A reflex action is involuntary and almost instant movement in response to 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'. A reflex arc is the Neural pathway that mediates a Reflex action. )

Reflexes are tested as part of a neurological examination to assess damage to or functioning of the central and peripheral nervous system. A neurological examination is the assessment of sensory neuron and motor responses especially Reflexes to determine whether the Nervous system In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. The peripheral nervous system ( PNS) resides or extends outside the Central nervous system (CNS which consists of the Brain and Spinal cord.

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. &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control Classical Conditioning (also Pavlovian or Respondent Conditioning) is a form of Associative learning that was first demonstrated by Ivan Pavlov

Reaction time

For a reflex, reaction time or latency is the time from the onset of a stimulus until the organism responds. Reaction time (RT is the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response

In humans, reaction time to visual stimuli is typically 150 to 300 milliseconds. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus VisiCorp 's VisiOn was a short-lived but influential Graphical user interface -based Operating environment program for IBM PC compatible A millisecond (from Milli- and Second; abbreviation ms is one thousandth of a Second. ^[2]

Human reflexes

The mechanism of the reflex arc. A reflex arc is the Neural pathway that mediates a Reflex action. Note that this image includes an interneuron in the monosynaptic patellar reflex for purposes of illustration. An interneuron (also called association neuron, local circuit neuron or relay neuron) is a neuron which connects Afferent neurons and Efferent The patellar reflex or knee-jerk is a Stretch reflex and is a Myotatic reflex.

Reflex actions include:

Tendon reflexes

The deep tendon reflexes provide information on the integrity of the central and peripheral nervous system. Tendon reflex (or T-reflex) is a feedback mechanism that controls increasing muscle tension by causing muscle relaxation before tension force becomes so great it may damage the 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. A reflex test that examines the function of the C5 reflex arc and to a lesser degree the C6 reflex arc The cervical spinal nerve 5 (C5 is a Spinal nerve of the Cervical segment. The cervical spinal nerve 6 (C6 is a Spinal nerve of the Cervical segment. The brachioradialis reflex is observed during a Neurological exam by striking the Brachioradialis tendon directly with a hammer when the patient's arm is resting. The cervical spinal nerve 7 (C7 is a Spinal nerve of the Cervical segment. The Extensor digitorum reflex is tested as part of the Neurological examination to asses the sensory and motor pathways within the C6 and C7 Spinal nerves. The triceps reflex, a deep tendon reflex, is a reflex as it elicits Involuntary contraction of the Triceps brachii muscle. The cervical spinal nerve 8 (C8 is a Spinal nerve of the Cervical segment. The patellar reflex or knee-jerk is a Stretch reflex and is a Myotatic reflex. The lumbar spinal nerve 2 (L2 is a Spinal nerve of the Lumbar segment. The lumbar spinal nerve 3 (L3 is a Spinal nerve of the Lumbar segment. The lumbar spinal nerve 4 (L4 is a Spinal nerve of the Lumbar segment. The ankle jerk reflex, also known as the Achilles reflex, occurs when the Achilles tendon is tapped while the foot is dorsi-flexed. The sacral spinal nerve 1 (S1 is a Spinal nerve of the Sacral segment. The sacral spinal nerve 2 (S2 is a Spinal nerve of the Sacral segment. In Medicine and Neurology, the Babinski response to the plantar reflex is a Reflex, named after Joseph Babinski ( 1857 - 1932) (a French The lumbar spinal nerve 5 (L5 is a Spinal nerve of the Lumbar segment. The H-reflex is a Reflectory reaction of muscles after Electrical stimulation of sensory fibers ( Ia afferents stemming from Muscle spindles) Tonic vibration reflex is a sustained contraction of a Muscle subjected to vibration

Reflexes involving cranial nerves

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. The accommodation reflex is a Reflex action of the Eye, in response to focusing on a near object then looking at distant object (and Vice versa The jaw jerk reflex is a reflex used to test the status of a patient's Trigeminal nerve (CN V The corneal reflex, also known as the blink reflex, is an involuntary Blinking of the Eyelids elicited by stimulation (such as touching or a foreign body Blinking, known less commonly as nictating, is the rapid closing and opening of the Eyelid. In Medicine, the caloric reflex test is a test of the Vestibulo-ocular reflex. The vestibulo-ocular reflex ( VOR) or oculovestibular reflex is a Reflex Eye movement that stabilizes images on the Retina during The pharyngeal reflex or gag reflex is a Reflex contraction of the back of the throat evoked by touching the Soft palate, that prevents something from Primitive reflexes are Reflex actions originating in the Central nervous system that are exhibited by normal infants but not neurologically intact adults in response ^[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:

• Anocutaneous 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. The asymmetrical tonic neck reflex ( ATNR) is a Primitive reflex found in newborn humans but normally vanishes by the child's first birthday Primitive reflexes are Reflex actions originating in the Central nervous system that are exhibited by normal infants but not neurologically intact adults in response The pharyngeal reflex or gag reflex is a Reflex contraction of the back of the throat evoked by touching the Soft palate, that prevents something from The Moro reflex, also known as the startle reflex, is one of the Infantile reflexes It may be observed in incomplete form in Premature birth after Suction is the flow of a fluid into a partial Vacuum, or region of low pressure The tonic labyrinthine reflex ( TLR) is a Primitive reflex found in newborn humans The anal wink, anal reflex, perineal reflex, or anocutaneous reflex is the Reflexive contraction of the external Anal sphincter upon Escape reflex, a kind of Escape response, is a simple Reflectory reaction in response to stimuli indicative of danger that initiates an escape motion of The mammalian diving reflex optimizes Mammals Respiration to stay underwater for a long time The oculocardiac reflex, also known as Aschner phenomenon, Aschner reflex, or Aschner-Dagnini reflex, is a decrease in Pulse rate associated The optokinetic reflex allows the Eye to follow objects in motion when the head remains stationary (e Photic sneeze reflex is a genetic Autosomal dominant trait which causes sneezing when exposed suddenly to bright light possibly many times consecutively The scratch reflex is a reflex transmitted by very sensitive nerve endings near the surface of the Skin via the Spinal cord, and is a reflex frequently The nociceptive withdrawal reflex (NWR is a Spinal reflex intended to protect the body from damaging stimuli The crossed extensor reflex is a Withdrawal reflex. When the reflex occurs the Flexors in the withdrawing limb contract and the Extensors relax while Muscular defense is a reflex of the Abdominal muscles to contract upon mechanical force to the Abdomen, and serves as protection Breathing takes Oxygen in and Carbon dioxide out of the body Aerobic Organisms require oxygen to create energy via respiration, in Digestion is the breaking down of chemicals in the body into a form that can be absorbed Measuring heart rate The Pulse rate (which in most people is identical to the heart rate can be measured at any point on the body where an Artery 's pulsation

See also

• Automatic behavior
• Voluntary action

References