1. The text explains how we might distinguish loudness for low-frequency sounds. How might we distinguish loudness for a high-frequency tone?2. In the English language, the letter t has no meaning out of context. Its meaning depends on its relationship to other letters. Indeed, even a word, such as to, has little meaning except in its connection to other words. So is language a labeled-line system or an across-fiber pattern system?3. How could you determine whether hypnosis releases endorphins?Write 4 sentences for each question
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OTHER SENSORY SYSTEMS
A. Sound and the Ear
1. Physics and Psychology of Sound
a. Sound waves are periodic compressions of air, water, or another medium.
b. Sound waves vary in amplitude and frequency.
c. Amplitude: Intensity of a sound wave. In general, sounds of greater amplitude
sound louder, but exceptions occur.
d. Frequency: Number of compressions per second, measured in hertz (Hz) of a
e. Pitch: The perception of frequency (the higher the frequency of a sound, the
higher its pitch).
f. Most adult humans can hear sounds ranging from 15 to almost 20,000 Hz.
g. The third aspect of sound is timbre, meaning tone quality or tone complexity.
2. Structures of the Ear
a. The anatomy of the ear is described in terms of three regions: the outer ear, the
middle ear, and the inner ear.
b. The outer ear includes the pinna (structure of flesh and cartilage attached to
the side of the head) and the auditory canal. The pinna helps us locate the
source of a sound by altering reflections of sound waves.
c. The middle ear is comprised of the tympanic membrane (eardrum), which
vibrates at the same frequency as the sound waves that strike it. Sound waves
reach the tympanic membrane through the auditory canal. The tympanic
membrane is attached to three tiny bones (hammer, anvil, and stirrup).
d. The inner ear consists of the oval window, which receives vibrations from the
tiny bones of the middle ear, and the cochlea, which contains three fluid-filled
tunnels: the scala vestibuli, scala media, and scala tympani.
e. The stirrup causes the oval window to vibrate, setting in motion all the fluid in
f. The auditory receptors (hair cells) lie between the basilar membrane and the
tectorial membrane in the cochlea.
g. When fluid in the cochlea vibrates, a shearing action occurs, which stimulates
hair cells; these cells then stimulate the auditory nerve cells (eighth cranial
B. Pitch Perception
1. Frequency and Place – your ability to understand speech or enjoy music depends on
your ability to differentiate among sounds of different frequencies.
Place Theory: Each area along the basilar membrane is tuned to a specific
frequency and vibrates whenever that frequency is present.
Each frequency activates hair cells at only one place along the basilar
membrane, and the brain distinguishes frequencies by which neurons are
activated. This theory has a downfall in that various parts of the basilar
membrane are bound too tight for any part to resonate like a piano string.
b. Frequency Theory: We perceive certain pitches when the basilar membrane
vibrates in synchrony with a sound, causing the axons of the auditory nerve to
produce action potentials at the same frequency.
i. The current theory is a modification of both place and frequency theories:
For low frequency sounds (below 100 Hz), the basilar membrane does
vibrate in synchrony with the sound wave in accordance with frequency
theory. The pitch of the sound is identified by the frequency of impulses
and the loudness is identified by the number of firing cells.
c. Volley principle of pitch discrimination: The auditory cortex as a whole can
have volleys of impulses up to about 4000 per second, even though no
individual axon approaches this frequency alone.
i. The volley principle is believed to be important for pitch perception below
4000 Hz, although it is unclear how the brain uses this information.
d. For high frequency sounds (above 4000 Hz), we use a mechanism similar to
place theory. High frequency vibrations strike the basilar membrane, causing a
traveling wave. This causes displacement of hair cells near the base (where the
stirrup meets the cochlea). Low frequency sounds produce displacement
farther along the membrane.
e. Tone deafness or amusia: A disorder where individuals are seriously impaired
at detecting small changes in frequency. Many relatives of those with amusia
have the same condition. It is associated with a thicker than average auditory
cortex in the right hemisphere but fewer than average connections from the
auditory cortex to the frontal cortex.
f. Absolute pitch or perfect pitch: The ability to hear a note and identify it
accurately. It is somewhat determined by genetic predisposition. The main
determinant is extensive musical training.
C. The Auditory Cortex
1. Auditory information passes through several subcortical structures with an
important crossover in the midbrain that enables each hemisphere of the forebrain
to get its major auditory input from the opposite ear.
2. Primary auditory cortex (area A1): Ultimate destination of auditory information
is located in the superior temporal cortex. Area A1 also is important for auditory
imagery. Similar to the visual system, the auditory system needs experience to
develop normally. Both constant noise and lack of exposure to sound will impair
the development of the auditory system.
3. Damage to the A1 does not leave someone deaf; it may hinder the ability to
recognize combinations or sequences of sounds, like music or speech.
In the primary auditory cortex, cells respond preferentially to certain tones. Cells
preferring a given tone in the auditory cortex cluster together providing a map of
the sounds referred to as a tonotopic map. Thus, the cortical area with the greatest
response indicates what sound or sounds are heard.
5. Cells outside area A1 respond best to auditory “objects” such as animal cries,
machinery noise, music, etc.
D. Hearing Loss
a. Conductive or middle-ear deafness: Failure of the bones of the middle ear to
transmit sound waves properly to the cochlea. Conductive deafness can be
caused by diseases, infections, or tumorous bone growth near the ear. This
deafness can be corrected by surgery or hearing aids.
b. Nerve or inner-ear deafness: Damage to the cochlea, hair cells, or auditory
nerve that causes a permanent impairment in hearing in one to all ranges of
frequencies. Nerve deafness can be inherited or caused by prenatal problems
and early childhood disorders.
c. Tinnitus: Frequent or constant ringing in the ear. Tinnitus is often produced by
nerve deafness. It is a phenomenon similar to phantom limb, where axons
corresponding to other parts of the body may invade the brain area previously
responsive to sounds, especially high-frequency sounds.
2. Heating, Attention, and Old Age
a. Many older people continue to have hearing problems despite wearing hearing
b. Part of the explanation is that the brain areas responsible for language
comprehension have become less active.
c. The rest of the explanation relates to attention. Many older people have a
decrease in their inhibitory neurotransmitters in the auditory portions of the
brain. As a result, they have trouble suppressing the irrelevant sounds and
attending to the important one. Also, instead of making a quick, crisp response
to each sound, the auditory cortex has delayed, spread-out responses to each
sound, such that the response to one sound partly overlaps the response to
E. Sound Localization
1. Determining the direction and distance of a sound requires comparing the responses
of the two ears.
a. One method is the difference in time of arrival at the two ears.
b. Another cue for location is the difference in intensity between the ears. For
high-frequency sounds, with a wavelength shorter than the width of the head,
the head creates a sound shadow, making the sound louder for the closer ear.
Adult humans are accurate at localization for frequencies above 2000 to 3000
Hz, and less accurate for progressively lower frequencies.
c. A third cue is the phase difference between the ears. Every sound wave has
phases with consecutive peaks 360 degrees apart.
II. The Mechanical Senses
A. The mechanical senses respond to pressure, bending, or other distortions of a receptor.
B. Vestibular Sensation
1. The vestibular organ monitors head movements and directs compensatory
movements of the eyes. It is critical for eye movements and maintaining balance.
2. The vestibular organ consists of the saccule, utricle, and three semicircular canals.
3. Calcium carbonate particles (otoliths) lie next to hair cells excite them when the
head tilts in different directions.
4. The three semicircular canals are filled with a jellylike substance and lined with
hair cells. Acceleration of the head causes this substance to push against hair cells,
which in turn causes action potentials from the vestibular system to travel via part
of the eighth cranial nerve to the brainstem and cerebellum.
1. The somatosensory system involves the sensation of the body and its movements,
including discriminative touch, deep pressure, cold, warmth, pain, itch, tickle, and
the position and movements of joints.
2. Somatosensory Receptors
a. Examples of touch receptors are pain receptors, Ruffini endings, Meissner’s
corpuscles, and Pacinian corpuscles.
b. Stimulation of touch receptors opens sodium channels in the axon, possibly
starting an action potential if the stimulation is strong enough.
c. Pacinian corpuscle detects sudden displacements or high-frequency vibrations
on the skin.
d. Receptors for heat and cold can be stimulated by certain chemicals as well as
mechanical stimulation. Capsaicin, a chemical found in hot peppers such as
jalapeños, stimulates the receptors for painful heat.
a. The sensation of tickle is interesting but poorly understood.
b. Why can’t you tickle yourself? When you touch yourself, your brain compares
the resulting stimulation to the “expected” stimulation and generates a weaker
somatosensory response than you would experience from an unexpected touch
4. Somatosensation in the Central Nervous System
a. Information from touch receptors in the head enters the CNS through the
cranial nerves. Information from touch receptors below the head enters the
spinal cord through the 31 spinal nerves and passes toward the brain.
b. Each spinal nerve has a sensory component and a motor component. Each
sensory spinal nerve innervates a limited area of the body called a dermatome.
c. Sensory information from the spinal cord is sent to the thalamus before
traveling to the somatosensory cortex in the parietal lobe.
d. The somatosensory cortex receives information primarily from the
contralateral side of the body.
Damage to the somatosensory cortex impairs body perceptions. A patient with
Alzheimer’s who exhibited such damage had trouble putting her clothes on
1. Pain, the experience evoked by a harmful stimulus, directs our attention towards
2. Stimuli and Spinal Cord Paths
a. Pain sensation begins with the least specialized of all receptors, a bare nerve
b. The axons carrying pain information have little or no myelin and therefore
conduct impulses relatively slowly, in the range of 2 to 20 meters per second
c. Thicker and faster axons convey sharp pain. The thinner ones convey duller
d. Mild pain causes the release of the neurotransmitter glutamate, whereas
stronger pain also releases several neuropeptides including substance P and
CGRP (calcitonin gene-related peptide).
e. The pain-sensitive cells in the spinal cord relay information to several sites in
i. One path extends to the ventral posterior nucleus of the thalamus and then
to the somatosensory cortex, which responds to painful stimuli, memories
of pain, and signals that warn of impending pain.
ii. The pain pathway crosses immediately from receptors on one side of the
body to a tract ascending the contralateral side of the spinal cord.
iii. Touch information travels up the ipsilateral side of the spinal cord to the
medulla, where it crosses to the contralateral side.
iv. Pain and touch reach neighboring sites in the cerebral cortex.
3. Emotional Pain
a. Painful stimuli also activate a path that goes through the reticular formation of
the medulla and then to several of the central nuclei of the thalamus, the
amygdala, hippocampus, prefrontal cortex, and cingulate cortex.
b. These areas react not to the sensation but to its emotional associations.
c. Hurt feelings can be like real pain (You can relieve hurt feelings with painrelieving drugs such as acetaminophen (Tylenol®)!
4. Ways of Relieving Pain
a. Insensitivity to pain is dangerous. People with a gene that inactivates pain axons
suffer repeated injuries and generally fail to learn to avoid dangers.
b. Opioids and Endorphins
i. Opioid Mechanisms: released by the brain to dull prolonged pain after you
are alerted of danger.
ii. Opioids bind to receptors in the spinal cord and periaqueductal gray area
to block the release of substance P and decrease prolonged pain.
iii. Endorphins: the transmitters that attach to the same receptors as morphine.
Different endorphins (naturally released by the brain) relieve different types
iv. Gate Theory: Information not related to pain travels to the spinal cord and
closes the “gates” for each pain message, thereby modulating the subjective
experience of pain. Although gate theory turned out to be wrong, the
general principle is valid: nonpain stimuli modify the intensity of pain.
i. A placebo is a drug or other procedure with no pharmacological effects.
ii. In medical research, an experimental group receives a potentially active
treatment and the control group receives a placebo.
d. Cannabinoids and Capsaicin
i. Cannabinoid (chemical related to marijuana): Blocks certain kinds of pain
through the periphery of the body rather than the CNS.
ii. Capsaicin: Stimulates receptors for heat. When rubbed onto a sore
shoulder, an arthritic joint, or other painful area produces a temporary
burning sensation followed by a longer period of decreased pain. High
doses, or low doses for a prolonged period, can damage pain receptors.
Eating it will not relieve your pain—unless your tongue hurts.
Sensitization of Pain
a. The body also has mechanisms to increase pain after tissue has been damaged
b. Pain sensitization is a result of the body releasing histamine, nerve growth
factor, and other chemicals that are necessary to repair the body.
c. Nonsteroidal anti-inflammatory drugs decrease pain by reducing the release of
chemicals from damaged tissue.
1. Exists in two forms
a. In response to tissue damage, due to release of histamine.
b. In response to contact with certain plants.
2. A particular spinal cord path conveys itch sensation.
a. Itch activates neurons in the spinal cord that produce a chemical called gastinreleasing peptide.
3. Itch is useful because it directs you to scratch the itchy area and remove whatever is
irritating your skin.
4. Vigorous scratching produces mild pain, and pain inhibits itch. Opiates reduce pain
and increase itch. The inhibitory relationship between pain and itch is evidence that
itch is not a type of pain.
III. The Chemical Senses
A. Chemical Coding
1. Labeled-line principle: Receptors of a sensory system that respond to a limited
range of stimuli and send a direct line to the brain.
Across-fiber pattern principle: Receptors of a sensory system respond to a wide
range of stimuli and contribute to the perception of each of them.
3. Vertebrate sensory systems probably do not have any pure labeled-line codes. Taste
and smell stimuli excite several kinds of neurons, and the meaning of a particular
response by a particular neuron depends on the responses of other neurons.
1. Taste results from the stimulation of taste buds. Taste differs from flavor, which is
the combination of taste and smell. Taste and smell axons converge into many of the
same cells in an area called the endopiriform cortex.
2. Taste Receptors
a. Taste receptors are actually modified skin cells that last only about 10-14 days
before being replaced.
b. Mammalian taste receptors are located in taste buds, which are located in
papillae (structures on the surface of the tongue). A given papillae may contain
from 0 to 10 taste buds and each taste bud contains about 50 receptor cells.
c. In adult humans, taste buds are located mainly on the outside edge of the
3. How Many Kinds of Taste Receptors?
a. We have long known of the existence of at least four types of “primary” tastes:
sweet, sour, salty, and bitter. Chemicals that alter one receptor but not others
have been used to identify taste receptor types.
b. Adaptation: Decreased response to a stimulus as a result of recent exposure to
it (e.g., if the tongue is soaked in two sour solutions, one after the other, the
second solution will not taste as sour as the first).
c. Cross-adaptation: A reduced response to one taste because of exposure to
another. There is little cross-adaptation in taste.
d. Umami: A taste associated with glutamate. Researchers have found a glutamate
taste receptor responsible for this fifth type of taste.
e. Different chemicals not only excite different receptors, they also produce
different rhythms of action potentials.
4. Mechanisms of Taste Receptors
a. Saltiness receptors work by allowing salt to cross the membrane. The higher
the concentration of salt, the greater the response of the receptors (i.e., the
larger the receptor potential).
b. Sourness receptors detect acids.
c. Sweetness, bitterness, and umami receptors work by activating a G-protein that
releases a second messenger within the cell.
d. To identify the wide range of chemicals that have a bitter taste, which are
usually toxic, we have not one bitter receptor but a family of about 25 bitter
5. Taste Coding in the Brain
a. The perception of taste depends on a pattern of responses across taste fibers.
Taste information from the anterior two-thirds of the tongue travels to the brain
via the chorda tympani, a branch of the seventh cranial nerve (facial nerve).
Information from the posterior tongue and throat is carried to the brain along
branches of the ninth and tenth cranial nerves.
c. These three nerves project to the nucleus of the tractus solitarius (NTS) in
the medulla. The NTS relays information to the pons, lateral hypothalamus,
amygdala, thalamus, and two areas of the cerebral cortex (the insula is
responsible for taste, and the somatosensory cortex is responsible for the sense
of touch on the tongue).
d. Each hemisphere of the cortex receives input mostly from the ipsilateral side of
6. Variations in Taste Sensitivity
a. Phenythiocarbamide (PTC) is a chemical whose taste is controlled by a single
dominant gene. Some people hardly taste PTC, others taste it as bitter, and
some taste it as extremely bitter.
b. The prevalence of nontasters of PTC varies across cultures and is not
obviously related to spiciness of traditional cuisine in those cultures.
c. People who are insensitive to the taste of PTC are less sensitive to other tastes
d. People who taste PTC as extremely bitter are supertasters and have the
highest sensitivity to all tastes.
e. Supertasters have the largest number of fungiform papillae (the type of papillae
near the tip of the tongue).
1. Olfaction: The sense of smell; the detection and recognition of chemicals that come
in contact with membranes inside the nose.
2. Continued stimulation of an olfactory receptor produces adaptation. This adaptation
is more rapid than that of sight or hearing.
3. Olfactory Receptors
a. Olfactory cells: Neurons that line the olfactory epithelium and are responsible
for smell. In mammals, each olfactory cell has cilia (threadlike dendrites)
where receptor sites are located.
b. Olfactory receptors are made up of a family of proteins that traverse the cell
membrane seven times and respond to chemicals outside the cell by causing
changes in a G-protein inside the cell. The G-protein provokes chemical
activities that lead to an action potential.
c. It is estimated that humans have hundreds of different types of olfactory
receptor protein …
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