Chapter 7  The Other Sensory Systems
Audition <ul><li>Our senses have evolved to allow us to detect and interpret biologically useful information from our envi...
Audition <ul><li>Audition  refers to our sense of hearing. </li></ul><ul><li>Audition depends upon our ability to detect s...
Audition <ul><li>The  amplitude  refers to the height and subsequent intensity of the sound wave. </li></ul><ul><li>Loudne...
Fig. 7-1, p. 196
Audition <ul><li>Anatomist distinguish between: </li></ul><ul><ul><li>The outer ear </li></ul></ul><ul><ul><li>The middle ...
Audition <ul><li>The outer ear includes the  pinna  and is responsible for: </li></ul><ul><ul><li>Altering the reflection ...
Audition <ul><li>The middle ear contains the  tympanic membrane  which vibrates at the same rate when struck by sound wave...
Fig. 7-2, p. 197
Audition <ul><li>The inner ear contains a snail shaped structure called the cochlea which contains three fluid-filled tunn...
Fig. 7-3, p. 198
Audition <ul><li>Pitch perception can be explained by the following theories: </li></ul><ul><li>Frequency theory -  the ba...
Fig. 7-4, p. 199
Audition <ul><li>The current pitch theory combines modified versions of both the  place theory  and  frequency theory : </...
Audition <ul><li>Volley principle  states that the auditory nerve can have volleys of impulses (up to 4000 per second) eve...
Audition <ul><li>The  primary auditory cortex  is the ultimate destination of information from the auditory system. </li><...
Audition <ul><li>The superior temporal cortex contains area MT which allows for the detection of the location of sound. </...
Fig. 7-5, p. 200
Audition <ul><li>The cortex is necessary for the  advanced  processing of hearing. </li></ul><ul><ul><li>Damage to A1 does...
Fig. 7-6, p. 201
Audition <ul><li>Areas around the primary auditory cortex exist in which cells respond more to changes in sound. </li></ul...
Audition <ul><li>About 99% of hearing impaired people have at least some response to loud noises. </li></ul><ul><li>Two ca...
Audition <ul><li>Conductive or middle ear deafness  occurs if bones of the middle ear fail to transmit sound waves properl...
Audition <ul><li>Nerve or inner-ear deafness  results from damage to the cochlea, the hair cells or the auditory nerve. </...
Audition <ul><li>Tinnitus  is a frequent or constant ringing in the ears. </li></ul><ul><ul><li>experienced by many people...
Audition <ul><li>Sound localization depends upon comparing the responses of the two ears. </li></ul><ul><li>Humans localiz...
Audition <ul><li>Three mechanisms: </li></ul><ul><ul><li>High-frequency sounds (2000 to 3000Hz) create a “sound shadow”, m...
Fig. 7-7, p. 202
Fig. 7-8, p. 203
Fig. 7-9, p. 203
The Mechanical Senses <ul><li>The mechanical senses include: </li></ul><ul><ul><li>The vestibular sensation </li></ul></ul...
The Mechanical Senses <ul><li>The  vestibular sense  refers to the system that detects the position and the movement of th...
The Mechanical Senses <ul><li>The  vestibular organ  consists of two otolith organs (the saccule and untricle) and three s...
Fig. 7-10, p. 206
The Mechanical Senses <ul><li>The vestibular sense is integrated with other sensations by the angular gyrus. </li></ul><ul...
The Mechanical Senses <ul><li>The  somatosensory system  refers to the sensation of the body and its movements. </li></ul>...
Fig. 7-11, p. 207
The Mechanical Senses <ul><li>The  pacinian corpuscle  is a type of touch receptor that detects sudden displacement or hig...
Fig. 7-12, p. 207
The Mechanical Senses <ul><li>Information from touch receptors in the head enters the CNS through the cranial nerves. </li...
Fig. 7-13, p. 208
The Mechanical Senses <ul><li>Each spinal nerve has a sensory component and a motor component and connects to a limited ar...
Fig. 7-14, p. 208
The Mechanical Senses <ul><li>Various aspects of body sensations remain partly separate all the way to the cortex. </li></...
The Mechanical Senses <ul><li>Pain depends on several types of axons, several neurotransmitters, and several brain areas. ...
Fig. 7-15, p. 210
The Mechanical Senses <ul><li>Opioid mechanisms  are systems that are sensitive to opioid drugs and similar chemicals.  </...
Fig. 7-16, p. 211
The Mechanical Senses <ul><li>Discrepancy in pain perception can partially be explained by genetic differences in receptor...
The Mechanical Senses <ul><li>Special heat receptors account for the pain associated with a burn. </li></ul><ul><li>Heat r...
The Mechanical Senses <ul><li>Pain activates the hypothalamus, amygdala, and cingulate cortex. </li></ul><ul><ul><li>resul...
Fig. 7-17, p. 211
The Mechanical Senses <ul><li>Mechanisms of the body to increase sensitivity to pain include: </li></ul><ul><ul><li>Damage...
The Mechanical Senses <ul><li>Pain is best controlled by preventing the brain from being bombarded with pain messages. </l...
The Mechanical Senses <ul><li>Morphine and other opiates are the primary drugs for controlling serious pain. </li></ul><ul...
The Mechanical Senses <ul><li>The release of histamines by the skin produce itching sensations. </li></ul><ul><li>The rele...
The Chemical Senses <ul><li>Coding in the sensory system could theoretically follow: </li></ul><ul><ul><li>The  labeled-li...
The Chemical Senses <ul><li>Vertebrate sensory systems probably have no pure label-lined codes. </li></ul><ul><li>The brai...
The Chemical Senses <ul><li>Taste refers to the stimulation of the taste buds. </li></ul><ul><li>Our perception of flavor ...
The Chemical Senses <ul><li>Receptors for taste are modified skin cells. </li></ul><ul><li>Taste receptors have excitable ...
The Chemical Senses <ul><li>Papillae  are structures on the surface of the tongue that contain the taste buds. </li></ul><...
Fig. 7-18, p. 217
The Chemical Senses <ul><li>Procedures that alter one receptor but not others can be used to identify taste receptors. </l...
The Chemical Senses <ul><li>Western societies have traditionally described sweet, sour, salty and bitter tastes as the “pr...
The Chemical Senses <ul><li>The saltiness receptor permits sodium ions to cross the membrane. </li></ul><ul><ul><li>result...
The Chemical Senses <ul><li>Different chemicals also result in different temporal patterns of action potentials and activi...
The Chemical Senses <ul><li>Bitter receptors are sensitive to a wide range of chemicals with varying degrees of toxicity. ...
The Chemical Senses <ul><li>Taste coding in the brain depends upon a  pattern  of responses  across  fibers in the brain. ...
The Chemical Senses <ul><li>Different nerves carry taste information to the brain from the anterior two-thirds of the tong...
Fig. 7-19, p. 219
The Chemical Senses <ul><li>Various areas of the brain are responsible for processing different taste information. </li></...
The Chemical Senses <ul><li>Genetic factors and hormones can account for some differences in taste sensitivity. </li></ul>...
Fig. 7-20, p. 220
The Chemical Senses <ul><li>Olfaction  is the sense of smell and refers to the detection and recognition of chemicals that...
Fig. 7-21, p. 221
The Chemical Senses <ul><li>Olfactory receptors are located on cilia which extend from the cell body into the mucous surfa...
The Chemical Senses <ul><li>Proteins in olfactory receptors respond to chemicals outside the cells and trigger changes in ...
Fig. 7-22, p. 222
The Chemical Senses <ul><li>Axons from olfactory receptors carry information to the olfactory bulb in the brain. </li></ul...
The Chemical Senses <ul><li>The olfactory bulb sends axons to the cerebral cortex where messages are coded by location. </...
Olfaction <ul><li>Olfactory receptors are replaced approximately every month, but are subject to permanent impairment from...
The Chemical Senses <ul><li>Individual differences in olfaction exist regarding olfaction. </li></ul><ul><li>Women detect ...
The Chemical Senses <ul><li>The  vomeronasal organ (VNO)  is a set of receptors located near the olfactory receptors that ...
The Chemical Senses <ul><li>The VNO and pheromones are important for most mammals, but less so for humans. </li></ul><ul><...
The Chemical Senses <ul><li>Synesthesia is the experience of one sense in response to stimulation of a different sense. </...
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  • Chapter7 Power Point Lecture

    1. 1. Chapter 7 The Other Sensory Systems
    2. 2. Audition <ul><li>Our senses have evolved to allow us to detect and interpret biologically useful information from our environment . </li></ul><ul><li>However, we do not detect all sensory information in the world. </li></ul><ul><li>Some sensory information lies beyond our ability to detect it. </li></ul><ul><li>We also tend to focus on information that is important or relevant. </li></ul>
    3. 3. Audition <ul><li>Audition refers to our sense of hearing. </li></ul><ul><li>Audition depends upon our ability to detect sound waves. </li></ul><ul><li>Sound waves are periodic compressions of air, water or other media. </li></ul><ul><li>Sound waves are “transduced” into action potentials sent to the brain. </li></ul>
    4. 4. Audition <ul><li>The amplitude refers to the height and subsequent intensity of the sound wave. </li></ul><ul><li>Loudness refers to the perception of the sound wave. </li></ul><ul><ul><li>Amplitude is one factor. </li></ul></ul><ul><li>Frequency refers to the number of compressions per second and is measured in hertz. </li></ul><ul><ul><li>Related to the pitch (high to low) of a sound. </li></ul></ul>
    5. 5. Fig. 7-1, p. 196
    6. 6. Audition <ul><li>Anatomist distinguish between: </li></ul><ul><ul><li>The outer ear </li></ul></ul><ul><ul><li>The middle ear </li></ul></ul><ul><ul><li>The inner ear </li></ul></ul>
    7. 7. Audition <ul><li>The outer ear includes the pinna and is responsible for: </li></ul><ul><ul><li>Altering the reflection of sound waves into the middle ear from the outer ear. </li></ul></ul><ul><ul><li>Helping to locate the source of a sound. </li></ul></ul>
    8. 8. Audition <ul><li>The middle ear contains the tympanic membrane which vibrates at the same rate when struck by sound waves. </li></ul><ul><li>Three tiny bones (malleus, incus, & stapes) transmit information to the oval window or a membrane in the middle ear. </li></ul>
    9. 9. Fig. 7-2, p. 197
    10. 10. Audition <ul><li>The inner ear contains a snail shaped structure called the cochlea which contains three fluid-filled tunnels (scala vestibuli, scala media, and the scala tympani). </li></ul><ul><li>Hair cells are auditory receptors that excite the cells of the auditory nerve when displaced by vibrations in the fluid of the cochlea. </li></ul><ul><ul><li>Lie between the basilar membrane and the tectorial membrane in the cochlea. </li></ul></ul>
    11. 11. Fig. 7-3, p. 198
    12. 12. Audition <ul><li>Pitch perception can be explained by the following theories: </li></ul><ul><li>Frequency theory - the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency. </li></ul><ul><li>Place theory - each area along the basilar membrane is tuned to a specific frequency of sound wave. </li></ul>
    13. 13. Fig. 7-4, p. 199
    14. 14. Audition <ul><li>The current pitch theory combines modified versions of both the place theory and frequency theory : </li></ul><ul><ul><li>Low frequency sounds best explained by the frequency theory. </li></ul></ul><ul><ul><li>High frequency sounds best explained by place theory. </li></ul></ul>
    15. 15. Audition <ul><li>Volley principle states that the auditory nerve can have volleys of impulses (up to 4000 per second) even though no individual axon approaches that frequency by itself. </li></ul><ul><ul><li>provides justification for the place theory and </li></ul></ul>
    16. 16. Audition <ul><li>The primary auditory cortex is the ultimate destination of information from the auditory system. </li></ul><ul><ul><li>Located in the superior temporal cortex. </li></ul></ul><ul><li>Each hemisphere receives most of its information from the opposite ear. </li></ul>
    17. 17. Audition <ul><li>The superior temporal cortex contains area MT which allows for the detection of the location of sound. </li></ul><ul><li>Area A1 of the brain is important for auditory imagery. </li></ul><ul><li>The auditory cortex requires experience to develop properly. </li></ul><ul><ul><li>Auditory axons develop less in those who are deaf from birth. </li></ul></ul>
    18. 18. Fig. 7-5, p. 200
    19. 19. Audition <ul><li>The cortex is necessary for the advanced processing of hearing. </li></ul><ul><ul><li>Damage to A1 does not necessarily cause deafness unless damage extends to the subcortical areas. </li></ul></ul><ul><li>The auditory cortex provides a tonotopic map in which cells in the primary auditory cortex are more responsive to preferred tones. </li></ul><ul><ul><li>Some cells respond better to complex sounds than pure tones. </li></ul></ul>
    20. 20. Fig. 7-6, p. 201
    21. 21. Audition <ul><li>Areas around the primary auditory cortex exist in which cells respond more to changes in sound. </li></ul><ul><li>Cells outside A1 respond to auditory “objects” (animal cries, machinery noise, music, etc.). </li></ul><ul><ul><li>Because initial response is slow, most likely responsible for interpreting the meaning of sounds. </li></ul></ul>
    22. 22. Audition <ul><li>About 99% of hearing impaired people have at least some response to loud noises. </li></ul><ul><li>Two categories of hearing impairment include: </li></ul><ul><ul><li>Conductive or middle ear deafness. </li></ul></ul><ul><ul><li>Nerve deafness. </li></ul></ul>
    23. 23. Audition <ul><li>Conductive or middle ear deafness occurs if bones of the middle ear fail to transmit sound waves properly to the cochlea. </li></ul><ul><li>Caused by disease, infections, or tumerous bone growth near the middle ear. </li></ul><ul><li>Can be corrected by surgery or hearing aids that amplify the stimulus. </li></ul><ul><li>Normal cochlea and normal auditory nerve allows people to hear their own voice clearly. </li></ul>
    24. 24. Audition <ul><li>Nerve or inner-ear deafness results from damage to the cochlea, the hair cells or the auditory nerve. </li></ul><ul><li>Can be confined to one part of the cochlea. </li></ul><ul><ul><li>people can hear only certain frequencies. </li></ul></ul><ul><li>Can be inherited or caused by prenatal problems or early childhood disorders (rubella, syphilis, inadequate oxygen to the brain during birth, repeated exposure to loud noises, etc). </li></ul>
    25. 25. Audition <ul><li>Tinnitus is a frequent or constant ringing in the ears. </li></ul><ul><ul><li>experienced by many people with nerve deafness. </li></ul></ul><ul><li>Sometimes occurs after damage to the cochlea. </li></ul><ul><ul><li>axons representing other part of the body invade parts of the brain previously responsive to sound. </li></ul></ul><ul><ul><li>Similar to the mechanisms of phantom limb. </li></ul></ul>
    26. 26. Audition <ul><li>Sound localization depends upon comparing the responses of the two ears. </li></ul><ul><li>Humans localize low frequency sound by phase difference and high frequency sound by loudness difference. </li></ul>
    27. 27. Audition <ul><li>Three mechanisms: </li></ul><ul><ul><li>High-frequency sounds (2000 to 3000Hz) create a “sound shadow”, making the sound louder for the closer ear. </li></ul></ul><ul><ul><li>The difference in the time of arrival at the two ears is most useful for localizing sounds with sudden onset. </li></ul></ul><ul><ul><li>Phase difference between the ears provides cues to sound location for localizing sounds with frequencies up to 1500 Hz. </li></ul></ul>
    28. 28. Fig. 7-7, p. 202
    29. 29. Fig. 7-8, p. 203
    30. 30. Fig. 7-9, p. 203
    31. 31. The Mechanical Senses <ul><li>The mechanical senses include: </li></ul><ul><ul><li>The vestibular sensation </li></ul></ul><ul><ul><li>Touch </li></ul></ul><ul><ul><li>Pain </li></ul></ul><ul><ul><li>Other body sensations </li></ul></ul><ul><li>The mechanical senses respond to pressure, bending, or other distortions of a receptor. </li></ul>
    32. 32. The Mechanical Senses <ul><li>The vestibular sense refers to the system that detects the position and the movement of the head. </li></ul><ul><ul><li>Directs compensatory movements of the eye and helps to maintain balance. </li></ul></ul><ul><li>The vestibular organ is in the ear and is adjacent to the cochlea. </li></ul>
    33. 33. The Mechanical Senses <ul><li>The vestibular organ consists of two otolith organs (the saccule and untricle) and three semicircular canals. </li></ul><ul><li>The otolith organs have calcium carbonate particles (otoliths) that activate hair cells when the head tilts. </li></ul><ul><li>The 3 semicircular canals are oriented in three different planes and filled with a jellylike substance that activates hair cells when the head moves. </li></ul>
    34. 34. Fig. 7-10, p. 206
    35. 35. The Mechanical Senses <ul><li>The vestibular sense is integrated with other sensations by the angular gyrus. </li></ul><ul><ul><li>Angular gyrus is an area at the border between the parietal and temporal cortex. </li></ul></ul>
    36. 36. The Mechanical Senses <ul><li>The somatosensory system refers to the sensation of the body and its movements. </li></ul><ul><ul><li>Includes discriminative touch, deep pressure, cold warmth, pain, itch, tickle and the position and movement of the joints. </li></ul></ul><ul><li>Touch receptors may be simple bare neurons, an elaborated neuron ending, or a bare ending surrounded by non-neural cells that modify its function. </li></ul>
    37. 37. Fig. 7-11, p. 207
    38. 38. The Mechanical Senses <ul><li>The pacinian corpuscle is a type of touch receptor that detects sudden displacement or high-frequency vibrations on the skin. </li></ul><ul><li>Mechanical pressure bend the membrane. </li></ul><ul><ul><li>increases the flow of sodium ions and triggers an action potential. </li></ul></ul>
    39. 39. Fig. 7-12, p. 207
    40. 40. The Mechanical Senses <ul><li>Information from touch receptors in the head enters the CNS through the cranial nerves. </li></ul><ul><li>Information from receptors below the head enter the spinal cord and travel through the 31 spinal nerves to the brain. </li></ul>
    41. 41. Fig. 7-13, p. 208
    42. 42. The Mechanical Senses <ul><li>Each spinal nerve has a sensory component and a motor component and connects to a limited area of the body. </li></ul><ul><li>A dermatome refers to the skin area connected to a single sensory spinal nerve. </li></ul><ul><li>Sensory information entering the spinal cord travel in well-defined and distinct pathways. </li></ul><ul><ul><li>Example: touch pathway is distinct from pain pathway. </li></ul></ul>
    43. 43. Fig. 7-14, p. 208
    44. 44. The Mechanical Senses <ul><li>Various aspects of body sensations remain partly separate all the way to the cortex. </li></ul><ul><li>Various areas of the thalamus send impulses to different areas of the somatosensory cortex located in the parietal lobe. </li></ul><ul><li>Different sub areas of the somatosensory cortex respond to different areas of the body. </li></ul><ul><li>Damage to the somatosensory cortex can result in the impairment of body perceptions. </li></ul>
    45. 45. The Mechanical Senses <ul><li>Pain depends on several types of axons, several neurotransmitters, and several brain areas. </li></ul><ul><li>Mild pain triggers the release of glutamate while stronger pain triggers the release of glutamate and substance P . </li></ul><ul><ul><li>Substance P results in the increased intensity of pain. </li></ul></ul><ul><ul><li>Morphine and opiates block pain by blocking these neurotransmitters. </li></ul></ul>
    46. 46. Fig. 7-15, p. 210
    47. 47. The Mechanical Senses <ul><li>Opioid mechanisms are systems that are sensitive to opioid drugs and similar chemicals. </li></ul><ul><li>Activating opiate receptors blocks the release of substance P in the spinal chord and in the periaqueductal grey of the midbrain. </li></ul><ul><li>Enkephalins refer to opiate-type chemical in the brain. </li></ul><ul><li>Endorphins - group of chemicals that attach to the same brain receptors as morphine. </li></ul>
    48. 48. Fig. 7-16, p. 211
    49. 49. The Mechanical Senses <ul><li>Discrepancy in pain perception can partially be explained by genetic differences in receptors. </li></ul><ul><li>Gate theory suggests that the spinal cord areas that receive messages from pain receptors also receive input from other skin receptors and from axons descending from the brain. </li></ul><ul><ul><li>These other areas that provide input can close the “gates” and decrease pain perception. </li></ul></ul>
    50. 50. The Mechanical Senses <ul><li>Special heat receptors account for the pain associated with a burn. </li></ul><ul><li>Heat receptors can also be activated by acids. </li></ul><ul><li>Capsaicin is a chemical found in hot peppers that directly stimulates these receptors and also triggers an increase in the release of substance P. </li></ul>
    51. 51. The Mechanical Senses <ul><li>Pain activates the hypothalamus, amygdala, and cingulate cortex. </li></ul><ul><ul><li>results in an emotional component to pain. </li></ul></ul><ul><li>A placebo is a drug or other procedure with no pharmacalogical effect. </li></ul><ul><li>Placebo’s decrease pain perception by decreasing the brains emotional response to pain perception and not the sensation itself. </li></ul>
    52. 52. Fig. 7-17, p. 211
    53. 53. The Mechanical Senses <ul><li>Mechanisms of the body to increase sensitivity to pain include: </li></ul><ul><ul><li>Damaged or inflamed tissue releases histamine, nerve growth factor, and other chemicals that increase the number of sodium gates in nearby pain receptors. </li></ul></ul><ul><ul><ul><li>Pain responses are thus magnified. </li></ul></ul></ul><ul><ul><li>Certain receptors become potentiated after an intense barrage of painful stimuli. </li></ul></ul><ul><ul><ul><li>leads to increased sensitivity or chronic pain later. </li></ul></ul></ul>
    54. 54. The Mechanical Senses <ul><li>Pain is best controlled by preventing the brain from being bombarded with pain messages. </li></ul><ul><li>Bombarding the brain with pain messages results in the increased sensitivity of the pain nerves and their receptors. </li></ul>
    55. 55. The Mechanical Senses <ul><li>Morphine and other opiates are the primary drugs for controlling serious pain. </li></ul><ul><li>Morphine inhibits slow, dull pain carried by thin unmyelinated axons. </li></ul><ul><ul><li>Sharp pain is conveyed by thicker myelinated axons. </li></ul></ul><ul><ul><li>Not influenced by morphine and endorphins. </li></ul></ul><ul><li>Ibuprofen, an anti-inflammatory drug, controls pain by reducing the release of chemicals from damaged tissues. </li></ul>
    56. 56. The Mechanical Senses <ul><li>The release of histamines by the skin produce itching sensations. </li></ul><ul><li>The release of histamine by the skin activates a distinct pathway in the spinal cord to the brain. </li></ul><ul><li>Impulses travel slowly along this pathway (half a meter per second). </li></ul><ul><li>Pain and itch have an inhibitory relationship. </li></ul><ul><ul><li>Opiates increase itch while antihistamines decrease itch. </li></ul></ul>
    57. 57. The Chemical Senses <ul><li>Coding in the sensory system could theoretically follow: </li></ul><ul><ul><li>The labeled-line principle in which each receptor responds to a limited range of stimuli and sends a direct line to the brain. </li></ul></ul><ul><ul><li>Across-fiber pattern in which each receptor responds to a wider range of stimuli and contributes to the perception of each of them. </li></ul></ul>
    58. 58. The Chemical Senses <ul><li>Vertebrate sensory systems probably have no pure label-lined codes. </li></ul><ul><li>The brain gets better information from a combination of responses. </li></ul><ul><ul><li>Example: auditory perception and color perception both rely on label-lined codes. </li></ul></ul><ul><li>Taste and smell stimuli activate several neurons and the meaning of the response of a single neuron depends on the context of responses by other neurons. </li></ul>
    59. 59. The Chemical Senses <ul><li>Taste refers to the stimulation of the taste buds. </li></ul><ul><li>Our perception of flavor is the combination of both taste and smell. </li></ul><ul><ul><li>Taste and smell axons converge in the endopiriform cortex. </li></ul></ul>
    60. 60. The Chemical Senses <ul><li>Receptors for taste are modified skin cells. </li></ul><ul><li>Taste receptors have excitable membranes that release neurotransmitters to excite neighboring neurons. </li></ul><ul><li>Taste receptors are replaced every 10 to 14 days. </li></ul>
    61. 61. The Chemical Senses <ul><li>Papillae are structures on the surface of the tongue that contain the taste buds. </li></ul><ul><li>Each papillae may contain zero to ten taste buds. </li></ul><ul><li>Each taste bud contains approximately 50 receptors. </li></ul><ul><li>Most taste buds are located along the outside of the tongue in humans. </li></ul>
    62. 62. Fig. 7-18, p. 217
    63. 63. The Chemical Senses <ul><li>Procedures that alter one receptor but not others can be used to identify taste receptors. </li></ul><ul><li>Adaptation refers to reduced perception of a stimuli due to the fatigue of receptors. </li></ul><ul><li>Cross-adaptation refers to reduced response to one stimuli after exposure to another. </li></ul>
    64. 64. The Chemical Senses <ul><li>Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and four types of receptors. </li></ul><ul><li>Evidence suggests a fifth type of glutamate receptor. </li></ul>
    65. 65. The Chemical Senses <ul><li>The saltiness receptor permits sodium ions to cross the membrane. </li></ul><ul><ul><li>results in an action potential. </li></ul></ul><ul><li>Sourness receptors close potassium channels when acid binds to receptors. </li></ul><ul><ul><li>results in depolarization of the membrane. </li></ul></ul><ul><li>Sweetness, bitterness, and umami receptors activate a G protein that releases a second messenger in the cell when a molecule binds to a receptor. </li></ul>
    66. 66. The Chemical Senses <ul><li>Different chemicals also result in different temporal patterns of action potentials and activity in the brain. </li></ul><ul><li>Taste is a function of both the type of cell activity, as well as the rhythm of cell activity. </li></ul>
    67. 67. The Chemical Senses <ul><li>Bitter receptors are sensitive to a wide range of chemicals with varying degrees of toxicity. </li></ul><ul><ul><li>Over 40 types of bitter receptors exist. </li></ul></ul><ul><li>Most taste cells contain only a small number of these receptors. </li></ul><ul><li>We are sensitive to a wide range of harmful substances, but not highly sensitive to any single one. </li></ul>
    68. 68. The Chemical Senses <ul><li>Taste coding in the brain depends upon a pattern of responses across fibers in the brain. </li></ul><ul><li>The brain determines taste by comparing the responses of several types of taste neurons. </li></ul><ul><li>Receptors converge their input onto the next cells in the taste system. </li></ul><ul><li>Cells thus respond best to a particular taste but others as well. </li></ul>
    69. 69. The Chemical Senses <ul><li>Different nerves carry taste information to the brain from the anterior two-thirds of the tongue than from the posterior tongue and throat. </li></ul><ul><li>Taste nerves project to a structure in the medulla known as the nucleus of the tractus solitarius (NTS). </li></ul><ul><ul><li>projects information to other parts of the brain. </li></ul></ul>
    70. 70. Fig. 7-19, p. 219
    71. 71. The Chemical Senses <ul><li>Various areas of the brain are responsible for processing different taste information. </li></ul><ul><ul><li>The somatosensory cortex responds to the touch aspect of taste. </li></ul></ul><ul><ul><li>The insula is the primary taste cortex. </li></ul></ul><ul><li>Each hemisphere of the cortex is also responsive to the ipsilateral side of the tongue. </li></ul>
    72. 72. The Chemical Senses <ul><li>Genetic factors and hormones can account for some differences in taste sensitivity. </li></ul><ul><li>Variations in taste sensitivity are related to the number of fungiform papillae near the tip of the tongue. </li></ul><ul><li>Supertasters have higher sensitivity to all tastes and mouth sensations in general. </li></ul>
    73. 73. Fig. 7-20, p. 220
    74. 74. The Chemical Senses <ul><li>Olfaction is the sense of smell and refers to the detection and recognition of chemicals that contact the membranes inside the nose. </li></ul><ul><li>Olfaction is more subject to adaptation than our other senses. </li></ul><ul><li>Olfactory cells line the olfactory epithelium in the rear of the nasal passage and are the neurons responsible for smell. </li></ul>
    75. 75. Fig. 7-21, p. 221
    76. 76. The Chemical Senses <ul><li>Olfactory receptors are located on cilia which extend from the cell body into the mucous surface of the nasal passage. </li></ul><ul><li>Vertebrates have hundreds of olfactory receptors which are highly responsive to some related chemicals and unresponsive to others. </li></ul><ul><li>Olfaction processes a wide variety of airborne chemicals, hence the need for many different types of receptors. </li></ul>
    77. 77. The Chemical Senses <ul><li>Proteins in olfactory receptors respond to chemicals outside the cells and trigger changes in G protein inside the cell. </li></ul><ul><li>G protein then triggers chemical activities that lead to action potentials. </li></ul>
    78. 78. Fig. 7-22, p. 222
    79. 79. The Chemical Senses <ul><li>Axons from olfactory receptors carry information to the olfactory bulb in the brain. </li></ul><ul><li>Coding in the brain is determined by which part of the olfactory bulb is excited. </li></ul><ul><li>Chemicals excite limited parts of the olfactory bulb with similar chemicals exciting similar parts. </li></ul>
    80. 80. The Chemical Senses <ul><li>The olfactory bulb sends axons to the cerebral cortex where messages are coded by location. </li></ul><ul><li>The cortex connects to other areas that control feeding and reproduction. </li></ul><ul><ul><li>Both behaviors are highly influenced by smell. </li></ul></ul>
    81. 81. Olfaction <ul><li>Olfactory receptors are replaced approximately every month, but are subject to permanent impairment from massive damage. </li></ul><ul><li>Anosmia refers to a general lack of olfaction. </li></ul><ul><li>Specific anosmia refers to the inability to smell a single type of chemical. </li></ul>
    82. 82. The Chemical Senses <ul><li>Individual differences in olfaction exist regarding olfaction. </li></ul><ul><li>Women detect odor more readily than men and brain responses are stronger. </li></ul><ul><li>The ability to attend to a faint odor and become more sensitive to it is characteristic of young adult women and thus seems to be influenced by hormones. </li></ul>
    83. 83. The Chemical Senses <ul><li>The vomeronasal organ (VNO) is a set of receptors located near the olfactory receptors that are sensitive to pheromones. </li></ul><ul><li>Pheromones are chemicals released by an animal to affect the behavior of others of the same species. </li></ul>
    84. 84. The Chemical Senses <ul><li>The VNO and pheromones are important for most mammals, but less so for humans. </li></ul><ul><li>The VNO is tiny in human adults and has no receptors. </li></ul><ul><li>Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa. </li></ul><ul><ul><li>Example: synchronization of menstrual cycle’s in women. </li></ul></ul>
    85. 85. The Chemical Senses <ul><li>Synesthesia is the experience of one sense in response to stimulation of a different sense. </li></ul><ul><ul><li>Estimates suggest 1 in every 500 people (Day, 2005). </li></ul></ul><ul><li>fMRI case studies show activity in both the auditory and visual cortex responsive to color when exposed to spoken language. </li></ul><ul><ul><li>Suggests some axons from one area have branches to other cortical regions. </li></ul></ul>
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