Question

K+ passage through open channels in stereocilia depolarizes the receptor hair cell, yet K+ passage through open channels at an inhibitory synapse hyperpolarizes the postsynaptic cell. What is responsible for the different outcomes in potential in these two situations? Hint: think about the charge of potassium and concentration in both scenarios

Answer 1

Ans,:-

concept :- For depolarisation to occur there is only one requirement . Influx of positive ion into the cell along the concentration gradient.

and for hyperpolarisation to occure there are two requirements . Ethier efflux of positive ion (like K+ )out of the cell causing interal of cell negative , or movement of Cl- ion inside the cell causing inside the cell more negative.

For stereocilia:-

The apical end is exposed to the K+-rich, Na+-poor endolymph, which is produced by dedicated ion pumping cells in the stria vascularis .

The basal end is bathed in the same fluid that fills the scala tympani, known as perilymph, which resembles other extracellular fluids in that it is K+-poor and Na+-rich. In addition, the compartment containing endolymph is about 80 mV more positive than the perilymph compartment (this difference is known as the endocochlear potential), while the inside of the hair cell is about 45 mV more negative than the perilymph (and 125 mV more negative than the endolymph). The resulting electrical gradient across the membrane of the stereocilia (about 125 mV) drives K+ through open transduction channels into the hair cell, even though these cells already have a high internal K+ concentration. K+ entry via the transduction channels leads to depolarization of the hair cell, which in turn opens voltage-gated Ca2+ and K+ channels located in the membrane of the hair cell soma ). The opening of somatic K+ channels favors K+ efflux, and thus repolarization; the efflux occurs because the perilymph surrounding the basal end is low in K+ relative to the cytosol.

For normal cell IPSP:-

for normal repolarisation of a cell eflux of K+ is required, and if excess k+ efflux occur it makes the cell more negative cause hyperpolarisation of cell. Thus for IPSP eflux of K+ is require.

and for depolarisation of steriocilia influx of K + is require. That's the main difference. But in both case the is passage of ion through K+ channel . Simple