title: Monosynaptic facilitation of group I afferents between brachioradialis and extensor carpi radialis in humans.
abstract: Spinal reflex arcs mediated by low-threshold (group I) afferents from muscle spindles and Golgi tendon organs modulate motoneuron excitabilities to coordinate smooth movements. In this study, the reflex arcs between the brachioradialis (BR) and extensor carpi radialis muscles (ECR) were examined in nine healthy human subjects using a post-stimulus time-histogram method. Electrical conditioning stimuli (ES) to the radial nerve branches innervating BR (BR nerve) and ECR (ECR nerve) with the intensity just below the motor threshold were delivered and firings of the ECR and BR motor units were recorded in 6 and 7 of the nine subjects, respectively. ES to the BR and ECR nerves induced a peak (facilitation) in 27/59 ECR and 22/68 BR motor units, respectively, in every subject. Such facilitation was never provoked by pure cutaneous stimulation. The remaining motor units received no effects by ES. The central synaptic delay of the facilitation was almost equal to that of the homonymous facilitation. These findings suggest that facilitation between BR and ECR exists in humans. Group I afferents should mediate the facilitation through a monosynaptic path in the spinal cord.
authors.affiliation: Yamagata City Hospital Saiseikan, Yamagata, Japan.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Shinozaki
authors.affiliation: Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nito
authors.affiliation: Shiseido General Hospital, Yamagata, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kobayashi
authors.affiliation: Okitama Public General Hospital, Kawanishi-Machi Higashiokitama-Gun, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hayashi
authors.affiliation: Department of Judo Therapy, Teikyo University Faculty of Medical Technology, Utsunomiya, Japan.
authors.forename: Takuji
authors.initials: T
authors.lastname: Miyasaka
authors.affiliation: Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Hashizume
authors.affiliation: Graduate School of Health Sciences, Matsumoto University, Matsumoto, Japan.
authors.forename: Masaomi
authors.initials: M
authors.lastname: Shindo
authors.affiliation: Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan. Electronic address: anaitoh@med.id.yamagata-u.ac.jp.
authors.forename: Akira
authors.initials: A
authors.lastname: Naito
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000502:physiology*; D004550:Elbow / Q000294:innervation / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D011930:Reaction Time; D012018:Reflex / Q000502:physiology*; D014953:Wrist / Q000294:innervation; D055815:Young Adult
keywords: Brachioradialis; Extensor carpi radialis; Group I afferents; Humans; Monosynaptic facilitation; Post-stimulus time-histogram