Experiment #2

Physiology of the Nerve

(Watch Tick Test for Auditory Acuity)

Submitted by:

Group no. 1

Baranda, Jaela Nicole

Corpuz, Israle Rhey

Martinez, Czarina Cherizze

Petilla, Kimberly Anne

Silbol, Belerubin

(4Bio-3)

Submitted to:

Associate Professor Josefino Castillo

Dr. Tan

December 9, 2010

Introduction:

A sensory system is a part of nervous system that is accountable for processing

sensory information. It consists of sensory receptors that receive stimuli from internal and

external environment, neural pathways that conduct this information to brain and parts of

brain that processes this information. The information is called sensory information and it

may or may not lead to conscious awareness called sensation. The system is stimulated

by sensory receptors; these are the organs which trigger action potentials on a sensory

neuron in response to a specific type of stimulus.

Sensory system can be classified into three basic sensory receptors. The first is

somatic receptors: receptors in the skin, muscles, and tendons. Secondly, the visceral

receptors, these are receptors in the internal organs. Finally, special receptors are the

receptors positioned in specific locations. Sensory receptors can be classified what they

are detecting like mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors

and nociceptors. The final method to classify is by either simple or complex. Simple

receptors are fairly small and are widely distributed throughout the body. Complex

receptors govern the five special senses of taste, smell, hearing, balance, and vision.

Auditory system is the sensory system for the sense of hearing. Sound can be

heard through a process which occurs in the ear. The ear has three main sections: the

outer, the middle, and the inner ear. The folds of cartilage surrounding the ear canal are

called the pinna. Sound waves, which are vibrations in the air, are reflected and

attenuated when they hit the pinna, and these changes provide additional information that

will help the brain determine the direction from which the sounds came. Entire audible

range extends from 20 to 20,000 Hz. Loudness of a sound is determined by the amplitude

of the sound waves and the bigger the amplitude of the sound wave, the larger the

amplitude of the vibration.

This experiment aims to evaluate the auditory system and perform the watch tick

test and hearing adaptation.

Materials and Methods

Watch Tick test for Hearing Acuity

For this test, the subject’s ear was plugged with cotton and had his eyes closed.

The watch was held against his auditory canal of the unplugged ear and was slowly

moved until the subject can’t hear it. The distance from ear to point where subject cannot

hear and where can hear again were measured. The difference was noted. The procedure

was also done with the other ear.

Auditory adaptation

A stethoscope was placed on the subjects ears. A tuning fork was vibrated at the

bell of the stethoscope. The tuning fork was removed. The subject was let alone for two

minutes without removing the stethoscope.

The tuning fork was again vibrated at the bell of the stethoscope but the rubber

tube leading to one ear was pressed firmly. The fork was moved away so that the sound

was barely heard on the free ear then the pressure on the tube on the other ear was

released. The sensation felt by the subject was recorded.

Results and Discussion

I. Watch Tick Test Auditory Acuity

Distance from ear to point

where subject cannot hear

Distance where subject

can hear again

Difference

Right 44 cm 36 cm 9cm

Left 51 cm 46 cm 5 cm

The subject’s ear was plugged with cotton while the other was not so that the

sound of the ticking clock would only be concentrated to the unplugged ear, and that to

avoid hearing other necessary noise. The subject’s eyes were closed so that the brain can

concentrate fully to its hearing senses. The distance measured refers to the distance the

subject can hear the ticking clock the farthest. In this case, the subject’s left ear has a

stronger sense of hearing since he can hear and cannot hear the tick of the clock the

farthest with the lesser difference from where he cannot hear the sound anymore to where

he can hear it again. This means that the left ear of the subject is dominant. The reason

for this is that a person has a dominant lobe of the brain and this dominant lobe of the

brain gives stronger function on that side of the body than the other side such as a left-

handed person has his right lobe of the brain dominant.

II. Auditory Adaptation

Sensation

Normal The subject can hear the sound of the tuning fork

Rubber Tubing Pressed At first, when the rubber tubing was pressed, the subject

can’t hear the sound but after releasing the rubber tube, the

sound was prolonged and heard again even when the tuning

fork was no longer at the bell of the stethoscope.

When sounds are transmitted through ossicular system into the central nervous

system, a reflex occurs after a latent period to cause contraction especially of the

stapedius muscle and to a lesser extent the tensor tympani muscle. The tensor tympani

muscle pulls the handle of the malleus inward while the stapedius muscle pulls the stapes

outward. These two forces oppose each other and thereby cause the entire ossicular

system to develop a high degree of rigidity and reducing the ossicular conduction of low-

frequency sound.

In the experiment, the tuning fork was vibrated at the bell of the stethoscope and

the tuning fork was removed and the subject took a rest for two minutes without

removing the stethoscope. Auditory adaptation was allowed to take place when the

subject was allowed to rest, accommodating the sound. When the tuning fork was then

vibrated again but this time, the rubber tube leading to one ear was pressed firmly, the

free ear heard the sound of vibration from the tuning fork, which means, sound was

adapted, the sensory nerves for hearing were able to adapt on the vibrating sound that is

why for the subject, the sound cannot be heard anymore, though there are still vibrations

from the tuning fork. But when the rubber tubing was released, the subject was able to

hear the sound of the tuning fork, even though the other ear wasn’t able to hear it

anymore. It’s because the other ear, where the rubber tube was released, was still

adapting to the sound of the vibrating fork. This phenomenon is also happening like for

example, when you are inside a room where the air conditioner is making noise, after

some time while you’re inside the room, you wouldn’t be able to really hear the noise

made by the air conditioner. This is because the sensory nerves responsible for hearing

were able to adapt the sound of the air conditioner. This is explained through the

propagation of action potential of the nerve. In a resting potential where the membrane is

said to be polarized, when a portion of the membrane gets excited, that excitable

membrane usually excites adjacent portions of the membrane and an explosive action

potential spreads resulting to depolarization. The depolarization process travels along the

entire extent of the fiber thus producing a nerve impulse. This resting potential of the

nerve is when we first hear a certain sound and if we get used to this sound and feel that

the sound isn’t there anymore, it is the action potential prevailing.

Post Laboratory Questions

1. What causes relative refractory periods?

Relative refractory period is a result when an excitation threshold of neural tissue is

raised and a stronger-than-normal stimulus is required to initiate an action potential.

2. Is auditory acuity same for both ears?

The normal auditory acuity for both ears is the same. But due to some factors it may

vary. For example, it could be due to a build up of wax in one ear more than the other.

Infection in one ear may also cause a loss of auditory acuity in the infected ear. Auditory

acuity is lost with age, and it may not be lost equally bilaterally, which would explain a

difference between the acuity in the two ears in older people. 25.9 Sound waves reach the

cochlea when conduction deafness is present through vibrations of the bones in the skull,

bypassing the outer and middle ear (Bone). Hearing is not as efficient through bone

conduction as it is through air conduction, but it is possible. Hearing aids are available for

people with conduction deafness which consists of a body-worn aid and a bone conductor

or vibrator attached to a headband, or it can be attached to special spectacles. 

3. What is near point Accommodation?

Accommodation is the mechanism by which the eye changes its refractive power by

altering the shape of its crystalline lens. During accommodation, the ciliary muscle

contracts allowing the zonular fibers to relax. This relaxation causes the equatorial edge

of the lens to move away from the sclera during accommodation resulting in increased

lens convexity (roundness). This increase in roundness primarily occurs on the front

surface of the lens.

References

http://www.absoluteastronomy.com/topics/Auditory_system

http://www.biology-online.org/9/8_sensory_systems.htm

Kandel, et al. Principles of Neuroscience. Fourth ed. pp 591–624. Copyright 2000, by

McGraw-Hill Co.

Hodgkin, A. L. (1963). The conduction of the nervous impulse. Liverpool University

Press

Wile, Jay L., Shannon, Marilyn M., The Human Body: Fearfully and Wonderfully Made!

2001. Published by Apologia Educational Ministries, Inc. Anderson, IN. Printed by CJK.

Cincinnati, OH. Sixth Printing 2008. p.257-261

Wilkinson, M. (2006).Essentials optics review for the boards.Med Rounds Publications