Central Nervous System

Question 1

1. The central nervous system (CNS) is
2. Neurons outside the CNS make up
3. Most neurons are in
4. CNS and PNS have cells called
5. The CNS contains ventricles filled with

Answer 1

1. Brain and Spinal Cord
2. Peripheral Nervous System
3. CNS
4. CNS and PNS also have cells called glia, which support and protect neurons, and are about as numerous.
5. The CNS contains ventricles filled with
   cerebrospinal fluid

Question 2

peripheral nervous system:
includes,
comprises of 2 systems x and y.
Part of y system is the

Answer 2

• The peripheral nervous system, or PNS, includes all neurons, and parts of neurons, outside the CNS.
• The PNS comprises the somatic nervous system, for controlling voluntary action via skeletal muscle, and the autonomic nervous
  system, for visceral functions such as heart rate and breathing.
• Part of the autonomic system is the enteric nervous system, which controls digestion and movements of the gut. It gets input from spinal cord, but can also work independently.

Question 3

Gray Matter & arrangements,
White Matter &arrangements,
clusters called in the PNS

Answer 3

• Gray matter consists of nerve cell bodies, unmyelinated axons, and dendrites. The cell bodies are arranged either in layers (in parts
  of the brain) or in clusters called nuclei
• White matter consists of myelinated axons running in bundles called tracts.
• In the peripheral nervous system, clusters of neurons are called ganglia (singular: ganglion), and bundles of axons are nerves.

Question 4

CNS and energy
1. The brain has just how much % of the body’s mass and consumes how much energy
2. how much glucose does the brain consume
3. how does the CNS save energy
a) Neurons communicate with each other by
b) The energy supply to the CNS can support

Answer 4

1. The CNS saves energy by limiting communication between neurons
2. Neurons communicate with each other by sending action potentials (spikes) down their axons, but those action potentials take a lot
   of energy.
3. The energy supply to the CNS can support only a low rate of firing, e.g. in cortex it permits an average rate per cell of just one spike every 6 s. At any moment, only ~4% of your neurons are firing

Question 5

Spinal Cord:
1. How many segments each with what
2. Each spinal nerve has a x which carries – signals. The — contains the — of the neurons carrying these signals
3. The ventral root
4. what is in the middle of the cord

Answer 5

1. The spinal cord has 31 segments, each with a pair of spinal nerves
2. Each spinal nerve has a dorsal root, which carries afferent (i.e. incoming, sensory) signals. The dorsal root ganglion contains the cell bodies of the neurons carrying these signals
3. The ventral root carries efferent (i.e. outgoing) signals from the CNS to the body, including motor signals (i.e. to skeletal muscles)
4. gray matter. the middle of the cord has a butterfly shape, with a dorsal and a ventral horn on each side

Question 6

1. The gray matter of the spinal cord consists of
2. sensory nuclei: somatix and visceral
3. Efferent nuclei: autonomic and motor

Answer 6

1. The gray matter consists of sensory and motor nuclei
2. Sensory nuclei are in the dorsal horn because sensory signals arrive on the dorsal root. Somatic sensory nuclei get signals from skin; visceral sensory nuclei get signals from the viscera (internal organs).
3. Efferent nuclei are ventral. Autonomic efferent nuclei send commands to glands and smooth muscle; motor nuclei send commands to skeletal muscle

Question 7

1. White matter consists of
2. Ascending tracts
3. Descending tracts
4. Proprispinal tracts

Answer 7

1. White matter consists of axon tract
2. Ascending tracts (green) carry sensory signals to the brain. They are mainly dorsal, because sensory signals arrive at the dorsal horn.
3. Descending tracts (pale blue) carry signals from the brain. They are mainly ventral, where outgoing signals leave the CNS.
4. Propriospinal tracts (not shown), stay in the spinal cord.

Question 8

1. 6 major divisions of the brain
2. what make up the brain stem
3. what is the brain stem
4. what arises from the brain stem

Answer 8

1. Cerebrum, Diencephalon, Midbrain, Pons, Medulla, Cerebellum
2. Medulla, pons, and midbrain make up
   the brain stem
3. The brain stem is the main control center for many autonomic functions and reflexes, such as breathing, swallowing, vomiting, and
   regulating blood pressure.
4. Cranial nerves III–X and XII arise from the brain stem

Question 9

1. what are cranial nerves
2. what are the parts of diencephalon and what do they do

Answer 9

1. Cranial nerves are ones that enter or leave the brain rather than the spinal cord
2. The diencephalon is the thalamus, hypothalamus, pituitary and pineal
   a) The thalamus processes information going to and from the cerebral cortex.
   b) The hypothalamus regulates behavioral drives, and endocrine and autonomic homeostasis.
   c) Pituitary and pineal secrete hormones

Question 10

1. The cerebrum has x connected by
2. The cerebral gray matter includes
3. Corpus callosum is
4. cerebral lateralization
5. Each hemisphere has x lobes and what are they
6. Each hemisphere also has a –, which is part of the —system

Answer 10

1. The cerebrum has 2 hemispheres connected by the corpus callosum
2. The cerebral gray matter includes the outer layer called the cortex, the limbic system (shown in a later slide), and the basal ganglia (which help control movement).
3. Corpus callosum is a large bundle of myelinated axons
4. The 2 hemispheres’ functions differ, i.e. we have cerebral lateralization
5. Each hemisphere has 4 lobes: Frontal, Temporal, Parietal, Occipital, Temporal
6. Each hemisphere also has a cingulate gyrus, which is part of the limbic system

Question 11

1. The limbic system is
2. it includes
3. it is concerned with

Answer 11

1. The limbic system is an evolutionarily old group of brain regions
2. It includes the cingulate gyrus, amygdala, and hippocampus
3. It is concerned with motivation, emotion, and memory, e.g. monkeys with amygdala lesions, unlike normal monkeys, are not
   frightened of snakes

Question 12

1. Every sensory system begins with

Answer 12

receptors

Question 13

1. what are receptors
2. in some senory systems receptors are x and in other they are y
3. receptor potential
4. Every type of receptor cell has an

Answer 13

1. These are cells which convert stimuli (e.g. light, sound) into electrical signals. The conversion is called transduction
2. In some sensory systems (such as vision) the receptor cells are neurons; in others (such as hearing) they are non-neuronal epithelial cells.
3. A receptor cell converts stimulus energy into a graded change in membrane potential called a receptor potential. The receptor may then release neurotransmitter to affect a neuron. If the receptor is itself a neuron, it may fire action potentials
4. Every type of receptor cell has an adequate stimulus

Question 14

1. what is adequate stimulus
2. 4 times of adequate stimuli
3. what is a receptor threshold
4. perceptual threshold

,

Answer 14

1. Its adequate stimulus is the form of energy to which it is most responsive, e.g. thermoreceptors respond most sensitively to temperature.
2. a) Chemoreceptors respond to specific molecules or ions, e.g. to glucose, or oxygen, or H
   b) Mechanoreceptors respond to mechanical energy such as pressure, vibration, gravity, and sound.
   c) Thermoreceptors respond to temperature.
   d) Photoreceptors respond to light.
3. Any receptor has a receptor threshold — the weakest stimulus that will cause a response in the receptor.
4. The perceptual threshold is different; it is the weakest stimulus that will cause a conscious perception in the organism, e.g. it takes ~40 odorant molecules for you to perceive a smell.

many receptors also respond to other forms of energy as well

Question 15

1. primary sensory neurons
2. series of neurons
3. convergence

Answer 15

1. The first neurons in the system (either the receptors or the cells immediately downstream) are called primary sensory neurons
2. Primary sensory neurons synapse onto secondary sensory neurons, and these synapse onto tertiaries, and so on.
3. At each stage, many presynaptic cells may contact any one postsynaptic cell. This convergence allows secondary and higher neurons to combine data from many receptors

Question 16

Sensory neurons carry information about many

aspects of the stimulus

1. stimulus modality
2. Sensory systems indicate modality by
3. population coding of intensity.
4. frequency coding.
5. Both population coding and frequency coding

Answer 16

1. One aspect is the stimulus modality, i.e. whether it is a light, a sound, a touch, etc.
2. Sensory systems indicate modality by labeled lines, meaning that the modality is revealed by which axons carry the signal, e.g. activity on neurons in the visual pathway means light; activity on neurons in
   the auditory pathway means sound.
3. Stronger stimuli may activate more neurons. This way of representing stimulus intensity, by the number of active neurons, is called population coding of intensity
4. Stronger stimuli may make the individual neurons fire at a faster rate. This is frequency coding
5. Both mechanisms may operate together: a stronger stimulus may increase the firing rates of neurons and also cause more neurons to be active.

Question 17

Receptors and neurons have dynamics

1. their activities may depend on 2 things (example)
2. Phasic
3. Tonic
4. Phasic-tonic

2-4 are types of dynamics

Answer 17

1. their activities may depend not only on the stimulus right now, but on how it changes through time. e.g. when a stimulus suddenly increases or decreases, many
   receptors and neurons respond briefly and then fall silent again. So these cells signal changes in stimuli, not steady levels
2. Phasic cells respond briefly to any change and then cease firing. many retinal cells are phasic (report changes in your visual world, as when something move)
3. Tonic cells maintain their activity when the stimulus is not changing, signalling its present level
4. Phasic-tonic cells react to change but don’t return all the way to zero firing when the stimulus is constant, so they also carry information about its steady level.

Question 18

making communication more efficient

1. what cells make communication more effeciant
2. temporal changes.
3. spatial changes
4. Sensory systems accentuate edges by

Answer 18

1. Phasic signals make communication more efficient because it is more efficient to report changes than to repeat similar messages over and over.
2. These kinds of changes through time, between one moment and the next, are called temporal changes.
3. It is also efficient to report spatial changes. Spatial changes are differences between neighboring regions in space, e.g. neighboring patches of retina or skin.Spatial change is also called contrast, and locations where there is strong contrast are called edges.
4. Sensory systems accentuate edges by lateral inhibition

Question 19

1. Lateral inhibition means that
   use example diagrams

Answer 19

Lateral inhibition means that cells inhibit their neighbors, or they inhibit the cells their neighbors excite.

Question 20

1. Most sensory pathways run via
2. Most pathways run through —, which is near —-, out to the s—- on the—
3. what is the exception
4. Equilibrium pathways project mainly
5. Sensory processing is

Answer 20

1. Most sensory pathways run via thalamus to cortex
2. Most pathways run through thalamus, which is near the center of the brain, out to the sensory cortices on the surface of the cerebrum
3. Olfactory (smell) pathways are an exception: they don’t project via thalamus.
4. Equilibrium pathways project mainly to cerebellum
5. Sensory processing is inference
   a) Our senses evolved to guide our behavior: A big part of this guidance is
   deducing what is going on around us, e.g. identifying things and so the brain has to infer.
   b) Because it has to guess, the brain can be fooled: your brain produces an interpetation that is more likely
   c) The brain mistrusts coincidences

Question 21

1. The eye is divided into 2 chambers by
2. the lens is
3. the lens is suspended by
4. what is infront of the lens and what is it filled with
5. behind the lens is, what is is filled with

Answer 21

1. The eye is divided into 2 chambers by the lens
2. The lens is a transparent disk that focuses light. It is suspended by ligaments called zonules
3. In front of the lens is the anterior chamber, filled with aqueous humor, a plasma-like fluid.
4. Behind is the vitreous chamber, filled with the vitreous body, a clear jelly that helps maintain the eyeball’s shape.

Question 22

1. what is the cornea
2. what is the retina
3. what is the pupil
   a) what can the pupil do
   b) pupil size is controlled by
   c) what happens to the pupil in bright/dark light
   d) the pupil also controls

Answer 22

1. Light enters the eye through the cornea. The cornea is a transparent bulge at the front of the eye, continuous with the white of the eye, or sclera — the outer wall of the eyeball.
2. Cornea and lens focus light on the retina, the inner lining of the eye that contains the photoreceptors.
3. Light passes from the cornea to the lens through a hole in the iris called the pupil.
   a) The pupil can change size
   b) Pupil size is controlled by smooth muscles in the iris
   c) Bright Light: pupils constrict (shrink) to 1.5 mm across, reducing the amount of light reaching the lens and parasympathetic signals from the brain contract the
   ring-shaped pupillary constrictor muscle, shrinking the pupil.
   Dark: In the dark they dilate (enlarge)to 8 mm, ~20 times bigger in area, to let in more light. In the dark, sympathetic signals contract the radial pupillary dilator muscle of the iris, dilating the pupil.
   d) The pupil helps to focus light. The pupil also controls depth of field. When the pupil is tightly constricted, we have full depth of field, i.e. everything we see is equally in focus. When the pupil is tightly constricted, we have full depth of field, i.e.
   everything we see is equally in focus

Question 23

1. Refraction
2. Light bends when
3. our corneas are made of – They bend light strongly because —
4. Light is refracted by both the – and –
5. The cornea is responsible for — of the eye’s refraction, and the lens for just —

Answer 23

1. allows us to get a retinal image that is both bright and in focus
2. Light bends when it enters a medium with a different refractive index
3. our corneas are made of clear collagen. They bend light strongly because there is a big difference between the refractive indices of air and collagen.
4. Light is refracted by both the cornea and the lens
5. The cornea is responsible for 2/3 of the eye’s refraction, and the lens for just 1/3.

Question 24

1. The lens is made of
2. lens is a mesh of – cells without –, packed with – and zippered together in – for –. It has no — but absorbs nutrients from –
3. The lens of the eye is x. A A x lens is — in the middle and – at the edges. It
   makes–.

Answer 24

1. The lens is made of clear cells
2. It is a mesh of long (12 mm) cells without nuclei, packed with clear proteins called crystallins, and “zippered” together in concentric layers for flexibility. It has no blood supply, but absorbs nutrients from the aqueous humor.
3. The lens of the eye is convex. A convex lens is fatter in the middle and thinner at the edges. It makes light rays converge to a focal point. Another example of a convex lens is a magnifying glass

Question 25

1. Refraction depends on x which is
2. That angle depends on
3. how can we alter these angles, and bend the light more or less

Answer 25

1. Refraction depends on the angle of incidence which is the angle at which the light ray hits the interface between the media; e.g. the angle at which it hits the lens surface.
2. That angle depends on the shape of the lens and the direction of the light ray; e.g. in the simplest case, if a ray strikes the lens at right angles then it doesn’t bend at all.
3. By changing the shape of the lens we can alter these angles, and so bend the light more or less

Question 26

1. and rounder lends — and so has a —
2. For clear vision, the focal point must
3. If the object draws closer but the lens stays flat,
4. To bring a closer object into focus, what do we do and how do we do this
5. Rounding the lens for near vision is called
   a) The closest point a person can focus is called
   b) presbyopia

Answer 26

1. A rounder lens bends light more, and so has a closer focal point
2. For clear vision, the focal point must fall on the retina
3. If the object draws closer but the lens stays flat, focus falls behind the retina
4. To bring a closer object into focus, we make the lens rounder. Parasympathetic nerve signals contract the ring-shaped, smooth ciliary muscle, reducing tension in the zonules, making the lens rounder, so light rays bend more and the focal point moves forward. Sympathetic signals relax the ciliary muscle, making the lens
   flatter for far vision.
5. Rounding the lens for near vision is called accommodation which is an unconscious reflex
   a) The closest point a person can focus is called their near point of accommodation.
   b) With advancing age the lens stiffens, hindering accommodation– a problem called presbyopia

Question 27

Refractive Errors

1. hyperopia and how is it solved
2. myopia and how its solved

Answer 27

1. In hyperopia (far-sightedness) the focal point falls behind the retina. The problem is solved by a convex lens in front of the eye so that the lens of the eye isn’t bending the light rays enough, and so the extra convex lens helps out.
   2.In myopia (near-sightedness) the focal point falls in front of the retina. The problem is solved by a concave lens in front
   of the eye. A concave lens causes light rays to spread out more — the
   opposite of what a convex lens does. In myopia, the lens of the eye is bending the light rays too much, and so the concave lens in front counteracts it by spreading the rays
   out slightly.

Question 28

1. where are photoreceptors
2. what are they
3. conversion and what is it called
4. Our retinas have 2 main types of photoreceptor: x and y
5. how many x and y and what are x and y

Answer 28

1. The photoreceptors are in the retina
2. They are light-sensitive neurons that convert light energy into electrical energy in cells
3. The conversion is called phototransduction.
4. Our retinas have 2 main types of photoreceptor: cones and rods
5. Each retina contains ~6 million cones and 120 million rods.Rods and cones are neurons, though they do not fire action
   potentials, but instead respond to stimuli with graded membrane potentials

Question 29

Structure of cones and rods

1. In the outer segment, the membrane folds into – which contain – that respond to -
2. In the inner segment are the – for –; and in a basal layer, — that releases —
3. Both receptor types point toward –

Answer 29

1. In the outer segment, the membrane folds into disk-like layers which contain the visual pigments that respond to light
2. In the inner segment are the nucleus and organelles for protein synthesis; and in a basal layer, a synapse that releases glutamate.
3. Both receptor types point toward the back of the eye

Question 30

1. Photoreceptors detect light using
2. When light hits them, pigment molecules –, starting a chemical cascade that —the cell, reducing —,
3. Each photoreceptor contains millions of molecules of its pigment, but each type of photoreceptor has just one type of pigment:
   —in rods, —- in 3 types of cone.

Answer 30

1. Photoreceptors detect light using membrane-bound visual pigments
2. When light hits them, pigment molecules change shape, starting a chemical cascade that hyperpolarizes the cell, reducing its release of glutamate, i.e. photoreceptors are more active in darkness.
3. Each photoreceptor contains millions of molecules of its pigment, but each type of photoreceptor has just one type of pigment:
   rhodopsin in rods, 3 other pigments in 3 types of cone.

Question 31

1. distribution of photoreceptors
2. They are most densely packed in the x, and especially in its central pit called the
3. what do we use for detailed vision
4. where are there no receptors in the x and what is this

Answer 31

1. Photoreceptors are not distributed uniformly
2. They are most densely packed in the macula, a central disk 1.5 mm across, and especially in its central pit called the fovea, 0.5 mm across
3. We use the fovea for detailed vision.
4. There are no receptors in the blind spot — the hole where axons carrying visual information exit the eyeball to form the optic nerve.

Question 32

1. Cones are for x light, rods for x
2. cones vs rods sensitivity and what are cones responsbile for
3. rods can detect what but they operate in
4. what lights go dim, rods
5. How are cones and rods distributed
6. The fovea contains. what contains mainly rods

Answer 32

1. Cones are for bright light, rods for dim
2. Cones are less sensitive than rods; they are responsible for vision in bright light and for distinguishing colors, but they don’t operate in dim conditions.
3. Rods can detect single photons. But they operate only in low light: in daylight they are “bleached out”, i.e. their rhodopsin is broken
   down so they can’t sense light.
4. When the lights go dim the rods dark adapt, i.e. they rebuild their
   stores of rhodopsin over ~30 minutes.
5. Cones and rods are distributed differently
6. The fovea contains almost exclusively cones. More-peripheral retina contains mainly rods.

Question 33

1. Photoreceptors synapse onto — which synapse onto —-
2. Convergence is greatest in – and least in —, where some receptors project —

Answer 33

1. Photoreceptors synapse onto bipolar cells, which synapse onto ganglion cells
2. Convergence is greatest in the peripheral retina and least in the fovea, where some receptors project 1:1 to bipolars.

Question 33

Bipolar Cells

1. What is a receptive field
2. what kind of receptive field does bipolar cells have
3. Bipolar-cell receptive fields can be x or y. Define x and y
4. Both types of bipolar cell react to –. They respond with —-. They do not fire —
5. Bipolar cells project to x. X differences and similarties to bipolar cells

Answer 33

1. Every neuron in the visual system has a receptive field, also called its visual field — the region of the retina where light affects the cell’s activity, i.e. the set of photoreceptors which affect the cell.
2. Bipolar cells have center-surround fields, with a round center region and a doughnut-shaped surround
3. Bipolar-cell receptive fields can be on-center or off-center
   a) On-center cells are excited by light in the center of their field, and inhibited by light in the surround. So these cells respond most when a light spot fills their center and the surround is dark.
   b) Off-center cells are inhibited by light in the center, and excited by light in the surround. They respond best when a dark spot fills their center and the surround is light.
4. Both types of bipolar cell react to contrast. When the lighting is uniform, whether bright or dim, neither type of
   bipolar cell responds, because the effects of the center and surround cancel, leaving the cell at its resting level of activity. They respond with graded membrane potentials; they do not fire action potentials.
5. Bipolar cells project to retinal ganglion cells which unlike photoreceptors and bipolar cells, do fire action potentials. Similarities: center surround receptive field that is on/off center. Ganglion cells detect contrast

Question 34

Ganglion cells in different parts of the retina have

different-sized RF

1. kind of input ganglion cells recieves in different places
2. So in the periphery, each ganglion cell is
3. And near the fovea, ganglion cells are
4. Ganglion cells are also classified based on
   a) Large, magnocellular ganglion cells, or M cells,
   b) Small, parvocellular ganglion cells, or P cells
   c) ~1% of retinal ganglion cells are melanopsin ganglion cells, which

Answer 34

1. A ganglion cell near the fovea gets input (via bipolars) from only a few photoreceptors, mostly cones. Farther out, each ganglion cell gets input from many receptors (up to 75,000), mostly rods.
2. So in the periphery, each ganglion cell is very sensitive to light but poor at reporting spatial detail because it blends information from a wide swathe of receptors.
3. And near the fovea, ganglion cells are less sensitive to light but have better spatial resolution because each one gets input from just a few densely packed cones
4. Ganglion cells are also classified based on how their signals are used in the brain
   a) Large, magnocellular ganglion cells, or M cells, provide information that is used by the brain to infer the movement of objects. These cells are phasic. ~10% of retinal ganglion cells are M.
   b) Small, parvocellular ganglion cells, or P cells, provide information that is used to infer form and fine detail, such as texture. ~70% of retinal ganglion cells are P.
   c) ~1% of retinal ganglion cells are melanopsin ganglion cells, which
   are photoreceptors, with their own visual pigment, melanopsin. They project to the suprachiasmatic nucleus, a center for circadian rhythms

Question 35

1. Visual information leaves the retinas in
2. Each of the million ganglion cells in each retina sends its axon out where through what
3. These million fibers from each eye form
4. Half the optic-nerve fibers cross at x
5. When each optic nerve reaches the x
6. Fibers from the — cross; those from the
   – do not.
7. Why do the fibers cross?

Answer 35

1. Visual information leaves the retinas in the optic nerves
2. Each of the million ganglion cells in each retina sends its axon out the back of the eye through the blind spot.
3. These million fibers from each eye form its optic nerve, also known as cranial nerve II.
4. Half the optic-nerve fibers cross at the optic chiasm
5. When each optic nerve reaches the optic chiasm, half its fibers cross to the other side of the brain.
6. Fibers from the nasal half of each retina cross; those from the temporal retinas do not.
7. In the eye, the right side of the scene (the right visual hemifield) projects onto the left side of each retina, i.e. onto the nasal side of the right retina and the temporal side of the left retina. Because the nasal fibers cross, all the information from the right hemifield comes together in the left cerebral hemisphere, and vice versa

Question 36

1. Information moves from x to y
   and then to z
2. what are optic tracts. They end in — in the — which project via—
3. where is V1

Answer 36

1. Information moves from chiasm to thalamus and then to cortex
2. The nerve bundles emerging from the chiasm are called the optic tracts. They end in the 2 lateral geniculate nuclei (LGN) in the thalamus, which project via the optic radiations to primary visual cortex, V1.
3. V1 is in the occipital lobe

Question 37

1. Many visual areas in the brain are organized in what way.
2. This arrangement is found in three things
3. why does the fovea get a lot of space
   4.

Answer 37

1. Many visual areas in the brain are organized retinotopically; That is, neurons close to each other in the brain get information from close-together parts of the retina.
2. This arrangement is found in the lateral geniculate nuclei, V1, and many higher visual processing areas
3. The fovea, which covers only a small area of the retina, projects to large areas in V. The fovea gets a lot of space because it has many photoreceptors, bipolars, and ganglion cells, and so carries a lot of information.

Question 38

1. Color depends on x
2. what is x
3. what range of x do we normally see and why
4. what can we also see

Answer 38

1. Color depends on wavelengths of light
2. the distance from one wave peak to the
   next — and different wavelengths correspond to different colors
3. The wavelengths we normally see range from 400 nm for violet to 700 nm for red. This is because The power in sunlight peaks there. Also, Earth’s atmosphere is most transparent to these wavelengths. And sea water, where eyes first evolved, is most transparent < 500 nm.
4. We can also see extremely powerful infrared lights, and people who have had their lenses removed can see some ultraviolet. But even so, the visible range is only a tiny part of the electromagnetic
   spectrum.

Question 39

1. the 3 types of cone that humans sense colour with and the percentage of cones that are this type
2. Each type of cone has its own type of x. All these x are similar to – but — and so all prefer different –
3. Because we sense color with 3 types of cone, we are called
4. Red and green cone pigments prefer —. Blue cone pigment prefers —. Rhodopsin
   prefers —. Melanopsin prefers —.
5. The brain infers color by
6. We can produce any color perception by

Answer 39

1. The 3 types are called red, green, and blue. In most people, ~63% of the cones are red, 31% are green, and just 6% are blue
2. Each type of cone has its own type of visual pigment. All these pigments are similar to rhodopsin but not identical to it, and so all prefer different wavelengths of light.
3. Because we sense color with 3 types of cone, we are called trichromats
4. Red and green cone pigments prefer yellow and yellow-green light. Blue cone pigment prefers blue. Rhodopsin prefers blue-green. Melanopsin prefers blue.
5. The brain infers color by comparing data from the 3 types of cone
6. We can produce any color perception by mixing 3 wavelengths

Question 40

1. Spectral colors
2. Extraspectral colors

Answer 40

1. Spectral colors are those that can be evoked by light of a single wavelength. They are the rainbow colors, from violet through blue, green, yellow and orange to red.
2. Extraspectral colors such as purple or white are evoked only by a mix of wavelengths, e.g. we see purple when 2 or more wavelengths affect red and blue cones more than green cones.

Question 41

1. Ganglion cell color signals are
   a) R + G cells, or the yellow channel
   b) 2 types form the red-green opponent channel.
   c) 2 types form the blue-yellow opponent channel.
2. Opponent channels are thought to explain

Answer 41

1. Ganglion cell color signals are combinations of cone signals
   a) Some ganglion cells are excited by red light and by green light. They are called R + G cells, or the yellow channel (because red and green make yellow)
   b) Some ganglion cells are excited by red light and inhibited by green (R – G). Others are inhibited by red and excited by green (G – R). These 2 types form the red-green opponent channel.
   c) Some are excited by blue light and inhibited by red and green, (B – R – G, which is the same as B – (R + G), i.e. blue minus yellow). Others are yellow minus blue. These 2 types form the blue-yellow opponent channel.

Question 42

1. The most common variant of color-blindness
2. Color blindness was the first human trait to be linked to a chromosome:
   a) The inheritance pattern of Daltonism
   b) what visual pigments lie on the X,chromosome. Problems at these loci underlie x% of all variations in
   color vision
   c) Women are seldom color blind because

Answer 42

1. The most common variant is red-green color blindness (Daltonism)
2. The inheritance pattern of Daltonism is that color blind fathers have color-normal daughters who have color blind sons.
3. The genes for red and green cone visual pigments lie on the Xchromosome. Problems at these loci underlie 95% of all variations in color vision. (The “blue” gene, on chromosome 7, is more stable).
4. Women are seldom color blind because if one X-chromosome codes a faulty pigment then the other X-chromosome compensates. If her 2 X-chromosomes code, say, 2 different functional “red” cone pigments then a woman may be a tetrachromat.

Question 43

1. what is reflectance
2. The light an object sends to our eyes depends on
3. what is color constancy
   4.

Answer 43

1. We call the intrinsic color of a surface its reflectance. The reflectance of a surface is its tendency to reflect certain wavelengths of light and absorb others. e.g. a yellow banana reflects yellow light more than other wavelengths; a green banana reflects
   green. The reflectance of an object carries information about it, e.g. about ripeness.
2. The light an object sends to our eyes depends on reflectance and illumination
3. . if you put a ripe banana in greenish light then the banana’s reflectance doesn’t change (it is still a yellow-colored object) but now it sends mainly green light to our eyes.our brains can usually infer the reflectance, so we see the ripe banana as yellow even in green light. This crucial ability is called color constancy.