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Consist of specialized sensory receptors located
in the head |
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Taste--gustation |
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Smell--olfaction |
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Sight--vision |
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Hearing--audition |
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Balance--equilibrium |
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These have specificity to stimulus |
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Transduction-conversion of stimulus to action
potential |
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Action potential leads to interpretation in CNS |
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Two ways of signalling |
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Tonic--always depolarizing |
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Phasic--usually quiet |
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Our dominant sense |
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Located in eyes, in orbits of skull |
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Surrounded by accessory structures |
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Positioned by six extrinsic muscles |
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Eyeball is a sphere of 3 layers (tunics) |
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The innermost (retina) is the sensory layer,
behind the choroid and sclera |
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Two layered innermost tunic of eye |
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Outer pigmented epithelial layer |
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Inner transparent neural layer, directly
connected to the brain via the optic nerve |
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Three types of neural cells--photoreceptors,
bipolar cells, and ganglion cells (axons run as CN II) |
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2.5x 109 cells in retinas, two types |
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Rods--dim, b/w peripheral vision |
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massed at periphery of retina |
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Cones--sharp, color focal vision |
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massed in center of retina (fovea) |
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Gradient in opposite directions |
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Light has energy, photon, wavelength |
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Light enters eye through clear cornea |
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Passes through clear lens, which changes shape
to bend light , focusing the image on retina |
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Light strikes photoreceptors; induces chemical
change to close Na+ gates |
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Hyperpolarized cell slows release NT |
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Elongated neurons, with tips in pigmented layer |
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Outer and inner segment then connected to cell
body, inner fiber |
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Rods cylindrical, cones pointy outer segment
gives name to cell |
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Outer segs contain discs with visual pigments
which absorb light |
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Visual pigments are retinal and opsin |
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Take on 4 forms (rhodopsin in rods) |
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When light absorbed, retinal changes shape,
opsin activated and cascade of reactions cause Na+ channel to
close, NT (glutamate) not released |
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Bipolar cells not stimulated, no signal sent to
ganglion cells |
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Retinal processing based on hyperpolarizing
cell, no signal |
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Ganglion cells read this as change in rate of
signal generation |
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Steady signal to brain changed |
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Processed & fused in thalamus |
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Cortical interpretation in occipital lobe |
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Notes