nbme questions

[MudPhud20XX]

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sorry to put nbme q here, but I would really appreciate some help with these 2 q.

1. A 65 yr old woman with severe sensorineural hearing loss undergoes surgical placement of a cochlear implant. This neural prosthesis converts sound energy to electrical signals, which results in stimulation of which of the following structures?

A. auditory nerve endings in the cochlea
B. cochlear nerve as it enters the pons
C. inner hair cells of the cochlea
D. olivocochlear efferent axons that innervate outer hair cells
E. oval window of the cochlea

I chose C and got it wrong as I though the Presbycusis was the damage of the hair cells. So I am debating btw A or B. Any thoughts?

2. A study is conducted of nerve regeneration after injury in an experimental animal. A nerve guidance conduit is placed within a 4 mm gap of a severed nerve. The conduit, filled with a keratin gel extracted from human hair, is found to enhance visible nerve regeneration across the gap. Microscopic exam of the regeneration site after initial exposure to the keratin gel would most likely show mitotic activity in which of the following cells?

A. fibroblasts
B. macrophages
C. neurons
D. plasma cells
E. schwann cells
F. undifferentitated stem cells

 

[fw5tape6kq]

For number 1, the answer is A. The cochlear implant functions to convert incoming sound waves of particular frequency directly into electrical signals that are connected to and propagate down the afferent fibers if CN VIII.

For number 2, the answer is E. Schwann cells myelinate axons of the PNS and increase the rate of electrical conduction down those axons. Unlike oligodendrocytes of the CNS, Schwann cells have the capacity to regenerate.

 

[zhopv10]

^yup i would just add some conceptual principles to keep in mind 1. Sensorineural refers to things relating to hair cells and proximal (from the brain perspective). Conductive hearing loss would be distal to the hair cells basically, you would differentiate this with the Weber and Rinne tests) Thus you know it is an answer in those systems. 2. It is also asking basically if you know what converts sound wave energy into electrical signal (hair cells) thus the device would be taking over that function. So where would the hair cells fit In on those answers? They synapse essentially with the nerve endings in the cochlea. Hence A.


The second one as said, Schwann cells mediate axonal regrow the and tracking in the periphery. Recall question IMO.