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76 Cards in this Set
- Front
- Back
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Vision (sight)
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perception of light emitted or reflected from objects in the environment
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Visible light
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electromagnetic radiation with wavelengths from 400 to 750 nm
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Light
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must cause a photochemical reaction in order to produce a nerve signal our brain can notice
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- radiation below 400 nm
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has so much energy it kills cells
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- radiation above 750 nm
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has too little energy to cause photochemical reaction (it only warms the tissue.)
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Eyebrows
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provide facial expression, protection from glare and perspiration.
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Eyelids (palpebrae)
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- block foreign objects and blink to moisten the eye's surface - meet at the corners lateral and medial commissures - consist of orbicularis oculi muscle and tarsal plate covered with skin outside and conjuctiva - eyelashes help keep debris from the eye |
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- Tarsal glands
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secrete oil that reduces tear evaporation
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Conjunctiva
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- transparent mucous membrane lines the eyelids and covers anterior surface of eyeball except cornea - Richly innervated and vascular (heals quickly) |
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Lacrimal Apparatus
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Tears flowing across eyeball wash away foreign particles, help with the diffusion of oxygen and carbon dioxide and contain bactericidal enzymes
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Tears originate
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in the lacrimal gland punctum, the lacrimal canal, and into the lacrimal sac and finally the nasolacrimal duct into the nasal cavity
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Extrinsic Eyes Muscles
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- Six muscles insert on the external surface of the eye - Innervated by cranial nerves III (Oculomotor), IV (Trochlear), and VI (abducens) |
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Six muscles insert on the external surface of the eye
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- 4 rectus muscles move the eye up, down, left, and right - superior and inferior oblique produce more complicated eye movements |
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The Tunics of the Eyeball
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- Fibrous Layer - Vascular Layer - Internal Layer |
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Fibrous Layer (tunica fibrosa)
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Sclera and Cornea
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Vascular Layer(tunica vasculosa)
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Choroid, ciliary body and the iris
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Internal Layer (tunica interna)
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Retina and optic nerve
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Series of transparent structures that bend or refract light rays to focus them on the retina |
- Cornea - Aqueous Humor - Lens - Vitreous Humor |
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Cornea
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The transparent covering of anterior surface of eyeball
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Aqueous Humor
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a clear serous fluid filling area in front of lens (between lens and cornea)
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Lens
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- suspended by ring of suspensory ligaments - capable of changing shape to help focus light rays - more rounded when there is no tension on it - somewhat flattened normally due to pull of suspensory ligaments |
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Vitreous Humor
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the jelly filling the space between the lens and retina
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Aqueous Humor
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serous fluid produced by the ciliary body that flows from posterior chamber through the pupil to the anterior chamber *reabsorbed into the canal of Schlemm (scleral venous sinus) |
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Neural apparatus
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includes the retina and the optic nerve
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Retina
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forms as an outgrowth of the diencephalon - attached only at optic disk where optic nerve begins, and at the ora serrata (its anterior margin) - pressed against rear of eyeball by vitreous body |
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Detached Retina
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- blow to head or lack of sufficient vitreous body - produces blurry areas in field of vision - can lead to blindness due to disruption of the blood supply |
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Cells on visual axis of the eye
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macula lutea (a 3mm area)
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-Fovea Centralis
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the center of macula nerve where the most finely detailed images are seen due to highly packed receptor cells *Eye exams provides direct evaluation of blood vessels |
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Optic disk or blind spot
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where optic nerve exits the posterior surface of the eyeball - no receptor cells are found in optic disk |
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Visual filling
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the brain filling in the green bar across the blind spot area
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Posterior layer of retina
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pigment epithelium - its purpose is to absorb stray light and prevent reflections |
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Photoreceptors cells are next layer
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derived from stem cells that produce ependymal cells
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Rod cells (Night vision)
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outer segment is a coin-like membranous discs studded with rhodopsin pigment molecules
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Cones cells (color vision in bright light)
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outer segment tapers to a point
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Nonreceptor Retinal cells
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- Bipolar cells - Ganglion cells - Scattered & amacrine cells |
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Bipolar cells (1st order neurons)
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synapse on ganglion cells
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Ganglion cells (2nd order neurons)
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axons of these form optic nerve
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- Scattered & amacrine cells from connections between other cells
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enhance perception of contrast, edges of objects and changes in light intensity
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Rhodopsin (visual purple)
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visual pigment of the rod cells
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Two major parts to the molecule
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-Opsin -Retinal |
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Opsin
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protein
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Retinal
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Vitamin A derivative
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Rod cells
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contain single kind of rhodopsin with an absorption peak at wavelength of 500 nm
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Cones contain
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photopsin
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3 opsin varieties contain
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different amino acids that determine which wavelengths of light are absorbed
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3 kinds of cones
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absorbing different wavelengths of light produce color vision
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Duplicity theory
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single type of receptor cell incapable of providing high sensitivity and high resolution
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-Sensitive night vision
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one type of cell (rods) and neutral
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-High resolution daytime vision
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different cell types (cones) circuitry and neutral circuitry
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Sensitivity of rod in dim light
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-extensive neuronal convergence -600 rods converge on 1 bipolar cell -many bipolar converge on each ganglion cell -high degree of spatial summation but no ability to resolve detail |
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✔ one ganglion cells receives |
information from 1 mm² of retina producing only a coarse image |
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Edge of retina with widely spaced rod cells
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is the low resolution system only altering us to motion
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Fovea contains
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only 4000 tiny cone cells and no rods -no neuronal convergence -each foveal cone cell has "private line to the brain" via bipolar cell and ganglion cell |
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Fovea (continued)
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high resolution vision, but with little spatial summation and less sensitivity to light intensity
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Primates have
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well developed color vision -nocturnal vertebrates have only rods |
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Cones are named for
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absorption peaks of photopsins |
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Blue cones peak
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sensitivity at 420 nm
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Green cones peak at
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531 nm
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Red cones peak at
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558 nm (orange-yellow)
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Perception of color is based on
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mixture of nerve signals
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Bony labyrinth
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passageways in the temporal bone
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Membranous labyrinth
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Fleshy tubes lining bony tunnels -filled with endolymph (similar to intracellular fluid) -floating in perilymph (similar to cerebrospinal fluid) |
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Stereocilia of hair cells attach to the
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gelatinous tectorial membrane organ of corti
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Inner hair cells
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where hearing comes from
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Outer hair cells
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Increases auditory precision
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Sound is produced by
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vibration of ossicles and then vibration of basilar membrane under hair cells |
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Vestibulocochlear nerve
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the vestibular and cochlear nerve unite to form this
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Stimulation of cochlear cells
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can happen as often as 20,000 times per second
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Equilibrium
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control of coordination and balance receptors in vestibular apparatus |
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Receptors in vestibular apparatus
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- semicircular ducts contain crista -saccule and utricle contain macula |
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Perceived by macula
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the perception of head orientation
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The perception of motion or acceleration
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- linear acceleration perceived by macula - angular acceleration perceived by crista |
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Sound
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any audible vibration of molecules
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Color blindness
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is hereditary lack of one more types of photopsin pigments |
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Red-green color blindness
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It's common lack either red or green cones incapable of distinguishing red from green sex-linked recessive (8% males) |
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Hearing range
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20-20,000 Hz
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