Overdose symptoms of the CNS and CVS typically begin as __________ signs and progress to potentially fatal __________ signs.

The correct choice indicates that overdose symptoms of the central nervous system (CNS) and cardiovascular system (CVS) typically begin as excitatory signs and can progress to potentially fatal depressive signs.

In the context of local anesthetic overdose, the initial excitatory signs arise due to increased neuronal excitability as the local anesthetic affects the CNS. This can include symptoms such as tinnitus, agitation, and seizures, which are all manifestations of heightened neural activity. As the overdose scenario worsens, the excitatory phase may give way to depressive signs, which reflect a state of decreased neural activity. This can lead to significant cardiovascular and respiratory depression, potentially resulting in apnea, bradycardia, or even cardiac arrest.

This understanding aligns well with the pharmacological effects of local anesthetics, where the initial excitatory CNS effects occur as the threshold for neuronal firing is altered before leading to a state of sedation and respiratory depression due to over-suppression of the nervous system. Thus, the progression from excitatory to depressive symptoms provides insight into the dangerous nature of local anesthetic toxicity.