What is the minimum level of stimulation needed to trigger a nerve impulse?
 

The correct option is the threshold stimulus

The minimum level of stimulation needed to trigger a nerve impulse is called the threshold stimulus. When a stimulus exceeds the threshold level, an action potential is triggered and the neuron becomes depolarized. 

Resting potential refers to the state of the neuron when it is not receiving any stimuli. 

Action potential refers to the electrical signal that travels along the neuron during the transmission of the nerve impulse. 

Refractory stimulus is not a commonly used term in the context of nerve impulses.