**Core Concept**
Local anaesthetics exert their effect by selectively blocking the voltage-gated sodium (Na+) channels in the neuronal membrane. This blockade prevents the rapid depolarization of nerve fibers, leading to a loss of excitability and ultimately, a loss of sensation.

**Why the Correct Answer is Right**
Local anaesthetics work by diffusing through the neuronal membrane and binding to the sodium channel from the inside. This binding causes a conformational change in the channel, which prevents the influx of sodium ions into the cell. The sodium channel's "gating" mechanism is thus inhibited, preventing the rapid depolarization that normally occurs when a nerve impulse is generated. The inside gate of the sodium channel is the site of action for local anaesthetics, making **Option A** the correct answer.

**Why Each Wrong Option is Incorrect**
**Option B:** Local anaesthetics do not act by inhibiting sodium channels from the outside; their mechanism requires them to diffuse through the membrane and bind to the channel from the inside.

**Option C:** Local anaesthetics do not act by inhibiting potassium (K+) channels; their primary mechanism is the blockade of sodium channels.

**Option D:** Local anaesthetics do not act by inhibiting potassium channels from the outside; their mechanism requires them to diffuse through the membrane and bind to the channel from the inside.

**Clinical Pearl / High-Yield Fact**
It's worth noting that local anaesthetics also have a secondary effect on potassium channels, leading to a slight depolarization of the nerve membrane. However, this effect is much weaker than their primary action on sodium channels.

**Correct Answer Line**
✓ Correct Answer: A. Na channel inhibition inside gate