Special Senses2

7/30/2019 Special Senses2

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VISION


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STRUCTURE OF THE EYE


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Retina-

Pigmented layer containing the receptor cells,

organized in 10 layers.

Contains the rods & cones and 4 types of neurons;

bipolar cells, ganglion cells, horizontal cells and

amacrine cells.


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Layers of retina.


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Receptors


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Optic nerve

Optic disk or blind spot(3mm medial &

slightly above the posterior pole).

Macula luteayellow pigmented spot , marks

the location of fovea centralis, rod free portion

with densely packed cones, has highest visual

acuity.

Visual axis (fixation point to fovea).

Optical axis (ant to post pole)


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Visual pathways


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Visual cortex


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Field of vision

Binocular vision- portion of field of vision

seen with both the eyes. Central part of the

field of vision of two eyes. Points on the

retina on which the image of an object must

fall to be seen binocularly as a single object

are corresponding points.

Imp for perception of depth & proportion ofobjects.


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Field of vision


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Pupillary light reflex

Constriction of the pupil on exposure to direct

light.

2 typesdirect light reflex.

- indirect (consensual light reflex).


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Accomodation reflex / Near response

Contraction of ciliary muscle via III nerve.

Constriction of pupil dt cont of sphincterpupillae.

Convergence of visual axis dt cont of medialrectus.


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Accomodation reflex


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Defects of image forming mechanisms

Presbyopialoss of accommodation with age.

Myopia or short-sightednessparallel rays oflight from distant object are focused in front of

the retina.

Hypermetropia or long-sightedness.


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Myopia & its correction


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Hypermetropia & its correction


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Color vision

Ability of the eye to discriminate between colors excited by

light of different wavelength. Function of cones and better appreciated in photopic vision.

3 types of cones-red, green & blue sensitive , whichcombinedly perform the fn of CV.

3 pri colorsred (723-647nm), green(575-492nm), &blue(492-450nm), all colors are admixture of these 3.

Normal person sees all wavelengths b/w violet & red.

In dim light, all colors are seen as grey (Purkinje shiftphenomenon).

Complementary colorsensation of white.


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Theories of color vision-

Trichromatic theory (Young-Helmholtz

theory).

Mullers Doctrine of Specific Nerve Energy

Theory -


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Color Blindness Trichromate .

Anomaly & Anopia Congenitalinherited condition, males affected

more. 2 types:

1. Dyschromatopsiacolor confusion dt deficiency

of mechanism to perceive colors. Protanomaly/protanopia-defective or complete

absence of red cone pigment.

Deuteranomaly/deuteranopia-green.

Tritanomaly/tritanopiblue. Acquireddt damage to macula or optic nerve.


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Tests for color vision-

Pseudo-isochromatic chart test.

Lantern test.

Holmgren wool test.


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HEARING


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OLFACTION


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Location of olfactory mucosa


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Olfactory mucosa


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Olfactory pathways


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Mechanism of olfaction.

Pain associated with olfaction.

Olfactory fatigue.


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TASTE


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TASTE RECEPTORS

ReceptorsChemoreceptor , located on theedges & dorsum of the tongue, on theepiglottis, soft palate and pharynx.

Papillaetaste buds located in the walls , 4types

1. Fungiform papillae .

2. Filiform papillae.

3. Vallate (circumvallate) papillae.

4. Foliate papillae.


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Location of taste receptors


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Taste bud


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Taste pathways

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Special Senses2