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Auditory and Vestibular Systems Quiz
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In auditory and vestibular hair cells, which sequence follows deflection towards the taller stereocilia?
- A Tip-link channels close, Na+ leaves into perilymph, the cell hyperpolarises and transmitter release stops You picked ✕
- B Tip-link channels open, Cl- enters from endolymph, the cell hyperpolarises and afferent firing falls You picked ✕
- C Tip-link channels stay fixed while basolateral Ca2+ pumps reverse endolymph K+ gradients You picked ✕
- D Tip-link channels open, K+ enters from endolymph, the cell depolarises, Ca2+ enters and transmitter is released You picked ✓
- E Tip-link channels open, K+ leaves the hair cell into perilymph, the cell hyperpolarises and glutamate release decreases You picked ✕
Correct!
Incorrect
The answer is D: Tip-link channels open, K+ enters from endolymph, the cell depolarises, Ca2+ enters and transmitter is released
Explanation
Why D is correct
See Shared Hair-Cell Rule. Option D is correct because bending the stereocilia towards the taller ones starts a fixed chain of events that is shared by hearing and balance. Stereocilia are the stiff, hair-like projections on top of a hair cell, arranged like a staircase. Tip links are fine filaments that join neighbouring stereocilia, so when the bundle leans towards the tall edge, they pull open mechanically gated cation channels at the tips. The tips are bathed in endolymph, a fluid unusually rich in potassium, so K+ flows into the cell and the cell depolarises (its inside becomes less negative). That opens voltage-gated calcium channels at the base of the cell, and Ca2+ entry triggers the release of glutamate (an excitatory transmitter) onto the sensory fibres of the vestibulocochlear nerve, which is cranial nerve VIII. Deflection towards the shorter stereocilia does the reverse: the channels close, the cell hyperpolarises and less transmitter is released. A simple way to remember it is "towards the tall: open, in, up", meaning channels open, K+ goes in and the signal goes up.
- Trigger: bending the stereocilia towards the taller ones pulls on tip links and opens mechanically gated channels
- Ion flow: K+ from the endolymph flows in and the cell depolarises
- Output: calcium entry releases glutamate onto cranial nerve VIII, and bending the other way closes the channels
Why the other options are incorrect
- A. Tip-link channels close, Na+ leaves into perilymph, the cell hyperpolarises and transmitter release stops: Closing channels, hyperpolarisation and less transmitter release describe bending towards the shorter stereocilia, which is the opposite of the stem. The ion movement is also wrong, because the signal depends on K+ entering from endolymph, not Na+ leaving into perilymph. Your answer
- B. Tip-link channels open, Cl- enters from endolymph, the cell hyperpolarises and afferent firing falls: The ion that flows in from endolymph is K+, not Cl-. Entry of K+ depolarises the cell, so opening the channels raises transmitter release and afferent firing rather than lowering it. Your answer
- C. Tip-link channels stay fixed while basolateral Ca2+ pumps reverse endolymph K+ gradients: Deflection changes how often the tip-link channels are open, and that change is the first step in the signal. Calcium entry at the base of the cell comes later, and no pump reverses the potassium gradient of endolymph. Your answer
- E. Tip-link channels open, K+ leaves the hair cell into perilymph, the cell hyperpolarises and glutamate release decreases: This starts correctly with the channels opening, but the direction of the ion flow is wrong. Potassium-rich endolymph drives K+ into the hair cell, so the cell depolarises and glutamate release increases. Your answer
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1
Which cell type in the organ of Corti is the principal afferent transducer of the cochlea?
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2
After the stapes footplate moves at the oval window, which mechanical sequence best explains deflection of cochlear hair bundles?
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