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Absolute refractory period: The period after a nerve’s depolarization during which a subsequent depolarization cannot occur, used for recharging the electrical potential.
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Absolute zero: Theoretically, the lowest possible temperature, equal to –273°C or –460°F. At this point, all atomic and molecular motion ceases.
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Absorption: The process of a medium collecting thermal energy and changing it to kinetic energy.
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Accommodation: The decrease in a nerve’s action potential frequency over time when exposed to an unchanging depolarization stimulus.
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Acetylcholine: Neurotransmitter responsible for transmitting motor nerve impulses.
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Acoustical interface: A surface where two materials of different densities meet.
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Acoustical spectrum: Energy transmitted through mechanical waves.
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Acoustical streaming: The unidirectional flow of fluids within the tissues caused by the application of therapeutic ultrasound.
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Actin: A contractile muscle protein.
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Actinomycosis: A disease state of actin caused by a fungus.
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Action potential: The change in the electrical potential of a nerve or muscle fiber when stimulated.
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Activities of daily living: Fundamental skills required for a certain lifestyle, including mobility, self-care, and grooming.
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Acupuncture points: Points on the skin theorized to control systemic functions. These points lie along 12 main channels, eight secondary channels, and a network of subchannels.
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Acute: Of recent onset. The period after an injury when the local inflammatory response is still active.
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ADA: See Americans With Disabilities Act.
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A-delta fibers: A type of nerve that transmits painful information that is often interpreted by the brain as burning or stinging pain.
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Adenosine triphosphate (ATP): An important source of energy for intracellular metabolism.
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Adriamycin: An antibiotic medication.
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Aerobic: Requiring the presence of oxygen.
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Afferent: Carrying impulses toward a central structure, for example, the brain.
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Alarm stage: The first stage in the general adaptation syndrome in which the body readies its defensive systems.
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Albinism: A condition in which the individual lacks pigmentation of the skin, hair, and eyes. The skin is prone to sunburns and the eyes are particularly sensitive to light (photophobia).
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Allograft: A replacement or augmentation of a biological structure with a synthetic one.
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Alpha-motoneurons: Efferent motor neurons that innervate muscle fibers.
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ALS: See Anterior lateral system.
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Alternating current: The uninterrupted flow of electrons marked by a change in the direction and magnitude of the movement.
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Americans With Disabilities Act: Legislation passed in 1990 (Public Law 101-336) that protects the rights of disabled individuals by creating standards to ensure access and prohibit discrimination in transportation, accommodation, public services, and so on.
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Amino acids: Building blocks of protein.
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Amperage: The rate of flow of an electrical current. One ...