Question

1. A depolarizing current   _________ the membrane potential relative to resting potential, and can in principle be carried ________.

A. raises (makes it less negative); only by cations

B. lowers (makes it more negative); by cations or anions

C. raises (makes it less negative); by cations or anions

D. lowers (makes it more negative); only by cations

2. Myelination increases conduction velocity of action potentials by ________ the length constant, ____________ the distance over which local passive current flow can effectively bring the membrane to threshold.

A. increasing; decreasing

B. decreasing; decreasing

C. increasing; increasing

D. decreasing; increasing

Answer 1

1. A depolarizing current   __raises (makes it less negative)__ the membrane potential relative to resting potential, and can in principle be carried ___only by cations_____. Hence the correct option is A. During the depolarisation state the sodium gated ion channels are opened thereby allowing the inflow of sodium ions into the cell and decreasing the membrane potential inside the cell. Hence the membrane potential inside the cell becomes less negative and this is done only by the sodium influx which are cations.

2. Myelination increases conduction velocity of action potentials by __increasing______ the length constant, _____increasing_______ the distance over which local passive current flow can effectively bring the membrane to threshold. Hence the correct option is: C. During conduction of action potential, the conduction velocity increases in myelinated axons and when the diameter of the axon is large and hence by increasing the diameter and length of axon, the length constant increases thereby increasing the distance by which the action potential can be transported effectively.

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