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Audition, the Body Senses, and the Chemical Senses

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Title: Audition, the Body Senses, and the Chemical Senses


1
Chapter 7
  • Audition, the Body Senses, and the Chemical Senses

2
Audition
  • The stimulus
  • Sounds vary in their
  • Pitch a perceptual dimension of sound
    corresponds to their fundamental frequency
  • Loudness corresponds to intensity
  • Timbre corresponds to complexity
  • Anatomy of the ear
  • Sound is funneled via the pinna (external ear)
    through the ear canal to the tympanic membrane
    (eardrum), which vibrates with the sound
  • The middle ear is located behind the tympanic
    membrane and includes the middle ear bones, the
    ossicles (malleus, incus and stapes)
  • The malleus connects with the tympanic membrane
    and transmits vibrations via the incus and stapes
    to the cochlea, the sructure that contains the
    receptors

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4
Anatomy of the ear
  • The cochlea is part of the inner ear it is
    filled with fluid, therefore sounds transferred
    through the air must be transferred into a liquid
    medium the ossicles aid in this transmission
  • The cochlea is divided into 3 sections the scala
    vestibuli, scala media, and scala tympani
  • The receptive organ, the organ of Corti, consists
    of the basilar membrane, the hair cells, and the
    tectorial membrane
  • The auditory receptor cells are called hair
    cells, and they are anchored, via Deiters cells,
    to the basilar membrane
  • Sound waves cause the basilar membrane to move
    relative to the tectorial membrane, which bends
    the cilia of the hair cells this bending
    produces receptor potentials

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6
Audition
  • Hair cells
  • Hair cells contain cilia (hair-like appendages
    involved in movement or in transducing sensory
    info)
  • The hair cells form synapses with dendrites of
    bipolar neurons whose axons bring auditory info
    to the brain
  • The Auditory pathway
  • The organ of Corti sends auditory info to the
    brain by means of the cochlear nerve, a branch of
    the vestibulocochlear nerve (8th cranial nerve)
  • The pathway goes through the midbrain to the
    auditory cortex located in the temporal lobe
  • Auditory info is represented tonotopically, i.e.
    topographically organized mapping of different
    frquencies of sound that are represented in a
    particular region of the brain

7
Perception of pitch
  • Place coding
  • Detecting moderate to high frequencies
  • The system by which info about different
    frequencies is coded (i.e. neural representation
    of info) by different locations on the basilar
    membrane
  • Good evidence is seen for place coding with
    cochlear implants (an electronic device
    surgically implanted in the inner ear that can
    enable a deaf person to hear) because most speech
    sounds are of higher frequencies, and cannot be
    represented by rate coding
  • Rate coding
  • Detecting low frequencies
  • The system by which info about different
    frequencies is coded by the rate of firing of
    neurons in the auditory system

8
Auditory perception
  • Perception of loudness
  • The axons of the cochlear nerve inform the brain
    of the loudness of a stimulus by altering their
    rate of firing (Louder the sound, higher rate of
    firing)
  • Perception of timbre
  • When the basilar membrane is stimulated by a
    complex sound (such as a musical instrument),
    different portions respond to each of the
    overtones (the frequency of complex tones that
    occurs at multiples of the fundamental frequency)

9
Perception of spatial location
  • Neurons in our auditory system respond
    selectively to different arrival times of the
    sound waves at the left and right ears in order
    to perceive the spatial location of a sound
    (phase difference)
  • By analyzing the timbre of a sound, we can
    perceive if a sound is in front or behind us

10
Vestibular system
  • Consists of the vestibular sacs (respond to the
    force of gravity and inform the brain about the
    heads orientation) and the semicircular canals
    (respond to angular acceleration, i.e. changes in
    head rotation, but not to steady acceleration)
  • The functions include balance, maintenance of the
    head in an upright position, and adjustment of
    eye movement to compensate for head movements
  • Anatomy
  • Vestibular sacs
  • Utricle saccule
  • In the canals, there is an enlargement called the
    ampulla, which is where the sensory receptors
    reside
  • The sensory receptors are hair-like and their
    cilia are embedded in the cupula

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12
Vestibular system
  • Pathway
  • Vestibular nerve is part of the 8th cranial nerve
  • Project to cerebellum, spinal cord, medulla, and
    pons
  • Also connects to 3rd, 4th and 6th CN (control eye
    muscles) in order to adjust eyes during any head
    movements

13
Somatosenses
  • Provide info about what is happening on the
    surface of our body and inside it
  • Cutaneous sense sensitivity to stimuli that
    involve the skin touch
  • Kinesthesia perception of the bodys own
    movement
  • Organic sense a sense modality that arises from
    receptors located within the inner organs of the
    body
  • Cutaneous senses respond to pressure, vibration,
    heating, cooling, and events caused by tissue
    damage
  • Kinesthesia is provided by stretch receptors in
    skeletal muscles and tendons that report changes
    in muscle length to the CNS

14
Somatosenses
  • Anatomy of the skin and its receptive organs
  • Humans have both hairy and glabrous (hairless)
    skin
  • Hairy skin
  • Free nerve endings detect painful stimuli and
    changes in temp
  • Ruffini corpuscles respond to indentation of
    skin
  • Pacinian corpuscles respond to rapid vibrations
  • Glabrous skin
  • Free nerve endings, Ruffini and Pacinian
    corpuscles
  • Meissners corpuscles touch-sensitive end
    organs
  • Merkels disk the touch-sensitive end organs
    found adjacent to sweat ducts

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16
Somatosenses
  • Touch perception
  • When the Pacinian corpuscle is bent relative to
    the axon, the membrane becomes depolarized
  • Most info about tactile stimulation is precisely
    localized
  • Adaptation
  • A moderate, constant stimulus applied to the skin
    fails to produce any sensation after it has been
    present for a while
  • Due to the physical
  • Temperature
  • 2 types of thermal receptors one responds to
    warmth, the other to coolness
  • Pain
  • Accomplished through free nerve endings on skin
  • At least 3 types of nociceptors

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18
Gustation
  • Stimuli
  • 5 qualities bitter, sour, sweet, salty, umami
  • Flavor is the combination of gustation (taste)
    and olfaction (smell)
  • Anatomy of taste bud and gustatory cells
  • Tongue, palate, pharynx and larynx contain
    10,000 taste buds
  • Most of these receptive organs are arranged
    around papillae
  • Fungiform papillae (anterior 2/3 of tongue)
  • Foliate papillae (edges of back of tongue)
  • Circumvallate papillae (posterior third of
    tongue)
  • Taste buds consist of groups of 20-50 receptor
    cells, with cilia located at the end of each cell
    that project through the opening of the taste bud
    (pore) into the saliva
  • Taste receptor cells form synapses with bipolar
    neurons whose axons convey gustatory info through
    the 7th, 9th and 10th CN

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20
Gustation
  • Perception of gustatory info
  • The tasted molecule binds with the receptor and
    produces changes in the membrane potential
  • Different substances bind with different types of
    receptors producing different taste sensations
  • Salty
  • Simple sodium channel, blocked by the drug
    amiloride
  • Sour
  • Respond to hydrogen ions in acidic solutions
  • Bitter
  • Typical stimulus is plant alkaloid such as
    quinine
  • Perhaps family of bitter receptors
  • GPCR called gusducin
  • Sweet
  • Respond to sugar molecules (e.g. glucose,
    fructose)
  • Also coupled to gusducin
  • Umami
  • Taste of MSG
  • Specialized metabotropic glutamate receptor may
    be responsible

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22
Gustation
  • Gustatory pathway
  • Info from anterior tongue travels through chorda
    tympani, a branch of the facial (7th) nerve info
    from posterior tongue travels through lingual
    branch of 9th CN 10th CN carries info from
    palate and epiglottis
  • First relay station is the nucleus of the
    solitary tract (NTS), in the medulla, which then
    projects to the thalamus, then to the primary
    gustatory cortex, located at base of frontal
    cortex and in the insular cortex

23
Olfaction
  • Stimulus
  • Odorants
  • Anatomy
  • 6 million olfactory receptors located on
    olfactory epithelium, located at the top of the
    nasal cavity
  • Receptor cells are bipolar neurons whose cell
    bodies lie in the cribiform plate
  • Olfactory bulbs lie at the base of the brain on
    the ends of the olfactory tracts
  • Each olfactory cell sends an axon onto the
    olfactory bulb, where it synapses with dendrites
    of mitral cells (in the olfactory glomeruli), and
    the projects thorough the olfactory tracts to the
    amygdala, pyriform cortex, and entorhinal cortex

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25
Olfaction
  • Transduction
  • A G protein called Golf activates an enzyme that
    opens sodium channels of the olfactory cell
  • In humans there are 500-1000 different olfactory
    receptors
  • Perception of specific odors
  • How can a (relatively) small amount of receptors
    lead to such a vast array of smells?
  • A particular odorant binds to more than one
    receptor, thus different odorants produce
    different patterns of activity in different
    glomeruli
  • The spatial pattern of olfactory info is
    maintained in the olfactory cortex
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