Chapter 10 Sensory Part 2

Chapter 10 Sensory Part 2 - Special Senses Vision Vision...

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Unformatted text preview: Special Senses: Vision Vision Chapter 10, cont’d Review eye anatomy, Review especially: especially: Path of light through eyeball Cellular layers of retina Intrinsic eye muscles Blind spot and fovea centralis Fig 10-28 Vision Process can be Divided into Three Steps Three 1. Light enters eye, is Light focused by lens onto retina 2. 2. Photoreceptors transduce Photoreceptors light energy into electrical signal signal 3. Processing via optic N. (II), Processing lateral geniculate body to Visual Cortex Visual Pupillary light Reflex Pupillary • Amount of light is changed Amount by altering pupil aperture from ∼ 1.5 – 8 mm • Pupillary constriction due Pupillary to the ciliary muscle via CN III (oculomotor) III • Pupillary reflex is Pupillary consensual consensual The Cornea and Lens and — Light is bent (refracted) when it Light passes from one medium to another another — Two thirds of refraction is by the Two cornea cornea — Focusing is done by the lens, Focusing which can alter its shape. which — Called accomodation — Ciliary muscle Ciliary Accommodation: Light is focused (to Accommodation Light keep objects in focus) by changing lens shape Lens attached to ciliary muscle via suspensory ligament (= zonulas) ligament Ciliary muscle contracts ...... See also Fig 10-32 Lens bulges up Lens Accommodation Accommodation Fig 10-31 Compare to Fig 10-33 Vision Problems Vision Emmetropia = Normal vision Normal Presbyopia (loss of accommodation; need reading glasses) glasses) Myopia (near-sightedness; retina too far away) Hyperopia (far-sightedness; retina too close) Astigmatism (asymmetry of cornea and/or lens) and/or Test of visual acuity in lab Retina Review Retina •Fovea = area of maximum acuity acuity •The neurons and blood The vessels are pushed off to the side to •The macula surrounds the The macula fovea fovea •Optic Disk Important concept from 1st part of chapter: Sensory Transduction at the photoreceptor converts visible light into Graded Potentials light Stimulus energy is transduced into a membrane potential change. membrane Phototransduction at Retina Phototransduction Neurons organized into Neurons layers layers Light = Electromagnetic Energy Electromagnetic Wavelength for visible Wavelength light: λ =? =? Some animals can see Some UV and IR waves UV PhotoPhotoReceptors Rods Monochromatic night time Monochromatic vision vision 1 pigment (Rhodopsin) Most numerous except in Most fovea fovea 20X more rods than cones Cones High acuity vision & daytime High color vision color Highest density in fovea 3 pigments (similar to rhodopsin) rhodopsin) Fig 10-38 Colorblindness Colorblindness “Color deficiency” more Color accurate term accurate ~ 10% of men, sex-linked trait L-, M- and S Cones detect L-, the colors the Most common is L-Cone Most deficiency (red-green) deficiency Very small differences in AA Very sequence of photochromic pigments in cones pigments Not in Book Phototransduction for Rhodopsin Rhodopsin Retinal absorbs 1 Retinal photon photon (similar for cone pigments) Rhodopsin splits: Rhodopsin Retinal is released from opsin due to conformational change conformational = “bleaching” How does this produce AP ? Retinal = Vit. A derivative Opsin = protein No Light: No Rhodopsin inactive Rhodopsin Cells have membrane potential of ~ - 40 mV (what does that mean, what is it due to ?) what Continuous (= tonic) NT Continuous release to adjacent bipolar cells bipolar Fig 10-39 Light: Light: 1. Rhodopsin splits 2. Activation of transducin 3. 2nd messenger cascade decreases cGMP levels decreases 4. Na+ channels close ⇒ NT release decreases decreases 1. 5. NT is glutamate Bipolar neurons receive NT 1. May be excitatory or inhibitory 120 x 106 Mio rods 120 6 x 106 cones only 1.2 x 106 axons enter optic nerve ⇒ mechanism? Visual processing in Visual visual cortex visual Optic nerves enter Optic brain at optic chiasma: some fibers cross sides ⇒ right side visual field to left side brain brain Visual Field and Binocular Vision Vision 3 vs. 2 dimensional view Fig 10-41 ...
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