Reflex

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For other uses, see Reflex (disambiguation).

A reflex action, differently known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.[1] Scientific use of the term "reflex" refers to a behavior that is mediated via the reflex arc; this does not apply to casual uses of the term "reflex".

Contents

  • 1 Human reflexes
    • 1.1 Stretch reflexes
    • 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[]

Stretch reflexes[]

The stretch reflexes (often called deep tendon reflexes, though not to be confused with Golgi 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.

  • 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)

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.

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
Glabellar reflex V VII
Vestibulo-ocular reflex VIII III, IV, VI +
Gag reflex IX X

Reflexes usually only observed in human infants[]

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.[2] 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)
  • Hand-to-mouth reflex[citation needed]
  • 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[]

Other reflexes found in the central nervous system include:

  • Abdominal reflexes (T6-L1)
    • Gastrocolic reflex
  • Anocutaneous reflex (S2-S4)
  • Cremasteric reflex (L1-L2)
  • 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 (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[]

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.[3] 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
2+ or ++ "Normal"
3+ or +++ Hyperactive without clonus
4+ or ++++ Hyperactive with clonus

See also[]

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

References[]

  1. ^ Purves (2004). Neuroscience: Third ion. Massachusetts, Sinauer Associates, Inc.
  2. ^ Neurologic Exam
  3. ^ University of Florida > Neurologic Examination Retrieved on May 9, 2009
  • v
  • t
  • 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
  • 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
Other
  • Myelinogenesis

M: CNS

anat (n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco (m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug (N1A/2AB/C/3/4/7A/B/C/D)

M: PNS

anat (h/r/t/c/b/l/s/a)/phys (r)/devp/prot/nttr/nttm/ntrp

noco/auto/cong/tumr, sysi/epon, injr

proc, drug (N1B)

  • v
  • t
  • 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
Stretch reflexes
  • upper limb: Biceps reflex C5/C6
  • Brachioradialis reflex C6
  • Triceps reflex C7/C8
    lower limb: Patellar reflex L2-L4
  • Ankle jerk reflex S1/S2
  • Plantar reflex L5-S2
Primitive reflexes
  • Galant
  • Gastrocolic
  • Grasp
  • Moro
  • Rooting
  • Stepping
  • Sucking
  • Tonic neck
  • Parachute
Superficial reflexes
  • Abdominal reflex
  • Cremasteric reflex
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
  • Golgi tendon reflex
  • Optokinetic
  • Startle reaction
  • Withdrawal reflex (Crossed extensor reflex)

M: PNS

anat (h/r/t/c/b/l/s/a)/phys (r)/devp/prot/nttr/nttm/ntrp

noco/auto/cong/tumr, sysi/epon, injr

proc, drug (N1B)

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