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SENSORY RECEPTORS. SENSORY RECEPTORS. Objectives: E - label the parts of the eye D – Describe their functions C – explain how parts function to adjust focus and the amount of light entering the eye The eye as a receptor vitreous humour choroid choroid iris retina cornea pupil aqueous humour ciliary body lens optic nerve Soper 2 p593 • Draw eye diagram and label functions • • • • • • • • Iris Cornea Sclera Choroid Ciliary muscles Conjunctiva Adjustment Longitudinal muscles • Radial muscles • Suspensory ligaments • • • • • • • • • • Lens Pupil Eyelid Aqueous humour Vitreous humour Retina Fovea Optic nerve Dilation Constriction • Far object • Close object Accomodation • This is the focusing of light by the lens Dilation & constriction • • • • • • • • Iris Cornea Sclera Choroid Ciliary muscles Conjunctiva Rhodopsin Longitudinal muscles • Radial muscles • Suspensory ligaments • cones • • • • • • • • • • Lens Pupil Eyelid Aqueous humour Vitreous humour Retina Fovea Optic nerve Visual accuity Constriction • Far object • Close object • Rods The retina Blood vessel in choroid optic nerve fibres nuclei of ganglion cells nuclei of bipolar cells synapses nuclei of retinal cells retinal rod and cone cells choroid LIGHT Inner segments of rod and cone cells cell bodies of rod and cone cells rod cell cone cell optic nerve fibres ganglion cell bipolar cell cell body rod cell synapse cone cell Structure of the retina Photoreceptor cells (Rods and cones) Bipolar neurones connect photoreceptors to optic nerve •rods connected in groups •cones connected singly Axons of ganglion cells • optic nerve • visual area of the brain Melanin – absorbs light to prevent internal reflection fovea Approx 1mm diameter on visual axis of eye Cones only Point of maximum intensity of vision Main point of interest in visual field focused here fovea blind spot All axons of ganlion cells converge here to form the optic nerve No photoreceptors so not capable of forming an image Rhodopsin located in membrane of discs Photosensitive pigment Rod cell is a modified bipolar neurone How cone cells work; colour vision • Cone cells work in basically the same way as rod cells. • However bleaching requires a much higher light intensity (so cone cells cannot function in dim light). There are three different types of rhodopsin (the opsin protein part differs), which have maximum absorption at different wavelengths so cones cells allow for the discrimination of colour; there are •blue-absorbing cones (max absorption at 445nm) •green-absorbing cones (max absorption at 535 nm) •red-absorbing cones (max absorption at 570 nm) • this is the trichromatic theory of colour vision • different colours are perceived as a result of the degree of stimulation of the blue + green + red cones (i.e. colours are the result of the mixture of inputs from all three cone types) • By population, about 64% of the cones are red-sensitive, about 32% green sensitive, and about 2% are blue sensitive for example: % refers to the light absorbed as a % of the maximum* 0% blue + 83% green + 83% red yellow 31% blue + 67% green + 26% red green •*hence the size of the generator potentials produced, which in turn determines the number of nerve impulses from each type of cone cell, which is then interpreted by the brain as a particular colour
