BIOL 252 1st Edition Lecture 7 Outline of Last Lecture I Gustation II Olfaction III Hearing and Equilibrium IV Poll Everywhere V Sensory Coding VI Cochlear Tuning VII Projection Pathway VIII Equilibrium Outline of Current Lecture I Equilibrium II Vision III Sensory Transduction in the Retina IV Generating Optic Nerve Signal V How do we have different sensitivities VI Color vision VII Visual Projection Pathway Current Lecture I Equilibrium a Static equilibrium i Saccule and utricle ii When head is tilted heavy otolithic membrane sags bending the stereocilia iii b Semicircular Ducts These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II Sensory organ Gelatinous membrane Cochlear ducts Organ of corti Tectorial membrane Utricle Saccule Macula Otolithic membrane Semicircular ducts Crista Cupula c Angular acceleration i Crista Ampullaris ii When head is turning cupula is pushed into endolymph iii Cupula hangs into endolymph as it turns is pushed into endolymph which is stationary iv Tells us which way we re moving in space d Vestibular Projection Pathway i Awareness of spatial orientation and movement vestibular cortex ii Cerebellum controls muscle movements according to how head moving in space Vision a Perception of objects in the environment by means of the light that they emit or reflect b Conjunctiva i Membrane that covers eyeball ii Starts at margins of eyelids iii Only other visible structure cornea c Lacrimal Apparatus i Lacrimal gland tears are produced source ii Sink medial lacrimal punctum iii Flows lateral to medial then to nasal cavity to help wash away foreign particles and prevent infection w lysozyme d Extrinsic Eyes Muscles i Extrinsic outside of ii Ciliary body and iris are examples of intrinsic iii Four of them rectus muscles straight located at 12 3 6 9 o clock iv 2 oblique muscles turning movements of eyeball e Fluids of the eye i Aqueous humor produced by ciliary body and absorbed through Scleral venous sinus 1 Anterior to the lens ii Draining of extra fluid by scleral venous sinus glaucoma not enough absorption iii Maintains curvature of cornea f Formation of image i Light through cornea ii Passes through pupil 1 Light through small hole causes inversion iii Neural components 1 Fovea centralis central pit 2 Surrounding that is macula lutea yellow patch a Where acute vision takes place good resolution for spatial discrimination and color determination 3 Job of extrinsic muscles focus light on fovea 4 Medially have optic disc a What is coming out Blood vessels b Axons headed for optic disc so no room for photoreceptors blind spot c If medially located on retina lateral part of vision is missing d Medial retina represents lateral field e Lateral retina represents medial field iv Want to limit or enhance amount of light and want to focus the image 1 Regulating light a Sympathetic nervous system stimulates dilators contract and pupil gets larger b Parasympathetic nervous system stimulates constrictors so pupils get smaller g Principle of Refraction i How do we focus light ii Cornea is more dense higher index of refraction n 1 38 vs air n 1 1 Site of greatest refraction 2 Lens can change shape a Adjust through ciliary muscle put tension on lens and can vary that tension iii Why do we do this 1 2 Light rays converge on focal plane behind the lens 3 Not always coming in parallel h Emmetropia true unadjusted vision i State in which the eye is relaxed and focused in an object more than 20 f ii Eyes are looking parallel to each other i III What happens when we look at something right in from of it i Convergence eyeballs turn inward ii Light ways are not parallel iii Image is in different location iv Near response bends light waves more substantially by creating thick lens compared to thin dense j Common Defects of image formation i Hyperopia farsightedness focused beyond retina ii Myopia nearsightedness 1 Image falls short of retina k Accommodation adjusting lens Sensory Transduction in the Retina a b c d e f Sclera white Retina thick part of the eye wall In front of the eye vitreous body thicker fluid vs aqueous humor Encountered many structures before getting here Rod and cone i Along w choroid holds pig ii Photoreceptor cells 1 ROD a Most sensitive b Used in low light circumstances night vision scotopic monochromatic vision c All over the retina 2 CONE a Location concentrated in fovea sparse in periphery b Can perceive color 3 Bipolar cells connected to both by synaptic vesicles 4 Cones contain photopsin pigment w 3 different amino acid sequences and 3 sensitivities to colors 5 S M L cones short medium long wavelength 6 Rods contain rhodopsin most sensitive to blue light but don t perceive a color w it iii Perception of everything happens in brain g Location and Action of Visual Pigments IV V VI i Membranous discs ii Produces a lot of surface area iii In membranes are pigment molecules called opsin 1 Opsin signals change in permeability of cell membrane but ofen bound up and prevented from signaling by retinal comes from Vitamin A 2 Has to different shapes 3 At one particular location switches from cis to trans 4 When no stimulation by light are in cis conformation 5 Photon comes in and energizes molecule trans 6 Retinal held by opsin a Each type of opsin is different 3 types of cone 1 rod type 7 Pigment molecules bound up to opsin 8 Membrane tells us how much cell membrane there is Generating Optic Nerve Signal a Light comes in dissociates retinal from opsin opsin signals to membrane channels b Don t memorize details How do we have different sensitivities a Rods signal to fewer number of bipolar cells exact same signal sent no matter which rod is hit converging circuit i Over given area greater chance of detecting photons if photons are scarce ii But lose resolution quality iii Over vast distance signal looks identical to the brain iv High sensitivity b Cones i Photopic system ii 1 1 ratio iii Each one looks different iv High resolution c Single type of receptor cannot produce both high sensitivity and high resolution Color vision a Color perception is based on mixture of nerves signals representing cones of different absorption peaks VII b c Color blindness missing a cone or a cone is duplicated i Ofen hereditary alteration or lack of one photopsin or another d Ex missing L cone e Each peak has two sides symmetry Visual Projection Pathway a Retinal ganglion cell s