title: Facilitation from hand muscles innervated by the ulnar nerve to the extensor carpi radialis motoneurone pool in humans:  a study with an electromyogram-averaging technique.
abstract: Effects of low-threshold afferents of hand muscles innervated by the ulnar nerve on an excitability of the extensor carpi radialis (ECR) motoneurone pool in humans were examined using an electromyogram-averaging (EMG-A) technique. Changes of EMG-A of ECR exhibiting 10% of the maximum contraction by electrical stimulation to the ulnar nerve at the wrist (ES-UN) and mechanical stimulation to the hypothenar muscles (MS-HTM) and first dorsal interosseus (MS-FDI) were evaluated in eight normal human subjects. The ES-UN with the intensity immediately below the motor threshold and MS-HTM and -FDI with the intensity below the threshold of the tendon(T)-reflex were delivered. Early and significant peaks in EMG-A were produced by ES-UN, MS-HTM, and MS-FDI in eight of eight subjects. The mean amplitudes of the peaks by ES-UN, MS-HTM, and MS-FDI were, respectively, 121.9%, 139.3%, and 149.9% of the control EMG (100%). The difference between latencies of the peaks by ES-UN and MS-HTM, and ES-UN and MS-FDI was almost equivalent to that of the Hoffmann(H)- and T-reflexes of HTM and FDI, respectively. The peaks by ES-UN, MS-HTM, and MS-FDI diminished with tonic vibration stimulation (TVS) to HTM and FDI, respectively. These findings suggest that group Ia afferents of the hand muscles facilitate the ECR motoneurone pool.
authors.affiliation: Department of Physical Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Suzuki
authors.forename: Keiichi
authors.initials: K
authors.lastname: Ogawa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Sato
authors.forename: Haruki
authors.initials: H
authors.lastname: Nakano
authors.forename: Hiromi
authors.initials: H
authors.lastname: Fujii
authors.forename: Masaomi
authors.initials: M
authors.lastname: Shindo
authors.forename: Akira
authors.initials: A
authors.lastname: Naito
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006181:H-Reflex; D006225:Hand; D006801:Humans; D008297:Male; D040542:Mechanotransduction, Cellular; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation*; D009475:Neurons, Afferent / Q000502:physiology*; D010812:Physical Stimulation; D011930:Reaction Time; D012026:Reflex, Stretch; D012684:Sensory Thresholds; D013997:Time Factors; D014459:Ulnar Nerve / Q000502:physiology*; D014732:Vibration; D055815:Young Adult