**Core Concept**
Local anaesthetics exert their effect by inhibiting the initiation and conduction of nerve impulses in sensory neurons. This occurs primarily by binding to voltage-gated sodium channels in the neuronal membrane, preventing the influx of sodium ions necessary for depolarization.

**Why the Correct Answer is Right**
Local anaesthetics bind to the intracellular side of voltage-gated sodium channels in neurons, stabilizing them in a closed state. This prevents the influx of sodium ions during depolarization, thereby blocking the generation of action potentials. The blockade is use-dependent and more effective at high concentrations or with prolonged exposure. This mechanism specifically interrupts signal transmission in nociceptive nerves, leading to temporary loss of sensation.

**Why Each Wrong Option is Incorrect**
Option A: Local anaesthetics do not interfere with neurotransmitter release; they act presynaptically on sodium channels, not on synaptic vesicle fusion.
Option C: They do not enhance inhibitory neurotransmitter release; this is a function of GABAergic or other inhibitory systems, not local anaesthetics.
Option D: Sodium efflux is not the key event blocked; the primary mechanism is prevention of sodium influx during depolarization, not inhibition of efflux.

**Clinical Pearl / High-Yield Fact**
The mechanism of action of local anaesthetics is **voltage-gated sodium channel blockade**, with the drug binding preferentially to the inactivated state of the channel—making the effect more pronounced with repeated stimulation (use-dependent blockade).

✓ Correct Answer: B. Block the influx of sodium into the cell