5.4-5.6

• Pinna


  The visible part of the ear that protrudes from our heads
• Auditory canal


  Part of the outer ear
• Tympanic membrane


  The eardrum, part of the outer ear
• Ossicles


  Three tiny bones in the middle ear: malleus (hammer), incus (anvil), and stapes (stirrup)
• Cochlea


  A fluid-filled, snail-shaped structure in the inner ear that contains the sensory receptor cells (hair cells) of the auditory system
• Sound wave transmission


  1. Travel along auditory canal

  2. Strike tympanic membrane, causing vibration

  3. Vibration moves the three ossicles

  4. Stapes presses into oval window

  5. Fluid in cochlea moves

  6. Hair cells in basilar membrane are stimulated

  7. Neural impulses travel along auditory nerve to brain
• Hair cells


  Auditory receptor cells embedded in the basilar membrane of the cochlea
• Basilar membrane


  A thin strip of tissue within the cochlea
• Auditory information processing


  1. Shuttled to inferior colliculus

  2. Shuttled to medial geniculate nucleus of thalamus

  3. Shuttled to auditory cortex in temporal lobe
• Temporal theory of pitch perception


  • Frequency is coded by the activity level of a sensory neuron
  • Hair cells fire action potentials related to the frequency of the sound wave
• Place theory of pitch perception

  • Different portions of the basilar membrane are sensitive to sounds of different frequencies
  • Base of basilar membrane responds best to high frequencies
  • Tip of basilar membrane responds best to low frequencies
• Both temporal and place theories explain different aspects of pitch perception
• Frequencies up to about 4000 Hz are encoded using both rate of action potentials and place cues
• Much higher frequency sounds can only be encoded using place cues
• Sound localization


  The ability to locate sound in our environments
• Place theory of pitch perception

  Different portions of the basilar membrane are sensitive to sounds of different frequencies
• Place theory of pitch perception

  • Base of the basilar membrane responds best to high frequencies
  • Tip of the basilar membrane responds best to low frequencies
• Hair cells in the base portion would be labeled as high-pitch receptors, while those in the tip of basilar membrane would be labeled as low-pitch receptors
• Both rate of action potentials and place contribute to our perception of pitch up to about 4000 Hz, but much higher frequency sounds can only be encoded using place cues
• Monaural cues


  • Provided by the interaction of each pinna with incoming sound waves, helpful in locating sounds above/below and in front/behind
• Binaural cues


  • Provide information on the location of a sound along a horizontal axis by relying on differences in patterns of vibration of the eardrum between our two ears
• Interaural level difference


  A sound coming from the right side is more intense at the right ear than the left ear due to attenuation as it passes through the head
• Interaural timing difference


  The small difference in the time at which a sound wave arrives at each ear
• Deafness


  The partial or complete inability to hear
• Congenital deafness


  • People born without hearing
• Conductive hearing loss


  • Problem delivering sound energy to the cochlea, e.g. blockage of ear canal, hole in tympanic membrane, issues with ossicles, fluid in space between eardrum and cochlea
• Sensorineural hearing loss


  • Most common form of hearing loss, can be caused by aging, trauma, infections, medications, noise exposure, tumors, toxins
• Ménière's disease


  Results in degeneration of inner ear structures leading to hearing loss, tinnitus, vertigo, increased inner ear pressure
• Chemical senses


  Taste (gustation) and smell (olfaction)
• Cochlear implants


  Electronic devices that receive sound information and directly stimulate the auditory nerve to transmit information to the brain
• Cochlear implants cannot treat sensorineural hearing loss, but some individuals may be candidates for them
• Chemical senses


  • Have sensory receptors that respond to molecules in food we eat or air we breathe
• Taste (gustation)


  There are at least six basic groupings: sweet, salty, sour, bitter, umami, and fatty
• Deaf culture


  Deaf people have their own language, schools, and customs, often using American Sign Language
• Taste perception


  1. Molecules from food/beverages dissolve in saliva and interact with taste receptors on tongue, mouth, and throat

  2. Taste receptor cells with hair-like extensions in taste buds detect taste molecules

  3. Chemical changes in receptor cells result in neural impulses transmitted to brain via nerves

  4. Taste information processed in medulla, thalamus, limbic system, and gustatory cortex
• One value of deaf culture is to continue traditions like using sign language rather than teaching deaf children to verbalize, read lips, or have cochlear implant surgery
• Smell (olfaction)


  • Olfactory receptor cells in nasal mucous membrane have hair-like extensions that detect odor molecules
  • Chemical changes in receptor cells result in signals sent to olfactory bulb and then to limbic system and olfactory cortex
• Dogs have 800-1200 functional genes for olfactory receptors, compared to fewer than 400 in humans and other primates
• Pheromones


  Chemical messages sent by one individual that provide information, often about reproductive status, to another individual
• Olfactory system


  • Tremendous variation in sensitivity across different species
  • Dogs have far superior olfactory systems than humans
  • Dogs can "smell" dangerous drops in blood glucose levels and cancerous tumors
  • Dogs have between 800 and 1200 functional genes for olfactory receptors, compared to fewer than 400 in humans and other primates