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Types of Hearing Loss

Close your eyes and concentrate. As you listen, you may notice a wide variety of activities around you. The sound of a lawnmower. A car passing by on the street. Or the rhythmic sound of your own breathing. What you are experiencing are the vibrations of sound that surround us.

Normally, the human ear is remarkably sensitive to a wide range   of acoustical activity, which is processed by the ear, our nervous system and brain into what we perceive as sound.

There can be many reasons why our ability to hear sounds diminishes. The ear is a delicate instrument. It may break down, or simply wear out.   The ear is composed of 3 parts: the outer, the middle, and inner ear. The outer ear consists of the pinna and the ear canal. From the pinna, sound enters the ear canal, which helps protect the ear drum and increases the loudness of certain pitches that are important for understanding speech.

Separating the outer ear from the middle ear is the eardrum, and connecting the eardrum to the inner ear are the ossicles: 3 tiny bones best known as the hammer, the anvil and the stirrup. The ossicles serve to pass the vibrations from the eardrum to the footplate of the stirrup at the cochlea, or snail, and at the same time amplifying and intensifying the movement. The middle ear also has a connection to the nose and throat via the Eustachian tube.

When sound cannot be transmitted normally through the ear canal and/or middle ear to the cochlea, it is referred to as a conductive hearing loss. Wax build-up and perforated eardrums are 2 typical causes of conductive hearing losses. Another may be damaged or defective oscicles.

As sound vibrations are transmitted to the cochlea in the inner ear, they set tiny hair cells in motion. These hair cells transform the vibrations into nerve impulses, which are picked up by the acoustic nerve and sent to the brain.

The inner ear is very fragile, so many things can go wrong. Exposure to loud sounds can damage the hair cells, so sound can't be converted into nerve impulses and transmitted to the brain. Disease, viruses, and infections can also injure the inner ear. So can aging. Hair cells may deteriorate as may nerve pathways, preventing the signal from the ear from reaching the brain. These types of problems are referred to as sensorineural hearing losses.

Sensorineural hearing losses affect our sensitivity to sounds, as well as our ability to discriminate between sounds. For example, individual words may seem unintelligible during conversation.

Hearing losses that are caused by both conductive and senso-rineural impairments are termed mixed or combined losses.

No matter what the nature of your hearing loss, a hearing care professional can conduct a painless investigation which takes less than an hour to perform, to evaluate your hearing loss and recommend the best treatment.

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How the Ear Works

Sound waves travel through the auditory canal and strike the eardrum, causing it to vibrate. The vibrations flow across the three small bones of the middle ear: hammer, anvil, stirrup or stapes. The Stirrup or Stapes passes the vibrations to an area called the "oval window", locked between the middle & inner ear. When the stapes vibrates with the sound waves passing through, fluid in the inner ear carries the vibrations into the canal of a delicate spiral structure called the cochlea. One part of the cochlea has thousands of hair cells which are connected to fibers that make up the auditory nerve. Each hair cell has many microscopic hairs at one end. Movements of the fluid with the aid of an overlaying membrane, bend the tiny hairs. Movement of the hair stimulate the hair cells to generate electrical impulses which are carried up the auditory nerve to the brain.

                

The pinna collects sound and provides natural loudness enhancement of sounds occurring in front of you. Using both ears produces a "stereo" effect and helps you to localize sound (to detect which direction a sound is coming from) and to "focus" on conversations when there is background noise.

                

The middle ear is an air-filled space behind the eardrum. The eustachian tube leads from the middle ear to the back of the throat and serves to equalize the air pressure on both sides of the eardrum, allowing for more efficient sound transmission. When you experience a rapid increase or decrease in air pressure, such as in an airplane, your ear feels plugged because the pressure on each side of the eardrum is unequal. When the eustachian tube opens to equalize the pressure you feel a “pop” and your ear feels normal again.

                

Did you know that your ear is also part of your balance system? The semicircular canals contain special cells that sense the motion and position of your head.

                

The hair cells located at the base of the cochlea respond best to high frequency sound and as you travel further and further along the length of the cochlea, the hair cells are tuned to progressively lower frequency sounds.

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Sound

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 see how this works, let's look at a simple vibrating object: a bell. When you hit a bell, the metal vibrates flexes in and out. When it flexes out on one side, it pushes on the surrounding air particles on that side. These air particles then collide with the particles in front of them, which collide with the particles in front of them, and so on. This is called compression.


  When the bell flexes away, it pulls in on the surrounding air particles. This creates a drop in pressure, which pulls in more surrounding air particles, creating another drop in pressure, which pulls in particles even farther out. This pressure decrease is called rarefaction.

 

In this way, a vibrating object sends a wave of pressure fluctuation through the atmosphere. We hear different sounds from different vibrating objects because of variations in the sound wave frequency. A higher wave frequency simply means that the air pressure fluctuation switches back and forth more quickly. We hear this as a higher pitch. When there are fewer fluctuations in a period of time, the pitch is lower. The level of air pressure in each fluctuation is the wave's amplitude, which determines how loud the sound is.

 

Of the five senses, hearing is probably the most important for our feeling of connection to the world around us. The sounds of our environment and the sounds of communication serve to link us to others in a way that vision alone cannot. We are submersed in our auditory world but we are only observers of our visual world. Sound provides the richness in our lives. Imagine a walk in the woods on a crisp autumn day. Hear the leaves crunching underfoot, the whisper of the wind in the trees, the honking of geese flying overhead, the laughter of children playing. We can close our eyes but our ears are always working. If the sounds around us begin to fade, we feel less a part of our world. Although people are quick to seek help for visual problems, hearing instrument use remains low despite great technological advances in the hearing healthcare field. Approximately 500 million people worldwide suffer from hearing loss.