Here we provide an overview of important structures of the ear, including some of our images taken using scanning electron microscopy. In our Auditory Science Laboratory we investigate different types of hearing loss, particularly those resulting from damage to the cochlea. In the following sections we show some microscope images of different types of cochlear damage.
When someone has a hearing problem there can be many causes, many types of anatomical change and a range of functional deficits. We investigate some of these in our laboratory and our web pages will outline some of the research that we have been carrying out to further understand the mechanisms of hearing and hearing loss.
Let’s start with a few basics. When we hear sounds we are detecting acoustic signals which are essentially vibrations in the air (unless you happen to live underwater). These signals are usually very complex and made up of many different frequency components which vary over time. Important signals for humans are speech signals because we use these to communicate with each other.
The eardrum and the ossicular chain convert the sound signals transmitted in air into a vibration of fluids within the cochlea. Some of our microscope images here show parts of this middle ear system.
The cochlea is a snail shaped, bony shell with three fluid filled chambers winding around from base to apex. As the middle ear ossicles vibrate they cause the fluid within the cochlea to move. This movement causes sensory haircells, located along the length of the cochlea, to produce a small electrical signals which are eventually relayed through the auditory nerve to several areas of the brain. This results in us “hearing” the sound.
Thus the function of the cochlea is to detect the vibrations caused by sound and to analyze their patterns of frequency components and rhythms and to represent this information in a form that can be processed by the auditory areas brain.
1. External ear (pinna)2.Temporal bone3. Eardrum
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7. External ear canal8. Malleus (hammer)9. Incus (anvil)10. Stapes (stirrup)11. Eustachian tube |
Anatomically the ear is divided into three parts; the outer or external ear, the middle ear and the inner ear. The main parts of the ear are shown in the diagram above.
When sound waves reach the pinna of the external ear ear they directed down the ear canal at the end of which is the eardrum (tympanic membrane). The acoustic signal causes vibrations of the eardrum. Attached to the inside of the eardrum, in the middle ear, are three tiny bones (the ossicles) forming a chain that transmit the vibrations from the eardrum to the cochlea of inner ear. These ossicles are called the hammer (malleus) the anvil (incus) and the stirrup (stapes). The last of these bones, the stapes, fills a window in the base of the cochlea.
The important cells in the cochlea that convert sound vibrations into electrical signals are called haircells. These cells have tiny hairs (strereocilla) that are deflected by sound vibrations and cause the generation of a small voltage signals. Some microscope images of haircells are shown here in our web pages.
There are many types of hearing loss that result from damage to the haircells. Some examples are illustrated in following web pages. Haircells can be directly damaged by very loud sounds, or by high concentrations of certain drugs. As we get older, there is a steady degeneration of haircells that causes age related hearing loss. There are many types of deafness from birth caused because the haircells do not develop properly.