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All About Ear Anatomy

Anatomy and Physiology of the Auditory System

The auditory system consists of several main parts that help carry sounds/signals to the brain. Although hearing seems like a simple feat, the transduction of a signal through the auditory system up to the brain is quite complex.

The Outer Ear

Beginning with the outer portion of the ear, the pinna helps pick up sounds and funnel them into the ear canal, anatomically known as the external auditory canal. The pinna helps individuals localize where sounds are coming from. Sound then travels down the ear canal where it eventually reaches the eardrum, or the tympanic membrane. The tympanic membrane is a thin membrane of skin that vibrates with sound stimulation.

The Middle Ear

Once sound vibrates the tympanic membrane, sound is transferred across three bones (ossicles) in the air filled middle ear space. These ossicles are the tiniest bones in the body known as the malleus, the incus, and the stapes. The stapes bone is shaped like a stirrup and has a round footplate. These three bones work together as a lever system to mechanically transduce sound through the middle ear to the inner ear. As sound reaches the stapes, the footplate pushes on what is referred to as the oval window. This window is the beginning of the inner ear system.

The Inner Ear

After sound reaches the oval window, the stimulation causes fluid in the inner ear system to move. The inner ear is a fluid filled space and therefore sound is hydromechanically transduced. Within the inner ear is an important hearing organ called the cochlea. The cochlea is a snail-shaped organ which has many tiny receptor hair cells embedded in a basilar membrane which respond to certain frequencies of sound. This is known as tonotopic organization in which the base of the membrane in the cochlea responds to higher pitches and the apex responds to lower pitches. As the hair cells are stimulated by the fluid moving in the cochlea, neurons attached to the hair cells receive the signal then send the auditory signal along the auditory nerve and up to the auditory cortex in the temporal lobe of the brain. Although we perceive and interpret sound within milliseconds, the pathway that sound travels to get to the brain is very complex, as detailed above.

There is much more detail related to the process of hearing and understanding, but the above is a basic overview of how individuals hear and interpret a signal. For a more in depth explanation, watch the links below.

The Connection between Hearing and Balance

Why Test My Hearing If I Have Vertigo?

As our name suggests, Jacksonville Hearing and Balance Institute helps patients with hearing and balance/dizziness issues. But how are hearing loss and dizziness related? If you have scheduled an appointment because of your dizziness, why would you need to have your hearing evaluated?

The answer to the above questions lies within the anatomy of our inner ear. The hearing and balance organs are both housed in the inner ear. The cochlea is necessary for hearing and the semicircular canals are part of our balance system.

There are multiple disorders that can cause disruptions in our hearing and balance. The type and configuration of hearing loss can help our providers better diagnose your dizziness. Meniere’s disease is one example of a disorder that is defined by the dizziness you are experiencing and the type of hearing loss that you may have. A patient with Meniere’s disease can experience dizziness for 30 minutes to multiple hours and have fluctuations in their hearing accompanied by a roaring tinnitus. Semi-circular Canal Dehiscence is another disorder that can be accompanied with hearing loss. A patient with SCCD may have a slight conductive component present on the audiogram even though they may not perceive a hearing deficit.

Jacksonville Hearing and Balance provides a comprehensive evaluation to help diagnose and treat your hearing loss and/or dizziness. For questions or to schedule an evaluation, you can reach us at (904)351-1904.

Noise-Induced Hearing Loss in the Military: A History

A Brief History

The introduction of the jet engine aircraft in the late 1940s and early 1950s raised concerns about hazardous noise and was one of the most important occurrences to the subsequent development of hearing conservation programs (Nixon, 1998). No sound of the jet engine’s magnitude had ever been routinely experienced in the military or by civilians. In 1952, the Navy conducted a study to evaluate the effects of the jet engine noise on personnel aboard the aircraft carrier USS Coral Sea. The study verified the seriousness of the high-intensity noise problem. In response to the problem, the NAS-NRC Armed Services Committee on Hearing and Bioacoustics (CHABA) was established in 1952 (Nixon, 1998). It was their job to examine the areas of (a) effects and control of noise, (b) auditory discrimination, (c) speech communications, (d) fundamental mechanisms of hearing, and (e) auditory standards. CHABA members were at the forefront of hearing conservation program (HCP) development. They began sponsoring and publishing reports related to noise in the military. They went on to publish a Memorandum No. 2 on “Hearing Conservation Data and Procedures” in 1956. The Memorandum described components of a hearing conservation program and provided recommendations for their implementation.

In 1956, the Air Force was the first to establish a comprehensive hearing conservation program. The Regulation was revised in 1973. Both were model programs after which many organizations within and outside the government were created (Nixon, 1998). In 1978, the Department of Defense Instruction (DODI) 6055.3 was published and contained requirements that attempted to make all hearing conservation programs uniform across services. By 1980, the three branches (Air Force, Army, and Navy) had established hearing conservation programs in compliance with DODI (Nixon, 1998). In 1987, the DODI was revised. The most current DODI is 6055.12, and ensures that all services have a hearing conservation program implemented and these programs should include: a) sound measurements, b) engineering control measures, 3) noise labels in hazardous areas/on equipment, d) issuance of hearing protective devices, e) appropriate education to all personnel working around hazardous noises, f) routine audiometric testing which is to be stored in the Defense Occupational and Environmental Health Readiness System (DOEHRS), g) access to materials, h) record keeping through DOEHRS, and i) program performance evaluations (DOD, 2010).

NIHL in the Military

Northeast Florida is home to many military installations, including Naval Air Station Jacksonville, Naval Station Mayport, Kings Bay Naval Base, Camp Blanding Joint Training Center, Naval Aviation Depot Jacksonville, and Marine Corps Blount Island Command, which together provide employment to more than 50,000 active duty, reserve, and civilian men and women. As of 2011, there were 2,226,883 military members in the United States serving (including active duty, National Guard, Air National Guard, and reserves). Within the military population, an estimated 60% of veterans returning home from war have a hearing loss (CDC, 2013). Disabilities of the auditory system, including hearing loss and tinnitus, are the third most common injury experienced by veterans (Helfer, Canham-Chervak, Canada, & Mitchener, 2010). As far back as World War II, handguns, rifles, artillery rockets, ships, aircraft carriers, vehicles, communications devices, and many more, have been sources of potentially damaging noise levels (Humes et al., 2006, p. 201). Hearing is critical to the performance of military personnel, and noise-induced hearing loss (NIHL) is a severe impairment that can potentially reduce military effectiveness.

Several studies have been conducted to document reports of military hearing loss and tinnitus and effects due to noise. Results from a study conducted in 2010 using data between 2003-2005, found that a total number of 88,285 hearing impairment and noise-induced hearing related injuries (NIHI) were documented—unspecified hearing loss, tinnitus, perforations of tympanic membrane, acoustic trauma, impairment of auditory discrimination, etc. (Helfer et al., 2010). Overall, NIHI visits were reported for 9.6 per 1000 personnel.

How Does NIHL Occur? How Can It Be Prevented?

            The How

Loud noises destroy the ear’s special cells, called “hair cells.” They lie within the sensory organ of the ear, called “the cochlea”. The cochlea cannot regrow new hair cells. Once they have become permanently damaged, they are no longer a useful part of the cochlea. Hair cells are important because they help translate sound into a signal the brain interprets, or “hears.” The hair cells can be damaged significantly by a single impulse sound — gunfire, for example, or by prolonged noise exposure at levels that are harmful to healthy hair cells (greater than 85 dB).

            Prevention

Prevention is key in helping to reduce the number of military members and veterans with NIHL. Hearing conservation programs are a step in the right direction. Hearing protection devices, such as passive and active earplugs and earmuffs will also aid in prevention when used properly. Engineering controls to help reduce excessive noise levels should also be implemented. Most importantly, education about the dangers of hazardous noise levels is paramount to further reducing the incidence of NIHL in military members and veterans. Over the past several years, all branches of the military have been making strides towards better education about hearing loss and taking steps towards providing the best hearing protection for soldiers.

For the general population, three strategies you can use for prevention are: 1) walk away- at further distances, dangerous noise levels are not as harmful to your ears, 2) turn it down- if you have the ability, make sure you are listening to things at safe levels, reference the dB level above, and 3) protect your ears- always have a pair of earplugs or muffs on hand when you go to concerts, loud sporting events, hit the shooting range, etc. And just remember, currently, there is no cure for hearing loss, so try to protect the healthy hair cells you have!

References:

DoD. 2010. Department of Defense Instruction 6055.12: DoD Hearing Conservation Program. Washington, DC: Department of Defense

Helfer, T. M., Canham-Chervak, M., Canada, S., & Mitchener, T. A. (2010). Epidemiology of hearing impairment and noise-induced hearing injury among U.S. military personnel, 2003-2005. American Journal of Preventative Medicines, 38(1S), S71-S77. doi: 10.1016/j.amepre.2009.10.025

Humes, L. E., Joellenbeck, L. M., & Durch, J. S. (2006) Noise and military service: Implications for hearing loss and tinnitus. Washington, DC: National Academies Press

Nixon, C.W. (1998). A glimpse of history: The origin of hearing conservation was in the military? Wright-Patterson Air Force Base, OH: U.S. Air Force Research Laboratory