Reflex

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In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action^[1] and nearly instantaneous response to a stimulus.^[2][3]

Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs via neural pathways in the nervous system called reflex arcs. A stimulus initiates a neural signal, which is carried to a synapse. The signal is then transferred across the synapse to a motor neuron, which evokes a target response. These neural signals do not always travel to the brain,^[4] so many reflexes are an automatic response to a stimulus that does not receive or need conscious thought.^[5]

Many reflexes are fine-tuned to increase organism survival and self-defense.^[6] This is observed in reflexes such as the startle reflex, which provides an automatic response to an unexpected stimulus, and the feline righting reflex, which reorients a cat's body when falling to ensure safe landing. The simplest type of reflex, a short-latency reflex, has a single synapse, or junction, in the signaling pathway.^[7] Long-latency reflexes produce nerve signals that are transduced across multiple synapses before generating the reflex response.