SENSORY RECEPTORS.

1. SENSORY RECEPTORS.

2. 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

3. The eye as a receptor

5. vitreous humour choroid choroid iris retina cornea pupil aqueous humour ciliary body optic nerve lens

6. Soper 2 p593 • Draw eye diagram and label functions

8. Lens • Pupil • Eyelid • Aqueous humour • Vitreous humour • Retina • Fovea • Optic nerve • Dilation • Constriction • Far object • Close object • Iris • Cornea • Sclera • Choroid • Ciliary muscles • Conjunctiva • Adjustment • Longitudinal muscles • Radial muscles • Suspensory ligaments

10. Accomodation • This is the focusing of light by the lens

11. Dilation & constriction

12. Lens • Pupil • Eyelid • Aqueous humour • Vitreous humour • Retina • Fovea • Optic nerve • Visual accuity • Constriction • Far object • Close object • Rods • Iris • Cornea • Sclera • Choroid • Ciliary muscles • Conjunctiva • Rhodopsin • Longitudinal muscles • Radial muscles • Suspensory ligaments • cones

13. The retina

15. Blood vessel in choroid

16. LIGHT optic nerve fibres nuclei of ganglion cells nuclei of bipolar cells synapses nuclei of retinal cells retinal rod and cone cells choroid

17. cell bodies of rod and cone cells Inner segments of rod and cone cells

19. rod cell cone cell

21. optic nerve fibres ganglion cell bipolar cell synapse cell body rod cell cone cell

22. Structure of the retina Photoreceptor cells (Rods and cones) Melanin – absorbs light to prevent internal reflection • 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

23. 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

24. fovea blind spot All axons of ganlion cells converge here to form the optic nerve No photoreceptors so not capable of forming an image

25. Rhodopsin located in membrane of discs Photosensitive pigment Rod cell is a modified bipolar neurone

27. 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).

28. 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)

31. this is the trichromatictheoryof 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

32. 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