Prepared by: Ahmet GÜNER

Your ears are extraordinary organs. They pick up all the sounds around you and then translate this information into a form your brain can understand.

One of the most remarkable things about this process is that it is completely mechanical.

Your sense of smell, taste and vision all involve chemical reactions, but your hearing system is based solely on physical movement.

In this lesson, we'll look at the mechanical systems that make hearing possible.

We'll trace the path of a sound, from its original source all the way to your brain, to see how all the parts of the ear work together.

When you understand everything they do, it's clear that your ears are one of the most incredible parts of your body!

To understand how your ears hear sound, you first need to understand just what sound is.

An object produces sound when it vibrates in matter. This could be a solid, such as earth; a liquid, such as water; or a gas, such as air.

Most of the time, we hear sounds traveling through the air in our atmosphere.

When something vibrates in the atmosphere, it moves the air particles around it.

Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air.

To hear sound, your ear has to do three basic things:

Direct the sound waves into the hearing part of the ear

Sense the fluctuations in air pressure Translate these fluctuations into an electrical

signal that your brain can understand

How Hearing WorksThe ear is made up of three different

sections: the outer ear, the middle ear, and the inner ear.

These parts work together so you can hear and process sounds.

The pinna, the outer part of the ear, serves to "catch" the sound waves.

Your outer ear is pointed forward and it has a number of curves. This structure helps you determine the direction of a sound.

If a sound is coming from behind you or above you, it will bounce off the pinna in a different way than if it is coming from in front of you or below you.

This sound reflection alters the pattern of the sound wave. Your brain recognizes distinctive patterns and determines whether the sound is in front of you, behind you, above you or below you.

When the sound waves hit the eardrum in the middle ear, the eardrum starts to vibrate.

Hammer, avnil and stirrup help sound move along on its journey into the inner ear.

Let’s watch how it works…

The vibrations then travel to the cochlea, which is filled with liquid and lined with cells that have thousands of tiny hairs on their surfaces.

There are two types of hair cells:

the outer and inner cells. The sound vibrations make the tiny hairs

move.

Let’s watch how it works…

The outer hair cells take the sound information, amplify it (make it louder), and tune it.

The inner hair cells send the sound information to your hearing nerve, which then sends it to your brain, allowing you to hear.

The Specificity of Receptors Depends on:

Each receptor has a low threshold for its particular stimulus. The threshold is the minimal strength of stimulus necessary to set off an impulse.

The receptor sends only one kind of message to the central nervous system no matter what the nature of the stimulus. This is known as Muller’s doctrine of specific nerve energies.

SoundHearing is one of the several ways of picking

up vibrations.Many receptors exist to detect vibrations,

ranging from simple sensory hairs to the ear.Vibrations are picked up by the organ of

Corti within the cochlea.Vibrations of the fluid in the cochlea causes

the basilar membrane to move, thereby bending the hairs and creating a generator potential.

This triggers impulses in the sensory neurons; the impulses then travel along the cochlear nerve to the brain.

Different pitches stimulate different parts of the cochlea.

Normally, the human ear can detect sounds ranging from 16 to 20,000 cycles per second.

Repeated or sustained exposure to loud noise destroys the neurons of the Organ of Corti.

Once destroyed, the hair cells are not replaced, and the sound frequencies interpreted by them are no longer heard.

Hair cells that respond to high frequency sound are very vulnerable to destruction, and loss of these neurons typically produces difficulty understanding human voices.

Much of this type of permanent hearing loss is avoidable by reducing exposure to loud noises in the environment, such as industrial and machinery noise, gunfire, and loud music

ProcedureThe sine wave generator is set up and

switched on in a room that is as quiet as possible.

The generator is set to 20 kHz and a value of 20 kHz is set on the digital display by turning the frequency knob.

The amplitude knob is fully turned on.

The headphones are connected to the headphone output of the sine wave generator and are placed on the head so that the ears are well covered.

The leader of the experiment gradually reduces the frequency until the test subject just hears the sound.

The measurement is recorded.

The measurement should be repeated several times with the same test subject.

The generator is then set to 200 Hz and a value of 10 Hz is set on the digital display by turning the frequency knob.

The amplitude knob is turned up halfway.

The leader of the experiment gradually increases the frequency until, according to the test subject, the individual sounds merge into a continuous tone.

This merging frequency is recorded. The measurement is repeated several times

with the same test subject.

The upper acoustic threshold and merging frequency should, for comparative purposes, also be determined in younger and older test subjects according to the procedure.