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Rheobase is a measure of membrane excitability. In neuroscience, rheobase is the minimal current amplitude of infinite duration (in a practical sense, about 300 milliseconds) that results in the depolarization threshold of the cell membranes being reached, such as an action potential or the contraction of a muscle.〔Ashley, et al. "Determination of the Chronaxie and Rheobase of Denervated Limb Muscles in Conscious Rabbits". ''Artificial Organs'', Volume 29 Issue 3 Page 212 - March 2005〕 In Greek, the root "rhe" translates to current or flow, and "basi" means bottom or foundation: thus the rheobase is the minimum current that will produce an action potential or muscle contraction. Rheobase can be best understood in the context of the strength-duration relationship (Fig. 1).〔Fleshman et al. "Rheobase, input resistance, and motor-unit type in medial gastrocnemius motoneurons in the cat." ''Journal of Neurophysiology'', 1981.〕 The ease with which a membrane can be stimulated depends on two variables: the strength of the stimulus, and the duration for which the stimulus is applied.〔Boinagrov, D., et al. (2010). "Strength-duration relationship for extracellular neural stimulation: Numerical and analytical models". ''Journal of Neurophysiology'', 194(2010), 2236–2248.〕 These variables are inversely related: as the strength of the applied current increases, the time required to stimulate the membrane decreases (and vice versa) to maintain a constant effect.〔 Mathematically, rheobase is equivalent to half the current that needs to be applied for the duration of chronaxie, which is a strength-duration time constant that corresponds to the duration of time that elicits a response when the nerve is stimulated at twice rheobasic strength.〔 The strength-duration curve was first discovered by G. Weiss in 1901, but it was not until 1909 that Louis Lapicque coined the term "rheobase".〔 Many studies are being conducted in relation to rheobase values and the dynamic changes throughout maturation and between different nerve fibers.〔Carrascal, et al. (2005). "Changes during postnatal development in physiological and anatomical characteristics of rat motoneurons studied in vitro". ''Brain Research Reviews'', 49(2005), 377–387.〕 In the past strength-duration curves and rheobase determinations were used to assess nerve injury; today, they play a role in clinical identification of many neurological pathologies, including as Diabetic neuropathy, CIDP, Machado-Joseph Disease,〔Nodera, H., & Kaji, R. (2006). "Nerve excitability testing in its clinical application to neuromuscular diseases". ''Clinical Neurophysiology'', 117(2006), 1902–1916.〕 and ALS.〔Mogyoros, I., et al. (1998). "Strength-duration properties of sensory and motor axons in amyotrophic lateral sclerosis". ''Brain'', 121(1998), 851–859.〕 ==Strength-Duration Curve== The strength-duration time constant (chronaxie) and rheobase are parameters that describe the strength-duration curve—the curve that relates the intensity of a threshold stimulus to its duration. As the duration of a test stimulus increases, the strength of the current required to activate a single fiber action potential decreases. The strength-duration curve is a plot of the threshold current (I) versus pulse duration (d) required to stimulate excitable tissue.〔Geddes, L. A. (2004). "Accuracy limitations of chronaxie values". ''IEEE Transactions on Biomedical Engineering'', 51(1).〕 As mentioned, the two important points on the curve are rheobase (b) and chronaxie (c), which correlates to twice the rheobase (2b). Strength-duration curves are useful in studies where the current required is changed when the pulse duration is changed.〔Geddes, L.A., & Bourland, J. D. (1985) "The Strength-Duration Curve". ''IEEE Transactions on Biomedical Engineering'', 32 (6). 458–459.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rheobase」の詳細全文を読む スポンサード リンク
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