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MIT 9 01 - The optic nerve carries the output of the eye

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MIT OpenCourseWare http://ocw.mit.edu 9.01 Introduction to Neuroscience Fall 2007 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.The optic nerve carries the output of the eye Figure by MIT OpenCourseWare. After figure 10.2 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968. E yeOptic NerveOptic ChiasmFinding the “receptive field” • Record the action potentials of an axon in the optic nerve • Present visual stimuli at various locations • Find the location at which a stimulus can cause changes in the firing rate.ON-center cell • There is a background firing rate. • The rate increases when the stimulus is in the receptive field (drawn circle). Image removed due to copyright restrictions.The cornea is more refractive than the lens of the eye Figure by MIT OpenCourseWare. After figure 9.7 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968. Focal Dal Dal Dal DistancistancistancistancistancistanceRefrefrefracactivtivtive Pe Pe Power (Der (Der (Der (Der (Dioptioptioptiopters) = ers) = ers) = ers) = ers) = ers) = ers) = 1Focal Dal Dal Dal Distancistancistancistancistancistance (m)e (m)e (m)e (m)e (m)Five classes of cells • Vertical elements – photoreceptors – bipolar cells – ganglion cells • Horizontal elements – horizontal cells – amacrine cellsThe retina has layers Image removed due to copyright restrictions.Cross section electron microscope image of the human retina.Figure 1 (Plate 32) in Boycott B. B. and J. E. Dowling. "Organizationof the Primate Retina: Light Microscopy." Phil Trans R Soc B 255, no. 799 (March 27, 1969): 109-184. doi: 10.1098/rstb.1969.0004.Retinal circuitry Figure by MIT OpenCourseWare. After figure 9.11 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968. Ganglion cellsDirect pathwayOutputInputPhotoreceptorsGanglion cell axonsprojecting to forebrainAmacrinecellBipolarcellHorizontalcellOpthalmoscopic view Image removed due to copyright restrictions.The retina, as viewed through an opthalmoscope.Figure 9.5 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 3rd ed. Baltimore, MD: Lippincott Williams& Wilkins, 2007. ISBN: 9780781760034.Variation in acuity with retinal Anstis, 1974 positionThe density of photoreceptors decreases in the periphery 90o70o50o30o10o10o30o050o70oDistance across retinaRodsConesFoveaBlind spotNumber/mm2RodsFigure by MIT OpenCourseWare.Rods and cones Figure by MIT OpenCourseWare. After figure 9.13 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968. Conephoto-receptorScotopic/night vision 1000 x more light sensitivePhotopic/day visionColor visionOutersegmentsInnersegmentsSynapticterminalsCell bodiesMembranous diskscontaining photopigmentRodphotoreceptorLight causes photoreceptors to hyperpolarize • Dark current due to open sodium channels • Light depletes cGMP, closing sodium channels Figure by MIT OpenCourseWare. After figure 9.17 a and b in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968. 0 mV0 mVVm}Na+Inner SegmentOuter SegmentLightDarkMembraneDepdarizationMembraneHyperpdarizationGMPcGMPcGMP}ON and OFF bipolar cells • Light has different effects on bipolar cells • ON cells depolarize • OFF cells hyperpolarizeTransient vs. sustained responses • Stimulus • Response timeTemporal antagonism • Stimulating the center causes a transient increase. • Removal of the stimulus causes a transient decrease (relative to background). Image removed due to copyright restrictions.Center-surround antagonism • OFF-center prefers: • ON-center prefers: – dark spot in center – light spot in center – light annulus – dark annulus Ganglion cellreceptive fieldOFF-center ganglioncell output:CenterDark spotPatch ofretinaSurroundFigure by MIT OCW. After figures 9.23 a, b, and c in: Bear, Mark F., Barry W. Connors, and MichaelA. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams &Wilkins, 2001. ISBN: 9780683305968.Horizontal cells are coupled by gap junctions Xin and Bloomfield Photo removed due to copyright restrictions.Resistive network model Figure 3 in Carver A. Mead and Misha Mahowald. "A Silicon Model of EarlyVisual Processing." In Computational Neuroscience. Cambridge, MA: MIT Press, 1993. Courtesy of Carver A. Mead and Misha Mahowald, authors,and Eric L. Schwartz, editor. Used with permission.Silicon retina Neuromorphic VLSI K. Zaghloul and K. Boahen, 2004 fKareem Zaghloul. Used with permission.Source: Zaghloul, Kareem A., and Kwabena Boahen. "A Silicon Retina that• • Courtesy o Reproduces Signals in the Optic Nerve." J Neural Eng 3 (2006) 257–267.Courtesy of IOP Publishing, Inc. Used with permission.fChevreul’s illusionLight: reality vs. perceptionReceptive field


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