Final answer:
The response at R2 after lidocaine administration may not necessarily be zero, because lidocaine inhibits voltage-gated Na+ channels and reduces action potential generation, but not all axons may be affected equally.
Step-by-step explanation:
The statement that the response at R2 after lidocaine administration might not be zero is true. This is because R2 is a summation of action potentials from multiple axons, and not all axons may be affected equally by lidocaine. Lidocaine functions by blocking voltage-gated Na+ channels, which are crucial for depolarization during the initiation of action potentials. If these channels are blocked, it interferes with the generation and propagation of action potentials, which is why lidocaine is often used as a local anesthetic to numb sensations, including pain.
However, not every axon will necessarily reach threshold for an action potential. Some axons may have a higher threshold or may not be as exposed to lidocaine due to differences in tissue distribution or concentration gradients. Furthermore, the effectiveness of lidocaine also depends on the specific characteristics of each axon, such as diameter and myelination, which can affect the drug's accessibility to the Na+ channels. Therefore, while lidocaine significantly reduces the likelihood of action potential generation and propagation, it may not completely abolish the response in all axons, hence the possibility of R2 not being zero.