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{{other uses|Reflex (disambiguation)}}▼
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{{redirect|Reflectory|the album by Pepper Adams|Reflectory (album)}}▼
▲{{short description|Automatic, involuntary response to a stimulus}}
▲{{
{{human centric|date=September 2022}}
In [[biology]], a '''reflex''', or '''reflex action''', is an involuntary, unplanned sequence or action<ref>{{cite web |author=parveen |date=November 11, 2020 |title=Reflex action {{!}} Definition, Types and Mechanism and Important solved questions |url=https://www.crackyourtarget.com/reflex-action.html |access-date=3 April 2021 |publisher=Crack Your Target}}</ref> and nearly instantaneous response to a [[Stimulus (physiology)|stimulus]].<ref>Purves (2004). ''Neuroscience: Third Edition''. Massachusetts, Sinauer Associates, Inc. {{ISBN|0-87893-725-0}}</ref><ref name="M-W">{{cite web |title=Definition of reflex |url=https://www.merriam-webster.com/dictionary/reflex |website=Dictionary by Merriam-Webster |date=25 December 2023 |language=en}}</ref>
==Types of human reflexes==▼
[[File:Improved General Reflex Diagram.png|thumb|429x429px|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 pathway]]s in the nervous system called [[reflex arc]]s. 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,<ref name=":02">{{Cite journal |date=2006-02-01 |title=Spinal reflexes, mechanisms and concepts: From Eccles to Lundberg and beyond |url=https://www.sciencedirect.com/science/article/pii/S0301008206000335 |journal=Progress in Neurobiology |language=en |volume=78 |issue=3–5 |pages=215–232 |doi=10.1016/j.pneurobio.2006.04.001 |issn=0301-0082|last1=Hultborn |first1=Hans |pmid=16716488 |s2cid=25904937 }}</ref> so many reflexes are an automatic response to a stimulus that does not receive or need conscious thought.<ref name="FD">{{cite web |title=tendon reflex |url=http://medical-dictionary.thefreedictionary.com/tendon+reflex |website=[[The Free Dictionary]]}}</ref>
Many reflexes are fine-tuned to increase organism survival and self-defense.<ref>{{Cite journal |last=Price |first=Joseph L. |date=2005-12-05 |title=Free will versus survival: Brain systems that underlie intrinsic constraints on behavior |journal=The Journal of Comparative Neurology |language=en |volume=493 |issue=1 |pages=132–139 |doi=10.1002/cne.20750 |pmid=16255003 |s2cid=18455906 |issn=0021-9967|doi-access=free }}</ref> This is observed in reflexes such as the [[Startle response|startle reflex]], which provides an automatic response to an unexpected stimulus, and the [[Cat righting reflex|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.<ref>{{Cite book |last=Pierrot-Deseilligny |first=Emmanuel |title=The Circuitry of the Human Spinal Cord: Its Role in Motor Control and Movement Disorders |publisher=Cambridge University Press |year=2005 |isbn=978-0-511-54504-7}}</ref> Long-latency reflexes produce nerve signals that are transduced across multiple synapses before generating the reflex response.
'''Myotatic reflexes'''▼
▲==Types of human reflexes==
===Autonomic vs skeletal reflexes===
''Reflex'' is an anatomical concept and it refers to a
loop consisting, in its simplest form, of a sensory
nerve, the input, and a motor nerve, the output.
Autonomic does not mean automatic. The term ''autonomic'' is an anatomical term and it refers
to a type of nervous system in animals and humans
that is very primitive. ''Skeletal'' or ''somatic'' are,
similarly, anatomical terms that refer to a type of
nervous system that is more recent in terms of
evolutionary development. There are autonomic
reflexes and skeletal, somatic reflexes.<ref>Nikoletseas Michael M. (2010) Behavioral and Neural Plasticity. {{ISBN|978-1-4537-8945-2}}</ref>
The myotatic or muscle [[stretch reflex]]es (sometimes known as ''deep tendon reflexes'') provide information on the integrity of the [[central nervous system]] and [[peripheral nervous system]]. This information can be detected using [[Electromyography|electromyography (EMG)]].<ref name=":1">{{Cite journal |last1=Tsuji |first1=Hironori |last2=Misawa |first2=Haruo |last3=Takigawa |first3=Tomoyuki |last4=Tetsunaga |first4=Tomoko |last5=Yamane |first5=Kentaro |last6=Oda |first6=Yoshiaki |last7=Ozaki |first7=Toshifumi |date=2021-01-27 |title=Quantification of patellar tendon reflex using portable mechanomyography and electromyography devices |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=2284 |doi=10.1038/s41598-021-81874-5 |issn=2045-2322 |pmc=7840930 |pmid=33504836 |doi-access=free|bibcode=2021NatSR..11.2284T }}</ref> Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.<ref name=":1" /> A stretch reflex is the contraction of a muscle in response to its lengthwise stretch.
* [[Biceps reflex]] ([[cervical spinal nerve 5|C5]], [[cervical spinal nerve 6|C6]])
* [[Brachioradialis reflex]] (C5, C6, [[cervical spinal nerve 7|C7]])
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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 to vibration.
===Tendon reflex===
A [[tendon reflex]] is the contraction of a muscle in response to striking its [[tendon]]. The [[Golgi tendon reflex]] is the inverse of a stretch reflex.
===Reflexes involving cranial nerves===
{| class="wikitable"
| '''Name''' || '''Sensory''' || '''Motor'''
|-
| [[Pupillary light reflex]] ||
|-
| [[Accommodation reflex]] || II || III
|- ▼
|-
| [[
| [[Corneal reflex]], also known as the [[blink]] reflex || V || [[Facial nerve|VII]]
|-
| [[Glabellar reflex]] || V || VII
|-
| [[Vestibulo-ocular reflex]] ||
|-
| [[Gag reflex]] ||
|}
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[[Image:Greifreflex.JPG|thumb|Grasp reflex]]<!-- Deleted image removed: [[Image:Flexor Reflex.jpg|thumb|spinal cord]] -->
[[Newborn babies]] have a number of other reflexes which are not seen in adults, referred to as '''primitive reflexes'''. These automatic reactions to stimuli enable infants to respond to the environment before any learning has taken place. They include:
▲* [[Asymmetrical tonic neck reflex]] (ATNR)
* [[Palmomental reflex]]
* [[Moro reflex]], also known as the startle reflex
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* [[Primitive reflexes#Rooting reflex|Rooting reflex]]
* [[Primitive reflexes#Sucking reflex|Sucking reflex]]
* [[Symmetrical tonic neck reflex]]
* [[Tonic labyrinthine reflex]]
===Other kinds of reflexes===
Other reflexes found in the central nervous system include:
* [[Abdominal reflex]]es (T6-L1)
* [[Gastrocolic reflex]]
* [[Anal wink|Anocutaneous reflex]] (S2-S4)
* [[Baroreflex]]
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* [[Cremasteric reflex]] (L1-L2)
* [[Diving reflex]]
* [[Lazarus sign]]
* [[Muscular defense]]
* [[Photic sneeze reflex]]
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* [[Startle reflex]]
* [[Withdrawal reflex]]
** [[Crossed extensor reflex]]
Many of these reflexes are quite complex, requiring a number of synapses in a number of different nuclei in the
Processes such as [[
===Grading===
{{Unreferenced section|date=April 2023}}
In [[medicine]], reflexes are often used to assess the health of the [[nervous system]]. [[physician|Doctors]] will typically grade the activity of a reflex on a scale from 0 to 4. While 2+ is considered normal, some healthy individuals are hypo-reflexive and register all reflexes at 1+, while others are hyper-reflexive and register all reflexes at 3+.
{|class="wikitable"
|'''Grade
|-
| 0 || Absent ("mute")
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| 3+ or +++ || Hyperactive ''without'' [[clonus]], with spread to adjacent muscle groups
|-
| 4+ or ++++ || Hyperactive
|}
Depending on where you are, another way of grading is from –4 (absent) to +4 (clonus), where 0 is "normal".
== Reflex modulation ==
[[File:Demonstration of reflex reversal.svg|thumb|An example of reflex reversal is depicted. Activating the same spinal reflex pathway can cause limb flexion while standing, and extension while walking.]]
A good example of reflex modulation is the [[stretch reflex]].<ref>{{Cite journal |
The underlying sites and mechanisms of reflex modulation are not fully understood. There is evidence that the output of sensory neurons is directly modulated during behavior—for example, through [[presynaptic inhibition]].<ref>{{cite journal |
==Other reflexes==
Breathing can also be considered both involuntary and voluntary, since breath can be held through [[internal intercostal muscles]].<ref>{{Cite journal |last1=Mitchell |first1=R. A. |last2=Berger |first2=A. J. |date=February 1975 |title=Neural regulation of respiration |url=https://pubmed.ncbi.nlm.nih.gov/1089375/ |journal=[[The American Review of Respiratory Disease]] |publisher=[[American Thoracic Society]] |volume=111 |issue=2 |pages=206–224 |doi=10.1164/arrd.1975.111.2.206 |doi-broken-date=31 January 2024 |issn=0003-0805 |pmid=1089375}}</ref><ref>{{Cite journal |last1=Park |first1=Hyeong-Dong |last2=Barnoud |first2=Coline |last3=Trang |first3=Henri |last4=Kannape |first4=Oliver A. |last5=Schaller |first5=Karl |last6=Blanke |first6=Olaf |date=February 6, 2020 |title=Breathing is coupled with voluntary action and the cortical readiness potential |journal=[[Nature Communications]] |publisher=[[Nature Portfolio]] |volume=11 |issue=1 |pages=289 |bibcode=2020NatCo..11..289P |doi=10.1038/s41467-019-13967-9 |issn=2041-1723 |pmc=7005287 |pmid=32029711 |doi-access=free}}</ref><ref>{{Cite news |date=2018-07-22 |title=21.10B: Neural Mechanisms (Cortex) |url=https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/21%3A_Respiratory_System/21.10%3A_Respiration_Control/21.10B%3A_Neural_Mechanisms_(Cortex) |access-date=2022-09-10 |website=[[LibreTexts|Medicine LibreTexts]] |language=en}}</ref>
== See also ==
* [[List of reflexes (alphabetical)]]▼
* [[All-or-none law]]
* [[Automatic behavior]]
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* [[Instinct]]
* [[Jumping Frenchmen of Maine]]
* [[Preflexes]]
* [[Voluntary action]]
== References ==
{{
{{Nervous system physiology}}
{{Reflex}}
{{Authority control}}
[[Category:Reflexes]]
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