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VISION PHYSIOLOGY - Quiz

VISION PHYSIOLOGY - Quiz. Dr. Martin – Lecture 14/15. Is vision the only aspect of light reception? No, also skin cells and neurons. Describe Benoit’s classic experiment?

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VISION PHYSIOLOGY - Quiz

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  1. VISION PHYSIOLOGY - Quiz Dr. Martin – Lecture 14/15

  2. Is vision the only aspect of light reception? • No, also skin cells and neurons. • Describe Benoit’s classic experiment? • He removed the eyes of ducks to demonstrate that one can get a seasonal response to light if one focuses light on the skull, (responsiveness to photoperiod continued in the absence of eyes, but not if light was prevented from entering the skull). • What did Locke discuss about vision in his essay? • He asked the question that if a person is born blind but had their vision restored, could they identify a sphere just by looking at it? • Answer is: No.

  3. What is special about Virgil (Oliver Sacks)? • He had eye damage at a young age. Doctors did not want to operate on his cataracts because they assumed he could not see. His fiancé wanted to have the operation, they did and it was a success. • What is the range of the visual light spectrum? • 380 –760nm • Do long or short waves have greater energy and cause more damage? • Short waves • Which color has a greater wave length red or blue? • Red (700nm)

  4. Does the fovea contain cones or rods? • Cones • What is the area around the fovea with yellow pigment? • Macula • What are scotomas? • Blind spots on the retina (no visual receptors) • What is the difference between scotoptic and photoptic vision? • Scotoptic – Low light and involves rod cells • Photoptic – high light conditions and involves cones

  5. What is the term for the conversion of light energy into neural signals via photoreceptors? • Transduction • What is transducin? • G-protein activated by the breakdown of visual pigment. Transducin activates a phosphodiesterase that changes cGMP to 5’GMP. cGMP is needed to keep Na+ channels open. Closure of these channels results in hyperpolarization of the photoreceptor membrane. • What is the point at which rays converge and pass through a single point? • Focal point

  6. What is the distance from the convex lens at which the rays converge to a point? • Focal length • If you take the reciprocal of the focal length, what do you know? • Refractive power of the lens • What is the refractive power of the lens at rest? • 66.7 diopters • What portion of ~67 diopters involves cones? • 43 of 67 cones, remainder is rods

  7. Where does the refraction of light occur? • Cornea and lens • How can you change the refractive power of the lens? • Changing the lens shape or with corrective glass or plastic lenses. • What is the term for maintaining a sharp image on the retina? • Accommodation • How is the refractive power increased in accommodation? • Contraction of the ciliary muscle releases tension on the lens

  8. In accommodation, what happens to the pupils as the object moves closer to the eye? • Pupils constrict • True or false, accommodation is a consensual reflex elicited by monocular stimulation? • True • Describe the efferent pathway of accommodation? • Superior colliculus  oculomotor complex  ciliary body  medial rectus m. • Does the accommodation reflex arc include the visual cortex? • yes

  9. Aging impairs ____________reflex, but not _____reflex? • Accommodation; light • In Argyll-Robertson pupil, _____ reflex is absent, but _______reflex is retained? • Light; accommodation • What does it mean if your visual acuity is 20/40? • It means that you see an object at 20 feet, that the average person can see at 40 feet • What is the significance of a visual acuity of 20/200? • Legally blind

  10. What are the 3 components of The Near Response (Synkinesis)? • 1. Accommodation • 2. Convergence of visual axis • 3. Pupillary constriction • What is meant by a Spherical Aberration? • Light entering at the edge of the lens is refracted more than at the center • Is this a physical problem that occurs with all lenses? • Yes • What is the eyes solution to Spherical Aberrations? • Cornea is flatter at the margins

  11. What is a Chromatic Aberration? • Short wavelengths (Blue) are refracted strongly than long waves (Red) • How does the eye deal with Chromatic Aberrations? • The fovea avoids short wavelengths by using red and green sensitive cones and blue absorbing pigment (macular yellow) • How many degrees of the visual field does the fovea receive? • 3 degrees • The maximum acuity of the fovea is points how many seconds apart? • 26 seconds

  12. What is emmetropia? • Normal state of the eye (shape of the eye) • What is the term for far-sightedness in which rays are brought to focus behind the eye? • Hypermetropia (hyperopia) • Which type of lens is needed to correct hyperopia? • Convex lens • What is the term for near-sightedness? • Myopia • What is usually the cause of myopia? • Eye is too long

  13. Which type of lens corrects myopia? • Concave lens • What is the term for an age related defect in which the lens is not accommodating? • Presbyopia • What is astigmatism? • The cornea has an uneven curvature ( rarely lens) • What is the term for the failure of the eye to fuse images due to abnormal conjugate movements? • strabismus

  14. What can result from strabismus in children? • Can result in suppression of one eye’s input to cortex leading to functional blindness in one eye. • How can the above be corrected? • By shortening the eye muscles • What is stereopsis? • Depth perception • How is depth perception created? • The same image is projected on correspondingly different points of the retina (retinal disparity)

  15. What are the 2 mechanisms for gaining information about depth perception? • 1. Determination of distance by comparison of size of known objects. • 2. Determination of distance by moving parallax • What is meant by moving parallax? • Objects near you pass over the retina more rapidly than those farther away • What is achromatopsia? • A rare disorder the affects the Pingelop people of the South Pacific. Even though they have cones, they can not see color. Gene involved is CNGB3.

  16. Does light induce depolarization or hyperpolarization of receptor cells? • Hyperpolarization • Does hyperpolarization activate or inhibit the release of neurotransmitter? • Inhibits NT release • Cones are thought to release _____ as a transmitter? • Glutamate • Receptor cells continuously add new membrane to the sheets of modified cilia that form the receptor surface. What is the disorder in which this process is disrupted? • Retinitis Pigmentosa

  17. Photoreceptor cells form ribbon-like synapses on which two cell types? • Bipolar and horizontal cells • Connectivity of the retina results in _____ inhibition? • Lateral • What are the 2 types of bipolar cells (dependent upon their response to receptor cell NT)? • 1. On-center (depolarizing)  Increase firing sequence. • 2. Off-center (hyperpolarizing)  firing rate drops • What is the result of stimulation of the entire bipolar receptive field? • Causes little change in the cell output

  18. Which cells contribute to center-surround antagonism? • Horizontal , amacrine and ganglion cells • Which photoreceptor cells have more of a 1:1 ratio with ganglion cells? • Cones • What is an electroretinogram? • Looks at evoked potentials as information enters the eye • What are the two types of retinal ganglion cells? • M-type and P-type

  19. What are the characteristics of M-type cells? • Low contrast • Large receptive fields • Rapid adaptation • Important in stimulus movement = M • What are the characteristics of P-type cells? • High contrast • Small receptive fields • Slow adaptation • Important for analysis of detail • Have color-opponent receptive fields where different wavelengths in center vs. surround cancel each other

  20. What is the major mechanism of dark adaptation? • Consists of changing the concentration of light sensitive pigments to correspond with the ambient light level • 1. Absolute threshold for vision requires only a few quanta of light. • 2. The dark adaptation curve indicates that rods and cones adapt at different rates • What is the secondary mechanism for regulating light entering the system? • Pupil reflex • What are the factors affecting dark adaptation? • Time and light wavelength

  21. Where do the retinal ganglion cells project? • Lateral geniculate • Superior colliculus • Pretectal area • Suprachiasmatic area of the hypothalamus • Does the right visual hemifield project the left or right LGN? • Left LGN • Where do the M-cells project? • Superior colliculus for visual reflexes • Magnocellular layers of the LGN for motion detection. • Connected to rods

  22. Where do the P-cells project? • Parvocellular layers of the LGN for visual detail • Connected to cones • What % of the LGN input comes from the retina? • 10%, rest from cortex • How many layers does the LGN have and which layer is most dorsal? • 6 layers and 6 is more dorsal. • Where does layers 6, 4 and 1 receive input from? • Contralateral nasal retina

  23. Where does layers 5,3, and 2 of the LGN receive input from? • Ipsilateral temporal retina • Which layers of the LGN are magnocellular, project to the cortex and are concerned with movement, depth and flicker? • Layers 1 and 2 • Which layers of the LGN are parvocellular, and projections are concerned with color, texture, shape and detail.

  24. LGN projects ipsilaterally via which two sets of fibers? • 1. Meyers loop projection passing into the temporal lobe containing projections of the upper visual field. • 2. Parietal geniculocalcarine fibers containing lower visual field projections. • What part of the cortex does the visual field project? • Upper and lower lips of the calcarine sulcus on the medial surface of the hemispheres marked by the Line of Gennari • Which part of the visual field is represented most caudally and by a proportionally larger area? • The macula

  25. How is feature extraction involved in the visual cortex? • It is related to the connectivity and receptive fields of cortical cells • Where does Brodman’s area 18 (extrastriate cortex) project? • To Areas 19,20,21 (inferotemporal cortex) and area 7 (posterior parietal cortex).

  26. What are the two principle theories of color vision? • 1. Young-Helmholtz Theory – Trichromats theory = 3 kinds of cones • Retinal cones process information more according to this theory. • 2. Hering’s Opponent Process Theory – Postulates 2 color elements • Retinal P-cells and LGN process information on color more according to this theory. • Which pigments are coded on the X-chromasome? • Green and Red-sensitive pigments • Where are genes for the blue-sensitive pigments coded? • Chromosome 7

  27. What is color blindness? • One or more pigments is defective or absent • What causes most color blindness? • Most is Inherited. Diseases of the retina may also induce it. • Is the fovea normally dichomatic or trichromatic? • Dichromatic  reduces chromatic aberration • What is Deuteranomoly? • Involves a defect in the middle wavelength sensitive pigment (green-sensitive)

  28. What % of males are deuteranomalous trichromats? • 5% • What % of males lack green-sensitive pigments completely and what is the term for these dichromats? • deuteranopes

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