Local anaesthetics act by inhibiting –
**Core Concept**
Local anaesthetics are a class of drugs that selectively block the conduction of nerve impulses, preventing the transmission of pain signals to the brain. This is achieved through a specific mechanism that involves the interaction with voltage-gated sodium channels in the neuronal membrane.
**Why the Correct Answer is Right**
Local anaesthetics work by binding to the sodium channel in its open or inactivated state, thereby blocking the influx of sodium ions into the neuron. This prevents the generation and propagation of action potentials, resulting in the loss of sensation. The most common site of action for local anaesthetics is the sodium channel's outer pore, where they bind to a specific site that is distinct from the binding site of tetrodotoxin.
**Why Each Wrong Option is Incorrect**
**Option A:** Voltage-gated potassium channels are not the primary target of local anaesthetics, although some local anaesthetics may also affect potassium channels at higher concentrations.
**Option B:** Local anaesthetics do not primarily act by inhibiting acetylcholinesterase, an enzyme involved in the breakdown of acetylcholine.
**Option C:** Local anaesthetics do not primarily act by inhibiting GABA receptors, which are involved in the regulation of inhibitory neurotransmission.
**Clinical Pearl / High-Yield Fact**
It's worth noting that local anaesthetics can also affect other ion channels, such as calcium channels, and may have additional effects on neuronal excitability and neurotransmitter release. However, their primary mechanism of action is through the inhibition of sodium channels.
**Correct Answer: D. Sodium channels.**