The table above provides the concentrations of sodium and potassium ions and the
ID: 3514296 • Letter: T
Question
The table above provides the concentrations of sodium and potassium ions and the electric potential (relative to the blood) in the hair cell and the endolymph of a vertebrate cochlea
Movement of the hair cilia results in an increase in the permeability of the membrane between these regions to monovalent cations, giving an increase in membrane conductance of 10-9 S.
a. (3 marks) In what direction do the ions move? Assuming that the channels are permeable to both potassium and sodium and that sodium and potassium have the same mobility, what is the contribution of potassium current relative to the sodium current?
b. (3 marks) What will the initial increase in electrical current be?
c. (4 marks) If the initial current flow is zero, how many ions will flow across the membrane in the first microsecond after a movement of the hair cilia?
potassium sodium Vr endolymph 150mM 7mM +80mM hair cell 150mM 7mM -70mMExplanation / Answer
a. By ATP Powered , the pump moves potassium and sodium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, 3 sodium ions are extruded from and 2 potassium ions are imported into the cell.Potassium is the major cation (positive ion) inside cells, while sodium is the major cation outside the cells. Difference between the concentrations of these charged particles causes difference in the electric potential between the inside and outside of cells, called as the membrane potential. The balance between potassium and sodium is maintained by ion transporters in the cell membrane. The potassium ion channels are tetramers with several conserved secondary structural elements. A number of potassium channel structures have been solved including voltage gated,ligand gated, tandem-pore, and inwardly rectifying channels, from prokaryotes and eukaryotes. The cell membrane potential created by potassium and sodium ions allows the cell to generate an action potential—a "spike" of electrical discharge. The ability of cells to produce electrical discharge is critical for body functions such as neurotransmission, muscle contraction, and heart function.
b. membrane potential will reach +30 mV by the time sodium has entered the cell.
c.The ratio of the sodium and potassium ions flow in the ratio of 3:2