Changes: Reflexes

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A reflex action is an automatic (otherwise called involuntary) neuromuscular action elicited by a defined stimulus.^[1] 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'.)

Mechanism

A reflex action or reflex is a biological control system linking stimulus to response and mediated by a reflex arc. Reflexes can be built-in or learnt. For example, a person stepping on a sharp object would initiate the reflex action through the creation of a nociceptive stimulus within specialized sense receptors located in the skin tissue of the foot. The resulting stimulus would be transmitted through an afferent nerve to the spinal cord. This stimulus is usually processed by an interneuron to create an immediate response to nociception by initiating a motor response to withdraw from the pain-producing object. This retraction would occur as the sensation is arriving in the brain and producing the subjective perception of pain, which would result in a more cognitive evaluation of the situation.

Reflexes are tested as part of a neurological examination to assess damage to or functioning of the 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 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 humans, reaction time to visual stimuli is typically 150 to 300 milliseconds.^[2]

Human reflexes

Main article: List of reflexes

ReflexArc1 — 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 reflexes 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 (C5, C6)
Brachioradialis reflex (C5, C6, C7)
Extensor digitorum reflex (C6, C7)
Triceps reflex (C6, C7, C8)
Patellar reflex or knee-jerk reflex (L2, L3, L4)
Ankle jerk reflex (Achilles reflex) (S1, S2)
Plantar reflex or Babinski reflex (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

Name	Sensory	Motor
Pupillary light 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 article: Primitive reflexes

File:Greifreflex.JPG

Grasp reflex

Newborn babies have a number of other reflexes which are not seen in adults, referred to as primitive reflexes.^[3] 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:

Abdominal reflex
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 breathing, digestion, and the maintenance of the heartbeat can also be regarded as reflex actions, according to some definitions of the term.

References

↑ Purves (2004). Neuroscience: Third Edition. Massachusetts, Sinauer Associates, Inc.
↑ Human Benchmark: Reaction Time Statistics. URL accessed on 2007-10-11.
↑ Neurologic Exam

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[1] Purves (2004). Neuroscience: Third Edition. Massachusetts, Sinauer Associates, Inc.

[2] Human Benchmark: Reaction Time Statistics. URL accessed on 2007-10-11.

[3] Neurologic Exam

[1]

[2]

[3]

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 {{ExpPsy}}
+A '''reflex action''' is an automatic (otherwise called involuntary) neuromuscular action elicited by a defined [[stimulus (physiology)|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'.)
-[[Image:ReflexArc1.jpg|right|thumb|500px|The mechanism of the [[reflex arc]]]]
+==Mechanism==
-A '''reflex action''' is an automatic (involuntary) neuromuscular action elicited by a defined [[stimulus (physiology)|stimulus]]. {{fn|1}}  A reflex action is mediated via the [[reflex arc]].
+A '''reflex action''' or '''reflex''' is a biological [[control system]] linking [[stimulation|stimulus]] to [[response]] and mediated by a [[reflex arc]].  Reflexes can be ''built-in'' or ''learnt''. For example, a person stepping on a sharp object would initiate the reflex action through the creation of a [[Pain and nociception|nociceptive]] [[Stimulus (physiology)|stimulus]] within specialized sense receptors located in the skin tissue of the foot.  The resulting stimulus would be transmitted through an [[afferent nerve]] to the [[spinal cord]].  This stimulus is usually processed by an [[interneuron]] to create an immediate response to nociception by initiating a [[Muscular contraction|motor response]] to withdraw from the pain-producing object. This retraction would occur as the sensation is arriving in the brain and producing the subjective perception of pain, which would result in a more [[cognitive]] evaluation of the situation.
+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]].
-==Explanation==
+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]].
-A '''reflex action''' or '''reflex''' is a biological control system linking [[stimulation|stimulus]] to response and mediated by a [[reflex arc]].  Reflexes can be ''built-in'' or ''learned''. It occurs very quickly before thinking.  Before the message is sent to the brain, the [[spinal cord]] senses the sensory [[stimulus]], and sends a signal ([[action potential]]) to an effector organ, (muscle) to create an immediate action to counter the stimulus. For example, a person stepping on a sharp object would initiate the reflex action through the creation of a stimulus, (pain) within specialized sense receptors located in the skin tissue of the foot. The resulting stimulus would be transmitted through [[afferent nerve|afferent]], or [[sensory neuron]]s and processed at the lower end of the [[spinal cord]], part of the [[central nervous system]]. This stimulus is processed by an [[interneuron]] to create an immediate response to pain by initiating a motor (muscular) response which is acted upon by muscles of the leg, retracting the foot away from the object. This activity would occur as the pain is arriving in the brain which would process a more [[cognitive]] evaluation of the situation.
-===Simple reflex===
+==Reaction time==
-A simple reflex is entirely automatic and involves no learning.
+For a reflex, [[reaction time]] or latency is the time from the onset of a stimulus until the [[organism]] responds.
+In [[human]]s, reaction time to [[Vision|visual]] stimuli is typically 150 to 300 milliseconds.<ref>{{cite web | url = http://www.humanbenchmark.com/tests/reactiontime/stats.php | accessdate = 2007-10-11 | title = Human Benchmark: Reaction Time Statistics }}</ref>
-An example is the [[escape reflex]] (e.g., the sudden withdrawal of a hand in response to a [[painful|pain]] stimulus), or the [[patellar reflex]] (the jerking of a leg when the kneecap is tapped). Sensory cells (receptors) in the stimulated body part send signals to the [[spinal cord]] along a sensory [[nerve cell]]. Within the spine a [[reflex arc]] switches the signals straight back to the muscles of the body (in this case the arm or the leg) (effectors) via an intermediate nerve cell and then a motor nerve cell; contraction of the leg occurs, and the muscle contracts (the arm or leg jerks upwards). Only three nerve cells are involved, and the [[brain]] is only aware of the response after it has taken place. Such reflex arcs are particularly common in animals, and have a high survival value, enabling organisms to take rapid action to avoid potential danger.
+==Human reflexes==
-===Conditioned reflex===
+{{Main|List of reflexes}}
-A conditioned reflex involves the modification of a reflex action in response to experience (learning). A stimulus that produces a simple reflex response becomes linked with another, possibly unrelated, stimulus. For example, a dog may salivate (a reflex action) when it sees its owner remove a tin-opener from a drawer because it has learned to associate that stimulus with the stimulus of being fed.
+[[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.]]
-===Reaction time===
+Reflex actions include:
-For a reflex, [[reaction time]] or latency is the time from the onset of a stimulus until the [[organism]] responds.
-==Human reflexes==
+===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]])
-Reflex actions seen in adult [[human]]s include:
+* [[Brachioradialis reflex]] (C5, C6, [[cervical spinal nerve 7|C7]])
-* [[Accommodation reflex]]
-* [[Achilles reflex]]
+* [[Extensor digitorum reflex]] (C6, C7)
+* [[Triceps reflex]] (C6, C7, [[cervical spinal nerve 8|C8]])
-* [[Anal wink|Anocutaneous reflex]]
+* [[Patellar reflex]] or knee-jerk reflex ([[lumbar spinal nerve 2|L2]], [[lumbar spinal nerve 3|L3]], [[lumbar spinal nerve 4|L4]])
-* [[Babinski reflex]]
+* [[Ankle jerk reflex]] (Achilles reflex) ([[sacral spinal nerve 1|S1]], [[sacral spinal nerve 2|S2]])
-* [[Biceps stretch reflex]]
+* [[Plantar reflex]] or Babinski reflex ([[lumbar spinal nerve 5|L5]], S1, S2)
-* [[Brachioradialis reflex]]
-* [[Corneal reflex]]
-* [[Crossed extensor reflex]]
-* [[Mammalian diving reflex]]
-* [[Gag reflex]]
-* [[Gastroc-Soleus reflex]]
-* [[H-reflex]]
-* [[Patellar reflex]] ([[knee-jerk reflex]])
-* [[Photic sneeze reflex]]
-* [[Pupillary reflex]]
-* [[Quadriceps reflex]]
-* [[Salivation]]
-* [[Scratch reflex]]
-* [[Sneeze]]
-* [[Tendon reflex]]
-* [[Triceps stretch reflex]]
-* [[Vestibulo-ocular reflex]]
-* [[Withdrawal reflex]]
+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.
-Processes such as [[breathing]], [[digestion]] and the maintenance of the [[Heart rate|heartbeat]] can also be regarded as reflex actions, according to some definitions of the term.
+===Reflexes involving cranial nerves===
-[[Newborn babies]] have a number of other reflexes which are not seen in adults, including:
-* [[suckling]]
+{| class="wikitable"
-* [[hand-to-mouth reflex]]
+| '''Name''' || '''Sensory''' || '''Motor'''
-* [[Moro reflex]], also known as the startle reflex
+ |-
-* [[grasp reflex]]
+ | [[Pupillary light 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 Neurologic Exam<!-- Bot generated title -->]</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===
-==Significance==
+Other reflexes found in the human nervous system include:
-The deep tendon reflexes 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.
+* [[Abdominal reflex]]
+* [[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==
-*[[Automatism]]
+*[[Automatic behavior]]
-*[[Automatism (case law)]]
+*[[Central pattern generators]]
+*[[Instinctive behavior]]
-*[[Autonomic nervous system]]
+*[[List of reflexes (alphabetical)]]
-*[[Sensory system]]
+*[[Muscle contractions]]
-*[[Spinal nociceptive reflex]]
+*[[Parkinsonism]]
-*[[Tonic vibration reflex]]
+*[[Preflexes]]
-*[[Unconditioned reflex]]
+*[[Taxis]]
+*[[Tropism]]
 *[[Voluntary action]]
-==External links==
+==References==
+{{reflist}}
-*[http://www.fpnotebook.com/NIC27.htm Reflexes in newborn babies]
+{{Nervous system physiology}}
-==References==
+{{Reflex}}
-{{fnb|1}} Purves (2004). ''Neuroscience: Third Edition''. Massachusetts, Sinauer Associates, Inc.
 [[Category:Reflexes]]
+[[Category:Animal physiology]]
+[[Category:Physiology]]
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