A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it elicits or influences a reflex via stimulus transduction. A stimulus is often the first component of a homeostatic.[1] In most contexts, in particular those involving humans, reflex actions are mediated via the reflex arc A reflex arc is the neural pathway that mediates a reflex action. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the; this is not always true in other animals, nor does it apply to casual uses of the term 'reflex'.
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Reaction time
For a reflex, reaction time Reaction time is the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response. RT is often used in experimental psychology to measure the duration of mental operations, an area of research known as mental chronometry. In psychometric psychology it is considered to be an index of speed of processing. That or latency is the time from the onset of a stimulus until the organism In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole. An organism may either be unicellular (single-celled) or be composed of, as in humans, many trillions of cells grouped into responds.
In animals Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also, reaction time to visual Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision . The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in stimuli is typically 150 to 300 milliseconds A millisecond is a thousandth (1/1,000) of a second.[2]
Human reflexes
Stretch reflexes
The stretch reflexes When muscle lengthens, the spindle is stretched and the activity increases. This increases alpha motorneuron activity. Therefore the muscle contracts and the length decreases as a result. The gamma co-activation is important in this reflex because this allows spindles in the muscles to remain taut therefore sensitive even during contraction (often called deep tendon reflexes, though not to be confused with Golgi tendon reflexes The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system. In a Golgi tendon reflex, skeletal muscle contraction causes the muscle to simultaneously lengthen and relax. This reflex is also called the inverse myotatic reflex, because it is the inverse of the stretch reflex. Though muscle tension is increasing) 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 Biceps reflex is a reflex test that examines the function of the C5 reflex arc and to a lesser degree the C6 reflex arc. The test is performed by using of a tendon hammer to quickly depress the biceps brachii tendon as it passes through the cubital fossa. Specifically, the test activates the stretch receptors inside the biceps brachii muscle which (C5 The cervical spinal nerve 5 is a spinal nerve of the cervical segment., C6 The cervical spinal nerve 6 is a spinal nerve of the cervical segment.)
- Brachioradialis reflex 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 . This reflex is caused by the C6 spinal nerve (C5, C6, C7 The cervical spinal nerve 7 is a spinal nerve of the cervical segment.)
- Extensor digitorum reflex 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. It is also known as Braunecker-Effenberg reflex, or BER (C6, C7)
- Triceps reflex The triceps reflex, a deep tendon reflex, is a reflex as it elicits involuntary contraction of the triceps brachii muscle. It is initiated by the Cervical spinal nerve 7 nerve root (the small segment of the nerve that emerges from the spinal cord). The reflex is tested as part of the neurological examination to assess the sensory and motor (C6, C7, C8 The cervical spinal nerve 8 is a spinal nerve of the cervical segment)
- Patellar reflex Striking the patellar tendon with a tendon hammer just below the patella stretches the quadriceps muscles in the thigh. This stimulates stretch sensory receptors that trigger an afferent impulse in a sensory nerve fiber of the femoral nerve leading to the lumbar region (L4) of the spinal cord. There, the sensory neuron synapses directly with a or knee-jerk reflex L2, L3, L4)
- Ankle jerk reflex The ankle jerk reflex, also known as the Achilles reflex, occurs when the Achilles tendon is tapped while the foot is dorsi-flexed. A positive result would be the jerking of the foot towards its plantar surface (Achilles reflex) (S1, S2 The sacral spinal nerve 2 is a spinal nerve of the sacral segment.)
- Plantar reflex In medicine and neurology, the Babinski response to the plantar reflex is a reflex, named after Joseph Babinski , a Polish neurologist, that can identify disease of the spinal cord and brain and also exists as a primitive reflex in infants. When non-pathological, it is called the plantar reflex, while the term Babinski's sign (or Koch's sign) or Babinski reflex (L5, S1, S2)
While the reflexes above are stimulated mechanically, the term H-reflex The H-reflex is a reflectory reaction of muscles after electrical stimulation of sensory fibers (Ia afferents stemming from muscle spindles) in their innervating nerves (for example, those located behind the knee). The H-reflex test is performed using an electric stimulator, which gives usually a square-wave current of short duration and small refers to the analogous reflex stimulated electrically, and Tonic vibration reflex Tonic vibration reflex is evoked by placing a vibrator — which in this case is typically an electrical motor with an eccentric load on its shaft — on a muscle's tendon. 30–100 Hz vibration activates receptors of the skin, tendons and, most importantly, muscle spindles. Muscle spindle discharges are sent to the spinal cord through afferent for those stimulated by vibration.
Reflexes involving cranial nerves
Reflexes usually only observed in human infants
Main article: Primitive reflexes Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants but not neurologically intact adults, in response to particular stimuli. These reflexes disappear or are inhibited by the frontal lobes as a child moves through normal child development. These primitive reflexes are also called Grasp reflexNewborn babies The term infant derives from the Latin word infans, meaning "unable to speak." It is typically applied to children between the ages of 1 month and 12 months . However, definitions vary between birth and 3 years of age have a number of other reflexes which are not seen in adults, referred to as primitive reflexes.[3] These include:
- Asymmetrical tonic neck reflex It is also known as the "fencing reflex" because of the characteristic position of the infant's arms and head, which resembles that of a classically trained fencer. When the face is turned to one side, the arm and leg on the side to which the face is turned extend and the arm and leg on the opposite side bend (ATNR)
- Grasp reflex Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants but not neurologically intact adults, in response to particular stimuli. These reflexes disappear or are inhibited by the frontal lobes as a child moves through normal child development. These primitive reflexes are also called
- Hand-to-mouth reflex
- Moro reflex 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 the 28th week of gestation, and is usually present in complete form by week 34 . It is normally present in all infants/newborns up to 4 or 5 months of age, and its absence indicates a profound disorder, also known as the startle reflex
- Rooting reflex Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants but not neurologically intact adults, in response to particular stimuli. These reflexes disappear or are inhibited by the frontal lobes as a child moves through normal child development. These primitive reflexes are also called
- Sucking
- Symmetrical tonic neck reflex (STNR)
- Tonic labyrinthine reflex The tonic labyrinthine reflex is a primitive reflex found in newborn humans. With this reflex, tilting the head back while lying on the back causes the back to stiffen and even arch backwards, causes the legs to straighten, stiffen, and push together, causes the toes to point, causes the arms to bend at the elbows and wrists, and causes the hands (TLR)
Other reflexes
Other reflexes found in the central nervous system include:
- Abdominal reflexes (T6-L1)
- Anocutaneous reflex (S2-S4)
- Cremasteric reflex (L1-L2)
- Mammalian diving reflex The mammalian diving reflex optimizes respiration which allows mammals to stay underwater for a long time. It is exhibited strongly in aquatic mammals , but exists in a weaker version in other mammals, including humans. Diving birds, such as penguins, have a similar diving reflex. Every animal's diving reflex is triggered specifically by cold
- Muscular defense Muscular defense is a reflex of the abdominal muscles to contract upon mechanical force to the abdomen, and serves as protection
- Scratch reflex The scratch reflex is a response to activation of sensory neurons whose peripheral terminals are located on the surface of the body. Some sensory neurons can be activated by stimulation with an external object such as a parasite on the body surface. Alternately, some sensory neurons can respond to a chemical stimulus that produces an itch
- Startle reflex The startle reaction, also called the startle response, startle reflex or alarm reaction, is the response of mind and body to a sudden unexpected stimulus, such as a flash of light, a loud noise , or a quick movement near the face. In human beings, the reaction includes physical movement away from the stimulus, a contraction of the muscles of the
- Withdrawal reflex The nociceptive withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli. The classic example is when a person touches something hot and withdraws their hand from the hot object. The heat stimulates temperature and pain receptors in the skin, triggering a sensory impulse that travels to the central nervous system
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 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 an animal). Others of these involve just a couple of synapses to function (eg., the withdrawal reflex The nociceptive withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli. The classic example is when a person touches something hot and withdraws their hand from the hot object. The heat stimulates temperature and pain receptors in the skin, triggering a sensory impulse that travels to the central nervous system). Processes such as breathing Breathing is the process that moves air in and out of the lungs. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose, digestion In mammals, food enters the mouth, being chewed by teeth, with chemical processing beginning with chemicals in the saliva from the salivary glands. Then it travels down the esophagus into the stomach, where hydrochloric acid kills most contaminating microorganisms and begins mechanical break down of some food , and chemical alteration of some. The, and the maintenance of the heartbeat Heart rate is the number of heartbeats per unit of time - typically expressed as beats per minute - which can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep. The measurement of heart rate is used by medical professionals to assist in the diagnosis and tracking of medical conditions. It can also be regarded as reflex actions, according to some definitions of the term.
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 Clonus is a series of involuntary muscular contractions due to sudden stretching of the muscle. Clonus is a sign of certain neurological conditions, and is particularly associated with upper motor neuron lesions such as in stroke, multiple sclerosis, spinal cord damage and hepatic encephalopathy. Unlike the small, spontaneous twitching known as |
| 4+ or ++++ | Hyperactive with clonus |
See also
- List of reflexes (alphabetical)
- All-or-none law The all-or-none law is the principle that the strength by which a nerve or muscle fiber responds to a stimulus is not dependent on the strength of the stimulus. If the stimulus is any strength above threshold, the nerve or muscle fiber will give a complete response or otherwise no response at all
- Automatic behavior
- Involuntary action
- Voluntary action
- Preflexes
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Wed, 11 Aug 2010 20:26:50 GMT+00:00
Bleacher Report ... were somewhat different from Lendl's, due to the fact Agassi is considered to have the gift of great hand-eye coordination and lightning-quick reflexes . ...
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