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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]
The simplest reflex is initiated by a stimulus, which activates an afferent nerve. The signal is then passed to a response neuron, which generates a response.
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.
^parveen (November 11, 2020). "Reflex action | Definition, Types and Mechanism and Important solved questions". Crack Your Target. Retrieved 3 April 2021.
^Purves (2004). Neuroscience: Third Edition. Massachusetts, Sinauer Associates, Inc. ISBN 0-87893-725-0
^"Definition of reflex". Dictionary by Merriam-Webster. 25 December 2023.
^Hultborn H (2006-02-01). "Spinal reflexes, mechanisms and concepts: From Eccles to Lundberg and beyond". Progress in Neurobiology. 78 (3–5): 215–232. doi:10.1016/j.pneurobio.2006.04.001. ISSN 0301-0082. PMID 16716488. S2CID 25904937.
^"tendon reflex". The Free Dictionary.
^Price JL (2005-12-05). "Free will versus survival: Brain systems that underlie intrinsic constraints on behavior". The Journal of Comparative Neurology. 493 (1): 132–139. doi:10.1002/cne.20750. ISSN 0021-9967. PMID 16255003. S2CID 18455906.
^Pierrot-Deseilligny E (2005). The Circuitry of the Human Spinal Cord: Its Role in Motor Control and Movement Disorders. Cambridge University Press. ISBN 978-0-511-54504-7.
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