Sunday, May 17, 2009


1. What is attenuation reflex?

When very loud sound is transmitted through ossicular system to CNS ,reflex is initiated with a latent period of 40 to 80 ms.this reflex causes contraction of tensor tympani muscle which pulls the malleus inward whereas contraction of stapedius muscle which pulls stapes outward. These two opposing effects make the ossicular system very rigid; therefore, it fails to vibrate with the sound wave. Thus, sound is not allowed to enter inner ear (it is attenuated) or its intensity is reduced by 30 to 40 decibels.

2. What is electro-olfactogram?

When an odorous substance gets absorbed on to the olfactory mucosa, electrical changes are setup.Monophasic negative potential is recorded which lasts for 4 to 6 seconds. This recorded response is known as electro-olfactogram.

3. What is purkinje shift?

In bright light ,cones are optimally functioning ,therefore the peak spectral sensitivity of retina is at 560 nm.In scotopic vision only rods are functional ,therefore peak spectral sensitivity of retina is at 500 nm.This shift of peak spectral sensitivity when a person goes from bright to dim light is known as purkinje shift.

4. What is flicker fusion frequency?

Images of any object remain on the retina for some time so that if pictures are shown one after the other, they give an appearance of being continuous. The critical frequency at which fusion occurs is known as flicker fusion frequency. Critical frequency is much higher in bright light.

5. What is the importance of light and dark adaptation?

Sensitivity of retina increases during darkness and decreases during exposure to light. Thus, sensitivity of retina is automatically adjusted to changes in illumination.

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