Chapter 15

·       Eye Diagrams

·       Structure of the Eyeball- layers, photoreceptors

-fibrous

      -outermost layer; dense avascular connective tissue

      -2 regions: sclera and cornea

-vascular

      -middle pigmented layer

      -3 regions: choroid, ciliary body, and iris

-sensory

      -retina: outer pigmented layer, neural layer (photo receptors: transduce light energy)

-photoreceptors:

      -rods: more numerous at peripheral region of retina, away from the macula lutea; operate in dim light; provide indistinct, fuzzy, non color peripheral vision

      -cones: found in the macula lutea; concentrated in the fovea centralis; operate in bright light; provide high-acuity color vision

·       Pathway of light entering the eye

-cornea, aqueous humor, lens, vitreous, humor, neural layer of retina, photoreceptors

·       Focusing for Close Vision

-light from a close object diverges as it approaches the eye

-requires that the eye make active adjustments

      -accommodation: changing the lens shape by ciliary muscles to increase refractory power

      -constriction: pupillary reflex constricts the pupils to prevent the most divergent light rays from entering the eye

      -convergence: medial rotation of the eyeballs toward the object being viewed

·       Emmetropic, myopic, hyperopic

-emmetropic: normal; focal point is on retina

-myopic: nearsighted; focal point is in front of retina

-hyperopic: farsighted; focal point is behind retina

·       Ear Diagram- outer, middle and inner

·       Properties of sound

-pitch

      -perception of different frequencies

      -normal range is from 20-20000 Hz

      -the higher the frequency, the higher the pitch

-loudness

      -subjective interpretation of sound intensity

      -normal range is 0-120 decibels (dB)

·       Transmission of sound to the internal ear

-sound waves vibrate the tympanic membrane

-ossicles vibrate and amplify the pressure at the oval window

-pressure waves move through perilymph of the scala vestibuli

·       Static and Dynamic Equilibrium

-vestibular receptors monitor static equilibrium

-semicircular canal receptors monitor dynamic equilibrium

·       Homeostatic Imbalances- Cataracts, Glaucoma, Macular Degeneration, Deafness

-cataracts

      -clouding of the lens

      -age related hardening or thickening

      -risks: diabetes, smoking, exposure to intense sunlight

      -vitamin c benefits

      -surgical removal

-glaucoma

      -pressure build up in the eye, puts pressure on the retina and optic nerve

      -inherited

      -causes blindness

      -pressure test

      -eye drops to lower pressure

-macular degeneration

      -progressive deterioration of the retina

      -main cause of vision loss over 65

-deafness

      -conduction

      -sensorineural

      -cochlear implants: cochlear damage, convert sound wave into electrical signal