Which of the following is true about the effect of local anesthetics on the CNS?

Local anesthetics can significantly affect the central nervous system (CNS) when administered, particularly in cases of overdose, which makes the understanding of their pharmacological effects crucial. When an overdose occurs, the initial response often involves CNS excitation, characterized by symptoms such as anxiety, restlessness, and tremors. This excitatory phase is followed by CNS depression, which can lead to symptoms like drowsiness, loss of consciousness, respiratory depression, and even coma.

The response to local anesthetics is dose-dependent, and the progression from excitation to depression reflects the drug's impact on neuronal excitability and synaptic transmission. Understanding this biphasic reaction is vital for dental professionals to anticipate the signs of toxicity and manage potential complications effectively.

Other options presented would not accurately describe the nature of local anesthetic effects on the CNS. For instance, local anesthetics can cross the blood-brain barrier under certain conditions, and not all overdose cases lead to tonic-clonic convulsions, as individual responses can vary significantly. Additionally, symptoms of toxicity may present within minutes of injection depending on several factors, including the dose and the specific local anesthetic used.