Final answer:
The minimal stimulus needed to cause a neuron to transmit an impulse is called the threshold. When the charge reaches the threshold of excitation, the action potential begins, resulting in the transmission of the impulse.
Step-by-step explanation:
The minimal stimulus needed to cause a neuron to transmit an impulse is called the threshold. When a neuron receives signals at the dendrites, small pores open on the neuronal membrane, allowing sodium ions to move into the cell. If the charge reaches the threshold of excitation, the neuron becomes active and the action potential begins, resulting in the transmission of the impulse.