Those automatic and very fast nervous system actions are called reflex actions (or reflexes).

What reflex actions are

  • A reflex action is an automatic, rapid response to a stimulus that does not involve the conscious part of the brain.
  • Reflexes protect the body from harm, for example pulling your hand away from something hot before you even “realize” it is hot.

How they work in the nervous system

  • The signal travels along a simple pathway called a reflex arc , typically going from sensory neuron → relay neuron in the spinal cord → motor neuron, bypassing conscious processing.
  • Because the pathway is short and avoids higher brain centers, the response happens very quickly, often in under half a second.

TL;DR: The type of actions involving the nervous system that are automatic and very fast are reflex actions (reflexes).

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