Reflex

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'.

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. Human reflexes are tested as part of a neurological examination to assess damage to and functioning of the central and peripheral nervous system.

Contents

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]

Human reflexes

The mechanism of the reflex arc. Note that this image includes an interneuron in the monosynaptic patellar reflex for purposes of illustration.

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.

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
Grasp reflex

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

Other reflexes

Other reflexes found in the human nervous system include:

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.

See also

References

  1. ↑ Purves (2004). Neuroscience: Third Edition. Massachusetts, Sinauer Associates, Inc.
  2. ↑ "Human Benchmark: Reaction Time Statistics". Retrieved on 2007-10-11.
  3. ↑ Neurologic Exam
Nervous system physiology: neurophysiology
Evoked potential
Bereitschaftspotential - P300 - Auditory evoked potential - Somatosensory evoked potentials - Somatosensory evoked potentials - Visual evoked potential - Excitatory postsynaptic potential
Other
Arousal (Wakefulness) - Axoplasmic transport - Intracranial pressure - Chronaxie - Lateralization of brain function - Membrane potential - Action potential - Nerve regeneration - Long-term potentiation - Reflex - Sensation - Sleep - Neurotransmission - Memory
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
Other
Baroreflex - Acoustic reflex - H-reflex - Oculocardiac reflex - Stretch reflex - Startle reaction - Optokinetic - Withdrawal reflex - Crossed extensor reflex - Golgi tendon reflex