Question

12. Immediately after an action potential is propagated, which one of the following ions rapidly diffuses out of the cell into the tissue fluid: A) sodium B) chloride C) calcium D) potassium E) magnesium
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Answer 1

Option D) potassium

• Potassium channels continue to remain open and allow positive ions to leave the neuron as the action potential passes through. In other words, the cell briefly becomes even more negatively charged than it is at rest, or hyperpolarizes.
• The influx of sodium depolarizes neighbouring axon segments to threshold, which causes the action potential to travel along the axon. Animation The voltage-gated sodium channels in the axonal membrane will open in response to a voltage shift that reaches the threshold.
• The cycle of inter-neuronal, synaptic communication that is essential to our comprehension of how the nervous system works is started by axonal action potentials.
• Since somatic intracellular/whole-cell recordings must necessarily measure a combination of the currents compartmentalised in the soma, dendrites, and axon, the field has accumulated a vast amount of knowledge about the signature action potential waveform, firing patterns, and underlying channel properties of many different cell types. The channel configuration in the axon is of special importance because several neuron types appear to have the lowest threshold for the activation of action potentials there.
• However, compared to the soma or dendrites, the axon is more experimentally inaccessible. The behaviour of the axonal action potential has recently been studied using single-fiber extracellular recording, direct intracellular recording, and optical recording techniques from axons.
• We are beginning to comprehend more fully how particular channels and other cellular characteristics influence action potential threshold, waveform, and timing, which are important factors influencing the release of downstream transmitters. A theme of axons with greater computational capacity than in conventional conceptualizations appears as a result of this additional investigation.

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