Chapter 9 Notes

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Human Biology
Professor Niemeier

Chapter 9  Cortex -> nourished by aqueous humour behind it  Macula -> mid retina; dark, yellow hue -> central vision -> no large blood vessels  Fovea -> dark spot, anatomical reference point, retina thinnest here -> central fovea  Lens suspended by zonule fibers attached to cilary muscles, attached to sclera  Between cornea and lens: aqueous humour -> watery  Between lens and retina; vitreous humour -> viscous, jelly-like  Cornea -> about 42 diopters  Lens -> about 12 diopters  Glasses -> about 4 diopters  Striabismus -> exptropia, esotropia o One eye supressed – amblyopic  Cataract – lens clouding  Glaucoma – increase in intraocular pressure – leads to blindness  Retinis pigmentosa -> progressive degeneration of photoreceptors o Unknown cause o Tunnel vision  Detached retina -> retina pulls away from underlying eye wall  Macular degeneration ->loss of central vision o No known cure  Emmetropic -> light focus on retina  Hyperopia -> light focuses behind retina -> convex -> eye too short (far-sightedness)  Myopia -> light focuses in front of retina -> concave -> eye too long (near-sightedness)  Astigmatism – curvature and refraction in horizontal and vertical axis is different  Presbyopia -> hardening of lens -> old age – bifocals -> concave at top, convex at bottom  Radial keratotomy  Photorefractive keratectomy (PFK)  Laser instu keratomilensis (LASIK)  Ciliary muscles o Constrict -> lens round and think  Increase in refractive power o Relax ->lens thin and flat  Decrease in refractive power  Pupillary light reflex -> change in pupil shape with light level o Consensual  Ganglision cell o Amacrine cell  Bipolar cell  Horizontal cell o Photoreceptor  Photoreceptors: only light-sensitive cells in retina exc. Circadian rhythms  Ganglions only output  More membranous disks = more sensitivity to light  Only rods work in scotopic conditions  Cones do more work in photopic conditions  Retina is duplex -> scotopic and photopic  Membranous disks of outer segment – photopigens  Photopigments absorb light o Action potential  Photoreceptor parts o Synaptic terminals o Inner segments (cell bodies) o Outer segments  Peripheral retina -> mostly rods  Fovea -> ONLY cones, no rods o Less photoreceptors per ganglion  Peripheral -> ood for dim light  Central -> high-resolution vision  Cones larger than rods  Good
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