Question

During the transmission of nerve impulse through a nerve fiber, the potential on the inner side of the plasma membrane has which type of electric charge?

• A. First positive, then negative and continue to be negative
• B. First negative, then positive and continue to be positive
• C. First positive, then negative and again back to positive
• D. First negative, then positive and again back to negative

Answer 1

The correct option is D First negative, then positive and again back to negative

When neurotransmitter molecules bind to receptors located on a neuron's dendrites, voltage-gated ion channels open. At excitatory synapses, positive ions flow into the interior of the neuron (negative) and depolarize the membrane, decreasing the difference in voltage between the inside and outside of the neuron. Once the sodium channels open, the neuron completely depolarizes to a membrane potential of about +40 mV (positive). The action potential travels down the neuron as $N{a}^{+}$ channels open. As soon as depolarization is complete, the $N{a}^{+}$ channels close. At the same time, voltage-gated $K^{+}$ channels open, allowing $K^{+}$ to leave the cell. As $K^{+}$ ions leave the cell, the membrane potential once again becomes negative. The diffusion of $K^{+}$ out of the cell hyperpolarizes the cell, making the membrane potential more negative than the cell's normal resting potential.

At this point, the sodium channels return to their resting state, ready to open again if the membrane potential again exceeds the threshold potential. Eventually, the extra $K^{+}$ ions diffuse out of the cell through the potassium leakage channels, bringing the cell from its hyperpolarized state back to its resting membrane potential (negative).