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5-350 (38)

Eyes, Ear

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Biological Sciences
Asish Mukhopadhyay

Eyes, Ear, Nose Sensory Receptor Cells sensory cilia – related to motile cilia, but central tubules are missing Light: rod photoreceptor rod uses rhodopsin and G-protein pathway for a.p. and nt release rhodopsin Sound: ciliary movement directly opens/closes membrane channels hair cells hair cell Chemicals: rhodopsin-like receptors G-protein coupled cascade to amplify original signal 1,000 different odorants can be detected Genetic defects of cilia  more than one cell affected (Usher’s Synd.) Usher’s Syndrome Early Evolution of Vertebrate sensory organs: cilia project from apical surface of epithelia least protected = olfactory epithelium mechanosensory cells – more extensive infolding photoreceptors – most extensive evolution folded into the neural tube  must face AWAY from light Sensory cell origins: embryonic primordia optic vesicle EYE – forebrain epithelium grows out  becomes OPTIC VESICLE vesicle becomes retina lens forms from ectoderm EAR/NOSE – from thickened surface ectodermal PLACODES ectodermal placodes ear: otic placode  otic vesicle  hair cells nose: olfactory placode **primordial tissues are source of neurons AND inductive signals for rest of organ** Eyes, Ear, Nose VISUAL SYSTEM EYE FIELD at anterior epiblast becomes committed to development eye field prechordal plate secretes SHH  prevents midline development precordal plate, shh allows for hypothamus/pituitary development eye field subdivides into 2 types of primordia: neural/forebrain eye  optic vesicle  optic cup optic vesicle, cup ectodermal  lens, cornea, eyelids reciprocal signaling between cup and lens is necessary lens makes FGF 1/2 for optic cup FGF 1,2 cup makes BMP 4/7 for lens BMP 4,7 signaling defects  anopthalmia, micropthalmia after contact is made between optic vesicle and lens placode: - lens placode pinches off to form lens and surface corneal epithelium lens, surface corneal epithelium - optic vesicle away from lens becomes RETINAL PIGMENT epi. retinal pigment (for photoreceptors) epithelium iris - edge of optic cup forms the iris - CHOROID FISSURE – seam along which cup fuses choroids fissue optic nerve runs along it improper closing  colobomas (conspicuous in iris) coloboma Pax6 PAX6 – essential for eye development; haploinsufficient no iris, corneal defects, no fovea ectopic expression can induce eye/lens formation Retinal Cell Types: develop at different times ganglion ganglion cells – long axons that make the optic nerve bipolar cells – connect ganglion to photoreceptors bipolar glial cells – structural scaffolding of retina glial photoreceptors – rods: low li
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