Chapter 7 – The Other Sensory Systems Flashcards
The intensity of a sound wave
Amplitude
Perception of the intensity of a sound
Loudness
A rapidly talking person sounds louder than slow music of the same physical amplitude
The number of cycles per second, measured in Hz
Frequency
The related aspect of perception of frequency
Pitch
Higher frequency sounds are higher in pitch.
With soundwaves, the height of each wave corresponds to ______, and the number of waves per second corresponds to _______
Amplitude; frequency
When it comes to structures of the ear, anatomists distinguish three parts:
The outer ear, the middle ear, and the inner ear
The outer ear structure of flesh and cartilage that sticks out from each side of the head
Pinna
By altering the reflections of sound waves, the pinna helps us locate the source of a sound. We have to learn to use that information because each person’s pinna is shaped differently from anyone else’s
The eardrum
Tympanic membrane
A membrane of the inner ear. The tympanic membrane connects to three tiny bones that transmit the vibrations to this area.
Oval window
The three tiny bones that transmit the vibrations of sound are known as:
Hammer, anvil, and stirrup
Latin names: malleus, incus, and stapes
Structure in the inner ear containing auditory receptors
Cochlea
A snail-shaped structure.
The auditory receptors that lie along the basilar membrane in the cochlea
Hair cells
Vibrations in the fluid of the cochlea displace the hair cells, thereby opening ion channels in its membrane. The hair cells excite the cells of the auditory nerve, which is part of the eighth cranial nerve
A cross-section through the cochlea, shows three long fluid-filled tunnels:
The scala vestibuli, scala media, and scala tympani
Concept that pitch perception depends on which part of the inner ear has cells with the greatest activity level
Place theory
According to this theory, each frequency activates the hair cells at only one place along the basilar membrane, and the nervous system distinguishes among frequencies based on which neurons respond.
The downfall of this theory is that the various parts of the basilar membrane are bound together too tightly for any part to resonate like a piano string.
Concept that the basilar membrane vibrates in synchrony with a sound, causing auditory nerve axons to produce action potentials at the same frequency
Frequency theory
For example, a sound at 50 Hz would cause 50 action potential’s per second in the auditory nerve.
The downfall of this theory in its simplest form is that the refractory period of a neuron falls far short of the highest frequencies we hear
Tenet that the auditory nerve as a whole produces volleys of impulses for sounds even though no individual axon approaches that frequency
Volley principle
For this principle to work, auditory cells must time their responses quite precisely, and the evidence says that they do. However, beyond about 4000 Hz, even staggered volleys of impulses can’t keep pace with the sound waves.
The hair cells along the basilar membrane have different properties based on their location, and they act as tuned resonators that vibrate only for sound waves of a particular frequency. The highest frequency sounds vibrate hair cells near the ______, and lower frequency sounds vibrate hair cells farther along the membrane near the ____
Base; apex
Impaired detection of frequency changes. For pitch perception, a fair number of people are not part of the normal distribution, includes an estimated 4% of people.
Amusia, often called “tone-deafness”
They have trouble recognizing tunes, can’t tell whether someone is singing off key, and do not detect a wrong note in a melody. Most people also have trouble singing even simple, familiar songs
Through which mechanism do we perceive low-frequency sounds, up to about 100 Hz?
At low frequencies, the basilar membrane vibrates in synchrony with the sound waves, and each responding axon in the auditory nerve sends one action potential per sound wave.
How do we perceive middle-frequency sounds, 100 to 4000 Hz?
At intermediate frequencies, no single axon fires an action potential for each sound wave, but different axons fire for different waves, and so a volley or group of axons fires for each wave
How do we perceive high-frequency sounds, above 4000 Hz?
At high frequencies, The sound causes maximum vibration for the hair cells at one location along the basilar membrane. High-frequency sounds excite hair cells near the base. Low-frequency sounds excite cells near the apex
What evidence suggests that absolute pitch depends on special experiences?
Absolute pitch occurs almost entirely among people who had early musical training and is also more common among people who speak tonal languages, which require greater attention to pitch
Area in the superior temporal cortex in which cells respond best to tones of a particular frequency
Primary auditory cortex or area A1
The organization of the auditory cortex strongly parallels that of the visual cortex.
The auditory cortex provides a kind of map of the sounds. Researchers call it a:
Tonotopic map
How is the auditory cortex like the visual cortex? 4
- Both vision and hearing have “what” and “where” pathways
- Areas in the superior temporal cortex analyze movement of both visual and auditory stimuli. Damage there can cause motion blindness or motion deafness.
- The visual cortex is essential for visual imagery, and the primary auditory cortex is essential for auditory imagery.
- Both the visual and auditory cortices need normal experience early in life to develop normal sensitivities.
What is one way in which the auditory and visual cortices differ?
Damage to the primary visual cortex leaves someone blind, but damage to the primary auditory cortex merely impairs perception of complex sounds without making the person deaf.
People with damage to the primary auditory cortex hear simple sounds reasonably well, unless the damage extends into sub cortical brain areas. Their main deficit is in the ability to recognize combinations or sequences of sounds, like music or speech.
Hearing loss that occurs if the bones of the middle ear fail to transmit sound waves properly to the cochlea
Conductive deafness or middle-ear deafness
Because people with conductive deafness have a normal cochlea and auditory nerves, they hear their own voices which can be conducted through the bones of the skull directly to the cochlea, bypassing the middle ear.
Hearing loss that results from damage to the cochlea, the hair cells, or the auditory nerve
Nerve deafness or inter-ear deafness
Can occur in any degree and may be confined to one part of the cochlea, in which case someone hear certain frequencies and not others.
Frequent or constant ringing in the ears
Tinnitus
Nerve deafness often produces tinnitus. In some cases, tinnitus is due to a phenomenon like phantom limb. Damaged part of the cochlea is like an amputation: if the brain no longer gets its normal input, axons representing other parts of the body may invade a brain area previously responsive to sounds, especially high frequency sounds
Which type of hearing loss would be more common among members of rock bands and why?
Nerve deafness is common among rock band members because their frequent exposure to loud noises causes damage to the cells of the ear
Describe the causes of nerve deafness
Can develop through inheritance or from a variety of disorders:
Exposure of the mother to rubella, syphilis, or other diseases or toxins during pregnancy; inadequate oxygen to the brain during birth; deficient activity of the thyroid gland; certain diseases, including multiple sclerosis and meningitis; childhood reactions to certain drugs, including aspirin; exposure to loud noises
Describe the causes of conductive deafness
Can be caused by diseases, infections, or tumourous bone growth. It is sometimes temporary, and if it persists, it can be corrected either by surgery or by hearing aids that amplify the stimulus.
Describe three methods of sound localization:
- Requires comparing the responses of the two ears. One cue for location is the difference in intensity between the ears. For high-frequency sounds, with wavelengths shorter than the width of the head, the head creates a sound shadow, making the sound louder for the closer ear.
- Difference in time of arrival at the two ears: sound coming from directly in front of you reaches both ears at once. A sound coming directly from the side reaches the closer ear about 600 µs before the other. Sounds coming from intermediate locations reach the two ears at delays between zero and 600 µs.
Most useful for localizing sounds with a sudden onset. - The phase difference between the ears: every sound wave has phases with two consecutive peaks 360° apart. If a sound originates to the side of the head, the sound wave strikes the two ears out of phase. How much out of phase depends on the frequency of the sound, the size of the head, and the direction of the sound. Useful for localizing sounds with frequencies up to about 1500 Hz in humans.
Which method of sound localization is more effective for an animal with a small head? Which is more effective for an animal with a large head? Why?
An animal with a small head localizes sounds mainly by differences in loudness because the ears are not far enough apart for differences in onset time to be very large. An animal with a large head localized sound mainly by differences in onset time because it’s ears are far apart and well-suited to noting differences in phase or onset time
Structures located in the vestibular organ, oriented in three planes and lined with hair cells; sensitive to the directional tilt of the head
Semicircular canals
Acceleration of the head at any angle causes the jelly like substance in one of these canals to push against the hair cells. Action potential’s initiated by cells of the vestibular system travel through part of the eighth cranial nerve to the brain stem and cerebellum.
Like the hearing receptors, the vestibular receptors are modified touch receptors. Calcium carbonate particles called _______ lie next to the hair cells. When the head tilts in different directions, they push against different sets of hair cells and excite them
Otoliths
People with damage to the vestibular system have trouble reading street signs while walking. Why?
The vestibular system enables the brain to shift eye movements to compensate for changes in head position. Without feedback about head position, a person would not be able to correct the eye movements, and the experience would be like watching a jiggling book page
Sensory network that monitors the surface of the body and it’s movements
Somatosensory system
Is not one sense but many, including discriminative touch, deep pressure, cold, warmth, pain, itch, tickle, and the position and movement of joints
Receptor that responds to a sudden displacement of the skin or high frequency vibrations on the skin
Pacinian corpuscle
A chemical, found in hot peppers, that produces a painful burning sensation by releasing substance P; high dosages damage pain receptors
Capsaicin
These somatosensory receptors respond to pain, warmth, and cold
Free nerve ending – unmyelinated or thinly myelinated axons
These somatosensory receptors respond to movement of hairs
Hair-follicle receptors
These somatosensory receptors respond to sudden displacement of skin; low frequency vibration or flutter
Meissner’s corpuscles
These somatosensory receptors respond to sudden displacement of skin; high-frequency vibration
Pacinian corpuscles
These somatosensory receptors respond to light touch
Merkel’s disks
These somatosensory receptors respond to stretch of skin
Ruffini endings
Area of the body connected to a particular spinal nerve
Dermatome
Each spinal nerve innervates or connects to a limited area of the body called a dermatome. Each dermatome overlaps 1/3 to 1/2 of the next dermatome.
In what way is somatosensation several senses instead of one?
We have several types of receptors, sensitive to touch, heat, and so forth, and different parts of the somatosensory cortex respond to different kinds of skin stimulation
Example: the various areas of the somatosensory thalamus send their impulses to different areas of the primary somatosensory cortex, located in the parietal lobe. Two parallel strips in the somatosensory cortex respond mostly to touch on the skin. Two other parallel strips respond mostly too deep pressure and movement of the joints and muscles. In short, various aspects of body sensation remain at least partly separate all the way to the cortex. Along each strip of this matter sensory cortex, different subareas respond to different areas of the body.
The somatosensory cortex acts as a map of body location
What evidence suggests that the somatosensory cortex is essential for the conscious perception of touch?
People are conscious of only those touch stimuli that produce sufficient arousal in the primary somatosensory cortex.
Example: if someone touches you quickly on two nearby points on the hand, you will probably have an illusory experience of a single touch midway between those two points. In other words, the activity corresponds to what you experience, not what has actually stimulated your receptors.
Cutaneous rabbit illusion: if someone taps you very rapidly six times on the wrist and then three times near the elbow, you will have a sensation of something like a rabbit hopping from the wrist to the elbow, with an extra, illusory, stop in between.
The experience evoked by a harmful stimulus which directs your attention toward a danger and holds your attention.
Pain
The prefrontal cortex, which is important for attention, typically responds only briefly to any new light, sound, or touch. With pain, it continues responding as long as the pain lasts
A neurotransmitter released by pain axons in the spinal cord
Substance P
The axons carrying pain information have little or no myelin and therefore conduct impulses relatively slowly, in the range of 2 to 20 m/s. The thicker and faster axons convey ______ pain. The thinner ones convey ______ pain, such as postsurgical pain.
Sharp; duller
Although pain messages reach the brain more slowly than other sensations, the brain processes pain information rapidly. Motor responses to pain are faster than motor responses to touch stimuli
Pain axons release two neurotransmitters in the spinal cord. Mild pain releases the neurotransmitter ________, whereas stronger pain releases both ________ and _________
Glutamate; glutamate; substance P
Although the spinal paths for pain and touch are parallel, what is one important difference between them?
The pain pathway crosses immediately from receptors on one side of the body to a tract ascending the contralateral side of the spinal cord. Touch information travels up the ipsilateral side of the spinal cord to the medulla, where it crosses to the contralateral side. So pain and touch reach neighbouring sites in the cerebral cortex.
Suppose you suffer a cut through the spinal cord on the right side only. For the part of the body below that cut, will you lose pain sensation on the left side or the right side? Will you lose touch sensation on the left side or the right side?
You will lose pain sensation on the left side of the body because pain information crosses the spinal cord at once. You will lose touch sensation on the right side because touch pathways remain on the ipsilateral side until they reach the medulla
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. These areas react not to the sensation but to its _____ ______
Emotional associations
Example: a hypnotic suggestion to feel no pain decreases the responses in the cingulate cortex without much affect on the somatosensory cortex. That is, someone responding to a hypnotic sensation still feels the painful sensation but reacts with emotional indifference.
How do jalapeños produce a hot sensation?
Jalapeños and other hot peppers contain capsaicin, which stimulates receptors that are sensitive to pain, acids, and heat
What would happen to a pain sensation if glutamate receptors in the spinal cord were blocked? What if substance P receptors were blocked?
Blocking glutamate receptors would eliminate weak to moderate pain. However, doing so would not be a good strategy for killing pain. Glutamate is the most abundant transmitter, and blocking it would disrupt practically everything the brain does. Blocking substance P receptors makes intense pain feel mild.
Systems that respond to opiate drugs and similar chemicals
Opioid mechanisms
The brain puts the brakes on prolonged pain through opioid mechanisms. Opiate receptors act by blocking the release of substance P.
Area of the brain stem that is rich in enkephalin synapses.
It was discovered that opiates bind to receptors found mostly in the spinal cord and this area of the midbrain
Periaqueductal gray area
Transmitters that attach to the same receptors as morphine
Endorphins
Inescapable pain is especially potent at stimulating endorphins and inhibiting further pain.
Idea that stimulation of certain axons can close the “gates” for pain messages
Gate theory
The discovery of endorphins provided physiological details for the gate theory. This theory was an attempt to explain why some people withstand pain better than others and why the same injury hurts worse at sometimes than others.
According to the gate theory. Spinal cord neurons that receive messages from pain receptors also receive input from touch receptors and from axons descending from the brain. These other inputs can close the gates for the pain Messages – we see now that they do so at least partly by releasing endorphins.
A drug or other procedure with no pharmacological effects
Placebo
People can experience pain relief from placebos. People who receive placebos do not just say the pain decreased; scans of the brain and spinal cord also show a decreased response to pain.
However, a placebos effects are mainly on emotional response to pain, not on the sensation itself. That is, a placebo decreases the response in the cingulate cortex but not the somatosensory cortex
______ does not block the sharp pain of the surgeons knife. For that, you need a general anesthetic. Instead, it blocks the slower, duller pain that lingers after surgery.
Morphine
Large diameter axons, unaffected by morphine, carry sharp pain. Thinner axons convey dull postsurgical pain, and morphine does inhibit them
Why do opiates relieve dull pain but not sharp pain?
Endorphins block messages from the thinnest pain fibers, conveying dull pain, but not from thicker fibers, carrying sharp pain
How do the pain-relieving effects of cannabinoids differ from those of opiates?
Unlike opiates, cannabinoids exert most of their pain-relieving effects in the peripheral nervous system, not the CNS
Damaged or inflamed tissue, such as sunburned skin, releases ______, nerve growth factor, and other chemicals that help repair the damage but also magnify the responses of nearby heat and pain receptors. Nonsteroidal anti-inflammatory drugs, such as ibuprofen, relieve pain by reducing the release of chemicals from damaged tissues.
Histamine
How do ibuprofen and other nonsteroidal anti-inflammatory drugs decrease pain?
Anti-inflammatory drugs block the release of chemicals from damaged tissue, which would otherwise magnify the effects of pain receptors
Why is it preferable to start taking morphine before an operation instead of waiting until later?
The morphine will not decrease the sharp pain of the surgery itself. However, it will decrease the barrage of pain stimuli that might sensitize pain neurons.
In what ways are hurt feelings similar to physical pain?
Hurt feelings activate the cingulate cortex, just as physical pain does. Also, acetaminophen relieves hurt feelings as well as physical pain
You have at least two kinds of itch. They feel about the same, but the causes are different. Describe them
- When you have mild tissue damage – such as when your skin is healing after a cut – your skin releases histamines that dilate blood vessels and produce an itching sensation
- Contact with certain plants, especially cowhage – a tropical plant with Barb hairs – also produces itch.
Antihistamines block the itch that histamines cause but not the itch that cowhage causes. Conversely, rubbing the skin with capsaicin relieved the itch that cowhage causes, but it has little effect on the itch that histamine causes
Itch axons activate certain neurons in the spinal cord that produce a chemical called ____-_____ _____. Blocking that peptide has been shown to decrease scratching in mice without affecting their responses to pain
Gastrin-releasing peptide
The itch pathways are ____ to respond, and when they do, the axons transmit impulses at the unusually slow velocity of only half a metre per second.
Slow
Itch is useful because it directs you to scratch the itchy area and remove whatever is irritating your skin. Vigourous scratching produces mild pain, and pain ______ itch. Opiates, which decrease pain, _____ itch.
Inhibits; increases
This inhibitory relationship between pain and itch is the strongest evidence that itch is not a type of pain
Do opiates increase or decrease itch sensations?
Opiates increase itch by blocking pain sensations. Pain decreases itch
Suppose someone suffers from constant itching. What kinds of drugs might help relieve it?
Two kinds of drugs might help – antihistamines or capsaicin – depending on the source of the itch. Also, drugs that block gastrin-releasing peptide might help
Concept that each receptor responds to a limited range of stimuli and has a direct line to the brain
Labeled-line principle
Idea that each receptor responds to a wide range of stimuli and contributes to the perception of every stimulus in its system
Across-fiber pattern principle
Occurs in colour perception, auditory pitch perception, and taste and smell
Of the following, which one uses and across-fiber pattern code?
A) flipping a light switch
B) playing a piano
C) dialling a telephone number
Dialing a telephone number is an example of an across-fiber pattern code, because the result depends on the combination of numbers. No one of its numbers by itself has a clear meaning
Taste results from stimulation of the ____ ____, The receptors on the tongue.
Taste buds
When we talk about the taste of food, we generally mean flavor, which is a combination of taste and smell. Where as other senses remain separate throughout the cortex, taste and smell axons converge onto many of the same cells in an area called the Endopiriform cortex
The taste receptors in the taste buds of mammals are located in these on the surface of the tongue
Papillae
A given papilla may contain up to 10 or more taste buds, and each taste bud contains about 50 receptor cells
In adult humans, taste buds lie mainly along:
The edge of the tongue
Decreased response to a stimulus as a result of recent exposure to it.
For example: tasting one sour solution after another will cause you to find that the second solution tastes less sour than usual, or not sour at all.
This phenomenon reflects the fatigue of receptors sensitive to sour tastes.
Adaptation
Reduced response to one taste after exposure to another.
Example: After tasting something sour, tasting something salty, sweet, or bitter will have taste about the same as usual.
Cross-adaptation
Evidently, the sour receptors are different from the other taste receptors. Similarly, you can show that salt receptors are different from the others and so forth.
In addition to the fact that different chemicals excite different receptors, they produce different rhythms of ___ ____.
Action potentials
The patterns of the action potential is actually code taste experiences.
Study: researchers stimulated rats brain cells responsive to taste with an electrical pattern matching that for quinine, which is bitter. The rats backed away from whatever they were drinking at the time, reacting as if they were tasting something bitter. Electrical stimulation at other temporal patterns did not cause this reaction
Describe the mechanisms of the different taste receptors
Salt: a saltiness receptor, which detects the presence of sodium, simply permits sodium ions on the tongue to cross its membrane.
Sour receptors detect the presence of acids
Sweetness, bitterness, and umami receptors resemble the metabotropic synapses discussed earlier. After a molecule binds to one of these receptors, it activates a G-protein that releases a second messenger within the cell.
Bitterness: bitter substances only common factor is that they are to some degree toxic. We have not one bitter receptor but a family of 25 or more. One consequence of having so many bitter receptors is that we detect a great variety of dangerous chemicals. The other is that because each type of bitter receptor is present in small numbers, we can’t detect very low concentrations of bitter substances
Although each receptor detects just one kind of taste, several receptors feet into the next set of cells in the taste system. So, beyond the receptors each neuron responds to two or more kinds of taste, and taste depends on a pattern of responses across fibers, not a system of pure labeled lines
Suppose you find a new, unusual-tasting food. How could you determine whether we have a special receptor for that food or whether we taste it with a combination of the other known taste receptors?
You could test for cross-adaptation. If the new taste cross-adapts with others, then it uses the same receptors. If it does not cross-adapt, it may have a receptor of its own. Another possibility would be to find some procedure that blocks this taste without blocking other tastes
Although the tongue has receptors for bitter taste, researchers have not found neurons in the brain cells that respond more strongly to bitter than to other tastes. Explain, then, how it is possible for the brain to detect bitter tastes.
Two possibilities: first, bitter taste produces a distinctive temporal pattern of responses in cells sensitive to taste. Second, even if no one cell responds strongly to bitter tastes, the pattern of responses across many cells may be distinctive. Analogously to vision, no cone responds primarily to purple, but we nevertheless recognize purple by its pattern of activity across a population of cones
If someone injected into your tongue a chemical that blocks the release of second messengers, how would it affect your taste experiences?
The chemical would block your experiences of sweet, bitter, and umami but should not prevent you from tasting salty and sour
Structure in the medulla that receives input from taste receptors
Nucleus of the tractus solitarius or NTS
People with heightened sensitivity to all tastes and mouth sensations.
Supertasters
Tend to have strong food preferences. On average, like their favourite foods more than other people, and avoid their least favourite foods more. Most also avoid strong-tasting or spicy foods.
Describe taste coding in the brain
Information from the receptors in the anterior two thirds of the tongue travel to the brain along the chorda tympani, a branch of the seventh cranial nerve or the facial nerve. Taste information from the posterior tongue and throat travels along branches of the ninth and 10th cranial nerves. If someone anesthetized your chorda tympani, you would no longer taste anything in the anterior part of your tongue. However, you would probably not notice because you would still taste with the posterior part – you could also experience taste phantoms.
The taste nerves project to the nucleus of the tractus solitarius,a structure in the medulla. From the NTS, information branches out, reaching the pons, the lateral hypothalamus, the amygdala, the ventral-posterior thalamus, and two areas of the cerebral cortex.
One of these areas, the somatosensory cortex, responds to the touch aspects of tongue stimulation. The other area, known as the insula, is the primary taste cortex. Each hemisphere of the cortex receives input mostly from the ipsilateral side of the tongue. One connection from the insula goes to a small portion of the frontal cortex, which maintains memories of recent taste experience.
What is the difference between tasters and supertasters?
The difference depends on the number of fungiform papillae near the tip of the tongue, with supertasters having the largest number
What causes supertasters to be more sensitive to taste than other people are?
They have more taste buds near the tip of the tongue
The sense of smell, which is the response to chemicals that contact the membranes inside the nose
Olfaction
Neurons responsible for smell, located on the olfactory epithelium in the rear of the nasal air passages
Olfactory cells
In mammals, each olfactory cell has cilia – threadlike dendrites – that extend from the cell body into the mucus surface of the nasal passage. Olfactory receptors are located on the cilia
How do olfactory receptors resemble metabotropic neurotransmitter receptors?
Like metabotropic neurotransmitter receptors, an olfactory receptor asked you a G-protein that triggers further events within the cell
Describe the numbers of olfactory receptors
The best estimate is that humans have several hundred olfactory receptor proteins. Although each chemical excites several types of receptors, the most strongly excited receptor inhibits the activity of other ones any process analogous to lateral inhibition. The net result is that a given chemical produces a major response in one or two kinds of receptors and weak responses in a few others
Describe the implications of the number of receptors for coding olfactory information
Researchers were surprised to find so many kinds of olfactory receptors given the few cones and five taste receptors. That diversity makes possible narrow specialization of functions.
Each olfactory receptor responds to only a few stimuli. The response of one receptor might mean, “a fatty acid with a straight chain of 3 to 5 carbon atoms” and the response of another might mean “either a fatty acid or an aldehyde with straight chain of 5 to 7 carbon atoms”. The combined activity of those two receptors identifies a chemical precisely.
Why so many receptor types? The main reason is that light energy can be arranged along a single dimension – wavelength. Olfaction processes airborne chemicals that do not range along a single continuum
Describe what happens when an olfactory receptor is stimulated
When it is stimulated, it’s axon carries an impulse to the olfactory bulb. Although the receptors sensitive to a particular chemical are scattered haphazardly in the nose, their axons find their way to the same target in the olfactory bulb, such that chemicals of similar smell excite neighbouring areas, and chemicals of different smell excite more separated areas. A slight change in a smell produces a striking change in which cells are active, where as a change in smell intensity produces much less change – cells of the olfactory bulb code the identity of smells
The olfactory bulb send axons to the olfactory Area of the cerebral cortex. A complex substance such as food activates a scattered population of cells.
Olfactory receptors are vulnerable damage because they are exposed to the air. Unlike your receptors for vision and hearing, which remain with you for a lifetime, an olfactory receptor has an average survival time of just over:
A month
At that point, a stem cell matures into a new olfactory cell in the same location as the first and expresses the same receptor protein. It’s axon then has to find its way to the correct target in the olfactory bulb. Each axon contains copies of its receptor protein, which it uses like an identification card to find its correct partner
Describe individual differences in olfaction
Women detect odours more readily than men, and the brain responses to odours are stronger in women than in men.
If people repeatedly attend to some faint odor, young adult women gradually become more and more sensitive to it, until they can detect it in concentrations 1/10000 of what they could at the start. Effect not present in men, girls before puberty, and women after menopause – apparently depends on female hormones
Through the wonders of bioengineering, researchers can delete a particular gene that controls the channel through which most potassium passes in the membranes of certain neurons of the olfactory bulb. Mice lacking this potassium channel had a greatly enhanced sense of smell.
What is the mean lifespan of an olfactory receptor?
Most survive a little more than a month before dying and being replaced
What kind of person becomes more sensitive to a smell after sniffing it repeatedly?
Young adult women become highly sensitive to a smell after sniffing it repeatedly
A set of receptors, located near, but separate from, the olfactory receptors. Specialized to respond only to pheromones
Vomeronasal organ or VNO
Chemicals released by an animal that affect the behaviour of other members of the same species
Pheromones
What is one major difference between olfactory receptors and those of the vomeronasal organ?
Olfactory receptors adapt quickly to a continuous odor, whereas receptors of the vomeronasal organ continue to respond. Also, vomeronasal sensations are apparently capable of influencing behaviour even without being consciously perceived
The experience some people have in which stimulation of one sense evokes a perception of that sense and another one also
Synesthesia
Example: one person with synaesthesia was able to find a 2 among a group of 5’s in a display consistently faster than other people, explaining that he just looked for a patch of Orange.
If someone reports seeing a particular letter in color, in what way is it different from a real color?
Someone who perceives a letter as yellow – when it is actually in black ink – can nevertheless see it on a yellow page
Describe the possible anatomical basis of synaesthesia
One hypothesis is that some of the axons from one cortical area branch into another cortical area.
For example, one woman suffered damage to the somatosensory area of her right Salamis. Initially she was in sensitive to touch and her left arm and hand. Over a year and a half, she gradually recovered part of her touch sensation. However, during that period, the somatosensory area of her right cortex was receiving little input. Some axons from her auditory system invaded the somatosensory cortex. As a result, she developed an unusual auditory-to-touch synesthesia. Many sounds cause her to feel an intense tingling
