What is the level of stimulation required to trigger a neural impulse?

• A. Synapse
• B. Threshold
• C. Endocrine System
• D. Hormones

Answer: (B)

The level of stimulation needed to trigger a neural impulse is the threshold. Neurons sit at rest with a baseline electrical potential, and inputs depolarize the membrane. When the depolarization reaches the threshold, voltage-gated sodium channels open, the membrane rapidly depolarizes, and an action potential occurs in an all-or-none event. If the stimulus is below threshold, the neuron does not fire, no matter how strong the subthreshold input is. Inputs can add up over time (temporal summation) or from different locations (spatial summation) to reach that threshold. The exact values can vary, but the concept remains: once the threshold is crossed, a full impulse is generated; below it, nothing happens. The other options describe parts of the signaling system—where signals are transmitted or who sends chemical messages—but they do not specify the trigger level for an impulse.