Below are descriptions of many different disorders which could affect hearing, which focus on the physiological effects of each. With your group, read through each of the below physiological descriptions of the mode of action of a disorder, and then discuss:
What tests might diagnose (or reveal) this issue?
Would we expect this to cause hearing loss? If so, how and why?
Would we expect this to cause balance issues, dizziness, or vertigo? If so, how and why?
Would any hearing loss be conductive or sensorineural?
Would the person still have OAEs? ABRs?
Would amplification (e.g. hearing aids, making the incoming signal louder as it enters the ear canal) help?
Would the person still hear sounds presented by bone conduction (e.g. with some middle ear implants, or with a bone-conduction speaker)?
Can you think of a way that this could be surgically addressed?
Take turns solving each question, and don’t worry if you don’t have a perfect answer. The goal here is to think aloud as a group, and if you get stuck, ask for help!
Quinine drugs like Hydroxyquinolone accumulate in the stria vascularis and disrupt the flow of K+ ions into the endolymph. These effects often reverse when the medication is discontinued.
There is too much endolymph (e.g. a serious over-pressure of endolymph) within the cochlea, utricle, saccule, and semicircular canals.
A tumor develops in the lining of the cochlear or vestibulocochlear nerve, compressing the neurons, suppressing their ability to fire, and damaging them.
For some genetically predisposed individuals, the aminoglycoside subfamily of antibiotics can trigger a chemical chain reaction leading to the rapid and permanent death of the hair cells in the cochlea and/or vestibular system.
For people with specific mutations of the GJB2 gene, the Connexin 26 (CX26) protein is rendered non-functional. The CX26 protein is understood to be essential for the movement of K+ ions both into the endolymph and out of the hair cells within the cochlea (but, interestingly, not within the vestibular system).
Mutations to GJB2 affecting CX26 are the most common cause of genetically caused deafness, and accounts for the hearing loss of many children who are Deaf.
Alcohol seeps into the endolymph of the vestibular ampullae, causing the endolymph’s density to change relative to normal, and making the cupula no longer neutrally buoyant, such that gravity now acts on the cristae.
Although many forms can cause similar troubles, imagine that the incus has broken away from the stapes and there is no physical coupling between the two.
The bone and tissue surrounding the stapes in the oval window grow and stiffen, freezing it in place
I hate even typing those two words together, but luckily it’s very rare, and often heals. Cochlear rupture is when one of the membranes within the cochlea (often Reissner’s) bursts or breaks, often at a junction and usually due to some variety of physical trauma, such that there is now a hole or tear connecting the scala media and scala tympani/vestibuli.
Imagine that, after a long, leisurely meal of 110dB tacos, you, alone in the elevator of Javier’s Cantina at UTC Mall, fire a large caliber (read: big boom) hunting rifle into a barrel of sand. Even assuming no ricochets or other bodily harm, this is wildly dumb. What might happen to your hearing anatomy?
A relatively uncommon congenital disorder where a baby is born with a abnormally small outer ear. It’s generally discussed in ‘grades’, so let’s separate this into two questions:
Grade 2: The pinna is improperly formed, and the ear canal is abnormally narrow or closed off
Grade 4 (also known as ‘anotia’): There is no outer ear, no ear canal, and no tympanic membrane
Usually caused by barotrauma or physical head trauma, in these situations, the round window bursts or balloons out (becomes a ‘fistula’), allowing perilymph to leak out. The degree of leakage and fistula can vary substantially from case to case.
A small, non-cancerous growth in the ear canal, often occurring at the edge of the tympanic membrane, often in response to past trauma or surgery. In problematic cases, it is resting ‘in the corner’, effectively attaching the wall of the ear canal to the tympanic membrane, and with some of its bulk/mass attached to the TM.
The Eustachian Tube is not working, and, for the purposes of this question, the person has a vacuum in the middle ear relative to the atmospheric pressure (e.g. they last equalized at altitude, and have moved to lower ground). Would it be meaningfully different if they had an overpressure relative to atmospheric?