A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.[1] A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.
Contents |
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]
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.
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...
| 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 |
| Vestibulo-ocular reflex | VIII | III, IV, VI + |
| Gag reflex | IX | X |
Newborn babies have a number of other reflexes which are not seen in adults, referred to as primitive reflexes.[3] These automatic reactions to stimuli enable infants to respond to the environment before any learning has taken place. They include:
Other reflexes found in the central nervous system include:
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 (eg., 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.
In medicine, reflexes are often used to asess the health of the central nervous system. Doctors will typically grade the activity of a reflex on a scale from 0 to 4:[4]
| Grade | Description |
| 0 | Absent |
| 1+ or + | Diminished |
| 2+ or ++ | "Normal" |
| 3+ or +++ | Hyperactive without clonus |
| 4+ or ++++ | Hyperactive with clonus |
|
|||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||