Depolarization of neuron is characterized by:
Correct answer: D. None of the above
- 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. None of the above
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.
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Coordination depends on receptors, neurons, synapses and nerve impulses, with reflex actions traced through the reflex arc and the roles of major brain regions. Chemical coordination covers endocrine glands and hormones, including how hormones regulate growth, metabolism, reproduction and internal balance, unlike rapid nervous control.
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