Anodal block occurs under which condition?

Anodal block refers to a phenomenon where the anode (positive electrode) effectively prevents the depolarization of an axon or nerve fiber when a stimulus is applied. In this scenario, reversing the positions of the cathode (negative electrode) and anode indeed leads to an anodal block because the cathode now becomes the site of greatest current density, resulting in depolarization of the nerve.

During normal conditions, when the anode is positioned correctly relative to the nerve fiber, it can create hyperpolarization, which inhibits nerve conduction. If the anode and cathode are reversed, the current distribution changes, allowing the cathode to depolarize the nerve effectively while simultaneously leading to the anodal block at the previously active anode.

This understanding is crucial in nerve conduction studies and neuromuscular physiology, as it illustrates how electrode placement and stimulation parameters can influence nerve excitability and conduction properties.