Depolarization of neuron is characterized by:
Correct answer: D. Increased Na+ permeability leading to an influx of Na+
- A. Na+ into the axon and K+ out of the axon
- B. K+ into the axon and Na+ out of the axon
- C. Na+ and K+ within the axon toward the axon terminal
- D. Increased Na+ permeability leading to an influx of Na+
Explanation
When a neuron fiber is stimulated by a stimulus of adequate strength (threshold stimulus), the stimulated area of the fiber becomes several times more permeable to Na+ than to K+ due to the opening of voltage-regulating Na+ gates. As a result, Na gates permit the influx of Na+ ions by diffusion. Since more Na+ ions are entering than leaving, the electrical potential of the membrane changes from -70 mV towards zero and then reaches 50 mV. This reversal of polarity across two sides of the membrane is called depolarization. This electropositive inside and electronegative outside last for about one millisecond till the Na+ gates are closed. Note that K+ is not involved in the depolarization of neurons. It is involved in repolarization and hyperpolarization.
This question appeared on the ETEA MDCAT 2018 paper, which you can sit online with every answer explained.
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About Neurons and Nerve Impulse
Neurons receive and transmit information through dendrites, the cell body and axons. The topic explains resting potential, depolarization, repolarization, refractory periods and saltatory conduction, followed by synaptic transmission through neurotransmitters. An action potential is distinct from the graded potential produced at a receptor.
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