Otitis Media, an ear infection, is the presence of fluid in the middle ear with or without accompanying symptoms such as pain, otorrhea (ear drainage), hearing loss, systemic signs of fever, irritability, headache, lethargy, anorexia, or vomiting (Klein, 1994). Otitis media is a result of congestion blocking the eustachian tube resulting in the accumulation of mucosa in the middle ear, if pathogenic bacteria are present in the middle ear before the obstruction, they can colonize the area and lead to infection. Children have shorter, wider, and more horizontal eustachian tubes; the tubes increase in length and angle with development. Otitis media mostly impacts children due to the large participation of Eustachian-tube dysfunction in the etiology of the disease. Children also have developing musculature that governs the opening and closing of the tube. These two characteristics lead to a higher predisposition of otitis media due to the restrictions of clearing drainage from the middle ear. Hearing impairment is a symptom of otitis media that can lead to learning or developmental restriction. Otitis media hearing impairment is due to the presence of fluid filling the middle ear preventing proper conduction of sound. Understanding how the ear conducts sound to activate the cochlear nerve can help us understand the negative effects of otitis media.
The external ear (pinna and ear canal) funnels sound waves toward the tympanic membrane, the ear drum. The sound waves then hit the tympanic membrane, or ear drum, in a way that causes it to vibrate. The tympanic membrane is the barrier between the external ear and the middle ear; it is connected to the middle ear bones (malleus, incus, and stapes). These bones amplify the sound waves into mechanical movements. The stapes bone is connected to the oval window. The oval window separates the fluid-filled inner ear from the air-filled middle ear. The pounding of the stapes on the oval window converts mechanical energy into fluid-filled waves in the cochlea. The cochlea is a shell-shaped structure containing three fluid-filled ducts (vestibular duct, cochlear duct, and tympanic duct). Within the cochlear duct, the organ of the Corti and tectorial membrane are located. The organ of Corti contains cells with hairlike projections, stereocilium, that detect the fluid-filled waves within the cochlea. Detection is caused by the movement of the stereocilium into the tectorial membrane, a membrane located on top of the organ of Corti where the stereocilium is embedded. The stereocilium has ion channels that open because of specific bending allowing cations to flow into the membrane and depolarize the cell. This depolarization causes the release of neurotransmitters from the hair cells that act on primary auditory neurons. The neurotransmitters cause an increase in the frequency of action potentials that are transmitted via the cochlear nerve. The cochlear nerve innervates on the cochlea nuclei in the medulla on its way to the auditory cortex. This conduction event allows the conversion of sound waves to action potentials. The basilar membrane, the membrane the organ of Corti rests upon, has variable sensitivity to sound wave frequency along its length. This variability in stiffness allows us to distinguish between varying frequencies.
The importance of treating otitis media is due to the restrictions placed on the middle ear bones from fluid filling the middle ear. The normal air-filled environment allows effective movement of the middle ear bones, a key amplifying step in the conduction process. Otitis media can result in a degree of hearing impairment. The median hearing loss is 25 dB, which is equivalent to putting ear plugs into the hearing canals (Klein, 1994). Besides the possible painful symptoms associated with an ear infection, hearing loss at a young age can be detrimental to reaching developmental milestones and effective learning for young children. Our society places a large amount of weight on hearing in traditional teaching settings. Without proper support for children identified with hearing loss, children’s learning capabilities are restricted. This is why antibiotic treatment and possible tympanostomy, surgery to place ear tubes in the ear drum, for recurrent ear infections are important mechanisms for treating otitis media and preventing lifelong ramifications.
References
Klein, J. O. (1994). Otitis Media. Clinical Infectious Diseases, 19(5), 823–832. http://www.jstor.org/stable/4458141
King Lab at Creighton University 