The Inner Ear and Ménière’s Disease
by Robert Tallitsch, PhD | December 1, 2022
Video over the anatomy of the inner ear and explanation of Ménière’s disease with a patient case example!
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Written by: Robert Tallitsch, PhD
An individual experiencing severe and incapacitating symptoms of vertigo, often accompanied by hearing loss and/or tinnitus, may be experiencing Ménière’s Disease (also termed idiopathic endolymphatic hydrops). Ménière’s Disease is a rare disease of the inner ear. In this Brain Builder we will discuss the anatomy of the ear and the symptoms, causes, and treatments of Ménière’s Disease.
Anatomy of the Ear
The ear is a complex organ that provides sensory input for hearing and balance. It is divided into three segments: external ear, middle ear, and inner ear.
The external ear, which is a pathway for sound waves, consists of the auricle (pinna) and the external auditory meatus (external auditory canal). The auricle “collects” sound waves, and the external auditory meatus conducts those vibrations to the tympanic membrane, which sits at the medial extremity of the external auditory meatus. The tympanic membrane separates the external ear from the middle ear.
The middle ear is a space within the petrous portion of the temporal bone. This space is termed the tympanum (tympanic cavity). It functions to transmit sound waves from the tympanic membrane of the external ear to the cochlea of the inner ear.
Three bony ossicles extend the width of the tympanum. These ossicles are (lateral to medial) the malleus, incus, and stapes (commonly termed the hammer, anvil, and stirrup). The ossicles are joined by synovial joints, thereby forming a “bony chain” that transmits sound vibrations to the inner ear at the oval window of the vestibule.
The auditory tube (Eustachian tube) connects the middle ear to the nasopharynx. It allows the equalization of pressure between the nasopharynx and the middle ear.
The inner ear, which contains sensory receptors for hearing and equilibrium, consists of a series of interconnected, fluid filled sacs and ducts. These sacs and ducts are suspended within a bony (osseous) labyrinth within the petrous portion of the temporal bone. This bony labyrinth is composed of the cochlea, vestibule, and three semi-circular canals. The bony labyrinth is lined by a serous membrane that secretes a fluid termed perilymph.
The Bony (Osseous) Labyrinth
The central part of the bony labyrinth is the vestibule. The vestibule communicates with the semi-circular canals posteriorly and the cochlea anteriorly.
There are three semi-circular canals: anterior, posterior, and lateral. They are aligned in the three planes of dissection (see the Brain Builder on the Planes of the Body and Anatomical Directions). Each semi-circular canal is connected at both ends to the vestibule.
The cochlea is a snail-shaped structure connected to the vestibule. The interior of the cochlea is divided into thirds. Between the scala tympani and the scala vestibuli is the cochlear duct. The scala tympani is connected to the middle ear by the round window, and the scala vestibuli is continuous the vestibule at the oval window.
Suspended within the perilymph of the bony labyrinth is the fluid-filled membranous labyrinth. The fluid contained within the membranous labyrinth is termed endolymph.
Sensory Organs of Balance
Utricle and saccule: Within the vestibule are two interconnected membranous sacs termed the utricle and saccule. The utricle and saccule contain sensory hair cells possessing long, hair-like processes. The tips of these hair-like processes are embedded within a gelatinous mass. The surface of this gelatinous mass contains densely packed calcium carbonate crystals termed statoconia. Exiting the basal portion of these sensory hair cells are nerve fibers that will ultimately unite with nerve fibers from the semi-circular ducts to form the vestibular portion of cranial nerve VIII (Vestibulocochlear nerve).
Semi-circular ducts: Within each semi-circular canal is a semi-circular duct. Each semi-circular duct is continuous with the utricle and saccule. The semi-circular duct has an expanded end termed the ampulla, which contains sensory receptors. Extending from the basal portion of these sensory receptors are nerve fibers that will also ultimately unite with nerve fibers from the utricle and saccule to form the vestibular portion of cranial nerve VIII (Vestibulocochlear nerve).
Organ of Hearing
Cochlear duct: The cochlear duct is located between the scala tympani and the scala vestibuli within the snail-shaped cochlea. The roof of the cochlear duct is formed by the vestibular membrane (vestibular surface membrane). This structure separates the endolymph of the cochlear duct from the perilymph of the scala vestibuli.
The floor of the cochlear duct is formed by the stiff basilar membrane, which separates the endolymph of the cochlear duct from the perilymph of the scala tympani.
The sensory organ of hearing is termed the Spiral Organ (organ of Corti), which sits on the basilar membrane inside of the cochlear duct. Cilia-like structures extend from the sensory hair cells sitting on the basilar membrane below to the vestibular membrane above. Extending from the basal portions of these sensory cells are nerve fibers that will ultimately unite to form the auditory (cochlear) portion of cranial nerve VIII (Vestibulocochlear nerve).
How do the vestibular and auditory structures of the ear work?
Organs of balance:
Utricle and saccule: When the head changes position vertically (sensed by the utricle) or linearly (sensed by the saccule) gravity causes the statoconia within the utricle or saccule to move as well. This movement of the statoconia bends the hair-like processes of the sensory cells, initiating the transmission of an action potential over the vestibular portion of cranial nerve VIII to the brain. This results in the sensation of either vertical or linear acceleration or deceleration of the head and body.
Semi-circular ducts: When the body changes position in a rotational manner endolymph within the semi-circular ducts begins to rotate. As the endolymph moves it causes bending of the hair-like processes of the sensory cells located within the ampulla of the semi-circular duct. This initiates the transmission of an action potential over the vestibular portion of cranial nerve VIII to the brain, resulting in the sensation of rotational movement of the head and body.
Organ of hearing:
The sensation of sound is started by the movement of a sound wave through the external ear until it encounters the tympanic membrane.
- The sound wave vibrates the tympanic membrane, which causes movement of the malleus, incus, and stapes.
- Movement of the stapes causes movement of the oval window
- Movement of the oval window causes perilymph movement within the fluid-filled scala vestibuli of the cochlea.
- Movement of the perilymph within the scala vestibuli causes vibration of the basilar membrane within the Spiral Organ.
- Vibration of the basilar membrane causes bending of the cilia-like structures of the hair cells. This initiates the transmission of an action potential over the cochlear portion of cranial nerve VIII to the brain, resulting in the sensation of sound.
Ménière’s Disease typically affects individuals between the ages of 40- and 60-years. Symptoms of Ménière’s Disease typically includes dizziness or vertigo and any of the symptoms listed below. All symptoms tend to start and end together.
- Hearing loss
- Sensation of “fullness” within the affected ear
- Tinnitus, which is a ringing, buzzing, or “roaring” sound within the ear
Although rare, it is possible for the symptoms of Ménière’s Disease to become permanent.
Although a definitive cause for Ménière’s Disease is unknown, an increase in endolymph and/or perilymph volume within the inner ear may be the cause. The increased fluid levels may be due to high blood pressure, allergies, autoimmune disorders, or reduced fluid reabsorption. Symptoms of Ménière’s Disease may also be brought on by increased fatigue or stress.
Confirmation of Ménière’s Disease is determined by a detailed patient history accompanied by hearing, balance, and electrocochleography (ECoG) tests. (ECoG tests determined the fluid pressure within the inner ear.)
There is no cure for Ménière’s Disease. However, symptoms may be reduced in severity and frequency through:
- Intratympanic injection of medications intended to reduce dizziness
- Anti-vertigo medications to reduce or stop acute episodes of Ménière’s Disease
- Low-salt diet
- Prescription of diuretics to reduce blood pressure and, hopefully, decrease the secretion of endolymph and perilymph within the ear
Acute or chronic episodes of vertigo and/or hearing loss can be debilitating, and may be indicative of Ménière’s Disease. One should contact their physician as soon as possible following such an episode in order to determine whether or not such episodes are indicative of Ménière’s Disease and to seek treatment.
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