Download The Nonvisual Sensory Systems

Chapter Seven
The Nonvisual Sensory Systems
Audition
Sound and the Ear
Physical and Psychological Dimensions of Sound
Amplitude=intensity of wave=loudness
frequency=number of waves/second=pitch
Figure 7.1 Four sound waves
The time between the peaks determines the frequency of the sound, which we
experience as pitch. Here the top line represents five sound waves in 0.1
second, or 50 Hz—a very low-frequency sound that we experience as a very
low pitch. The other three lines represent 100 Hz. The vertical extent of each
line represents its amplitude or intensity, which we experience as loudness.
Anatomy of the Ear
Structures of the Ear
Pinna-cartilage attached to the side of the head
Tympanic Membrane-eardrum
middle ear bones-hammer/anvil/stirrup
oval window-membrane leading to inner ear
cochlea-three fluid-filled tunnels
scala vestibuli
scala media
scala tympani
basilar membrane-flexible membrane
tectorial membrane-rigid membrane
hair cells-auditory receptors
Figure 7.2 Structures
of the ear
When sound waves
strike the tympanic
membrane in (a), they
cause it to vibrate three
tiny bones—the
hammer, anvil, and
stirrup—that convert the
sound waves into
stronger vibrations in
the fluid-filled cochlea
(b). Those vibrations
displace the hair cells
along the basilar
membrane in the
cochlea. (c) A cross
section through the
cochlea. The array of
hair cells in the cochlea
is known as the organ
of Corti. (d) A closeup of
the hair cells.
Pitch Perception
Theories of Pitch Perception
Frequency theory-the basilar membrane vibrates in synchrony
with a sound, causing auditory nerve axons to produce
action potentials at the same frequency
Place theory-the basilar membrane resembles the strings of a
piano in that each area along the membrane is tuned to a
specific frequency and vibrates whenever that frequency is
present
Volley principle-the auditory nerve as a whole can have volleys
of impulses up to about 5,000 per second, even though no
individual axon can approach that frequency by itself
Figure 7.4 The basilar membrane of the human cochlea
High-frequency sounds produce their maximum displacement near the base.
Low-frequency sounds produce their maximum displacement near the apex.
Figure 7.5 Traveling waves in the basilar membrane
set up by different frequencies of sound
Note that the peak displacement is closer to the base of
the cochlea for high frequencies and is toward the apex for lower frequencies.
In reality the peak of each wave is much narrower than shown here.
Pitch Perception in the Cerebral Cortex
Primary auditory cortex
Each cell responds best to one tone
Cells preferring a given tone cluster together
Secondary auditory cortex
Each cell responds to a complex combination of sounds
Figure 7.6 Route of auditory impulses from the receptors
in the ear to the auditory cortex
The cochlear nucleus receives input from the ipsilateral ear only (the one on the same
side of the head). All later stages have input originating from both ears.
Hearing Loss
Conductive Deafness
bones of the middle ear fail
caused by tumors, infection, disease
usually corrected by surgery or hearing aids
Nerve Deafness
damage to cochlea, hair cells or auditory nerve
usually treated with hearing aids
caused by genetics, disease, ototoxic drugs, etc.
Localization of Sound
Sound Shadow-loudest in nearest ear
Time of arrival-arrives at one ear soonest
Phase difference-sounds arrive out of phase
dependent on frequency
Figure 7.10 Phase differences between the ears as a cue for sound localization
Note that a low-frequency tone (a) arrives at the ears slightly out of phase. The ear for
which the receptors fire first (here the person’s left ear) is interpreted as being closer to
the sound. If the difference in phase between the ears is small, then the sound source
is close to the center of the body. However, with a high-frequency sound (b) the phase
differences become ambiguous. The person cannot tell which sound wave in the left ear
corresponds to which sound wave in the right ear.
The Mechanical Senses
Vestibular Sensation
Utricle and saccule
Contain calcium carbonate crystals that bend hair cells
when the head is moved
Semicircular canals
oriented in three different planes
canals are filled with jellylike substance that moves with
movement of the head causing bending of hair cells
Figure 7.11
Structures for
vestibular sensation
(a) Location of the
vestibular organs.
(b) Structures of the
vestibular organs. (c)
Cross section through
an otolith organ.
Calcium carbonate
particles, called
otoliths, press against
different hair cells
depending on the
direction of tilt and
rate of acceleration of
the head.
The Mechanical Senses
Somatosensation-the sensation of the body and its movements
Somatosensory Receptors
Vary in complexity and stimuli that they respond to
Ex: Pacinian Corpuscle-detects sudden displacements or
high-frequency vibrations on the skin
Mechanical Senses
Somatosensation cont’d
Input to the Spinal Cord and the Brain
Sensory information is brought in via spinal nerves
innervating dermatomes
specific pathways dedicated to different kinds of
information transfer information to the brain
Pain
Transmission
moderate-glutamate
intense-glutamate and substance P
Gate Theory
the spinal cord receives messages from pain and other receptors
of the skin and descending pathways of the brain
if pathways other than pain are sufficiently active, they close the
“gates” for pain messages
Modification of pain messages
Opiates-decrease substance P activity
The Chemical Senses
General Issues About Chemical Coding
each taste and smell stimulus excites several kinds of
receptors
the meaning of a particular response depends on the context of
responses by other receptors
Figure 7.12 Some sensory receptors found in the skin,
the human body’s largest organ
Different receptor types respond to different stimuli, as described in Table 7.1.
Somatosensation
Table 7.1
The Chemical Senses
Taste
Taste Receptors-taste buds located in papillae
How Many Kinds of Taste Receptors-at least four
Sweet, Salty, Bitter, Sour…Umami?
Mechanisms of Taste Receptors
Salt-allows sodium ions to pass through membrane
Sour-closes potassium channels
Sweet, Bitter and Umami-activate metabotropic
mechanisms
Figure 7.19 The organs of taste
The tip, back, and sides of the tongue are covered with taste buds.
Taste buds are located in papillae.
Chemical Senses
The Coding of Taste Information-taste depends on a pattern of
responses across fibers
Taste Coding in the Brain
carried along 7th, 9th, and 10th cranial nerves
nerves project to nucleus of the tractus solitarius (medulla)
projecting to the pons, the lateral hypothalamus, the
amygdala, the ventral-posterior thalamus, and cortex
Figure 7.20 Major routes of impulses related to the
sense of taste in the human brain
The thalamus and cerebral cortex receive impulses from both the left and
the right sides of the tongue.
Video
Olfaction
Olfactory Receptors
Cilia extend to mucous of the sinus
receptors located in cilia
transferred to olfactory bulb (coded in terms of what area
of the bulb is excited)
projects to forebrain and prefrontal cortex
Figure 7.21 Olfactory receptors
(a) Location of receptors in nasal cavity. (b) Closeup of olfactory cells.
The Chemical Senses
Vomeronasal Sensation and Pheromones
Pheromones are chemicals released by an animal that affect
the behavior of other members of the same species
Human body secretions have subtle pheromone effects
Figure 7.23 The human vomeronasal organ
This organ detects certain chemicals, especially those found on the human skin,
but produces no conscious experience. Perhaps for that reason, researchers
were slow to discover this organ.