A physiological tremor at 8–12 Hz is noted in a patient's outstretched hand. This frequency corresponds to the natural resonance of which oscillatory loop?

• A Stretch reflex servo loop, where the time delay from spindle activation to motor neuron discharge determines oscillation frequency ✓
• B Cerebello-thalamo-cortical loop operating at its resonant frequency
• C Basal ganglia direct pathway oscillation via striato-thalamo-cortical circuits
• D Peripheral motor unit firing synchronisation in slow-twitch fibres

Explanation

Physiological tremor (8–12 Hz) arises from the mechanical resonance of the limb combined with oscillation in the stretch reflex loop. The time delays inherent in the afferent limb (muscle spindle → dorsal root → spinal cord) and efferent limb (alpha motor neuron → neuromuscular junction → muscle contraction → force generation) create a feedback loop that oscillates at 8–12 Hz. Enhanced physiological tremor (anxiety, thyrotoxicosis, beta-agonists, caffeine) amplifies this oscillation. Cerebellar (intention) tremor is ~3–5 Hz, faster cerebellar tremor ~5–8 Hz; resting Parkinsonian tremor is 3–6 Hz.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.