During repolarization of nerve:
Correct answer: A. Na+ channels are closed and K+ channels are open
- A. Na+ channels are closed and K+ channels are open
- B. Both K+ and Na+ gates are closed
- C. K+ gate closes and Na+ gate opens
- D. Both gates remain open
Explanation
The voltage-gated sodium (Na+) channels that opened during the depolarization phase to allow Na+ ions to enter the cell begin to inactivate shortly after opening. This inactivation closes the channels and prevents further Na+ influx, stopping the depolarization process. Almost simultaneously with sodium channel inactivation, voltage-gated potassium (K+) channels open. This allows K+ ions to flow out of the neuron, down their concentration gradient. The efflux of K+ ions is crucial because it helps to counteract the depolarization caused by the influx of Na+ ions.
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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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