Reflex
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{{for|the novel|reflex (novel)}}
A '''reflex action''' is involuntary and almost instant movement in response to [[stimulus]].<ref>Purves (2004). ''Neuroscience: Third Edition''. Massachusetts, Sinauer Associates, Inc. </ref> In most contexts, especially involving humans, a reflex action is mediated via the [[reflex arc]] (although this is not always true in other animals, or in more casual usage of the term 'reflex'.)
Reflexes are tested as part of a [[neurological examination]] to assess damage to or functioning of the [[Central nervous system|central]] and [[peripheral nervous system]].
Reflexes may be trained, such as during repetition of motor actions during sport practice, or the linking of stimuli with [[Autonomic nervous system|autonomic reactions]] during [[classical conditioning]].
==Reaction time==
For a reflex, [[reaction time]] or latency is the time from the onset of a stimulus until the [[organism]] responds.
In [[animals]], reaction time to [[Visual perception|visual]] stimuli is typically 150 to 300 [[millisecond]]s.<ref>{{cite web | url = http://www.humanbenchmark.com/tests/reactiontime/stats.php | accessdate = 2007-10-11 | title = Human Benchmark: Reaction Time Statistics }}</ref>
==Human reflexes==
[[Image:ReflexArc1.jpg|right|thumb|300px|The mechanism of the [[reflex arc]]. Note that this image includes an [[interneuron]] in the monosynaptic [[patellar reflex]] for purposes of illustration.]]
Reflex actions include:
===Tendon reflexes===
The deep [[tendon reflex]]es provide information on the integrity of the central and peripheral nervous system. Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.
* [[Biceps reflex]] ([[cervical spinal nerve 5|C5]], [[cervical spinal nerve 6|C6]])
* [[Brachioradialis reflex]] (C5, C6, [[cervical spinal nerve 7|C7]])
* [[Extensor digitorum reflex]] (C6, C7)
* [[Triceps reflex]] (C6, C7, [[cervical spinal nerve 8|C8]])
* [[Patellar reflex]] or knee-jerk reflex ([[lumbar spinal nerve 2|L2]], [[lumbar spinal nerve 3|L3]], [[lumbar spinal nerve 4|L4]])
* [[Ankle jerk reflex]] (Achilles reflex) ([[sacral spinal nerve 1|S1]], [[sacral spinal nerve 2|S2]])
* [[Plantar reflex]] or Babinski reflex ([[lumbar spinal nerve 5|L5]], S1, S2)
While the reflexes above are stimulated mechanically, the term [[H-reflex]] refers to the analogous reflex stimulated electrically, and [[Tonic vibration reflex]] for those stimulated by vibration.
===Reflexes involving cranial nerves===
{| class="wikitable"
| '''Name''' || '''Sensory''' || '''Motor'''
|-
| [[Pupillary reflex]] || II || III
|-
| [[Accommodation reflex]] || II || III
|-
| [[Jaw jerk reflex]] || V || V
|-
| [[Corneal reflex]], also known as the [[blink]] reflex || V || VII
|-
| [[Caloric reflex test]]/[[Vestibulo-ocular reflex]] || VIII || III, IV, VI +
|-
| [[Gag reflex]] || IX || X
|}
===Reflexes in infants only===
{{main|Primitive reflexes}}
[[Image:Greifreflex.JPG|thumb|Grasp reflex ]]
[[Newborn babies]] have a number of other reflexes which are not seen in adults, referred to as '''primitive reflexes'''.<ref>http://www.fpnotebook.com/Neuro/Exam/NrlgcExm.htm</ref> These include:
* [[Asymmetrical tonic neck reflex]] (ATNR)
* [[Grasp reflex]]
* [[Hand-to-mouth reflex]]
* [[Moro reflex]], also known as the startle reflex
* [[Sucking]]
* Symmetrical tonic neck reflex (STNR)
* [[Tonic labyrinthine reflex]] (TLR)
===Other reflexes===
Other reflexes found in the human nervous system include:
* [[Anal wink|Anocutaneous reflex]]
* [[Bulbocavernosus reflex]]
* [[Escape reflex]]
* [[Mammalian diving reflex]]
* [[Oculocardiac reflex]]
* [[Optokinetic reflex]]
* [[Photic sneeze reflex]]
* [[Scratch reflex]]
* [[Withdrawal reflex]]
**[[Crossed extensor reflex]]
* [[Muscular defense]]
Processes such as [[breath]]ing, [[digestion]], and the maintenance of the [[Heart rate|heartbeat]] can also be regarded as reflex actions, according to some definitions of the term.
==See also==
*[[Automatic behavior]]
*[[Voluntary action]]
==References==
{{reflist}}
{{Nervous system physiology}}
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