4-9-10 The Nervous System - The Senses-color

4-9-10 The Nervous System - The Senses-color - Clicker...

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Unformatted text preview: Clicker Question Retroviruses use the enzyme ___________ to insert their hereditary material into the DNA of the host. This enzyme is one of the targets of drugs designed to treat people with AIDS. A) DNA ligase B) DNA polymerase C) RNA polymerase D) Eco R1 E) integrase The annual Roots and Shoots Earth Day 5k 2010 Saturday May 1st 10:30 am! Prizes for top runners! Registration at 10:00 *Rain or Shine* At the entrance to the Cornell Plantations Arboretum. All Benefits go to the Finger Lakes Land Trust: Get registration papers at http://rootsandshoots. cornell.googlepages.com or on Ho Plaza earth day or fill one out day-of the run *$10 before or $13 day of. Cash or check made to Finger Lakes Land Trust Also purchase a souvenir green cotton t-shirt with the logo above in white ink ($5 preregistration, $7 day of) (register by April 22nd to ensure supplies) Contact aw374 for more information Where Where are we? Last Last time I talked about… HIV/AIDS HIV/AIDS Life: The Ability to Sense and Respond Appropriately to the Environment Consciousness, as defined as an awareness awareness of the external environment the first environment—the first step responding step in responding appropriately to the environment, is a characteristic of life and may have begun with the first cell. Today Today I will talk about… Consciousness Consciousness Plants Plants sense and respond to the environment. Biomimicry Biomimicry How How cells specialized in sensing a given physical or physical or chemical chemical environmental stimulus function when they are grouped together in a sensory organ. sensory How How the sense organs send information to the brain. The The brain also influences our perceptions. Plants Sense and Respond to the Environment If If we were to walk quietly and observantly through a garden at the Cornell Cornell Plantations Plantations, it would become increasingly clear that it is a normal and ubiquitous property of plants to sense sense and respond to respond their environment. Plants Sense and Respond to the Environment: Phototropism http://www.plantations.cornell.edu/ Plants sense the direction of light and bend or turn direction toward the light. Some plants can track the movement of the sun. Sun Stalkers 1 Biomimicry: Biomimicry: Sun Tracking Solar Panels are 38% More Efficient Plants Sense and Respond to the Environment: Gravitropism Plants sense the vector vector of gravity and the shoots bend up; away from the source of the gravitational force, and the roots bend down; toward the source of the gravitational force. Biomimicry Plants Sense and Respond to the Environment: Thigmotropism Venus’ Fly Traps Can Sense Touch, Capture Their Prey, Secrete Digestive Enzymes and Absorb the Nitrogenous Nutrients Plants, particularly vines, have a sense of touch. When the touch tendrils come tendrils come in contact with a support, they quickly respond to the mechanical force and curl around the mechanical support. Thigmo is the Greek word for touch. Thigmo Mimosa Can Sense Touch and Heat Plants Sense and Respond to the Environment: Photoperiodism Plants sense day day length (or really the length length of the night) so that they can so that they can flower flower in the spring or fall, when the days are short, or in the summer, when the days are long. 2 Crocuses Open in the Morning and Close at Night http://www.strawberybanke.org/ Circadian (about a day) Rhythms Plants sense the duration of time duration of time and move their leaves throughout a 24 h cycle. http://plantsinmotion.bio.indiana.edu/redirect.html 3 StimulusStimulus-Response Coupling in Plants Environmental Environmental Stimuli (chemical and (chemical physical stimuli from the “real world”) Receptors Receptors (proteins e.g. phytochrome, phytochrome, phototropin, phototropin, which depend on genes and environment, deconstruct an deconstruct environmental stimulus) Signal Signal Transduction Chains (e.g. cAMP, transcription factors, Ca2+, cAMP, cGMP, cGMP, amplify the small environmental energy input to activate cells) Responses Responses (e.g. phototropism, gravitropism, gravitropism, flowering are adaptive) The Living World is But Mankind in the Making Raoul Francé (1905) wrote, “What “What grander lesson could the speechless plants give than that which they have taught us: that taught us: that their sense life is a primitive form, the beginning of the human mind... it tells us that after all the living world is but mankind in the making, and that we are but a part of all.” The Senses We taste We taste our world, smell our smell world, feel our world, hear our feel hear world and see our world. see The The sense organs collect information from the external information from the external world world so that the brain can form brain an internal representation of the internal external world. The The environmental stimuli are deconstructed deconstructed by the sense organs and then reconstructed in reconstructed the brain to create perceptions. perceptions Our Internal Representation of the World Environmental Environmental Stimuli (chemical and physical stimuli (chemical from the “real world”) “real Receptors Receptors (proteins, which depend on genes and environment, deconstruct environmental stimulus) deconstruc Signal Signal Transduction Chains (ions, cAMP, cGMP, amplify cAMP, cGMP, the small environmental energy input to activate neurons) Responses Responses (neurotransmitter (e.g. serotonin, glutamate, etc.) release activates sensory neurons that go to the brain) Brain Brain (integrates various sensory inputs and reconstructs reconstructs the environmental stimulus to give us our perception of our the world) Real World Stimuli Chemical Chemical Tastes Tastes Odors Odors Physical Ph Pressure Pressure Temperature Temperature Sound Sound Light Light 4 Allegory of the Five Senses by Theodoor Rombouts (1600s) Allegory of the Five Senses by Jan Brueghel (1618) Allegory of the Five Senses by Gérard de Lairesse (1671) Allegory of the Five Senses by Kevin Best (2009) Reception of Real World Stimuli Chemoreceptors Chemoreceptors Receptors Receptors on the tongue for taste Receptors Receptors in the nose for odors The Sense of Taste Mechanoreceptors Mechanoreceptors Receptors Receptors in the skin respond to pressure, pressure, pain and light touch Receptors Receptors in the cochlear respond to sound Thermoreceptors Thermoreceptors Receptors Receptors in the skin respond to hot or cold Photoreceptors Photoreceptors Receptors Receptors in the eyes respond to light 5 The Sense of Taste: All Flavors Can (Probably) Be Deconstructed into Five Basic Tastes Salty Salty Salty (The taste of table salt; NaCl) Sour Sour (The taste of acetic acid; vinegar) Sweet Sweet (The taste of sugar; glucose) Bitter Bitter (The taste of tonic water; quinine) Umami Umami (The taste of cheese; sodium glutamate) Sour or Acidic Sweet Bitter: Quinine Umami: Umami: Glutamate (An Amino Acid) 6 “Aji No Moto” means “Essence of Taste” Glutamate Glutamate is also used as a flavor enhancer. flavor Glutamate Glutamate was first isolated as a flavor enhancer in 1908 by Kikunae Ikeda from Kombu, Kombu, a seaweed. Glutamate was then produced from Glutamate hydrolyzed wheat gluten, a protein that is about 25% glutamate. Some people were allergic to this wheat product. Currently Currently glutamate is produced by bacteria (Micrococcus glutamicus) that ferment the sugars produced by hydrolyzed corn starch in the presence of nitrogen (ammonia or urea). www.starch.dk envis.kuenvbiotech.org/bacteria Ikeda, Kombu and Monosodium Glutamate Ikeka, Kombu and monosodium glutamate www.ajinomotofoods.com Tongue: Organ Involved in Taste Five Kinds of Taste Buds Deconstruct Complex Tastes and they are Reconstructed by the Brain Each papilla Each papilla (→) on the tongue contains several taste buds. Each taste taste bud contains one type of taste taste cell. The The taste cells contain microvilli, microvilli which increase the surface area of which increase the surface area of the the taste cell and extend from the taste cells into the pore. The The microvilli of each taste cell contain the receptors for a taste. receptors Each Each taste cell responds to a given responds taste stimulus by secreting the stimulus secreting the neurotransmitter neurotransmitter serotonin, which activates sensory neurons that go to the brain. Taste Receptors Salty Salty (Receptor is Na channel) Sour Sour (Receptor is potassium (K+) channel, which is blocked by H+) Sweet (Receptor is stimulatory Sweet (Receptor is stimulatory G-protein linked glucose receptor) Bitter Bitter (Receptor is inhibitory GGprotein linked) Umami Umami (Receptor is inhibitory G-protein-linked glutamate proteinreceptor) StimulusStimulus-Response Coupling in Taste Cells. The Response of Each Taste Cell Is to Release Neurotransmitters that Activate Sensory Neurons 7 The Sensory Neurons Alert the Brain About the Food You Eat The Everyday Definition of “Taste” Also Depends on Inputs from Our Other Senses, Including, Our Sense of Smell, Our Sense of Touch and Our Sense of Sight Curt Richter Suggested that Taste and Eating Behavior May be Involved in Maintaining Homeostasis of the Internal Milieu Taste and Eating Behavior May be Involved in Maintaining Homeostasis of the Internal Milieu The adrenal The adrenal glands produce the mineralcorticoid, aldosterone mineralcorticoid, aldosterone, which causes the kidneys to reabsorb salt kidneys reabsorb (NaCl) necessary to maintain blood NaCl) necessary volume. In In humans, people that do not produce sufficient aldosterone due to Addison's aldosterone disease or an adrenal tumor excrete NaCl in the urine and consequently crave salt in their diets (and even eat pure salt). Our Our bodies may seek out foods that may contain the nutrients we need. A Bitter Receptor Binds Phenylthiocarbamide When Arthur Fox first prepared a sample of phenylthiocarbamide (PTC) in his laboratory at Du Pont in 1931, C. R. Noller, his coworker complained about coworker complained about the bitter taste of the dust that floated around the lab. Fox tasted the crystals and assured Dr. Noller that they were not only not bitter, but tasteless. Some people find the chemical bitter and others find it tasteless. 8 A Dinner Demonstration Albert F. Blakeslee performed a taste test using PTC at a dinner for 250 people at the 1934 American Association for the Advancement of Science Meeting in Berkeley. He observed that, “Those who had seen how differently from “Those themselves others had reacted to the tests were perhaps a trifle more inclined to be tolerant of the opinions of other people.” Biological Individuality Albert Blakeslee’s preparation to study human individuality came from his experience with plants. He was working with Verbena in Verbena 1917 when he realized that the pi fl pink flowers that were so th fragrant to him were odorless to his assistant and the red ones that were fragrant to his assistant were not to Blakeslee. Some members of the laboratory agreed with Blakeslee, others with the assistant, and a few found both colors fragrant. The Greatest Gift of Science “It can hardly be emphasized too strongly that it is not man’s material comforts nor even the alleviation of his physical pains which are the greatest gifts of which are the greatest gifts of science science to mankind. Science has freed men’s minds. Foremost among liberating ideas is the belief that there is order and law in the universe and that this order can be discovered by questioning nature herself.” -Albert Blakeslee, 1942 Genetics of PTC Tasting The allele The allele that produces the “PTC “PTC tasting” receptor is dominant. The allele The allele that produces a nonnontasting receptor is recessive recessive. Three SNPs in the TAS2R38 Gene that Codes for the PTC Receptor 9 The Sense of Smell Nose: Organ of Smell Biological Individuality 10 Odor Perception We have a large number of odor receptors in our nose— each capable of interacting with a specific set of odor molecules. Th The odor receptors are on the th cilia cilia (c), which increase the surface area of the olfactory sensory neurons. Electrophysiological studies show that different olfactory sensory neurons are activated (e.g. depolarized) by different odorants. Strategy to Find Odorant Receptors Richard Axel and Linda Buck (1988) knew that each odorant induced a GTP-dependent increase in cAMP in the sensory cells, they assumed that the odorant receptors would be related to other types of receptors that interact with G-proteins. The genes for many G-proteincoupled receptors had already been cloned and from these gene sequences, Axel and Buck made primers for the potential G-proteincoupled odorant receptor genes. Odorant Receptors Axel and Buck exposed single mouse olfactory sensory neurons to a series of odorants, using calcium imaging to visualize which odorant a given sensory neuron perceived. Then they used RT (reverse transcriptase)-PCR and the primers they made to find the the primers they made to find the G-protein-linked receptor for the perceived odorant in each cell. They found that there are about 500 different genes that code for odorant receptors and that only one type of odorant receptor is expressed per olfactory sensory neuron. The 100s of odorant receptors can deconstruct complex scents into 10,000s of individual components. Each Odorant binds to a Different Combination of Receptors. The Large Number of Receptor Combinations is the Basis for our Ability to Distinguish 10,000s of Different Odorants with 100s of Receptors. 11 Each olfactory receptor gene is expressed in about 1/1000 neurons and those neurons are randomly scattered throughout the olfactory epithelium. Odorant receptors are randomly arranged in the olfactory epithelium, but all the neurons from a single receptor type converge before going to the brain. The activated olfactory neurons release the neurotransmitter, glutamate. Richard Axel and Linda Buck (2004) The Sense of Touch Aristotle: The Sense of Touch is Indispensably Necessary “If an animal is to survive, its body must have tactile sensation…it is clear that without touch it is impossible for an animal to exist….The loss of this one sense alone must bring about the death of an animal…for it is the only one which is indispensably necessary to what is an animal.” Pleasure and Pain 12 Skin: The Organ of Touch Biological Individuality www.mfa.org Sensory Receptors in Skin Mechanoreceptors Mechanoreceptors respond to strong pressure, pain and light touch. The pain receptors can also be triggered by histamine. histamine Heat Heat receptors respond to heat. Th They can also be triggered by capsaicin capsaicin, from chili peppers. The The various receptors in the skin affect each other. For example, stimulating the heat receptors overwhelms the neurons that signal the presence of pain so they are unable to transmit the pain messages to the brain. Capsaicin Pain Relievers The “Coolness” of Menthol Alleviates Pain Menthol Menthol produces a cooling sensation and numbs pain when it binds to the cold receptor. cold Stimulating the cold Stimulating the cold receptors receptors overwhelms the neurons that signal the presence of pain so they cannot transmit the pain messages to the brain. The The cold sensation from menthol feels better than the pain sensation. 13 The Sense of Hearing Ears: The Organs of Hearing Biological Individuality The Compressions and Rarefactions of Air Are the Stimulus of Sound The number of oscillations of air per second determine the pitch and the amplitude of the oscillations determine the loudness. Hearing Sound in the form of longitudinal pressure waves is collected by the outer ear and travels down the auditory outer canal where it sets the eardrum into motion. The vibrations eardrum continue to pass through the air-filled middle ear (hammer, airmiddle anvil and stirrup), where they are amplified, to the oval window, which is a hole in the skull bone, to the fluid-filled fluidinner inner ear (cochlea). 14 Hearing Within Within the cochlea are the hair hair cells, which are the sensory cells for hearing. The The hair cells that sense each frequency are all the same, but they differ in their placement on the differ in their placement on the basilar basilar membrane. The hairs that sense high frequencies are close to close the oval window and the hairs that sense low frequencies are far from far from it. The The hair cells sense the movement of the basilar membrane and transmit the auditory information to sensory neurons. Basilar Basilar Membrane According to Hermann von Helmholtz, the basilar membrane is like the strings in a pianoforte. Near the oval strings in window the basilar membrane is narrow and stiff (like the narrow strings for high notes) and at the other end it is wider and wider more flexible (like the strings for low notes). Each region is sensitive to a given pitch. Each region moves to the frequency frequency (pitch) and amplitude (loudness) of the amplitude incoming sound waves. Pianoforte and Basilar Membrane Wave Travels Along the Basilar Membrane Georg Georg von Békésy dissected the heads of fresh cadavers so that he could observe the movement of the basilar membrane when it was exposed to sounds of various frequencies various frequencies. He He replaced the fluid that surrounded the basilar basilar membrane with a solution containing aluminum particles. Using a strobe light and a microscope, he saw that sound induced a traveling wave along traveling the basilar membrane. Position of Crests of Traveling Waves • Von Békésy saw that the position of the crest of the traveling wave depended on the frequency of the stimulating sound waves. • As von Helmholtz predicted, the highest crest of the traveling wave appeared at the stiffer basal part near the oval window for high-frequency pitches and at the more flexible apical part far from the oval window for low frequency pitches. Basilar Membrane and Tectorial Membrane In the region of the basilar membrane where the basilar crest occurs, the hair cells come in contact with the tectorial tectorial membrane above them. 15 Deconstructing Pitch Only Only the hair cells on the portion of the basilar membrane that come in contact with the tectorial membrane contribute sensory input to the brain. Th The mechanical contact with the the tectorial membrane stimulates ion channels in the ion hair cell to open. The incoming ions depolarize the membrane depolarize the and the hair cell secretes the neurotransmitter neurotransmitter glutamate, which induces action potentials in the sensory neuron that goes to the brain. Deconstructing Loudness • Loud sounds move the whole basilar membrane more than soft sounds. • The loud sounds cause the hair cells that are in contact with the tectorial contact with the tectorial membrane to depolarize more than the soft sounds. • This causes the sensory neurons that go from the hair cells to the brain to carry more frequent action potentials. Scientific Progress “Some researchers are of the opinion that it is no longer necessary to study the history of science because science had progressed so fast and always linearly that earlier experiences are linearly that earlier experiences are of no value. I do not believe this, but believe, like many of my otological colleagues, that scientific progress is more like a spiral, as in the cochlea of the ear, which always progresses in one direction, but with many ups and downs and with many repetitions of earlier forms.” -Georg von Békésy, 1974 Just as the Effectiveness of a Limb Requires the Action of Opposing Muscles, Good Science Relies of Good Criticism According to Georg von Békésy, “Everyone needs a good friend; even a scientist does. But what a scientist needs more than a friend is a good enemy. Usually a good enemy later becomes a very good friend. Then it is the obligation of the scientist to find other good enemies.” Cochlear from a 5 mo old human fetus. Direction of Sound Sound Sound from a given direction direction hits the two ears at different different times. The The brain uses this information to determine the direction from direction from which a high frequency sound hi hi comes. comes. It It is easy to tell the direction of high frequency sounds coming from the side. But if a high side frequency sound, like a siren, comes from our midline, it is midline hard to tell if a sound is coming from the front or back. Direction of Sound Since Since all frequencies (f) of sound pass through the air at the same speed (v = 300 m/s), the wavelength speed (v wavelength (λ) of sound is inversely proportional to the frequency frequency of the sound, according to the following relation: λ = v/f . 16 Direction of Sound The wavelengths The wavelengths of high frequency sounds (10,000/s) are very short short (3cm). This makes it easy to tell the direction from which the sound is coming. To hear good surround sound the tweeters must be placed sound, the tweeters must be placed in in a room, car or movie theatre in a prescribed way. The wavelengths The wavelengths of low frequency sounds (100/s) is very long (3 m). long (3 This makes it impossible to tell the direction from which the sound is coming from. For this reason, the subwoofer can be placed anywhere. Direction of Sound Because Because the wavelength of sound coming from a rumbling stomach is about 1 m, which is larger than the di distance between our ears (0.1 (0 m), m), it is difficult to tell the direction from which the sound is coming. When When someone’s stomach rumbles, everyone nearby thinks it was his/her stomach. The Sense of Sight Eyes: The Organs of Vision Eyes: Biological Individuality 17 Jane Elliott: Using Eye Color to Teach about Racism Theories of Vision: Pinhole Camera AlAl-Haytham (1088) suggested that images are formed by the pupil pupil of the eye, in a manner similar to the way that they are formed by a pinhole. pinhole The similarity between the eye The similarity between the eye and pinhole and a pinhole camera was also noticed by Leonardo da Vinci. However However no one was able to reasonably explain the logical consequence that, if an eye formed images just like a pinhole camera, then the world should appear upside down. upside http://www.pbs.org/wgbh/pages/frontline/shows/divided/ Johannes Kepler Johannes Johannes Kepler (1604) developed, what is in essence, our current theory of vision. Kepler Kepler inserted an eyeball, whose back had been scraped away to expose the retina, in the pinhole of a pinhole camera. He discovered that the eye contains series of hard and soft He discovered that the eye contains a series of hard and soft elements elements that act as a convex lens, which projects an inverted image of the object on the concave retina. The The image formed on the retina is an inverted point-byinverted point-bypoint replica that represents the brightness and color of the object. Kepler Kepler dismissed the problem of the “upside up world” encountered da Vinci by suggesting that the brain subsequently “flips” the inverted image. The Addition of a Lens to a Pinhole Camera “Catches” More Rays From Each Point on the Object So The Image is Brighter; But Focus Must be Exact The cornea The cornea is fixed and can only focus distant objects on the retina retina. The lens is elastic and The lens is elastic and can can change its shape to focus near and far objects on the retina. The The lens muscles muscles contract (accommodate) to focus near objects and relax to focus distant objects. Together the Cornea and Lens Focus Light from Near and Far Objects to Form an Image Nearsightedness Nearsightedness In In a normal eye, the image is projected onto the retina. If If the eyeball is elongated, the image projected by the cornea comes to a focus near the lens. near Nearsi htedness can be corrected with ight can spectacles spectacles with diverging lenses. 18 Farsightedness If If the cornea is too flat, the image projected by the cornea comes to a focus far from the lens. far Farsightedness Farsightedness can be corrected with spectacles with converging lenses. Laser Eye Surgery LASIK: Laser Eye Surgery for Nearsightedness, Farsightedness and Astigmatism Carves the Cornea So that the Image Falls on the Retina Light Receptors on Retina There There are two classes of light receptor cells in the retina retina. The rods see shades rods of gray and are used at night. The cones are used to cones sense color during the day sense color during the day. The The light receptor cells of the retina contain pigments that can absorb light. The rods contain rhodopsin and rhodopsin the cones contain blueblue absorbing, green-absorbing green or red-absorbing red photopsins photopsins. http://webvision.med.utah.edu/ Signal Transduction in Rods Light Receptors on Retina The The absorption of light by rhodopsin activates a G-Protein, which activates phosphodiesterase, an enzyme that breaks down cGMP. cGMP The The decrease in cGMP closes sodium channels and the sodium plasma membrane hyperpolarizes. This reduces the hyperpolarizes. This secretion of the neurotransmitter, glutamate. All the colors of the rainbow are deconstructed by the three types of cone cells and reconstructed by the brain. 19 Color Vision: It is Hard to Believe that Others See Things Differently than We Do John Dalton (1794) said, “With respect to colours that were white yellow green white, yellow or green, I readily assented to the appropriate term. term. Blue, purple, pink, and purple pin crimson crimson appeared rather less discriminable; discriminable; being, according to my idea, all referable to blue. blue I have often seriously asked a person whether a flower was blue pink but blue or pink, but was generally considered to be in jest.” A Shoemaker Named Harris Confused Red and Green “He observed…that, when young, other children could discern cherries on a tree by some pretended difference in colour, though he could only distinguish them from the leaves by their differences of size and shape.” The Three Primary Colors Can Be Explained by Three Photoreceptors • Thomas Young (1802), a polymath, started with the assumption that a single visual receptor could not respond to every color in the rainbow rainbow. • Young proposed that there were three color receptors, one for red, one for green and one for violet, and the fact that there were three primary colors whose mixing could produce all colors was a consequence of the three receptors. • Hermann von Helmholtz, another polymath imagined that the three photoreceptors would be characterized by three overlapping mathematical curves. • He then established the absorption spectrum of the each absorption spectrum of the each photoreceptor by testing the ability of people to match colors using various intensities of three differently colored light. • People with normal color vision required three colors to match, while color blind people required only two. This is What a Person Sees Who has Violet, Green and Red Photoreceptors This is What You Would See if You Lacked the Red Photoreceptor (Red-Green Color Blindness) 20 This is What You Would See if You Lacked the Green Photoreceptor (Red-Green Color Blindness) This is What You Would See if You Lacked the Violet Photoreceptor (Blue-Yellow Color Blindness) Dalton Discovered that Color Blindness was Sex Linked. Indeed, the Genes that Code for Color Receptors are on the X-Chromosome XWhat What you should see if you have: 1. Normal Color Vision: Normal A: 29, B: 45, C: --, D: 26 --, 2. Red 2. Red-Green Color-Blind: Color A: 70, B: --, C: 5, D: ---, 3. Red Color-blind: Red ColorA: 70, B: --, C: 5, D: 6 --, 4. Green Color-Blind: Green ColorA: 70, B: --, C: 5, D: 2 --, Dalton (1794) noted, “It is remarkable that I have not heard of one female subject to this peculiarity.” The Discovery of Vitamin A Elmer V. McCollum discovered vitamin A as a fat-soluble factor in milk and leaves that promoted growth and prevented eye disorders. colorvisiontesting.com Through Column Chromatography, Paul Karrer Isolated and Determined the Structure of Vitamin A (retinol) from Cod Liver Oil and Carotene, its Precursor from Plants Paul Karrer 21 George Wald George Wald (1934) discovered that vitamin A was a component of the retina and won the Nobel Prize in 1967 for working out the photochemistry of vision. Vitamin A is converted to 11-cis retinal, a part of rhodopsin and the three photopsins. Vitamin A • The photoreceptor pigments (retinal) are made from vitamin A (retinol) supplied by the blood. • A molecule of β-carotene (provitamin A) can be broken down in the body to form two molecules of vitamin A (retinol). • The provitamin A content of orange-pigmented vegetables is very high. • The photoreceptor pigment is destroyed by the absorption of light and the photoreceptor pigment must be continually regenerated. George Wald: Experiments “I have often had cause to feel that my hands are cleverer than my head. That is a crude way of characterizing the dialectics of experimentation. When it is going well, it is like a quiet conversation with Nature. One asks a question and gets an answer; then one asks the next question, and gets the next answer. An experiment is a device to make Nature speak intelligibly. After that one has only to listen.” Vitamins are Multifunctional: Retinoic Acid In the skin, retinol (vitamin A) is converted to retinoic acid, a molecule that stimulates skin cells to produce more collagen produce more collagen, a protein found in healthy, young-looking skin. This is a slow process and for faster results, retinoic acid can be applied directly. Optical Illusions Circles or a Spiral? Do we believe what we see? or Do we see what we believe? 22 Phantom Dots Invisible Triangles 2 D or 3 D? 2D or 3D? Optical Illusions in Art What do you see? How do you see people and society? 23 Does the Brain Influence What We See? Who saw the next painting differently after reading the Da Vinci Code? di The Brain Also Influences How We Taste It’s Time to Study the Brain: Burton Green Wilder Brain Collection We learn to like learn new new foods and drinks. 24 Burton Green Wilder: Biology Class in McGraw Hall at Cornell 25 ...
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