Allan is 48 years old and works as a business executive. One day after returning from a lunch meeting, Allan felt as though his office was spinning around him

Question

His left ear had a feeling of fullness, and he heard ringing in it. He was so dizzy that he reclined in his office chair and closed his eyes, not wanting to move his head for fear the spinning would start again. The following evening, a similar event happened at home. His wife was concerned about the vertigo he was experiencing and how irritated he was by the tinnitus. When the same event happened 1 month later, Allan said his hearing was affected when the attack was at its worst. His wife insisted it was time he took some time off work to see his family physician.

What inner ear disorder produces the triad of vertigo, tinnitus, and hearing loss? What is the pathophysiology of this condition?

What are the sensory functions of the semicircular canals and the utricle and saccule?

Allan's symptoms included a feeling of fullness in his ear accompanied by hearing loss. How does endolymph contribute to the function of hearing? What is the role of the endolymphatic potential?

Answer 1

Allan is experiencing the symptoms of Ménière disease. The disease is thought to result from the impaired filtration and excretion of the endolymphatic sac. The condition may be exacerbated by an abnormal increase in endolymph production. This excessive production may occur on its own, or as a compensatory mechanism for an abnormal decrease in perilymph.

The sensory cells of the utricle and saccule respond to static head position in relation to gravitational pull. They also provide sensory input for changes in linear motion and changes in head position.
The semicircular canals are positioned to detect rotational movements of the head. They sense head tilting with acceleration and detect turning movements in concert with locomotion.

Endolymph is a potassium-rich fluid contained in the scala media of the cochlea. It receives sound waves as they pass through the perilymph of the scala vestibuli and translate across the vestibular membrane. When the endolymph is set in motion, the basilar membrane vibrates and the receptor cells in spiral organ of Corti are stimulated so that the perception of sound occurs.
The endolymphatic potential exists because of an electrolyte gradient in the cochlear apparatus, maintained by Na+/K+ active transport pumps. The resting membrane potential between endolymph and perilymph acts to sensitize the hair cells of the spiral organ of Corti, allowing them to perceive the quietest of sounds.