Question

Case Study:

(Modified from “A ‘Deafinite’ Cause for Alarm” Garlinger, Mitrano-Towers, Innella, & Stephens)

Edith, a 67 year old woman was admitted to the hospital for a severe bacterial infection. To treat the infection she was given an IV drip of the antibiotic, gentamicin. Aiming to be released from the hospital earlier, Edith waited for her nurse to leave and pushed down the plunger on the syringe attached to her IV so that she could get the medicine faster, and be released sooner. When the nurse returned to Edith’s hospital room, she discovered what Edith had done and was displeased at Edith’s actions to increase her dose of antibiotic. Edith was released to the care of her husband, John, a few days later, and given instructions for an oral antibiotic to continue treatment.

“OK, Edith, it’s been a long day, let’s get to bed” suggested her husband John.

Edith didn’t respond to John, until John was able to visually get her attention and ask her again. Edith explained that she hadn’t heard him and was experiencing a ringing in her ears.

The next morning, when Edith awoke, she immediately noticed that her hearing was muffled and she was having difficulty hearing in general. Both of them worried, John quickly took Edith to the Emergency Room.

Questions:

1- Based on your knowledge of the auditory system, list the possible structures that could be responsible for Edith’s hearing loss?

2- what types of tests could be conducted to diagnose Edith’s hearing loss. For each test you identify, indicate the predicted results for Edith’s case. (Don’t go crazy- just find 1-3 tests).

3- Briefly summarize how sound waves enter the outer ear and cause mechanical movements of the middle ear, specifying each affected structure.

4- How are the mechanical movements of the middle ear transferred to the cochlear of the inner ear?

5- The basilar membrane runs down the middle of the cochlea. What does it mean that the basilar membrane is ‘displaced’ by the vibrations of the stapes footplate at the oval window?

6- Based off Edith’s test results, what main structure within the inner ear is likely at the cause of Edith’s symptoms? Why?

Answer 1

1. Gentamycin belongs to the aminoglycoside group of antibiotics that causes ototoxicity and in this ototoxicity, hair cells in cochlea and vestibule are the affected structures.

2. rinne test and weber test

finding in rinne test will be that sound next to ear will be heard longer than sound behind the ear but not double the time of sound behind the ear wheras the weber test finding will be that sound will be heard best in normal ear.

3. The outer ear collects sound waves from the environment and funnels them down the ear canal to the eardrum. Vibrations are made when sound hits the eardrum. Vibrations are passed along tiny bones (ossicles) in the middle ear. The ossicles consist of the malleus, incus, and stapes. The stapes delivers vibrations to the cochlea in the inner ear. The cochlea is a spiral tube filled with liquid and lined with hair cells that are microscopic in size. When the vibration hits the cochlea, it causes the liquid, and subsequently the hair cells, to move. The movement of hair cells generates nerve signals that our brain then understands as sound. But here hair cells not working so nerve impulse is not generated and hearing loss occurs.

4. The mechanical vibrations of the stapes footplate at the oval window creates pressure waves in the perilymph of the scala vestibuli of the cochlea. These waves move around the tip of the cochlea through the helicotrema into the scala tympani and dissipate as they hit the round window. The wave motion is transmitted to the endolymph inside the cochlear duct. As a result the basilar membrane vibrates, which causes the organ of Corti to move against the tectoral membrane, stimulating generation of nerve impulses to the brain.

5. no it is not displaced rather it is the normal location of basilar membrane.

6. Cochlea is the structure which is affected as it is responsible for hearing in a person