Hearing,%20Balance,%20and%20the%20Cutaneous%20and%20Chemical%20Senses - PowerPoint PPT Presentation

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Chapter 7 Hearing, Balance, and the Cutaneous and Chemical Senses The Chemical Senses Chemical senses include the gustatory and olfactory systems. – PowerPoint PPT presentation

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Title: Hearing,%20Balance,%20and%20the%20Cutaneous%20and%20Chemical%20Senses

Chapter 7
  • Hearing, Balance, and the Cutaneous and Chemical

The Auditory System
  • Sound - Vibrations in a material medium, such as
    air, water, or metal.
  • Sound waves vary along three dimensions
  • Frequency refers to the number of vibrations per
    second and is measured in hertz (Hz). We
    perceive the frequency of a sound as pitch.
  • Amplitude refers to the loudness of a sound wave
    and is measured in decibels (dB).
  • Timbre refers to the combination of multiple
    frequencies that make up complex sounds and give
    them their characteristic qualities.

Wave Forms for the Three Dimensions of a Sound
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The Human Ear
The Transduction of Sound Waves into Neural
  • The inner hair cells have a resting potential of
    -60 mV.
  • When cilia bend in the direction of the longest
    cilium the membrane depolarizes.
  • This leads to a rapid influx of Ca2 ions into
    the hair cells, which results in the release of

Auditory Pathways
Cochlea Cross Section
Pitch Perception Early Research
  • Place Theory of Pitch Perception
  • The view that different sounds activate nerve
    fibers at different locations on the basilar
  • High-pitched sounds activate the nerve fibers at
    the base of the membrane near the oval window
  • Low-pitched sounds stimulate nerve fibers at the
    opposite end of the basilar membrane.

Pitch Perception Early Research
  • Frequency Theory of Pitch Perception
  • The view that the firing rate in the auditory
    nerve matches the frequency of the sound. That
    is, the basilar membrane vibrates in synchrony
    with the sound wave.
  • We now know that the firing rate matches the
    frequency because of the volley principle
  • while one group of neurons in the auditory nerve
    is firing, another group is recovering from its
    previous activity
  • the end result being that the combined firing of
    all the groups matches the frequency of the

Pitch Perception Current Theory
  • The current theory of pitch perception uses a
    combination of the previous theories
  • From 20 Hz to 400 Hz, frequency theory accounts
    for pitch perception (the firing rate of
    individual neurons in the auditory nerve directly
    matches the frequency of the sound).
  • From 400 Hz to 4 kHz, volley principle takes
  • Beyond 4 kHz, place theory comes into play (the
    place of maximal vibration on the basilar
    membrane determines the pitch that we perceive).
  • Additionally, both place theory and the volley
    principle work for sounds from about 1 kHz to 4
    kHz (may explain our greater sensitivity to
    pitches within this range).

Detection of Loudness
  • The nervous system has two mechanisms for
    determining the intensity of a stimulus
  • The rate of firing of individual neurons
  • The number of neurons firing
  • The higher the firing
  • rate, or the greater the
  • number of neurons
  • firing, the more intense
  • the stimulus.

Detection of Sound Complexity
  • Pure tones are sounds of only one frequency
    complex sounds have two or more frequencies.
  • Combination of frequencies produces what we
    perceive as the timbre of a particular sound.
  • According to the place theory, because each sound
    frequency activates a specific part of the
    basilar membrane, a complex sound produces a
    unique pattern of neural activity.

Sound Localization
  • For both low-pitched sounds and high-pitched
    sounds, the cues to sound localization are based
    on differential time of arrival at the two ears.
  • As long as the sound does not come from the
    median plane, the sound will arrive at one ear
    slightly before it gets to the other ear, which
    allows us to locate the direction from which a
    sound comes from.

The Role of the Auditory Cortex in Sound
  • Auditory receptors encode sound
  • Frequency
  • Intensity
  • Timbre
  • Receptors send this information to the primary
    auditory cortex.
  • In auditory cortex, some neurons respond
    selectively to specific aspects of sounds others
    react to more complex aspects of the sound

The Role of the Auditory Cortex in Sound
  • Sound is identified as the neural information
    moves from the primary auditory cortex to the
    anterior part of the lateral surface of the
    superior temporal gyrus
  • Sound is localized as it moves to the posterior
    part of the superior temporal gyrus and then to
    the parietal cortex

Cochlea Implants
The Vestibular Sense
  • The sense responsible for maintaining balance.
  • Enables us to walk on two feet, keep our head
    upright, and adjust our eye movements to
    compensate for our head movements.

Phillippe Petit
Components of the Vestibular System
  • Vestibular sacs - Provide information about the
    position of the head relative to the body.
  • Utricle and saccule -The two vestibular sacs
    containing the vestibular receptor cells, or hair
  • Semicircular canals - Fluid-filled canals that
    provide information related to head movements or
  • Ampulla, crista, cupula

Vestibular Pathways
  • Vestibular hair cells
  • convert information about passive head movement
    and active head rotation into an increase or
    decrease in neurotransmitter release
  • synapse with bipolar neurons
  • Cell bodies of bipolar neurons form
  • vestibular ganglia (receive input from vestibular
    hair cells)
  • axons of the vestibular ganglia become the
    vestibular nerve (combine with cochlear nerve
    fibers to form the auditory nerve)

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Motion Sickness
  • Feelings of dizziness and nausea occur when the
    body is moved passively without motor activity
    and corresponding feedback to the brain.
  • Two types of motion sickness
  • Detects movements but motor actions that could
    have produced the movement have not occurred
  • Detects movement
  • inconsistent with the
  • information about movement
  • sensed by the eyes

The Somatosenses
  • The skin sensations of touch, pain, temperature,
    and proprioception.
  • Proprioception -The somatosense that monitors
    body position and movement, acts to maintain body
    position, and ensures the accuracy of intended
  • located in the muscles, tendons, and joints
  • essential to the control of movement.

Skin Receptors
  • The functions of the skin include
  • protecting the internal organs from injury
  • helping regulate body temperature by producing
    sweat, which cools the body when it becomes too
  • providing a first line of defense against
    invading microorganisms.

Receptive Fields and Adaptation Rates of Touch
Skin Receptors
Skin ReceptorsGlabrous Skin
Somatosensory Pathways
  • The dorsal column-medial lemniscal system
  • begins in the spinal cord and transmits
    information about touch and proprioception to the
    primary somatosensory cortex.
  • The anterolateral system
  • begins in the spinal cord and transmits
    information about temperature and pain to the
    brain stem, reticular formation, and the primary
    and secondary somatosensory cortices.
  • The spinocerebellar system
  • begins in the spinal cord and transmits
    proprioceptive information to the cerebellum.

The Somatosensory Cortex
The Experience and Control of Pain
  • Pain has both negative and positive functions
  • Chronic pain can be the bane of a persons
  • However, under ordinary circumstances, pain is
    extremely useful, warning us of potential injury
    and inducing us to seek appropriate treatment.

Gate-Control Theory of Pain
  • Melzack Wall (1965)
  • Gate-control theory of pain - Input from pain
    receptors will produce the perception of pain
    only if the message first passes through a gate
    in the spinal cord and lower brain stem
  • Theory emphasizes that messages from the brain
    can open or close the spinal cord gate, helping
    us to understand the psychological nature of pain
    - why our sensation of pain can be affected by
    our thoughts and feelings.

Gate-Control Theory of Pain
Neuromatrix Theory of Pain
  • Melzack (1999)
  • Neuromatrix theory of pain - A theory that
    accounts for types of pain unexplained by the
    gate-control theory of pain.
  • Severe, chronic pain existing in the absence of
    injury or disease.

The Chemical Senses
  • Chemical senses include the gustatory and
    olfactory systems.
  • Both are intermingled in our eating experiences,
    in that much of what we report as the taste of
    food actually comes from its odor.

Taste and Smell
  • Gustatory sense -The sense of taste.
  • Tastes can be classified according to four
    primary sensations
  • Sweet (stimulate sugar receptors)
  • Sour (stimulate H receptors)
  • Bitter (stimulate alkaloid compound receptors)
  • Salty (stimulate NaCl receptors)

Taste Receptors
  • Papilla - A small, visible bump on the tongue
    that contains taste bumps.
  • Taste bud - A cluster of taste receptors that lie
    either near or within a papilla.
  • Three kinds of papillae contain taste buds
  • Foliate
  • Circumvallate
  • Fungiform

Types of Papillae and Distribution of Taste
Genetics of Taste
  • People differ in their sensitivity to bitter and
    some sweet tastes.
  • These individual differences appear to be partly
    related to the number of taste buds on the
  • Supertasters (25 of people) have the most taste
    buds - about 425 per square cm on the tongue tip.
  • Medium tasters (50 of people) have about 184
    taste buds per square cm.
  • Non-tasters (25 of people) have about 96 per
    square cm.

Mechanisms of Taste Reception
  • Mechanism differs for each of the four basic
  • Salty food activates a taste receptor by causing
    Na ions to move through Na ion channels in the
    cell membrane.
  • H ions in sour foods and sugar molecules in
    sweet foods close the K ion channels in receptor
    membranes, preventing K ions from leaving the
  • In bitter foods, alkaloid compounds trigger the
    movement of Ca2 ions into the cytoplasm from
    storage sites in the taste receptor, increasing
    the release of neurotransmitters.

Gustatory Pathways
  • The sense of smell.
  • Habituation - can occur quickly with smells.
    Whether pleasant or unpleasant, we rapidly get
    used to smells.
  • This sensory adaptation is caused by decreased
    responding by receptors when they are exposed to
    the same stimulus for a continuous period of time.

Olfactory Receptors
  • Olfactory epithelium - The mucous membrane in the
    top rear of the nasal passage lined by olfactory
  • Humans have approximately 50 million olfactory
    receptors that detect smell
  • other species, such as dogs, may have up to 20
    times as many, with each cell having more than 10
    times as many cilia.

Olfactory Receptors and Pathways
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