**Core Concept**
Local anesthesia involves the blockade of nerve conduction, which is achieved by inhibiting the sodium channels responsible for the initial depolarization phase of the action potential. The sequence of events in local anesthesia is crucial for understanding its effects.

**Why the Correct Answer is Right**
The first sequence to go in local anesthesia is the sodium channel blockade, specifically the rapid, voltage-dependent closure of the sodium channels. This is due to the binding of the local anesthetic molecule to the sodium channel, which alters its conformation and reduces its permeability to sodium ions. This blockade of sodium channels prevents the initial depolarization phase of the action potential, leading to the loss of excitability of the nerve.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the initial sequence to go in local anesthesia is not the potassium channels, which are involved in repolarization.
**Option B:** Incorrect because the calcium channels are not directly involved in the initial sequence of local anesthesia, although they may play a role in modulating the effect.
**Option C:** Incorrect because the chloride channels are not the primary target of local anesthetics.

**Clinical Pearl / High-Yield Fact**
Local anesthetics work by stabilizing the inactive state of sodium channels, making it difficult for them to return to the active state, which is essential for the generation of action potentials. This is why local anesthetics are most effective when applied to the nerve before the action potential is generated.

**Correct Answer:** A. Sodium channels.