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absolute refractory period Brief time period (0.5 microsecond) following membrane depolarization during which the membrane is incapable of depolarizing again.

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absorption Energy that stimulates a particular tissue to perform its normal function.

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accommodation Adaptation by the sensory receptors to various stimuli over an extended period of time.

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ACTHAdrenocorticotropic hormone. This hormone stimulates the release of glucocorticoids (cortisol) from the adrenal glands.

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acidic reaction The accumulation of negative ions under the positive pole that produces hydrochloric acid.

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acoustic microstreaming The unidirectional movement of fluids along the boundaries of cell membranes resulting from the mechanical pressure wave in an ultrasonic field.

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action potential A recorded change in electrical potential between the inside and outside of a nerve cell, resulting in muscular contraction.

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active electrode(1) The electrode that is used to drive ions into the tissues. (2) An electrode attached directly to the skin over a muscle that picks up the electrical activity produced by a muscle contraction.

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acupressure The technique of using finger pressure over acupuncture points to decrease pain.

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acute injury An injury in which active inflammation is present that includes the classic symptoms of tenderness, swelling, redness, and so on.

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afferent (1) Conduction of a nerve impulse toward an organ. (2) Axons from neurons carrying a signal toward the spinal cord (a sensory fiber).

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air space plate A capacitor type electrode in which the plates are separated from the skin by the space in a glass case. Used with shortwave diathermy.

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alkaline reaction The accumulation of positive ions under the negative electrode that produces sodium hydroxide.

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all-or-none response The depolarization of nerve or muscle membrane is the same once a depolarizing intensity threshold is reached; further increases in intensity do not increase the response.

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alternating current Current that periodically changes its polarity or direction of flow.

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ampere Unit of measure that indicates the rate at which electrical current is flowing.

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amplitude (1) The variation in pressure found along the path of the wave in units of pressure (N/m2). (2) The intensity of current flow as indicated by the height of the waveform from baseline. (3) The size of the potential. In a sensory nerve assessment, this represents the summed action potential traveling across one point of that nerve. In a motor nerve assessment, this represents the summed action potentials traveling across the collective muscle fibers under the pickup electrode. Motor amplitudes are typically much larger than sensory action potentials.

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analgesia Loss of sensibility to pain.

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annulus fibrosus The interlacing cross-fibers of fibroelastic tissue that are attached to adjacent vertebral bodies that contain the nucleus pulposus.

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anode The positively charged electrode.

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anterior ...

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