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Anonymous at Wed, 18 Sep 2024 03:12:39 UTC No. 16385603

I attempted to ask my neuroscience professor a few questions earlier, although I'm still not sure I fully understand. I'm hoping you guys can help.

1. How does an action potential work? I understand it as being the difference between the extracellular and intracellular voltages. In other words, the resting potential of -70 m/v describes the intracellular space as being 70 m/v less than the extracellular space.
But in order to reach the -55 m/v threshold to initiate an action potential, one would need to decrease the difference between the two (depolarize); in order for that to occur, one would either need to increase the intracellular voltage, or decrease the extracellular voltage. Only the latter (to my knowledge) is possible prior to the initiation of the action potential/the opening of voltage-gated ion channels, and I understand this process (of decreasing the extracellular voltage) as occurring due to an accumulation of Na+ ions.
However, these seem contradictory: How can one be decreasing the extracellular voltage when an accumulation of positive Na+ ions would, ostensibly, be doing the opposite (increasing the voltage)?

2. How do postsynaptic potentials (PSPs) — in the process of attempting to initiate or discourage an action potential — travel from a neuron's dendrites to its axon? Does it simply travel across the cytoplasm of the soma (although, if so, would the flood of ions traveling through affect the neuron's organelles)? Or are the traveling ions released into the extracellular space (and, if so, through what mechanism)?

3. In heterozygote individuals (one dominant allele; one recessive allele), are both genes on each chromosome pair expressed, that is, made into proteins? Or does expression only apply to the dominant gene?
If they're both expressed, manufacturing proteins which aren't used seems like a waste of energy — and, seemingly, would go against nature's tendency to prioritize efficiency.

Thank you!