Reflex (unloading) and (defensive capitulation) responses in human neck muscle.
1. We studied unloading and stretch responses in human neck muscle during manoeuvres in which the head pulled against a 2-3 kg weight which could be abruptly released or applied electromagnetically. 2. During head tracking in pitch, unloading of the weight induced inhibition of EMG in the contracting sternocleidomastoid at a mean latency of 24.9 ms in normal subjects and at 41 ms in bilateral labyrinthine-defective subjects, with antagonist (trapezius) excitation at 30.5 and 41.3 ms, respectively. During tracking in yaw, unloading induced inhibition in the contracting splenius capitis (SpC) at a mean latency of 20.4 ms in normal subjects and 25 ms in labyrinthine-defective subjects, with excitation in the antagonist SpC at 22.2 and 24 ms, respectively. 3. If subjects tried to resist an unexpected sideways tug on the head a burst occurred in the stretched SpC at a mean latency of 53.5 ms. When subjects relaxed there was excitation of the shortening of SpC at 75.9 ms, which assisted the imposed motion and is possibly a "defensive reflex".
Corna
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S
Salvatore Maugeri Foundation, Division of Physical Therapy and Rehabilitation, Instituto di Ricovero E Cura A Carattere Scientifico, Novara, Italy.
Ito
Y
Y
von Brevern
M
M
Bronstein
A M
AM
Gresty
M A
MA
D000328:Adult; D000368:Aged; D004576:Electromyography; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007759:Labyrinth Diseases / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D009334:Neck Muscles / Q000294:innervation / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology*; D012399:Rotation; D012438:Saccades / Q000502:physiology