A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.^[1] In most contexts, in particular those involving humans, reflex actions are mediated via the reflex arc; this is not always true in other animals, nor does it apply to casual uses of the term 'reflex'.

Contents 1 Reaction time 2 Human reflexes 2.1 Tendon reflexes 2.2 Reflexes involving cranial nerves 2.3 Reflexes usually only observed in human infants 2.4 Other reflexes 2.5 Grading 3 See also 4 References

[edit] 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 stimuli is typically 150 to 300 milliseconds.^[2]

[edit] Human reflexes

[edit] 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.

[edit] 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

[edit] Reflexes usually only observed in human infants

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)

[edit] Other reflexes

Other reflexes found in the central nervous system include:

• Anocutaneous reflex
• Bulbocavernosus reflex
• Escape reflex
• Oculocardiac reflex
• Optokinetic reflex
• Photic sneeze reflex
• Mammalian diving reflex
• Muscular defense
• Scratch reflex
• 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 CNS (e.g., the escape reflex). Others of these involve just a couple of synapses to function (eg., the withdrawal reflex). 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.

[edit] Grading

The activity of a reflex is usually graded on a scale from 0 to 4:^[4]

Grade	Description
0	Absent
1+ or +	Hypoactive
2+ or ++	"Normal"
3+ or +++	Hyperactive without clonus
4+ or ++++	Hyperactive with clonus

[edit] See also

• List of reflexes (alphabetical)
• All-or-none law
• Automatic behavior
• Involuntary action
• Voluntary action
• Preflexes

[edit] References

v • d • e Nervous system physiology: neurophysiology / clinical neurophysiology Primarily CNS Arousal (Wakefulness) · Intracranial pressure · Lateralization of brain function · Sleep · Memory Primarily PNS Reflex · Sensation Both Evoked potential Bereitschaftspotential · P300 · Auditory evoked potential · Somatosensory evoked potentials · Somatosensory evoked potentials · Visual evoked potential Other short term Neurotransmission · Chronaxie · Membrane potential · Action potential · Postsynaptic potential (Excitatory, Inhibitory) Long term Axoplasmic transport · Nerve regeneration · Neuroplasticity/Synaptic plasticity (Long-term potentiation, Long-term depression) central nervous system navs: anat/physio/dev, noncongen/congen/neoplasia, symptoms+signs/eponymous, proc peripheral nervous system navs: anat/histo/physio/dev, noncongen PNS somatic/autonomic/congen/neoplasia, symptoms+signs/eponymous, proc

v • d • e Nervous system physiology: neurophysiology - reflex Cranial nerve midbrain: Pupillary light reflex · Accommodation reflex pons/medulla: Jaw jerk reflex · Corneal reflex · Caloric reflex test/Vestibulo-ocular reflex/Oculocephalic reflex · Pharyngeal (gag) reflex Tendon reflexes upper limb: Biceps reflex C5/C6 · Brachioradialis reflex C6 · Extensor digitorum reflex C6/C7 · Triceps reflex C7/C8 lower limb: Patellar reflex L2-L4 · Ankle jerk reflex S1/S2 · Plantar reflex Primitive reflexes Galant · Gastrocolic · Grasp · Moro · Rooting · Stepping · Sucking · Tonic neck Lists general · alphabetical · by organ Cardiovascular Bainbridge reflex · Bezold-Jarisch reflex  · Coronary reflex  · Mammalian diving reflex  · Oculocardiac reflex Baroreflex Reflex bradycardia  · Reflex Tachycardia Respiratory Churchill-Cope reflex Other Acoustic reflex · H-reflex · Stretch reflex · Golgi tendon reflex · Optokinetic · Startle reaction · Withdrawal reflex (Crossed extensor reflex)