Asignal is transmitted down the of a nerve cell.

synapse

Explanation:

We know that nerve impulses, signals, must pass from cell to cell for a response to a given signal to occur. For this to happen, the presence of a specialized region called the synapse is required. Synapse is the structure that allows signals to be transmitted from one nerve cell to another.

Synapse can be defined as the region of proximity between the end of a neuron and a neighboring cell, where nerve impulses are transformed into chemical impulses due to the presence of chemical mediators.