Title: Hearing,%20Balance,%20and%20the%20Cutaneous%20and%20Chemical%20Senses
1Chapter 7
- Hearing, Balance, and the Cutaneous and Chemical
Senses
2The 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.
3Wave Forms for the Three Dimensions of a Sound
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5The Human Ear
6The Transduction of Sound Waves into Neural
Impulses
- 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
glutamate.
7Auditory Pathways
8Cochlea Cross Section
9Pitch Perception Early Research
- Place Theory of Pitch Perception
- The view that different sounds activate nerve
fibers at different locations on the basilar
membrane. - 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.
10Pitch 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
sound.
11Pitch 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
over. - 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).
12Detection 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.
13Detection 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.
14Sound 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.
15The Role of the Auditory Cortex in Sound
Recognition
- 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
stimulus.
16The Role of the Auditory Cortex in Sound
Recognition
- 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
17Cochlea Implants
18The 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
19Components 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
cells. - Semicircular canals - Fluid-filled canals that
provide information related to head movements or
rotations. - Ampulla, crista, cupula
20Vestibular 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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22Motion 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
23The 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
movements - located in the muscles, tendons, and joints
- essential to the control of movement.
24Skin 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
hot - providing a first line of defense against
invading microorganisms.
25Receptive Fields and Adaptation Rates of Touch
Receptors
26Skin Receptors
27Skin ReceptorsGlabrous Skin
28Somatosensory 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.
29The Somatosensory Cortex
30The Experience and Control of Pain
- Pain has both negative and positive functions
- Chronic pain can be the bane of a persons
existence. - However, under ordinary circumstances, pain is
extremely useful, warning us of potential injury
and inducing us to seek appropriate treatment.
31Gate-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
structures. - 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.
32Gate-Control Theory of Pain
33Neuromatrix 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.
34The 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.
35Taste and Smell
36Gustation
- 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)
37Taste 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
38Types of Papillae and Distribution of Taste
Receptors
39Genetics 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
tongue - 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.
40Mechanisms of Taste Reception
- Mechanism differs for each of the four basic
tastes - 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
cell. - 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.
41Gustatory Pathways
42Olfaction
- 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.
43Olfactory Receptors
- Olfactory epithelium - The mucous membrane in the
top rear of the nasal passage lined by olfactory
receptors. - 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.
44Olfactory Receptors and Pathways