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Cutaneous withdrawal reflexes of the upper extremity
M K Floeter1, C Gerloff, J Kouri
1EMG Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1404, USA.
Muscle & Nerve
|May 8, 1998
Summary
Electrical stimulation of fingers evokes upper limb reflexes, causing hand withdrawal while releasing grip. This complex motor pattern, observed via electromyography (EMG), shows prominent habituation and specific muscle activation timing.
Area of Science:
- Neuroscience
- Human Motor Control
- Somatosensory System
Background:
- Understanding upper limb reflexes is crucial for diagnosing neurological conditions.
- Cutaneous reflexes play a significant role in protective movements and motor control.
Purpose of the Study:
- To characterize the electromyogram (EMG) reflexes of the upper limb elicited by electrical stimulation of the fingers.
- To investigate the timing and characteristics of these cutaneous reflexes in relation to voluntary movements.
Main Methods:
- Recorded surface electromyogram (EMG) from multiple upper extremity muscles.
- Stimulated a finger using paired ring electrodes with a train of 4-10 shocks at 300 Hz.
- Determined optimal stimulus intensity (4-6 times perceptual threshold) for evoking EMG activity.
Main Results:
- Identified an effective stimulus protocol for evoking EMG activity in relaxed arm muscles.
- Observed prominent habituation of the evoked reflexes.
- Measured short latencies (<100 ms) for proximal and forearm muscles, preceding voluntary withdrawal by at least 40 ms.
Conclusions:
- Cutaneous stimulation of the fingers elicits a complex motor pattern involving hand withdrawal.
- The timing of EMG activity aligns with the E2 component of the cutaneomuscular reflex and a silent period in active hand muscles.
- This reflex pattern facilitates simultaneous hand withdrawal and grasp release.