How Do We Hear?
The anatomy of the hearing system can be divided into three components:
- Outer ear
- Middle ear
- Inner ear
The balance mechanism is also called the vestibular system. It is made up of three semi-circular canals and two otolithic organs. The vestibular sensors detect angular movements, direction and velocity of the head. This information about equilibrium is sent to the brain by the vestibular nerves, a functionally separate division of the auditory vestibular nerve, the VIIIth cranial nerve.
How Hearing Works
Hearing begins when the outer ear, the visible portion of the ear that is on the outside of the head, channels sound waves down the auditory canal. This tube-like passageway is lined with tiny hairs and small glands that produce earwax.
The middle ear lies at the end of the auditory canal. It is composed of the eardrum and three small bones, known by the layman as the hammer, the anvil and the stirrup. When sound waves hit the eardrum, it vibrates and, in turn, moves the hammer. The hammer moves the anvil, which moves the stirrup, transmitting the vibrations into the inner ear. The middle ear functions to amplify sound, which is why significant hearing loss can result from any disruption in any of the parts.
The inner ear has two divisions: one for Hearing, the other for Balance. The division for hearing consists of the cochlea and the nerve of hearing. It converts sound waves into nerve impulses that travel to the brain via the movement of tiny hair cells. The brain, in turn, allows us to hear…as long as the message it is receiving is not distorted due to problems in the process just described.
How Balance Works
The balance mechanism is also called the vestibular system. It is made up of three semi-circular canals and two otolithic organs. Movement of fluid in the semicircular canals signals the brain about the direction and speed of rotation of the head–for example, whether we are nodding our head up and down or looking from right to left. Each semicircular canal has an enlarged end portion, which contains hair cells. Rotation of the head causes a flow of fluid, which in turn causes displacement of the top portion of the hair cells that are embedded in the jelly-like structure known as “Cupula”. Two other organs that are part of the vestibular system are utricle and saccule. These are called the otolithic organs and are responsible for detecting linear acceleration, or movement in a straight line. The hair cells of the otolithic organs are blanketed with a jelly-like layer studded with tiny calcium stones called “Otoconia”. When the head is tilted or the body position is changed with respect to gravity, the displacement of the stones causes the hair cells to bend.
The balance system is more complex than the auditory system.
It requires an accurate integration of multiple sensory inputs and a rapid and appropriate motor response:
Internal reference – Vestibular system provides brain with 2/3 of information it receives about where the head is in space.
External reference – Visual & Somatosensory systems provides brain with 1/3 of information it receives about where the head is in space.
Central Nervous System compares inputs and produces appropriate muscle responses to maintain control of the head & body in space.
Hearing and Balance Coordination
The hearing and balance organs are connected to each other within the inner ear. This same inner ear fluid also fills the balance canals. Because these organs are connected, about 30% of profoundly deaf people are estimated to have vestibular (inner ear balance) problems. Hard of hearing people may also have vestibular problems. Some of the signs of impaired vestibular function can include:
- Infants who cannot sit unsupported by 6-7 months
- Infants who are not walking by 15 months
- Clumsiness, difficulty walking on uneven surfaces
- Poor balance in darkness, difficulty riding a bicycle, disorientation when swimming with eyes closed
- Difficulty keeping a stable view of the world when you are jogging or riding in a car over a bumpy road.
Maintaining your balance is a complex process that relies on information from your senses and coordinated movements from different parts of your body.
Link of the page “Hearing Information and section How balance works” On the side.
Tinnitus (Ringing in ears)
While tinnitus typically begins with a hearing loss, it is not exclusively an auditory problem. It is a result of neurological changes within the auditory system and within the parts of the brain that influence conscious attention and emotional state.
No single explanation applies to all cases, but the process outlined below describes one of the more commonly accepted theories about what causes tinnitus.
When the natural balance is upset by a hearing loss, the neurological activity is altered, and this altered activity is then interpreted by the brain as sound. This results in whistling or ringing sounds commonly known as tinnitus.
Tinnitus most commonly results from hearing loss caused by exposure to excessive or loud noises, however it can also be caused by aging, ototoxic drugs, Temporo-mandibular joint disorder (TMJ), depression, anxiety, Lyme disease or thyroid disorders, as well as ear infections or wax in the ear.
The good news is that in today’s technology there are management options and devices available that can significantly reduce tinnitus awareness and disturbance for over 90% of suitable patients affected by tinnitus.
Our Audiologist at Ear & Hear clinic has received training in tinnitus assessment and management by USA’s leading tinnitus management group “Sound Cure”.
Vestibular Evoked Myogenic Potential (VEMP) Testing
The purpose of the VEMP test is to determine if the saccule, one portion of the otoliths, as well the inferior vestibular nerve and central connections, are intact and working normally. The saccule, which is the lower of the two otolithic organs, has a slight sound sensitivity and this can be measured. VEMPs are recorded using an evoked response computer, a sound generator, and surface electrodes to pick up neck muscle activation or other muscles.
Nystagmography Tests (Coming Soon): This is a series of tests designed to document your ability to follow visual objects with your eyes and how your eyes respond to some types of information from your vestibular system. To monitor the movements of your eyes, your Audiologist may place electrodes around your eyes (electronystagmography–ENG) or may use an infrared video camera (IR video nystagmography). Eye movement tests are useful, because some patients with balance system problems have problems seeing clearly when moving, or they get the erroneous sense that objects are moving.
Occupational hearing loss is one of the most common work-related illnesses. Approximately 22 million U.S. workers exposed to hazardous noise levels at work, and an additional 9 million exposed to ototoxic chemicals. An estimated $242 million is spent annually on worker’s compensation for hearing loss disability.
Ear & Hear clinic conduct hearing monitoring in the companies and helps in implementing a successful hearing loss prevention program.