TTX (tetrodotoxin) is a potent neurotoxin that specifically blocks voltage-gated sodium (Na⁺) channels, which are crucial for the generation and propagation of action potentials in neurons. Here's how blocking these channels with TTX affects the various aspects you've mentioned:
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The resting membrane potential: TTX does not significantly affect the resting membrane potential. The resting membrane potential is primarily maintained by the differential distribution of ions across the membrane and the activity of potassium channels, rather than sodium channels. So, the answer is no, TTX does not block the resting membrane potential.
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The action potential generation at the stimulus: TTX would block action potential generation at the site of stimulation because action potential initiation depends on the influx of sodium ions through voltage-gated Na⁺ channels. If these channels are blocked, the neuron cannot depolarize sufficiently to reach the threshold needed to generate an action potential. Thus, the answer is yes, TTX blocks the action potential generation at the stimulus.
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The propagation of the action potential to R1: If TTX is applied before action potential has reached R1, then it will impede the ability of the neuron to propagate the action potential to R1. However, if an action potential has already been generated and is moving towards R1, TTX’s presence can hinder that propagation. Thus, the answer is yes, TTX blocks the propagation of the action potential to R1.
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The propagation of the action potential from R1 to R2: Since TTX blocks the sodium channels, once it reaches R1, the action potential cannot be propagated along the axon to R2 because the required depolarization cannot take place. Consequently, the answer is yes, TTX blocks the propagation of the action potential from R1 to R2.
In summary, blocking voltage-gated sodium channels with TTX affects action potential generation and propagation but does not affect the resting membrane potential.
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