![]() ![]() Most cases of action tremor are characterized by relatively rhythmic bursts of grouped motor neuron discharges that occur not quite synchronously in opposing muscle groups as shown in Fig. The tremor is accentuated as greater precision of movement is demanded, but it does not approach the degree of augmentation seen with cerebellar intention tremor. More particularly, the tremor is absent when the limbs are relaxed but becomes evident when the muscles are activated. A postural tremor occurs with the limbs and trunk actively maintained in certain positions (such as holding the arms outstretched) and may persist throughout active movement. 5) and postural tremors, which are either the enhanced physiologic variety or essential tremor ( Fig. ![]() Action tremors can be conveniently divided into two categories: goal directed action tremor of the ataxic type related to cerebellar disorders (discussed in Chap. Palate, sometimes facial, pharyngeal, proximal limb musclesĪction tremors are evident during use of the affected body part, as opposed to tremor that is apparent in a position of rest or repose. Hands and forearms, fingers, feet, lips, tongueĪnxiety, fright, β-adrenergics, alcohol withdrawal, xanthines, lithium, exercise, fatigueĬlonazepam, alcohol, β-adrenergic antagonists Certain abnormal tremors, namely, the metabolic varieties of postural or action tremor and at least one type of familial tremor, are considered by some to be variants or exaggerations of physiologic tremor-i.e., "enhanced physiologic tremor," as discussed further on. As Marsden has pointed out, several additional factors-such as spindle input, the unfused grouped firing rates of motor neurons, and the natural resonating frequencies and inertia of the muscles and other structures-are probably of greater importance. Several hypotheses have been proposed to explain physiologic tremor, a traditional one being that it reflects the passive vibration of body tissues produced by mechanical activity of cardiac origin, but this cannot be the whole explanation. It ranges in frequency between 8 and 13 Hz, the dominant rate being 10 Hz in adulthood and somewhat less in childhood and old age. The movement is so fine that it can barely be seen by the naked eye, and then only if the fingers are firmly outstretched in most instances special instruments are required for its detection though asking the patient to aim a laser pointer at a distant target will often expose it. It is present in all contracting muscle groups and persists throughout the waking state and even in certain phases of sleep. A normal, or physiologic, tremor is embedded in the motor system.
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