Akademik

1. A stimulant. 2. That which can elicit or evoke action (response) in a muscle, nerve, gland or other excitable tissue, or cause an augmenting action upon any function or metabolic process. [L. a goad]

- adequate s. a s. to which a particular receptor responds effectively and that gives rise to a characteristic sensation; e.g., light and sound waves that stimulate, respectively, visual and auditory receptors.

- aversive s. a noxious s. such as an electric shock used in aversive training or conditioning. SEE ALSO: aversive training.

- conditioned s. 1. a s. applied to one of the sense organs ( e.g., receptors of vision, hearing, touch) which are an essential and integral part of the neural mechanism underlying a conditioned reflex; See classical conditioning, higher order conditioning. 2. a neutral s., when paired with the unconditioned s. in simultaneous presentation to an organism, capable of eliciting a given response.

- discriminant s. a s. which can be differentiated from all other stimuli in the environment because it has been, and continues to serve as, an indicator of a potential reinforcer.

- heterologous s. a s. that acts upon any part of the sensory apparatus or nerve tract.

- heterotopic s. any electrical activation from an abnormal locus.

- homologous s. a s. that acts only on the nerve terminations in a special sense organ.

- inadequate s. SYN: subthreshold s..

- liminal s. SYN: threshold s..

- maximal s. a s. strong enough to evoke a maximal response.

- square wave stimuli electrical stimulation in which the intensity of the current is brought suddenly to a given level and maintained at that level until it suddenly is cut off; this type of s. is particularly useful in obtaining a strength-duration curve.

- subliminal s. SYN: subthreshold s..

- subthreshold s. a s. too weak to evoke a response. SYN: inadequate s., subliminal s..

- supramaximal s. a s. having strength significantly above that required to activate all of the nerve or muscle fibers in contact with the electrode; used when response of all the fibers is desired.

- threshold s. a s. of threshold strength, i.e., one just strong enough to excite. SEE ALSO: adequate s.. SYN: liminal s..

- train-of-four s. a method for measuring magnitude and type of neuromuscular blockade, based upon the ratio of the amplitude of the fourth evoked mechanical response to the first one, when four supramaximal 2-Hz electrical currents are applied for 2 s to a peripheral motor nerve.

- unconditioned s. a s. that elicits an unconditioned response; e.g., food is an unconditioned s. for salivation, which in turn is an unconditioned response in a hungry animal. See classical conditioning.

stim·u·lus 'stim-yə-ləs n, pl -li -.lī, -.lē

1) STIMULANT (1)

2) an agent (as an environmental change) that directly influences the activity of living protoplasm (as by exciting a sensory organ or evoking muscular contraction or glandular secretion) <a visual \stimulus>

n. (pl. stimuli)

any agent that provokes a response, or particular form of activity, in a cell, tissue, or other structure, which is said to be sensitive to that stimulus.