Question

Use what you know about the physiology of neurons to answer the following questions. Treat each of these questions as unrelated to each other. a. Imagine that a mutation makes Na* leak channels just as common as K' leak channels. Explain the effect of this mutation on the resting potential of this neuron. 3. b. The intracellular:extracellular ratio of K' ions is normally 150:4mM. Imagine that you decrease that ratio to 150: 20mM. Describe the subsequent effect on the resting potential: identify the ions responsible, explain how their movement changes, and whether this brings the neuron closer to or further from, its threshold potential Imagine that in a different neuron, voltage-gated K+ channels open quickly, only 0.3ms after voltage- gated Na* channels. Predict changes in timing, amplitude and shape of the AP (if any) by drawing one labeled diagram comparing a normal AP (solid line) to your AP (dashed line), and by explaining in words why these changes occur. Label the axes, depolarization, and repolarization phases of your curve. (6) C.

Answer 1

Let us first start the answer with what is resting potential?

Resting potential is basically a voltage across a resting neuron which is determined by the concentration gradient.

K+ ions play much more wider role than Na+ ions.

a) Here, the question arises if the Na+ ions leak the channel, what will be the effect on resting potential?

K+ ions are in higher concentration and Na+ ions and Cl- are in lower concentration within the cell and the Cl- and Na+ ions are in higher concentration and K+ ions are in lower concentration outside the cell.

If the K+ ions, as usual, crossed the membrane down the gradient, the inside of the cells looses its positive charge and makes the resting potential negative.

But in mutation, as the Na+ ions moves across the cell membrane, also along the gradient, it makes the cell positive by entering into the cell, making the resting potential positive.

b) If the ratio of K+ ions inside the cell is decreased, the cell will come into negative state and the ions responsible for this is Cl- ions.

Movement of the ions shall be the one, which is crossing the membrane more readily. In this case, K+ ions are crossing teh membrane and Na+ ions also entering the cell, thus bringing the neuron in equilibrium position, near to teh threshold potential.

c)The K+ channels open quickly after the Na+ channels. So, the quick interchanging of both the ions occur, making the resting potential from negative to the postive +30 by going through repolarization and hyperpolarization.

t30 Threshold afu

The duration of the opening of the channel increases its amplitude.