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Lecture 15

Outline of Lecture 15

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Biological Sciences
Asish Mukhopadhyay

Outline of Lecture 15 Special Senses: Eye, Ear, and Nose I. Overview of sensory cells of the eye, ear, and nose - Due to evolution, the cilia of sensory cells are on the topographical outer surface of the body - Quickies on each system - Eye: signal through a 7TM containing rhodopsin, coupled to G-protein; retina is part of the forebrain (diencephalon), lens derives from lens placode of surface ectoderm - Ear: mechanoreceptive cilia directly tranduce vibration to ion channel opening; derives from otic placode of ectoderm overlying hindbrain (rhombomeres 5,6) - Nose: odorant binds and signals through GPCR/cAMP; derives from olfactory placode of forebrain (telencephalon) II. The Eye A) Embryology of the eye - Optic vesicle derives from neural plate, lens from surface ectoderm - Neural crest and mesoderm contribute to other eye tissues (cornea, choroids, sclera, etc) - Shh splits the eye field by inhibiting eye dev. along the midline - Reciprocal induction: BMP4 and BMP7 from optic vesicle induces lens primordium, and FGF1 and FGF2 from lens induces optic vesicle (eye primordium) - PAX6 can induce eye development ectopically B) Layout of the optic cup - Lens placode pinches off to form lens vesicle; surface ectoderm becomes cornea - Optic vesicle invaginates to form optic cup around the lens (ventral portion fuses) - Inner layer of optic cup becomes retina and outer layer becomes retinal pigment epithelium - Photoreceptors point away from light into ventricular space between layers of optic cup - Fovea at back of retina is thinner to allow for sharper vision at that region (less non-photoreceptor cells in the way to scatter light) C) Cells types of the retina - Ganglion cells: their axons project through optic nerve to brain; formation requires Math5 txn factor - Bipolar cells: relay signals from photoreceptors to ganglions; dev. requires Chx10 txn factor - Mueller glial cells: retina scaffold, ganglion axon guidance, neurotransmitter recycling - Amacrine and horizontal cells: no detail given - Photoreceptors - Rods: for low light - Cones: comes in red, green, blue - Photosensitive ganglions: involved in pupil contraction and circadian rhythm; detect light with melanopsin (this is Wai-King Yau’s work) D) Eye connections to brain - Portion of ganglions from each eye cross brain midli
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