Final answer:
Yes, the voltage-gated Na⁺ channels between the stimulus and R1 are affected by TTX, which blocks these channels and prevents the initiation or propagation of action potentials.
Step-by-step explanation:
The voltage-gated Na⁺ channels are indeed sensitive to tetrodotoxin (TTX), a potent neurotoxin. TTX specifically binds to these channels and blocks the flow of Na⁺ ions through them, inhibiting their function. Therefore, if TTX is present, it would affect the voltage-gated Na⁺ channels between the stimulus and R1, preventing action potentials from being initiated or propagated. An action potential begins when a specific kind of channel, such as a ligand-gated or mechanically-gated Na⁺ channel, responds to a stimulus by allowing Na⁺ to enter the neuron. This influx of Na⁺ starts the depolarization process which, if reaching the threshold, will cause the voltage-gated Na⁺ channels to open. However, if TTX is present, it would inhibit this sequence of events, preventing normal nerve signal transmission.