1. Can humans or non-human animals see in the dark?

2. NO……You need light!

3. Light?  Waves of electromagnetic energy  Photons: = discrete particles of energy  Travel in space at high speeds (186,000/second!)  Measure in length nanometers (billionth of a meter) So, we call these wavelenths Visable to humans  380 – 760 nm

4. Visible Spectrum of Wavelength - Humans *snakes see infrared (too long for humans)

6. Anatomy of the Eye 4. Iris: muscle, control of light intake, color (melanin) 5. Pupil: hole in iris -- dilates/contract based on available light 10. Optic Nerve 6. Lens: adjusts the eye’s focus (20%) accomdation 2. Cornea: covers iris & pupil focusing begins (80%) 3. Anterior Chamber (aqueous): clear fluid  nutrients/shape 7. Vitreous Humor: gives eyeball shape 1. Sclera: covering of eye 1. 8. 2. 3. 4. 5. 6. 7. 9. 10. 8. retina: transduction rods & cones 9. Fovea: acuity, cones

7. Anatomy of the Eye Light entering the eye

8. Lens of the eye inverts the visual image – Upper half of visual field projects onto the ventral portion of the retina … Lower half of visual field projects to the dorsal portion of the retina Thank God (or whomever) that the visual cortex inverts it back to its original orientation! The visual system is like a Camera

9. Normal Vision Problem in lens  Cataracts protein clumping together Problem in the macula (fovea) Macular Degeneration: loss of acuity and center vision

10. Anatomy of the Eye - Retina Retina: Photoreceptors Transduction of light Into electrical chemical Message Instead of NT Binding to receptor… Light cause cascade of Intercellular messages

11. Cell Layers in the Retina …notice anything funky about the set up? Ganglion Cell Axons form optic nerve

13. Rods (scotopic) -responsible for night vision -very sensitive to light (low levels) -found in the periphery of retina - more than cones - Provide monochromatic info (Achromatic) - Provides poor acuity - Night blindness Cones (photopic): -responsible for day vision (sensitive to mod-hi light) - found in fovea - provides greater acuity - trichromatic – color vision - legally blind (day blindness)

14. All sensory info must under go a series of 3 steps (sight, sound, touch): 1.RECEPTION: Absorption of physical energy by a receptor light  PHOTORECEPTORS 2. TRANSDUCTION: Conversion of one form of energy to another light  electrical chemical message 3. CODING: The one-to-one correspondence with a stimuli and the nervous system activity AP  send message to visual cortex Conversion of light to neural signal: visual transduction

15. Anatomy of the Eye – Blind Spot blind spot

16. The blind Spot 1 million nerve fibers * Exercise in book (pg 139)

17. Glaucoma: problem in the Anterior Chamber  fluid there doesn’t drain correctly which puts pressure on the back of the eye especially the optic nerve Damage to the optic nerve = Glaucoma

18. Optic Tract 1/2 axons go to right side of the brain 1/2 go to left side of brain Not the same in all animals – depending on location of eyes Ex: Rabbits & Guinea Pigs IPSI & CONTRALATERAL PATHWAYS

19. How does the signal get to the Visual Cortex? VIA the Retinal Ganglion Cell Axons OPTIC TRACT