a vertebrate Lens Artery and vein Vitreous humor Blind spot 51

29.8 Humans have single-lens eyes that focus by changing position or shape
The outer surface of the human eyeball is a tough, whitish layer of connective tissue called the sclera. At the front of the eye, the sclera becomes the transparent cornea,which lets light into the eye and also helps focus light. The sclera surrounds a pigmented layer called the choroid. The anterior choroid forms the iris, which gives the eye its color. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Bits of cellular debris often drift within the vitreous humor, temporarily showing up in our field of view. These bits are commonly called “floaters.” 2. Some students might be familiar with the test for glaucoma in which a puff of air is shot at the eye. This blast of air distorts the eyeball and provides a measurement of the internal pressure. Dribbling a basketball and squeezing a tennis ball are examples of other tests of internal pressure. 3. The ciliary muscles of the eye can become fatigued if one focuses closely for long periods. Students who spend hours reading might find it difficult to focus closely, especially at the end of a long day. Staring off into the distance is relaxing in part because the ciliary muscles can relax. 4. The lacrimal canal connects the inner corner of the eye to the sinus cavity. Our noses might run when we cry because some surplus tears drain into our nose. © 2012 Pearson Education, Inc. 52

The lens and ciliary body divide the eye into two fluid-filled chambers. The large chamber behind the lens is filled with a jellylike vitreous humor. The smaller chamber in front of the lens contains the thinner aqueous humor. These humors help maintain the shape of the eyeball and circulate nutrients and oxygen to the lens, iris, and cornea. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Bits of cellular debris often drift within the vitreous humor, temporarily showing up in our field of view. These bits are commonly called “floaters.” 2. Some students might be familiar with the test for glaucoma in which a puff of air is shot at the eye. This blast of air distorts the eyeball and provides a measurement of the internal pressure. Dribbling a basketball and squeezing a tennis ball are examples of other tests of internal pressure. 3. The ciliary muscles of the eye can become fatigued if one focuses closely for long periods. Students who spend hours reading might find it difficult to focus closely, especially at the end of a long day. Staring off into the distance is relaxing in part because the ciliary muscles can relax. 4. The lacrimal canal connects the inner corner of the eye to the sinus cavity. Our noses might run when we cry because some surplus tears drain into our nose. © 2012 Pearson Education, Inc. 53

The conjunctiva lines the inner surface of the eyelids and folds back over the white of the eye (but not the cornea). Conjunctivitis is an inflammation of the conjuctiva by bacteria or a virus. A gland above the eye secretes tears that clean and moisten the eye. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Bits of cellular debris often drift within the vitreous humor, temporarily showing up in our field of view. These bits are commonly called “floaters.” 2. Some students might be familiar with the test for glaucoma in which a puff of air is shot at the eye. This blast of air distorts the eyeball and provides a measurement of the internal pressure. Dribbling a basketball and squeezing a tennis ball are examples of other tests of internal pressure. 3. The ciliary muscles of the eye can become fatigued if one focuses closely for long periods. Students who spend hours reading might find it difficult to focus closely, especially at the end of a long day. Staring off into the distance is relaxing in part because the ciliary muscles can relax. 4. The lacrimal canal connects the inner corner of the eye to the sinus cavity. Our noses might run when we cry because some surplus tears drain into our nose. © 2012 Pearson Education, Inc. 54

The lens focuses light onto the retina by bending light rays. Focusing can occur in two ways. In squids and fishes, the lens focuses by moving back and forth. In mammals, the lens focuses by changing shape using muscles attached to the choroid and ligaments that suspend the lens. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. Bits of cellular debris often drift within the vitreous humor, temporarily showing up in our field of view. These bits are commonly called “floaters.” 2. Some students might be familiar with the test for glaucoma in which a puff of air is shot at the eye. This blast of air distorts the eyeball and provides a measurement of the internal pressure. Dribbling a basketball and squeezing a tennis ball are examples of other tests of internal pressure. 3. The ciliary muscles of the eye can become fatigued if one focuses closely for long periods. Students who spend hours reading might find it difficult to focus closely, especially at the end of a long day. Staring off into the distance is relaxing in part because the ciliary muscles can relax. 4. The lacrimal canal connects the inner corner of the eye to the sinus cavity. Our noses might run when we cry because some surplus tears drain into our nose. © 2012 Pearson Education, Inc. 55

Ciliary muscle contracted Choroid Ligaments slacken
Figure 29.8 Ciliary muscle contracted Choroid Ligaments slacken Retina Light from a near object (diverging rays) Lens Cornea Sclera Near vision (accommodation) Ciliary muscle relaxed Ligaments pull on lens Figure 29.8 How human lenses focus light Light from a distant object (parallel rays) Distance vision 56

29.9 CONNECTION: Artificial lenses or surgery can correct focusing problems
Visual acuity is the ability of the eyes to distinguish fine detail. Visual acuity is measured by reading standardized eye charts from a distance of 20 feet. The ability to see normally at 20 feet is 20/20 vision. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips Challenge students to explain why an image appears clearer as we move closer to it. In general, it has to do with the number of rods and cones in the retina that are used to form the image. When we see an object at a distance, perhaps using only 10% of our field of vision, we use a proportional amount of rods and cones to form the image (about 10%). When we move closer, the image forms a larger percentage of our field of view and a proportionally higher number of rods and cones paint the picture. Like the images displayed on computer monitors or printed in newspapers, this image is formed by a series of dots: the more dots used to form the picture, the clearer the image. © 2012 Pearson Education, Inc. 57

29.9 CONNECTION: Artificial lenses or surgery can correct focusing problems
Three vision problems are common. 1. Nearsightedness is the inability to focus on distant objects, usually caused by an eyeball that is too long. 2. Farsightedness is the inability to focus on close objects, usually caused by an eyeball that is too short. 3. Astigmatism is blurred vision caused by a misshapen lens or cornea. Corrective lenses can bend light rays to compensate for each of these problems. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips Challenge students to explain why an image appears clearer as we move closer to it. In general, it has to do with the number of rods and cones in the retina that are used to form the image. When we see an object at a distance, perhaps using only 10% of our field of vision, we use a proportional amount of rods and cones to form the image (about 10%). When we move closer, the image forms a larger percentage of our field of view and a proportionally higher number of rods and cones paint the picture. Like the images displayed on computer monitors or printed in newspapers, this image is formed by a series of dots: the more dots used to form the picture, the clearer the image. © 2012 Pearson Education, Inc. 58

Animation: Near and Distant Vision
Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips Challenge students to explain why an image appears clearer as we move closer to it. In general, it has to do with the number of rods and cones in the retina that are used to form the image. When we see an object at a distance, perhaps using only 10% of our field of vision, we use a proportional amount of rods and cones to form the image (about 10%). When we move closer, the image forms a larger percentage of our field of view and a proportionally higher number of rods and cones paint the picture. Like the images displayed on computer monitors or printed in newspapers, this image is formed by a series of dots: the more dots used to form the picture, the clearer the image. Animation: Near and Distant Vision Right click on animation / Click play © 2012 Pearson Education, Inc. 59

Diverging corrective Focal lens point Shape of normal eyeball Lens
Figure 29.9A Diverging corrective lens Focal point Shape of normal eyeball Figure 29.9A A nearsighted eye (eyeball too long) Lens Focal point Retina 60

Converging corrective lens Focal point Shape of normal eyeball Focal
Figure 29.9B Converging corrective lens Focal point Shape of normal eyeball Figure 29.9B A farsighted eye (eyeball too short) Focal point 61

29.10 The human retina contains two types of photoreceptors: rods and cones
The human retina contains two types of photoreceptors. 1. Rods contain the visual pigment rhodopsin, which can absorb dim light, and can detect shades of gray in dim light. 2. Cones contain the visual pigment photopsin, which absorbs bright colored light, and allow us to see color in bright light. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. The inheritance patterns of colorblindness are discussed in Module 9.22. 2. A dark pigment layer behind the rods and cones absorbs light that has passed through these photoreceptor cells. This prevents reflected light from interfering with the detection of new light. Albino vertebrate pupils appear red because the light transmitted through the retina is not absorbed by a pigment layer and instead reflects off red blood cells in the choroid layer of the eye. © 2012 Pearson Education, Inc. 62

Rod Synaptic Membranous disks terminals containing visual Cell
Figure 29.10A Rod Synaptic terminals Membranous disks containing visual pigments Cell body Cone Figure 29.10A Photoreceptor cells 63

29.10 The human retina contains two types of photoreceptors: rods and cones
When rhodopsin and photopsin absorb light, they change chemically, and the change alters the permeability of the cell’s membrane. The resulting receptor potential triggers a change in the release of neurotransmitter from the synaptic terminals. This release initiates a complex integration process in the retina. Student Misconceptions and Concerns Many common visual phenomena may have been noticed but not understood by students. Students have experienced or know about floating specks in the visual field, difficulty focusing on text late at night, and colorblindness. However, few students have the ability to accurately explain these and many other phenomena related to vision. These familiar subjects of curiosity can be used in your class to encourage reflective critical thought using the information provided in Modules 29.7– Insight into their explanations and other questions can be found in the Teaching Tips directly below. Teaching Tips 1. The inheritance patterns of colorblindness are discussed in Module 9.22. 2. A dark pigment layer behind the rods and cones absorbs light that has passed through these photoreceptor cells. This prevents reflected light from interfering with the detection of new light. Albino vertebrate pupils appear red because the light transmitted through the retina is not absorbed by a pigment layer and instead reflects off red blood cells in the choroid layer of the eye. © 2012 Pearson Education, Inc. 64

Retina Optic nerve Retina Neurons Photoreceptors Rod Cone Optic nerve
Figure 29.10B Retina Optic nerve Retina Neurons Photoreceptors Rod Cone Optic nerve fibers Figure 29.10B The vision pathway from light source to optic nerve To the brain 65

Retina Neurons Photoreceptors Rod Cone Optic nerve fibers To the brain
Figure 29.10B_1 Retina Neurons Photoreceptors Rod Cone Optic nerve fibers Figure 29.10B_1 The vision pathway from light source to optic nerve (detail) To the brain 66

29.11 Taste and odor receptors detect chemicals present in solution or air
Taste and smell depend on chemoreceptors that detect specific chemicals in the environment. Chemoreceptors in taste buds detect molecules in solution and lining the nasal cavity detect airborne molecules. Taste and smell interact. Much of what we taste is really smell. Student Misconceptions and Concerns We tend to think the world is that which we perceive. These modules on the sensory systems provide hints of the world that other organisms detect. From sounds and wavelengths above and below our spectrum to concentrations of scents beyond our detection, other organisms may perceive the world very differently from us. Consider encouraging your students to imagine the world as other organisms perceive it and thereby gain insight into their existence. Teaching Tips Students that have sampled colognes or perfumes may have noticed that after an initial sniff, the scent tends to linger. Assuming that the scented liquid was not touched to the nose region, the lingering smell may result from its persistence in the mucus covering the sensory cells. Without the cilia of the olfactory region to sweep away the mucus containing the scent, the smell might last much longer. © 2012 Pearson Education, Inc. 68

29.11 Taste and odor receptors detect chemicals present in solution or air
Taste receptors are located in taste buds on the tongue and produce five taste sensations: sweet, salty, sour, bitter, and umami (the savory flavor of meats and cheeses). Student Misconceptions and Concerns We tend to think the world is that which we perceive. These modules on the sensory systems provide hints of the world that other organisms detect. From sounds and wavelengths above and below our spectrum to concentrations of scents beyond our detection, other organisms may perceive the world very differently from us. Consider encouraging your students to imagine the world as other organisms perceive it and thereby gain insight into their existence. Teaching Tips Students that have sampled colognes or perfumes may have noticed that after an initial sniff, the scent tends to linger. Assuming that the scented liquid was not touched to the nose region, the lingering smell may result from its persistence in the mucus covering the sensory cells. Without the cilia of the olfactory region to sweep away the mucus containing the scent, the smell might last much longer. © 2012 Pearson Education, Inc. 69

Brain A c t i o n p e a l s Olfactory bulb Nasal cavity Bone
Figure 29.11 Brain A c t i o n p e a l s Olfactory bulb Nasal cavity Bone Epithelial cell Sensory neuron (chemo- receptor) Figure Smell in humans Odorous substance Cilia Mucus 70

29.12 CONNECTION: “Supertasters” have a heightened sense of taste
About 25% of humans are “supertasters” with up to three times the sensitivity to bitter. Supertasters are more likely to avoid spinach, broccoli, cabbage, coffee, and alcoholic beverages and be obese. Student Misconceptions and Concerns We tend to think the world is that which we perceive. These modules on the sensory systems provide hints of the world that other organisms detect. From sounds and wavelengths above and below our spectrum to concentrations of scents beyond our detection, other organisms may perceive the world very differently from us. Consider encouraging your students to imagine the world as other organisms perceive it and thereby gain insight into their existence. Teaching Tips Module describes the heightened sensitivity of supertasters, people who have an increased ability to detect bitter flavors. If students are not assigned this module, you may consider challenging your class to predict some of the consequences. As noted in Module 29.12, supertasters may be less likely to eat a well-balanced diet that includes vegetables, leading to an increased risk of obesity and colon cancer. © 2012 Pearson Education, Inc. 71

Figure 29.12 Figure Food preferences and supertasters 72

29.13 Review: The central nervous system couples stimulus with response
The nervous system receives sensory information, integrates it, and commands appropriate responses, either an action or no action. Student Misconceptions and Concerns We tend to think the world is that which we perceive. These modules on the sensory systems provide hints of the world that other organisms detect. From sounds and wavelengths above and below our spectrum to concentrations of scents beyond our detection, other organisms may perceive the world very differently from us. Consider encouraging your students to imagine the world as other organisms perceive it and thereby gain insight into their existence. Teaching Tips You may wish to challenge your students who engage in sports to reflect on strategies that improved their performance. In addition to cardiovascular conditioning, basic motor skills, and strategy, students might list concentration and focus. Focus and concentration increase our awareness of the world around us and permit quick adjustments to changes in that environment. Humans acquire an advantage in sports, just as animals do in life-sustaining or life-threatening situations, by paying close attention to their perceptions. © 2012 Pearson Education, Inc. 73

You should now be able to
Describe the essential roles of sensory receptors. Explain how electromagnetic receptors help the hammerhead shark perceive its world. Define sensory transduction, receptor potential, and sensory adaptation, and provide examples of each. Describe the five general categories of sensory receptors found in animals and provide examples of each. © 2012 Pearson Education, Inc. 74

List the structures of the ear in the sequence in which they participate in hearing. Explain how body position and movement are sensed in the inner ear. Explain what causes motion sickness and what can be done to prevent it. Compare the structures and functions of the eye cups of planarians, the compound eyes of insects and crustaceans, and the single-lens eyes of humans. © 2012 Pearson Education, Inc. 75

Describe the parts of the human eye and their functions. Explain the causes and symptoms of myopia, hyperopia, presbyopia, and astigmatism. Compare the structures, functions, distributions, and densities of rods and cones. Explain how odor and taste receptors function. Describe the role of the central nervous system in sensory perception. © 2012 Pearson Education, Inc. 76

No signal Increasing signal Figure 29.UN01
Figure 29.UN01 Reviewing the Concepts, 29.2 77

Organ of Corti (inside the cochlea)
Figure 29.UN02 Outer ear Middle ear Inner ear Eardrum Bones Organ of Corti (inside the cochlea) Figure 29.UN02 Reviewing the Concepts, 29.4 78

Ciliary muscle contracted Choroid Ligaments slacken Retina
Figure 29.UN03 Ciliary muscle contracted Choroid Ligaments slacken Retina Light from a near object (diverging rays) Lens Cornea Figure 29.UN03 Reviewing the Concepts, 29.8 Sclera 79

are grouped into several types
Figure 29.UN04 Sensory receptors are grouped into several types pain and thermoreceptors electromagnetic receptors (a) (b) involved in involved in many types found in sensitive to touch, hearing, balance taste and smell human skin (c) Figure 29.UN04 Connecting the Concepts, question 1 many are most common are (d) (e) 80

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