Weeks 5-8 Flashcards
What are chromosomes?
Strands of genes that comes in pairs
How do male mammal chromosomes differ from others?
They have unpaired X and Y chromosomes with different genes
How are DNA and RNA (ribonucleic acid) related?
DNA serves as a template for the synthesis of RNA.
What is messenger RNA?
A template for the synthesis of protein molecules
What are the four bases in DNA?
Adenine
Guanine
Cytosine
Thymine
How does the order of bases affect RNA and DNA?
Determines the order of corresponding bases along an RNA molecule, which in turn determines the order of amino acids that compose a protein.
E.g. Cytosine + adenine + guanine result in the protein adding glutamine
What does homozygous mean?
What does heterozygous mean?
You have the same genes on your two copies of a chromosome.
You have an unmatched pair of genes.
What’s an example of heterozygous genes?
A gene for blue eyes on one chromosome and a gene for brown eyes on the other.
What are dominant, recessive, and intermediate genes?
Dominant
Strong effect in either the homozygous or heterozygous condition
Recessive
Shows its effects only in the homozygous condition
E.g. A gene for brown eyes is dominant and a gene for blue eyes is recessive. If you have one gene for brown eyes and one gene for blue, you will have brown eyes.
Why can’t genes be used to make predictions?
Almost any characteristic depends on more than one gene.
Changes in environment can increase or decrease the expression of a gene.
What are autosomal chromosomes and genes?
Chromosomes that are non sex-linked. Genes on autosomal chromosomes are called autosomal genes.
How are chromosomes contributed during reproduction?
Female contributes an X.
Male contributes either an X or a Y.
Which genes are scientists referring to when they refer to sex-linked genes?
X-linked genes.
Y chromosome is small with relatively few genes of its own.
Why does red-green colourblindness occur?
A man may have the recessive form of the gene on his X chromosome because he has no other X chromosome.
A woman is colour deficient only when she has the gene on both of her chromosomes; it is thus more rare for women.
What is a codon?
A sequence of 3 RNA bases
Represents a type of amino acid
What are sex-linked genes?
Genes on the sex chromosomes (designated X and Y in mammals).
USUALLY referring to X-linked genes.
What are autosomal genes?
Genes that are not sex-linked
What causes a man to be colour blind?
What causes a woman to be colour blind?
Having recessive form of gene on his X chromosome (he has no other X chromosome that can see colour).
Affects 8% of population.
Having recessive form of gene on BOTH X chromosomes (if only one carries it, she can see colour).
Affects less that 1% of population.
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- How does a sex-linked gene differ from a sex-limited gene?
- A sex-linked gene is on the X or Y chromosome.
A sex-limited gene is on an autosomal chromosome, but activated in one sex more than the other.
Why are most gene mutations disadvantageous?
Evolution has had eons to select the best makeup of each gene
What happens when a gene is duplicated or deleted?
What disorders might be related to duplications or deletions?
Part of a chromosome that usually appears once might appear twice or not at all.
It is possible for these to be helpful, but most are not.
Microduplications / microdeletions are responsible for several psychological or neurological disorders, probably including some cases of schizophrenia.
What field deals with changes in gene expression?
Epigenetics
Which cells are the only ones not to contain DNA?
Red blood cells
How does gene activity change over time?
Genes may be more or less active during different stages of life, such as fetal, infancy, adolescence, adulthood etc.
A gene may be active in one person and not another.
Various experiences may turn a gene on or off, such as forming a new habit.
How do experiences modify genetic expression?
Proteins called histones bind DNA into a shape like string wound around a ball. Histone molecules in the ball have loose ends to which certain chemical groups can attach. To activate a gene, the DNA must partially unwind from the histones.
New experiences (such as maternal deprivation, exposure to drugs, new learning, etc) alter the chemical environment within the cell.
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What are some ways that identical twins may differ?
Handedness
Mental health
- How does an epigenetic change differ from a mutation?
- A mutation is a permanent change in part of a chromosome.
An epigenetic change is an increase or decrease in the activity of a gene or group of genes.
- How does adding a methyl or acetyl group to a histone protein alter gene activity?
- Adding a methyl group turns genes off.
An acetyl group loosens histone’s grip and increases gene activation.
Is singing ability depend on heredity or environment?
Both
How do we determine the heritability of a characteristic?
- Monozygotic (from one egg) and dizygotic (from two eggs) twins
A stronger resemblance between monozygotic twins than dizygotic indicates a genetic contribution. - Studies of adopted children
Tendency for adopted children to resemble their biological parent indicates hereditary influence.
However bio mother contributes not just genes but also prenatal environment. - Identifying specific genes linked to some behaviour. There are two approaches:
“Candidate gene” approach - identified one gene with significant influence and other genes with moderate influence. However many studies have yielded small or uncertain effects.
“Genome wide association study” - examines all genes while comparing two groups, such as people with and without schizophrenia.
BUT this approach tests thousands of hypotheses at once (one for each gene) and there is risk of seeing an apparent effect by accident, especially in studies with a small sample.
Can also have misleading results when applied to ethnically diverse sample; what is a disorder is more common in one ethnic group than another? Then any other gene that is common in that ethnic group will appear to be a risk factor!
What behaviours have been found to have significant heritability?
Almost all, including loneliness, neuroticism, TV watching, childhood misbehaviour, social attitudes, cognitive performance, educational attainment, and speed of learning a second language.
Religious affiliation is NOT heritable.
- What are the main types of evidence to estimate the heritability of some behavior?
- One type of evidence is greater similarity between monozygotic twins than dizygotic twins. Another is resemblance between adopted children and their biological
parents. A third is a demonstration that a particular gene is more common than average among people who show a particular behavior.
- Suppose someone determines the heritability of IQ scores for a given population. Then society changes in a way that provides the best possible opportunity for everyone within that population. Will heritability of IQ increase, decrease, or stay
the same?
- Heritability will increase. Heritability
estimates how much of the variation is due to differences in genes. If everyone has the same environment, then differences in environment cannot account for much
of the remaining differences in IQ scores. Therefore, the relative role of genetic differences will be greater.
- What example illustrates the point that even if some characteristic is highly heritable, a change in the environment can alter it?
- Keeping a child with the PKU gene on a strict lowphenylalanine diet prevents the mental retardation that the gene ordinarily causes. The general point is that sometimes a highly heritable condition can be modified environmentally.
How can evolution be described in terms of genetics?
A change over generations in the frequency of various genes in a population
Does the use or misuse of some structure or behaviour cause an evolutionary increase or decrease in that feature?
No - e.g. using your muscles will not result in your children having bigger muscles.
Have humans stopped evolving?
No - if people with certain genes have more than the average number of children, their genes will spread in the population.
Does evolution mean improvement?
Not necessarily. It improves “fitness”, the number of copies of one’s genes that endure in later generations. But it may promote features that become disadvantageous in new environments. E.g. Peacock tail feathers may attract predators in new environments.
Does evolution benefit the individual or the species?
Neither: It benefits the genes!
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- Many people believe the human appendix is useless. Will it become smaller and smaller with each generation?
- No. Failure to need a structure does not make it smaller in the next generation. The appendix will shrink only if people with a gene for a smaller appendix reproduce more successfully than other people do.
What evolutionary explanation might account for goose bumps in humans?
The behaviour involved in our remote furred ancestors to provide warmth or amplify size when threatened, and we inherited the mechanism.
How might natural selection promote altruism?
Kin selection - selection for a gene that benefits the individual’s relatives.
Reciprocal altruism - individuals help those that will return the favour.
Group selection - altruistic groups thrive better than less cooperative ones
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- What is a sex-linked gene?
A. A gene that influences sexual behavior
B. A gene that has greater effects on one sex than the other
C. A gene on either the X or Y chromosome
D. A gene that becomes activated during sexual behavior
C. A gene on either the X or Y chromosome
- What is a sex-limited gene?
A. A gene that influences sexual behavior
B. A gene that has greater effects on one sex than the other
C. A gene on either the X or Y chromosome
D. A gene that becomes activated during sexual behavior
B. A gene that has greater effects on one sex than the other
3. What does a microdeletion remove? A. Part of a protein B. Part of a brain wave C. Part of a chromosome D. Part of a neuron
C. Part of a chromosome
- How does an epigenetic change differ from a mutation?
A. An epigenetic change is a duplication or deletion of part of a gene.
B. An epigenetic change alters gene activity without replacing any gene.
C. An epigenetic change alters more than one gene at a time.
D. An epigenetic change is beneficial, whereas a mutation is harmful.
B. An epigenetic change alters gene activity without replacing any gene.
- How does adding a methyl or acetyl group to a histone protein alter gene activity?
A. A methyl group turns genes off. An acetyl group loosens histone’s grip and increases gene activation.
B. A methyl group turns genes on. An acetyl group tightens histone’s grip and decreases gene activation.
C. A methyl group increases the probability of a mutation, whereas an acetyl group decreases the probability.
D. A methyl group decreases the probability of a mutation, whereas an acetyl group increases the probability.
A. A methyl group turns genes off. An acetyl group loosens histone’s grip and increases gene activation.
- Most estimates of heritability of human behavior use what type(s) of evidence?
A. Studies of changes in behavior as people grow older
B. Studies of similarities between parents and children
C. Comparisons of twins and studies of adopted children
D. Comparisons of people living in different cultures
C. Comparisons of twins and studies of adopted children
- What is the difference between monozygotic (MZ) and dizygotic (DZ) twins?
A. MZ twins develop from two eggs, whereas DZ twins develop from a single egg.
B. MZ twins develop from a single egg, whereas DZ twins develop from two eggs.
C. MZ twins are one male and one female, whereas DZ twins are of the same gender.
D. MZ twins are of the same gender, whereas DZ twins are one male and one female.
B. MZ twins develop from a single egg, whereas DZ twins develop from two eggs.
- Which of the following offers strong evidence that environmental changes can largely counteract the effect of a gene?
A. The effects of temperature on children with autism spectrum disorder
B. The effects of diet on children with phenylketonuria (PKU)
C. The effects of muscle training on children who have suffered a concussion
D. The effects of sleep on children with malaria
B. The effects of diet on children with phenylketonuria (PKU)
- Which of these is responsible for evolutionary changes in a species?
A. Using or failing to use part of the body increases or decreases its size for the next generation.
B. A gene that has long-term benefits to the species will become more common.
C. Individuals with certain genes reproduce more than average.
D. Evolutionary changes anticipate the adaptations that will be advantageous in the future.
C. Individuals with certain genes reproduce more than average.
- What, if anything, can we predict about the future of human evolution?
A. People will get smarter, wiser, and more cooperative.
B. People will not change, because evolution no longer affects humans.
C. People will become more like whichever people tend to have the most children.
D. We cannot make any of these predictions.
C. People will become more like whichever people tend to have the most children.
- Why do human infants show a grasp reflex?
A. The reflex is an accidental by-product of brain development.
B. The reflex is an imitation of actions the infant sees adults doing.
C. The reflex helps the infant develop motor skills that will be helpful later.
D. The reflex was advantageous to infants of our remote ancestors.
D. The reflex was advantageous to infants of our remote ancestors.
What genes regulate the expression of other genes and control the start of anatomical development?
What effects do mutations of these genes have in humans?
Homeobox genes
Brain disorders and physical deformities
When does the human central nervous system begin to form?
When the embryo is about two weeks old
When do first muscle movements in fetuses occur?
7.5 weeks
Which brain areas are most likely to deteriorate in conditions such as Alzheimers?
Those that are slowest to develop, like the prefrontal cortex
Describe the growth and development of neurons.
- Proliferation - production of new cells
- Migration - cells move to different areas
- Differentiation - cells become neurons or glia
- Synaptogenesis - neurons form synapses. Continues throughout lifespan.
- Myelination - process by which glia produce myelin sheath
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Which kinds of neurons can be formed new in adults?
Olfactory receptors
Hippocampus (2% per year)
Basal ganglia
How could researchers determine whether new neurons form in the adult brain in humans?
Carbon dating using 14C.
Researchers have found 14C concentrations corresponding to the year of birth in various studies.
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- What was Sperry’s evidence that axons grow to a specific target instead of attaching at random?
- If he cut a newt’s eye and inverted it, axons grew back to their original targets, even though the connections were inappropriate to their new positions on the eye.
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- If axons from the retina were prevented from showing spontaneous activity during early development, what would be the probable effect on development of the thalamus?
- The axons would attach based on a chemical gradient but could not fine-tune their adjustment based on experience. Therefore, the connections would be less precise.
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What is neural Darwinism?
In the development of the nervous system, we start with more neurons and synapses than we can keep. The most successful combinations survive, and the others fail.
What did Rita Levi-Montalcini discover about the relationship between muscles and axons?
Muscles don’t determine how many axons form; they determine how many survive.
What happens to cells that do not receive nerve growth factor (NGF) from a muscle?
It dies through a process called apoptosis.
What does loss of cells during the natural course of development in the brain indicate?
Maturation of successful cells is linked to simultaneous loss of less successful ones
What is a neurotrophin?
Chemical that promotes the survival and activity of neurons.
Essential for growth of axons and dendrites, formation of new synapses, and learning.
What condition is linked to abnormalities in brain-derived neurotrophic factors (BDNF)?
Depression
- What process assures that the spinal cord has the right number of axons to innervate all the muscle cells?
- The nervous system builds more neurons than it needs and discards through apoptosis those that do not make lasting synapses.
- What class of chemicals prevents apoptosis in the sympathetic nervous system?
- Neurotrophins, such as nerve growth factor
- At what age does a person have the greatest number of neurons— early in life, during adolescence, or during adulthood?
- The neuron number is greatest early in life.
What effect does a mother drinking during pregnancy have on the child?
- Thinning of the cerebral cortex
- Fetal alcohol syndrome
- Interferes with neuron proliferation
- Impairs neuron migration and differentiation
- Impairs synaptic transmission
What effect does alcohol have on neurons?
Alcohol kills neurons by apoptosis by inhibiting receptors for glutamate, the brain’s main excitatory transmitte and enhances receptors for GABA, the main inhibitory transmitter.
- Anesthetic drugs and anxiety-reducing drugs increase activity of GABA, decreasing brain excitation. Why would we predict that exposure to these drugs might be dangerous to the brain of a fetus?
- Prolonged exposure to anesthetics or anxiety-reducing drugs might increase apoptosis of developing neurons. Increased GABA activity decreases excitation, and developing neurons undergo apoptosis if they do not receive enough excitation.
- In the ferret study, how did the experimenters determine that visual input to the auditory portions of the brain actually produced a visual sensation?
- They trained the ferrets to respond to stimuli on the normal side, turning one direction in response to sounds and the other direction to lights. Then they presented light to the rewired side and saw that the ferret again turned in the direction it had associated with lights.
How do dendrites change as we age?
The central structure becomes stable by adolescence, but the branches remain flexible throughout life.
What accounts for enchanced neuronal changes of an enriched environment in rats?
Mostly physical activity, but also partially the interesting experiences and social interactions.
What is far transfer?
The idea that training in a difficult subject will enhance intellect in other ways too. It has only a weak effect.
- An enriched environment promotes growth of axons and dendrites in laboratory rodents. What is known to be one important reason for this effect?
- Animals in an enriched environment are more active, and their exercise enhances growth of axons and dendrites.
Do blind people actually become better at other senses?
Sort of - rather they improve their attention to other senses. E.g. Blind people have greater than average touch sensitivity, especially those that read braille.
What surprising finding did researchers discover about brain activity in blind people?
Substantial activity in the occipital cortex, which is usually limited to visual information.
In people blind since birth, the occipital cortex also responds to auditory information.
A similar finding occurred in people deaf from birth; touch and vision come to activate what would be the auditory cortex in deaf people.
- Name two kinds of evidence indicating that touch information from the fingers activates the occipital cortex of people blind since birth.
- First, brain scans indicate increased activity in the occipital cortex while blind people perform tasks such as feeling two objects and saying whether they are the same or different. Second, temporary inactivation of the occipital cortex blocks blind people’s ability to perform that task, without affecting the ability of sighted
people.
How do we know that brain differences in students are the results of training, not the cause of interest in a subject?
Longitudinal studies of students before and after training showed brain differences in those who took training, but no changes in those who didn’t.
- Which brain area shows expanded representation of the left hand in people who began practicing stringed instruments in childhood and continued for many years?
- Somatosensory cortex (postcentral gyrus) of the right hemisphere.
What is focal hand dystonia or “musician’s cramp”?
- Extensive practice of violin, piano, or other instruments causes expanded representation of the fingers in the somatosensory cortex, as well as displacement of representation of one or more fingers in the motor cortex.
If the sensory representation of two fingers overlaps too much, the person cannot feel them separately or move them separately.
- Why is immaturity of the prefrontal cortex not a satisfactory explanation for risky behaviors in adolescents?
- As the teenage years progress, risky behavior tends to increase, even though the prefrontal cortex is becoming more mature.
Why might cognition in older people be underestimated? 3 reasons.
- People deteriorate at different rates. Those who exercise more often maintain good cognitive function.
- Those who may be slower in certain intellectual activities have developed a great base of knowledge and experience to draw on.
- Older people find ways to compensate for losses, such as by activating more widespread brain areas to compensate for decreased arousal in one or two areas.
What procedures might help slow cognitive decline in old age?
Exercise!
Potentially chemical interventions, such as blood transfusion, although this requires more research.
- In early brain development, what is the relationship between the sensory systems and muscle movements?
A. The sensory systems develop before the first muscle movements.
B. The first muscle movements occur at the same time as when the sensory systems develop.
C. The first muscle movements occur before the sensory systems develop.
D. First vision develops, then movements, and then the other sensory systems.
C. The first muscle movements occur before the sensory systems develop.
- Which parts of the cerebral cortex are most likely to deteriorate in Alzheimer’s disease and other conditions?
A. The areas that mature at the earliest ages, such as the primary visual cortex.
B. The areas most distant from the heart, such as the parietal cortex.
C. The areas responsible for emotional processing, such as the amygdala.
D. The areas that mature at the latest age, such as the prefrontal cortex.
D. The areas that mature at the latest age, such as the prefrontal cortex.
- In which areas of the human brain do some new neurons develop during adulthood?
A. The primary visual cortex and the primary auditory cortex
B. The hippocampus and the basal ganglia
C. The olfactory bulbs and the areas responsible for speech
D. The corpus callosum and the cerebellum
B. The hippocampus and the basal ganglia
- When Sperry cut a newt’s optic nerve and turned the eye upside down, what happened?
A. Axons of the optic nerve grew randomly and attached diffusely to target cells.
B. Axons of the optic nerve grew back to their original targets.
C. Axons of the optic nerve grew back to targets appropriate to their new location in the eye.
D. At first the axons grew back randomly, but then they established appropriate connections by learning.
B. Axons of the optic nerve grew back to their original targets.
5. In the sympathetic nervous system, which of the following prevents apoptosis? A. Steroid hormones B. Nerve growth factor C. Physical exercise D. Myelination
B. Nerve growth factor
- Why does the spinal cord have the right number of axons to innervate all the muscle cells?
A. Each muscle cell sends a chemical message telling the spinal cord to make a neuron.
B. The genes cause a certain number of neurons to form and the same number of muscles to form.
C. Immature cells divide, with one daughter cell becoming a neuron and the other becoming a muscle.
D. The spinal cord makes an excess of neurons, but those that fail to innervate a muscle die.
D. The spinal cord makes an excess of neurons, but those that fail to innervate a muscle die.
7. At what age does a person have the largest number of neurons? A. Before or shortly after birth B. Equally at all times of life C. Adolescence D. Adulthood
A. Before or shortly after birth
- If a pregnant woman drinks alcohol, alcohol harms the brain of the fetus not only while it is in the system, but also while it
is washing away after drinking. What is the danger while alcohol is washing away?
A. Temperature in the brain may decrease.
B. Blood pressure in the brain may decrease.
C. Excess inhibition at GABA synapses can lead to apoptosis.
D. Overstimulation at glutamate synapses can poison the mitochondria.
D. Overstimulation at glutamate synapses can poison the mitochondria.
- In the ferret study, what evidence indicated that visual input to the auditory portions of the brain actually produced a visual sensation?
A. Bright flashes of light to the rewired eye caused the ferrets to blink both eyes.
B. Recordings from individual cells of the rewired temporal cortex showed the same patterns usually seen in cells of the occipital cortex.
C. Ferrets could find their way around an unfamiliar room even with the normal eye closed.
D. Ferrets that learned to turn one way in response to light in the normal eye turned the same way to light in the rewired eye.
D. Ferrets that learned to turn one way in response to light in the normal eye turned the same way to light in the rewired eye.
10. An enriched environment including social interactions promotes growth of axons and dendrites in laboratory rodents. What else can produce the same effect? A. Improved diet B. Physical activity C. Exposure to music D. Extra sleep
B. Physical activity
- According to most research, what are the effects of computerized programs to practice memory skills?
A. Temporary improvement of the skills that were practiced
B. Temporary improvement of both the practiced skills and general intelligence (“far transfer”)
C. Long-term improvement of both the practiced skills and general intelligence (“far transfer”)
D. No benefits, not even temporarily
A. Temporary improvement of the skills that were practiced
- If a person is born blind, what happens to the occipital (“visual”) cortex?
A. Its cells shrink and gradually die.
B. Its cells remain intact but forever inactive.
C. Its cells become responsive to touch or hearing.
D. Its cells become spontaneously active, producing hallucinations.
C. Its cells become responsive to touch or hearing.
- In people who practice violin or other stringed instruments for many years, what changes in the cerebral cortex?
A. Both hemispheres begin controlling speech equally.
B. Parts of the occipital cortex stop responding to vision and switch to hearing.
C. A larger than average portion of the cortex responds to the passage of time.
D. A larger than average portion of the cortex responds to fingers of the left hand.
D. A larger than average portion of the cortex responds to fingers of the left hand.
- What causes musician’s cramp?
A. Changes in the muscles and tendons of the hand
B. Rewiring of the cerebral cortex
C. Loss of myelin on the motor nerves to the hand
D. Changes in the touch receptors of the hand
B. Rewiring of the cerebral cortex
- What is the most likely biological explanation for increased risky behavior among adolescents?
A. Immaturity of the prefrontal cortex
B. Increased activity in brain areas that anticipate reward
C. Increased activity in brain areas responsible for depressed mood
D. Immaturity of the corpus callosum
B. Increased activity in brain areas that anticipate reward
- Why do many older people continue to hold important jobs in spite of the declines in memory and brain function that are known to occur in old age?
A. Laws prevent them from being fired.
B. Most of their jobs don’t require much brain activity.
C. Old people take the credit for work that younger people actually do.
D. The declines on average do not apply to all people.
D. The declines on average do not apply to all people.
How do we know that we see light rays, and that we don’t send out sight rays?
When we open our eyes, we can already see light - we don’t have to wait for sight rays to reach their destination.
Ibn al-Haytham
- If someone electrically stimulated the auditory receptors in your ear, what would you perceive?
- Because of the law of specific nerve energies, you would perceive it as sound, not as shock. (Of course, a strong enough shock might spread far enough to excite
pain receptors also.)
- If it were possible to flip your entire brain upside down, without breaking any of the connections to sense organs or muscles, what would happen to your perceptions of what you see, hear, and so forth?
- Your perceptions would not
change. The way visual or auditory information is coded in the brain does not depend on the physical location within the brain. Seeing something as “on top” or “to the left” depends on which neurons are active but does not depend on the physical location of those neurons.
Explain how the eye works.
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What cells does light pass through en route to the receptors?
Ganglion, amacrine and bipolar cells.
Where is the blind spot and why?
The point at which the optic nerve exits through the back of the eye.
- The blind spot has no receptors because it is occupied by exiting axons and blood vessels.
How can we see properly despite the blind spot?
Everything the blind spot of one eye can’t see, the other eye can see.
What are the differences between foveal vision and peripheral vision?
Foveal - better acuity (sensitivity to detail)
Peripheral - better sensitivity to dim light
What might interfere with peripheral vision?
Other nearby objects
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What are the two types of receptors and what are they good at?
Rods
Abundant in periphery of retina
Respond to faint light, but not useful in daylight
Cones
Abundant in and near fovea
More useful in bright light
Essential for colour vision
- You sometimes find that you can see a faint star on a dark night better if you look slightly to the side of the star instead of straight at it. Why?
- If you look slightly to the side, the light falls on an area of the retina with more rods and more convergence of input.
- If you found a species with a high ratio of cones to rods in its retina, what would you predict about its way of life?
- We should expect this species to be highly active during the day and seldom active at night.
List colours in order of shortest to longest wavelengths.
Violet Blue Green Yellow Orange Red
Why do males and females of some birds look the same to us, but different to each other?
They can see ultraviolet light, and the males reflect more UV light.
What is trichromatic theory or Young-Helmholtz theory?
We perceive colour through the relative rates of response by three kinds of cones, each one sensitive to a different set of wavelengths.
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Opponent-process theory
We perceive colour in terms of opposites. The brain has a mechanism that perceives colour on a continuum from red to green, another from yellow to blue, another from white to black. After you stare at one colour in one location for long enough you fatigue that response and swing to the opposite.
- Examine Figure 5.9. According to the trichromatic theory, what causes you to perceive red?
- Activity of the long-wavelength cone is not sufficient. In fact, notice that the long-wavelength cone responds to what we call yellow more than to what we call red. A perception of red occurs only if the long-wavelength cone has a high ratio of response relative to the other two types of cone
What is retinex theory?
The cortex compares information from various parts of the retina to determine the brightness and colour for each area.
Accounts for colour and brightness optical illusions.
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- When a television set is off, its screen appears gray. When you watch a program, parts of the screen appear black, even though more light is actually showing on the screen than when the set was off. What accounts for the black perception?
- The black experience arises by contrast with the brighter areas around it.
- Figure 5.9 shows light at about 510 nm as green. Why should we nevertheless not call it “green light”?
- Color perception depends not just on the wavelength of light from a given spot but also the light from surrounding areas. As in Figure 5.13, the context can change
the color perception.
- Why is color vision deficiency a better term than color blindness?
- Very few people see the world entirely in black and white. The more common condition is difficulty discriminating red from green.
- What happens when you see something?
A. You send out sight rays that strike the object.
B. Light rays reflect off the object and strike your retina.
C. You send out sight rays, and light reflecting off the object strikes your retina.
D. You neither send out sight rays nor receive light rays onto your retina.
B. Light rays reflect off the object and strike your retina.
- What is the route from retinal receptors to the brain?
A. Receptors send axons directly to the brain.
B. Receptors connect to bipolars, which connect to ganglion cells, which send axons to the brain.
C. Receptors connect to ganglion cells, which connect to bipolars, which send axons to the brain.
D. Receptors connect to amacrine cells, which send axons to the brain.
B. Receptors connect to bipolars, which connect to ganglion cells, which send axons to the brain.
- Where does the optic nerve exit from the retina?
A. At the blind spot
B. At the fovea
C. From the edge of the fovea
D. Diffusely from all parts of the retina
A. At the blind spot
- Why is vision most acute at the fovea?
A. The fovea is closest to the pupil.
B. The fovea has an equal ratio of cones to rods.
C. The cornea produces the least distortion of light at the fovea.
D. Each receptor in the fovea has a direct line to the brain.
D. Each receptor in the fovea has a direct line to the brain.
- Vision in the periphery of the retina has poor sensitivity to detail but great sensitivity to faint light. Why?
A. Toward the periphery, the retina has more midget ganglion cells.
B. Toward the periphery, the retina has more cones and fewer rods.
C. Toward the periphery, the retina has more convergence of input.
D. Toward the periphery, the light falls farther from the blind spot.
C. Toward the periphery, the retina has more convergence of input.
- Why do some people have greater than average sensitivity to brief, faint, or rapidly changing visual stimuli?
A. They do not have a blind spot in their retina.
B. The blind spot in their retina is smaller than average.
C. They have more axons from the retina to the brain.
D. They have four types of cones instead of three.
C. They have more axons from the retina to the brain.
- Suppose you perceive something as red. According to the trichromatic theory, what is the explanation?
A. Light from the object has excited your long-wavelength cones more strongly than your other cones.
B. Light from the object has excited your short-wavelength cones more strongly than your other cones.
C. Ganglion cells that increase response to red and decrease their response to green are firing strongly.
D. The cortex compares activity over all parts of the retina and computes that one area is red.
A. Light from the object has excited your long-wavelength cones more strongly than your other cones.
- If you stare at a white circle surrounded by a green background, and then look at a white surface, you perceive a green circle
surrounded by a red background. What does this observation imply about the opponent-process theory?
A. We perceive colors based on the pattern of input to the bipolar and ganglion cells of the retina.
B. The mechanisms of color vision vary from one species to another.
C. Opponent-process color perception depends on the visual cortex, not just the cells in the retina.
D. The opponent-process theory is wrong.
C. Opponent-process color perception depends on the visual cortex, not just the cells in the retina.
- An object that reflects all wavelengths equally ordinarily appears gray, but it may appear yellow, blue, or any other color,
depending on what?
A. Brightness of the light
B. Contrast with surrounding objects
C. The culture in which you grew up
D. The ratio of cones to rods in your retina
B. Contrast with surrounding objects
- Color vision deficiency demonstrates which fundamental point about perception?
A. Color is in the brain and not in the light itself.
B. Each sensory system depends on a different part of the cerebral cortex.
C. Color perception varies because of cultural influences.
D. Fatiguing a receptor can lead to a negative afterimage.
A. Color is in the brain and not in the light itself.
What do rods and cones of the retina make synapses with?
Horizontal cells and bipolar cells
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What forms the optic nerve?
Axons of the ganglion cells
Where do most ganglion cell axons go?
Where do some others go?
Lateral geniculate nucleus, part of the thalamus
Superior colliculus
Hypothalamus (that controls waking/sleeping schedule)
- Where does the optic nerve start and where does it end?
- It starts with the ganglion cells in the retina. Most of its axons go to the lateral geniculate nucleus of the thalamus, but some go to the hypothalamus and superior colliculus.
