The Info List - Reflex

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A reflex, or reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus.[1][2] A reflex is made possible by neural pathways called reflex arcs which can act on an impulse before that impulse reaches the brain. The reflex is then an automatic response to a stimulus that does not receive or need conscious thought.[3]


1 Human reflexes

1.1 Tendon reflex 1.2 Reflexes involving cranial nerves 1.3 Reflexes usually only observed in human infants 1.4 Other reflexes 1.5 Grading

2 See also 3 References

Human reflexes[edit] Myotatic reflexes The myotatic reflexes (also known as deep tendon reflexes), provide information on the integrity of the central nervous system and peripheral nervous system. Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.[citation needed] A stretch reflex is the contraction of a muscle in response to its lengthwise stretch.[4]

Biceps reflex (C5, C6) Brachioradialis reflex (C5, C6, C7) Extensor digitorum reflex (C6, C7) Triceps reflex (C6, C7, C8) Patellar reflex
Patellar reflex
or knee-jerk reflex (L2, L3, L4) Ankle jerk reflex (Achilles reflex) (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 to vibration. Tendon reflex[edit] A tendon reflex is the contraction of a muscle in response to striking its tendon.[4] The Golgi tendon reflex is the inverse of a stretch reflex. Reflexes involving cranial nerves[edit]

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

Glabellar reflex V VII

Vestibulo-ocular reflex VIII III, IV, VI +

Gag reflex IX X

Reflexes usually only observed in human infants[edit] Main article: Primitive reflexes

Grasp reflex

Newborn babies
Newborn babies
have a number of other reflexes which are not seen in adults, referred to as primitive reflexes.[5] These automatic reactions to stimuli enable infants to respond to the environment before any learning has taken place. They include:

Asymmetrical tonic neck reflex
Asymmetrical tonic neck reflex
(ATNR) Palmomental reflex Moro reflex, also known as the startle reflex Palmar grasp reflex Rooting reflex Sucking reflex Symmetrical tonic neck reflex (STNR) Tonic labyrinthine reflex (TLR)

Other reflexes[edit] Other reflexes found in the central nervous system include:

Abdominal reflexes (T6-L1)

Gastrocolic reflex

Anocutaneous reflex (S2-S4) Baroreflex Cough reflex Cremasteric reflex
Cremasteric reflex
(L1-L2) Diving reflex Muscular defense Photic sneeze reflex Scratch reflex Sneeze 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 (e.g., 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. Grading[edit] In medicine, reflexes are often used to assess the health of the nervous system. Doctors will typically grade the activity of a reflex on a scale from 0 to 4.[6] 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+.

Grade Description

0 Absent

1+ or + Hypoactive

2+ or ++ "Normal"

3+ or +++ Hyperactive without clonus

4+ or ++++ Hyperactive with clonus

See also[edit]

List of reflexes (alphabetical) All-or-none law Automatic behavior Conditioned reflex Instinct Jumping Frenchmen of Maine Voluntary action Preflexes


^ Purves (2004). Neuroscience: Third Edition. Massachusetts, Sinauer Associates, Inc. ^ "Definition of REFLEX". www.merriam-webster.com.  ^ "tendon reflex". TheFreeDictionary.com.  ^ a b "tendon reflex". TheFreeDictionary.com.  ^ Neurologic Exam ^ University of Florida > Neurologic Examination Retrieved on May 9, 2009

v t e

Physiology of the nervous system

Primarily CNS



Intracranial pressure Lateralization of brain function Sleep Memory

Primarily PNS

Reflex Sensation


Evoked potential

Bereitschaftspotential P300 Auditory evoked potential Somatosensory evoked potentials Visual evoked potential

Other short term

Neurotransmission Chronaxie Membrane potential Action potential Postsynaptic potential

Excitatory Inhibitory

Long term

Axoplasmic transport Neuroregeneration/Nerve regeneration Neuroplasticity/Synaptic plasticity

Long-term potentiation Long-term depression



v t e

Nervous system
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

Stretch reflexes

upper limb: Biceps reflex C5/C6 Brachioradialis reflex C6 Triceps reflex C7/C8 lower limb: Patellar reflex
Patellar reflex
L2-L4 Ankle jerk reflex S1/S2 Plantar reflex
Plantar reflex

Primitive reflexes

Galant Gastrocolic Grasp Moro Rooting Stepping Sucking Tonic neck Parachute

Superficial reflexes

Abdominal reflex Cremasteric reflex


general alphabetical by organ


Bainbridge reflex Bezold–Jarisch reflex Coronary reflex Diving reflex Oculocardiac reflex


bradycardia Reflex


Churchill–Cope reflex


Acoustic reflex H-reflex Golgi tendon reflex Optokinetic Startle response Withdrawal reflex (Crossed extensor reflex) Symmetrical