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(ak-tig′ră-fē) [acti(vity) + -graphy] The monitoring of body movements with a small device usually attached to the wrist or foot, used in sleep medicine (and sometimes in anesthesia or critical care medicine) to determine whether and how well a person is resting or sleeping. In sleep medicine, actigraphy can aid in the diagnosis of insomnia, obstructive sleep apnea, and periodic limb movements. It is used in anesthesia to determine depth of sedation, e.g., during recovery from surgery.


(ak′tĭn) [act + -in] One of the contractile proteins that make up the sarcomeres of muscle tissue. During contraction, the actin filaments are pulled toward the center of the sarcomere by the action of myosin filaments, and the sarcomere shortens. Actin is also found in the cytoskeleton of many kinds of cells, where it contributes to cell shape and movement.

filamentous a. The polymerized form of actin.

globular a. The monomeric form of actin.

acting out

Expressing oneself through actions rather than speech.

neurotic a.o. 1. A form of transference in which tension is relieved when one responds to a situation as if it were the same situation that originally gave rise to the tension. It is a displacement of behavioral response from one situation to another. 2. In psychoanalysis, a form of displacement in which the patient relives memories rather than expressing them verbally.


(ak-tin′ik) [Gr. aktis, ray] 1. Pert. to radiant energy, such as x-rays, ultraviolet light, and sunlight, esp. the photochemical effects. 2. Pert. to the ability of radiant energy to produce chemical changes. actinically (-i-k(ă)lē), adv.


(ak′tĭ-nīd″) [actin- + -ide] Any of the radioactive heavy metals designated on the periodic table of elements with atomic numbers 89–103. The actinides include naturally occurring elements, e.g., actinium and uranium, and artificial elements, e.g., fermium.


(ak″tĭ-nid′ē-ă) SEE: kiwifruit.


(ak′tĭ-nĭzm) [actin- + -ism] The property of radiant energy that produces chemical changes, as in photography or heliotherapy.


(ak-tin′ē-ŭm) [actin- + -ium] SYMB: Ac. A radioactive element, atomic mass (weight) (most stable isotope) 227, atomic number 89.

actino-, actin-

[Gr. aktis, stem aktin-, ray] 1. Prefixes meaning ray or radiation. 2. Prefixes meaning having a radiating structure, e.g., Actinomyces.


(ak″tĭ-nō″bă-sil′ŭs) [actino- + bacillus] A genus of aerobic gram-negative coccobacilli that are parasites of hoofed mammals, and, rarely, of humans. The now-preferred but less common name is Aggregatibacter. SEE: Aggregatibacter. SEE: ...

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