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any substance that causes an increase in activity in various parts of the nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
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 or directly increases muscle activity. Cerebral, or psychic, stimulants act on the central nervous system and provide a temporary sense of alertness and well-being as well as relief from fatigue. Drugs such as caffeinecaffeine
, odorless, slightly bitter alkaloid found in coffee, tea, kola nuts (see cola), ilex plants (the source of the Latin American drink maté), and, in small amounts, in cocoa (see cacao). It can also be prepared synthetically from uric acid.
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 and the amphetaminesamphetamine
, any one of a group of drugs that are powerful central nervous system stimulants. Amphetamines have stimulating effects opposite to the effects of depressants such as alcohol, narcotics, and barbiturates.
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 belong in this category, and several groups of drugs chemically similar to antihistaminesantihistamine
, any one of a group of compounds having various chemical structures and characterized by the ability to antagonize the effects of histamine. Their principal use in medicine is in the control of allergies such as hay fever and hives.
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 and phenothiazinesphenothiazine
, any one of a class of drugs used to control mental disorders. Phenothiazines, along with other antipsychotic, or neuroleptic, drugs are used for such disorders as schizophrenia, paranoia, mania, psychosis resulting from mental deficiency, some forms of senility,
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 also act as mild psychic stimulants (see psychopharmacologypsychopharmacology
, in its broadest sense, the study of all pharmacological agents that affect mental and emotional functions. The term is usually applied more specifically to the study and synthesis of drugs used in the control of psychiatric illnesses, namely the
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). Cocainecocaine
, alkaloid drug derived from the leaves of the coca shrub. A commonly abused illegal drug, cocaine has limited medical uses, most often in surgical applications that take advantage of the fact that, in addition to its anesthetic effect, it constricts small arteries,
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, besides its effect as a local anesthetic, also stimulates the central nervous system, producing excitement and erratic behavior. The hallucinogenic drugshallucinogenic drug
, any of a group of substances that alter consciousness; also called psychotomimetic (i.e., mimicking psychosis), mind-expanding, or psychedelic drug.
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 are also central nervous system stimulants.

A second class of stimulants that affect the medulla and spinal cord includes derivatives of niacinamide (nicotinic acid amide) and other chemically diverse compounds; they are sometimes used to speed the return to wakefulness after anesthesiaanesthesia
[Gr.,=insensibility], loss of sensation, especially that of pain, induced by drugs, especially as a means of facilitating safe surgical procedures. Early modern medical anesthesia dates to experiments with nitrous oxide (laughing gas) by Sir Humphry Davy of England
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 or to counteract barbiturate poisoning. Ammonia, in smelling salts, is also a medullary stimulant; the alkaloid strychnine is a spinal-cord stimulant.

Other substances act mainly on the autonomic nervous system. Drugs that stimulate the parasympathetic portion of the autonomic nervous system, such as pilocarpinepilocarpine
, naturally occurring alkaloid obtained from plants of the genus Pilocarpus (family Rutaceae). By mimicking the effects of acetylcholine, pilocarpine acts as a stimulant of the parasympathetic nervous system.
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, physostigmine, and neostigmineneostigmine
, drug used to mimic the effects of stimulation of the parasympathetic nervous system. Along with several other drugs that have a similar mode of action, it inhibits the action of the enzyme cholinesterase, which destroys the substance acetylcholine at nerve endings.
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, cause contracted pupils, salivation and sweating, slowed heartbeat, and lowered blood pressure. Drugs such as norepinephrine, epinephrineepinephrine
, hormone important to the body's metabolism, also known as adrenaline. Epinephrine, a catecholamine, together with norepinephrine, is secreted principally by the medulla of the adrenal gland.
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, and other catecholaminescatecholamine
, any of several compounds occurring naturally in the body that serve as hormones or as neurotransmitters in the sympathetic nervous system. The catecholamines include such compounds as epinephrine, or adrenaline, norepinephrine, and dopamine.
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 and synthetic analogs stimulate the sympathetic portion of the autonomic nervous system, resulting in dilated pupils, rapid heartbeat, and increased blood pressure. Because the sympathetic and parasympathetic systems have opposing physiological effects, stimulation of one system amounts to depression of the other. Some of the alkaloids from the ergotergot
, disease of rye and other cereals caused by the fungus Claviceps purpurea. The cottony, matlike body, or mycelium, of the fungus develops in the ovaries of the host plant; it eventually turns into a hard pink or purple body, the sclerotium, or ergot, that resembles
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 fungus act by direct stimulation of smooth muscle, inducing contractions in uterine and intestinal muscle.



a medicinal preparation used therapeutically to stimulate the sensory nerve endings of the skin and mucosa. The group of stimulants includes substances that are different in origin and chemical structure, for example, ammonia water and such volatile oils as oil of mustard, camphor, menthol, and oil of turpentine.

Stimulants are rubbed into or applied to the skin to weaken the inflammatory process in myositis, neuritis, and arthralgia. Bitters such as tincture of wormwood (absinthium tincture) and centaury are taken orally to stimulate the appetite. The receptors of the oral cavity perceive the sensation of the bitter taste of bitters, which induces a reflex intensification of the excitability of the feeding center and a subsequent increase in appetite. Steam from ammonia water irritates the sensory receptors of nasal mucosa, which causes a reflex intensification of the tone of the respiratory and vasomotor centers.


Anichkov, S. V., and M. L. Belen’kii. Uchebnik farmakologii, 2nd ed. Leningrad, 1968.
Mashkovskii, M. D. Lekarstvennye sredstva, parts 1–2, 7th ed. Moscow, 1972.



A drug or agent that temporarily acts on muscles, nerves, or a sensory end organ, producing an increase in its state of activity.


1. a drug or similar substance that increases physiological activity, esp of a particular organ
2. increasing physiological activity; stimulating
References in periodicals archive ?
The experiment in this report provided evidence of protection from extinction in a conditioned taste aversion preparation by performing extinction treatment with the target CS (S) conjointly with a second CS (A), consisting of either an excitor (group 0A-2AS) or an extensively extinguished CS (group 10A-2AS).
2007), the finding that an excitor (group 0A-2AS) can protect the target CS from extinction can be interpreted as indicative of a putative second-order conditioning process.
By contrast, presenting an excitor (A) during extinction treatment with CS S should increase the expectation of the absent US (i.
Furthermore, if a moderate amount of extinction treatment with CS A (group 5A-2AS) resulted in this CS being neither a strong excitor nora strong inhibitor prior to compound treatment (i.
observed that the joint nonreinforced presentation of two excitors protected the target CS from extinction (also see Lovibond et al.
An analysis of sucrose consumption (the known excitor for the subsequent summation test) on the conditioning trial revealed no group differences (F < 1).
This figure shows that the groups did not differ in the amount they consumed of the test excitor B, and that both groups drank more of the compound than of the test excitor presented alone.
Moreover, in order to properly evaluate the possible contribution of generalization decrement, the present experiment included test conditions in which the subjects received the test excitor in compound with either a familiar CS (that is, the previously extinguished of pre-exposed flavor) or a novel, nonfamiliar flavor.
Finally, the test phase explored the effects of compounding the excitor B independently with A, the extinguished or preexposed flavor, and with C, the novel flavor.
On the first day, hall of the animals on each group received the test excitor presented in compound with the familiar flavor (BA), while the remaining subjects had access to the excitor in compound with the novel flavor (BC).